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  • 1.
    Alonso Aller, Elisa
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Eklöf, Johan S.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Kloiber, Ulrike
    Linderholm, Hans W.
    Nordlund, Lina M.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Monitoring of a protected multi-specific tropical seagrass meadow reveals a pattern of decline and recoveryManuscript (preprint) (Other academic)
    Abstract [en]

    In a changing environment, there is an increasing interest to monitor ecosystems to understand their responses to environmental change. Seagrass meadows are highly important ecosystems, but at the same time they are under a constant threat from human activities, as well as climate impacts, and marked declines have been observed worldwide. Despite increasing efforts, monitoring of multi-specific tropical seagrass meadows is scarce, particularly in developing regions. Here we analysed data from the first 10 years of a monitoring programme in a marine protected area in Zanzibar (Tanzania) to assess temporal changes in seagrass cover and species composition and to detect potential drivers of change. The seagrass meadow experienced a strong gradual decline in seagrass cover and changes in species composition, followed by a period of recovery. However, the timing and length of these temporal patterns varied in space (between transects). Of the climate variables considered, cloud cover, temperature, storm occurrence, sunspot activity and the height of the diurnal low tide seemed to influence seagrass cover, although only to a small extent, suggesting that the monitored seagrass meadow may be influenced by other unmeasured factors. Considering our results, seagrass meadows seem to be highly dynamic at small spatial scales even in the absence of major local anthropogenic impacts. Further monitoring programmes should be developed in the region to gain a better understanding of seagrass temporal variability and causes of change.

  • 2.
    Alonso Aller, Elisa
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Eveleens Maarse, Floriaan K. J.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Gren, Michaela
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Nordlund, Lina Mtwana
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. WIO CARE, Zanzibar, Tanzania.
    Jiddawi, Narriman
    Eklöf, Johan S.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Single and joint effects of regional- and local-scale variables on tropical seagrass fish assemblages2014In: Marine Biology, ISSN 0025-3162, E-ISSN 1432-1793, Vol. 161, no 10, p. 2395-2405Article in journal (Refereed)
    Abstract [en]

    Seagrass beds are highly important for tropical ecosystems by supporting abundant and diverse fish assemblages that form the basis for artisanal fisheries. Although a number of local- and regional-scale variables are known to influence the abundance, diversity and assemblage structure of seagrass-associated fish assemblages, few studies have evaluated the relative and joint (interacting) influences of variables, especially those acting at different scales. Here, we examined the relative importance of local- and regional-scale factors structuring seagrass-associated fish assemblages, using a field survey in six seagrass (Thalassodendron ciliatum) areas around Unguja Island (Zanzibar, Tanzania). Fish density and assemblage structure were mostly affected by two regional-scale variables; distance to coral reefs, which positively affected fish density, and level of human development, which negatively affected fish density. On the local scale, seagrass biomass had a positive (but weaker) influence on fish density. However, the positive effect of seagrass biomass decreased with increasing level of human development. In summary, our results highlight the importance of assessing how multiple local and regional variables, alone and together, influence fish communities, in order to improve management of seagrass ecosystems and their services.

  • 3.
    Andersson, Mathias H
    et al.
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Asplund, Maria E
    Department of Marine Ecology, Göteborg University.
    Öhman, Marcus C
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Importance of Using Multiple Sampling Methodologies for Estimating of Fish Community Composition in Offshore Wind Power Construction Areas of the Baltic Sea2007In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 36, no 8, p. 634-636Article in journal (Refereed)
    Abstract [en]

    It is standard procedure that an Environmental Impact Assessment (EIA) is conducted before larger constructions are built. To adequately describe the impact, methods used in an EIA should be carefully adapted considering both the character of the constructions under development and the environment that will be affected. Various sampling techniques are applied to estimate fish abundances and species composition. Methods used, including trawling, seine and gill netting, angling, echo-sound sampling, fishery data, video recordings, dredging, and visual counts using SCUBA, will all give different estimates of fish community composition.

  • 4.
    Berkström, Charlotte
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Lindborg, Regina
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Stockholm University, Stockholm Resilience Centre.
    Mwandya, Augustine W.
    Stockholm University, Faculty of Science, Department of Zoology.
    Yahya, Saleh A. S.
    Stockholm University, Faculty of Science, Department of Zoology.
    Kautsky, Nils
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Nyström, Magnus
    Stockholm University, Stockholm Resilience Centre.
    Exploring 'knowns' and 'unknowns' in tropical seascape connectivity with insights from East African coral reefs2012In: Estuarine, Coastal and Shelf Science, ISSN 0272-7714, E-ISSN 1096-0015, Vol. 107, p. 1-21Article in journal (Refereed)
    Abstract [en]

    Applying a broader landscape perspective to understand spatio-temporal changes in local populations and communities has been increasingly used in terrestrial systems to study effects of human impact and land use change. With today’s major declines in fishery stocks and rapid degradation of natural coastal habitats, the understanding of habitat configuration and connectivity over relevant temporal and spatial scales is critical for conservation and fisheries management of the seascape. Coral reefs, seagrass beds and mangroves are key-components of the tropical seascape. The spatial distribution of these habitat-types may have strong influences on cross-habitat migration and connectivity patterns among organisms. However, the consequences of seascape fragmentation and ecological connectivity are largely unknown. Here, we review the literature to provide an overview of current knowledge with regards to connectivity and food-web interactions within the tropical seascape. We show that information on fish acting as mobile links and being part of nutrient transfer and trophic interactions is scarce. We continue by making an in-depth analysis of the seascape around Zanzibar (Eastern Africa) to fill some of the knowledge gaps identified by the literature survey. Our analysis shows that (i) fifty percent of all fish species found within the Zanzibar seascape use two or multiple habitat-types, (ii) eighteen percent of all coral reef-associated fish species use mangrove and seagrass beds as juvenile habitat, and (iii) macrocarnivores and herbivores are highly represented among those coral reef fish species that use mangrove and seagrass beds as juvenile habitat. We argue that understanding the inter-linkages within and between habitat-types is essential for successful management of the tropical seascape.

  • 5.
    Berkström, Charlotte
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Lindborg, Regina
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Thyresson, Matilda
    Stockholm University, Faculty of Science, Stockholm Resilience Centre.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Assessing connectivity in a tropical embayment: Fish migrations and seascape ecology2013In: Biological Conservation, ISSN 0006-3207, E-ISSN 1873-2917, Vol. 166, p. 43-53Article in journal (Refereed)
    Abstract [en]

    Seascape connectivity and configuration of multiple habitats are important features to include in marine spatial planning, and protecting seascapes with high connectivity is recommended. The present study examines the potential connectivity of reef fish assemblages in a shallow-water conservation area in Zanzibar (Tanzania) by analysing relationships between a set of habitat variables and fish diversity and density for different functional groups (based on diet) and life stages of fish using PLS-analysis. We combined spatial pattern metrics (habitat type, patch size, distance to patch) and dispersal abilities of a number of fish species using buffer radius to answer the questions; (i) do coral reefs with high connectivity to seagrass habitats have higher abundances and higher species richness of fish that undertake routine migrations during their life-history? and (ii) do coral reefs closer to mangrove forest support higher abundances of nursery species (i.e., fish species that use mangrove and seagrass beds as juvenile habitat)? Habitat mosaics surrounding fish survey sites and within-patch measurements inside fish survey sites were quantified at multiple scales (meters to kilometers) using aerial photography and scuba. Fish data was collected using a standardized point census method. We found that both fine- and broad-scale variables were important in structuring fish communities and connectivity with surrounding habitats, where predominantly seagrass beds within a 750 m radius had a positive influence on fish abundances of invertebrate feeders/piscivores (especially for lutjanids and lethrinids). Additionally, fine-scale seagrass cover had a positive influence on nursery species. Depth also had a positive influence on total species richness and the abundance of invertebrate feeders/piscivores. This study highlights the importance of combining connectivity and habitat configuration at different scales to fully understand and manage the tropical seascape.

  • 6.
    Berkström, Charlotte
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Lindborg, Regina
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Thyresson, Matilda
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Seascape configuration influences connectivity of reef fish assemblagesManuscript (preprint) (Other academic)
    Abstract [en]

    Shallow-water habitats within tropical seascapes are intimately connected through ontogenetic and/or feeding migrations of fish. Knowledge on connectivity in the Indo-Pacific region is however sparse. Landscape ecology has been suggested as a useful approach when studying seascape connectivity. In this study, we examine the influence of habitat connectivity on reef fish assemblages in shallow-water habitats surrounding Zanzibar (Tanzania), using a seascape approach. We tested the relationships between a set of landscape and habitat variables and fish diversity and density for different functional groups and life stages. Habitat data was collected at scales ranging from 1m to >2km using aerial photography and ground-truthing. Fish data was collected using a standardised point census method. Furthermore, semi-structured interviews with 127 fishers in the bay were conducted to account for different fishing activity. We show that coral reefs in a complex seascape of Zanzibar are connected to seagrass beds through migration of fish. Habitat connectivity of seagrass and seagrass/coral mix within a 750m radius of coral reefs had a positive influence on fish abundances in the functional group of invertebrate feeders/piscivores, especially within the family Lutjanidae and Lethrinidae. Within-patch seagrass cover had a positive influence on nursery species. Depth also had a positive influence on fish assemblages, highlighting the importance of considering a third dimension, not accounted for in terrestrial studies. Generally, fishing activity between sites did neither influence species richness nor abundance, except for the abundance of juvenile parrotfish. We demonstrate that a landscape ecology approach, combining connectivity and habitat variables, is important for understanding and managing the tropical seascape, although it must be applied at relevant scales, habitat metrics and seascape configurations to fully capture ecological connectivity.

  • 7.
    Buapet, Pimchanok
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Prince Songkla University, Thailand.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Björk, Mats
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Photosynthetic activity of seagrasses and macroalgae in temperate shallow waters can alter seawater pH and total inorganic carbon content at the scale of a coastal embayment2013In: Marine and Freshwater Research, ISSN 1323-1650, E-ISSN 1448-6059, Vol. 64, no 11, p. 1040-1048Article in journal (Refereed)
    Abstract [en]

    Many studies have reported fluctuations in pH and the concentration of dissolved inorganic carbon (DIC) in shallow coastal waters as a result of photosynthetic activity; however, little is known about how these fluctuations vary with degree of exposure among habitats, and at different scales. In the present study, diel variation in seawater pH was apparent in aquaria experiments with Zostera marina and Ruppia maritima. These pH variations were affected by light regime, biomass level and plant species. Subsequently, the natural variability in seawater pH and the concentration of DIC was assessed in six shallow embayments (three sheltered and three exposed) during sunny days. From the outer part towards the interior part of each bay, the following four habitats were identified and studied: the bay-mouth open water, seagrass beds, mixed macrophyte belts and unvegetated bottoms. The two vegetated habitats and unvegetated bottoms were characterised by higher pH and a lower concentration of DIC than in the bay-mouth water. The mixed macrophytes habitat showed slightly higher pH and a lower concentration of DIC than the seagrass and unvegetated habitats. No significant effect of exposure was detected. Our findings clearly showed that the photosynthetic activity of marine macrophytes can alter the coastal pH and the concentration of DIC and that the effects can be observed at the scale of a whole bay.

  • 8.
    Buapet, Pimchanok
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Prince Songkla University, Thailand.
    Rasmusson, Lina M.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Björk, Mats
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Photorespiration and carbon limitation determine productivity in temperate seagrasses2013In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 8, no 12, article id e83804Article in journal (Refereed)
    Abstract [en]

    The gross primary productivity of two seagrasses, Zostera marina and Ruppia maritima, and one green macroalga, Ulva intestinalis, was assessed in laboratory and field experiments to determine whether the photorespiratory pathway operates at a substantial level in these macrophytes and to what extent it is enhanced by naturally occurring shifts in dissolved inorganic carbon (DIC) and O2 in dense vegetation. To achieve these conditions in laboratory experiments, seawater was incubated with U. intestinalis in light to obtain a range of higher pH and O2 levels and lower DIC levels. Gross photosynthetic O2 evolution was then measured in this pretreated seawater (pH, 7.8–9.8; high to low DIC:O2 ratio) at both natural and low O2concentrations (adjusted by N2 bubbling). The presence of photorespiration was indicated by a lower gross O2 evolution rate under natural O2 conditions than when O2 was reduced. In all three macrophytes, gross photosynthetic rates were negatively affected by higher pH and lower DIC. However, while both seagrasses exhibited significant photorespiratory activity at increasing pH values, the macroalga U. intestinalis exhibited no such activity. Rates of seagrass photosynthesis were then assessed in seawater collected from the natural habitats (i.e., shallow bays characterized by high macrophyte cover and by low DIC and high pH during daytime) and compared with open baymouth water conditions (where seawater DIC is in equilibrium with air, normal DIC, and pH). The gross photosynthetic rates of both seagrasses were significantly higher when incubated in the baymouth water, indicating that these grasses can be significantly carbon limited in shallow bays. Photorespiration was also detected in both seagrasses under shallow bay water conditions. Our findings indicate that natural carbon limitations caused by high community photosynthesis can enhance photorespiration and cause a significant decline in seagrass primary production in shallow waters.

  • 9. Bucas, M.
    et al.
    Bergström, U.
    Downie, A-L
    Sundblad, G.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    von Numers, M.
    Siaulys, A.
    Lindegarth, M.
    Empirical modelling of benthic species distribution, abundance, and diversity in the Baltic Sea: evaluating the scope for predictive mapping using different modelling approaches2013In: ICES Journal of Marine Science, ISSN 1054-3139, E-ISSN 1095-9289, Vol. 70, no 6, p. 1233-1243Article in journal (Refereed)
    Abstract [en]

    The predictive performance of distribution models of common benthic species in the Baltic Sea was compared using four non-linear methods: generalized additive models (GAMs), multivariate adaptive regression splines, random forest (RF), and maximum entropy modelling (MAXENT). The effects of data traits were also tested. In total, 292 occurrence models and 204 quantitative (abundance and diversity) models were assessed. The main conclusions are that (i) the spatial distribution, abundance, and diversity of benthic species in the Baltic Sea can be successfully predicted using several non-linear predictive modelling techniques; (ii) RF was the most accurate method for both models, closely followed by GAM and MAXENT; (iii) correlation coefficients of predictive performance among the modelling techniques were relatively low, suggesting that the performance of methods is related to specific responses; (iv) the differences in predictive performance among the modelling methods could only partly be explained by data traits; (v) the response prevalence was the most important explanatory variable for predictive accuracy of GAM and MAXENT on occurrence data; (vi) RF on the occurrence data was the only method sensitive to sampling density; (vii) a higher predictive accuracy of abundance models could be achieved by reducing variance in the response data and increasing the sample size.

  • 10.
    Dahl, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Deyanova, Diana
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Gütschow, Silvia
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Asplund, Maria E.
    Lyimo, Liberatus D.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Karamfilov, Ventzislav
    Santos, Rui
    Björk, Mats
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Sediment Properties as Important Predictors of Carbon Storage in Zostera marina Meadows: A Comparison of Four European Areas2016In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 11, no 12Article in journal (Refereed)
    Abstract [en]

    Seagrass ecosystems are important natural carbon sinks but their efficiency varies greatly depending on species composition and environmental conditions. What causes this variation is not fully known and could have important implications for management and protection of the seagrass habitat to continue to act as a natural carbon sink. Here, we assessed sedimentary organic carbon in Zostera marina meadows (and adjacent unvegetated sediment) in four distinct areas of Europe (Gullmar Fjord on the Swedish Skagerrak coast, Asko in the Baltic Sea, Sozopol in the Black Sea and Ria Formosa in southern Portugal) down to similar to 35 cm depth. We also tested how sedimentary organic carbon in Z. marina meadows relates to different sediment characteristics, a range of seagrass-associated variables and water depth. The seagrass carbon storage varied greatly among areas, with an average organic carbon content ranging from 2.79 +/- 0.50% in the Gullmar Fjord to 0.17 +/- 0.02% in the area of Sozopol. We found that a high proportion of fine grain size, high porosity and low density of the sediment is strongly related to high carbon content in Z. marina sediment. We suggest that sediment properties should be included as an important factor when evaluating high priority areas in management of Z. marina generated carbon sinks.

  • 11.
    Dahl, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Deyanova, Diana
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Lyimo, Liberatus D.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. University of Dodoma, Tanzania.
    Näslund, Johan
    Samuelsson, Göran S.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Mtolera, Marten S. P.
    Björk, Mats
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Effects of shading and simulated grazing on carbon sequestration in a tropical seagrass meadow2016In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 104, no 3, p. 654-664Article in journal (Refereed)
    Abstract [en]

    1. There is an ongoing world-wide decline of seagrass ecosystems, one of the world's most efficient carbon sink habitats. In spite of this, there is a clear lack of studies experimentally testing the effects of anthropogenic disturbances on carbon sequestration of seagrass systems. 2. We assessed the effects of two disturbances of global concern on the carbon sink function in a five-month in situ experiment within a tropical seagrass (Thalassia hemprichii) meadow by testing the impacts of shading and simulated grazing at two levels of intensity using shading cloths and clipping of shoot tissue. We measured the effects of these disturbances on the carbon sequestration process by assessing the net community production (NCP), carbon and nitrogen content in tissue biomass, and organic matter and THAA (total hydrolysable amino acids) in the sediment down to 40 cm depth. 3. Treatments of high-intensity shading and high-intensity clipping were similarly impacted and showed a significantly lower NCP and carbon content in the below-ground biomass compared to the seagrass control. No significant effects were seen in organic carbon, total nitrogen, C:N ratio and THAA in the sediment for the seagrass treatments. However, both clipping treatments showed different depth profiles of carbon and THAA compared to the seagrass control, with lower organic carbon and THAA content in the surface sediment. This can be explained by the clipping of shoot tissue causing a less efficient trapping of allochthonous carbon and reduced input of shredded seagrass leaves to the detritus sediment layer. In the clipping plots, erosion of the surface sediment occurred, which was also most likely caused by the removal of above-ground plant biomass. 4. Synthesis. Our findings show that during the course of this experiment, there were no impacts on the sedimentary carbon while the high-intensity disturbances caused a clear depletion of carbon biomass and reduced the seagrass meadow's capacity to sequester carbon. From a long-term perspective, the observed effect on the carbon biomass pool in the high-intensity treatments and the sediment erosion in the clipping plots may lead to loss in sedimentary carbon.

  • 12.
    Dahl, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Infantes, Eduardo
    Clevesjö, Rosanna
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Linderholm, Hans W.
    Björk, Mats
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Increased current flow enhances the risk of organic carbon loss from Zostera marina sediments: Insights from a flume experimentManuscript (preprint) (Other academic)
  • 13.
    Dahl, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Infantes, Eduardo
    Clevesjö, Rosanna
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Linderholm, Hans W.
    Björk, Mats
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Increased current flow enhances the risk of organic carbon loss from Zostera marina sediments: Insights from a flume experiment2018In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 63, no 6, p. 2793-2805Article in journal (Refereed)
    Abstract [en]

    Hydrodynamic processes are important for carbon storage dynamics in seagrass meadows, where periods of increased hydrodynamic activity could result in erosion and the loss of buried carbon. To estimate hydrodynamic impacts on the resuspension of organic carbon (C-org) in seagrass-vegetated sediments, we exposed patches (0.35 x 0.35 cm) of Zostera marina (with different biomass, shoot densities, and sediment properties) to gradually increased unidirectional (current) flow velocities ranging from low (5 cm s(-1)) to high (26 cm s(-1)) in a hydraulic flume with a standardized water column height of 0.12 m. We found that higher flow velocities substantially increased (by more than threefold) the proportion of C-org in the suspended sediment resulting in a loss of up to 5.5% +/- 1.7% (mean +/- SE) C-org from the surface sediment. This was presumably due to increased surface erosion of larger, carbon-rich detritus particles. Resuspension of C-org in the seagrass plots correlated with sediment properties (i.e., bulk density, porosity, and sedimentary C-org) and seagrass plant structure (i.e., belowground biomass). However, shoot density had no influence on C-org resuspension (comparing unvegetated sediments with sparse, moderate, and dense seagrass bed types), which could be due to the relatively low shoot density in the experimental setup (with a maximum of 253 shoots m(-2)) reflecting natural conditions of the Swedish west coast. The projected increase in the frequency and intensity of hydrodynamic forces due to climate change could thus negatively affect the function of seagrass meadows as natural carbon sinks.

  • 14.
    Deyanova, Diana
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Asplund, Maria E.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Franco, Joao N.
    Rasmusson, Lina M.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Dahl, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Infantes, Eduardo
    Lundberg, Petter
    Engström, Pia
    Björk, Mats
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Plant- and habitat productivity in a temperate seagrass systemManuscript (preprint) (Other academic)
    Abstract [en]

    Seagrass meadows are highly productive coastal habitats. Yet, little is known about the contribution of seagrass plants to the total seagrass habitat. To clarify the particular role of the seagrass plants for carbon capture in temperate environments, a one-year study was performed in seagrass meadows on the Swedish west coast. We aimed to assess the link between the net primary productivity of seagrass plants per se, the net production of the seagrass community and the net production of the entire system. To be able to predict effects of environmental changes on seagrass productivity, results were related to changes in water temperature, oxygen levels, light conditions and ice cover. Results showed large variations in net plant productivity across seasons, generally following light- and temperature variability, and ranging from very high (20.03 g C m-2 24h-1 ) in the summer to negative rates (-1.60 g C m-2 24h-1 ) in the least productive winter month. The patterns of variability in seagrass productivity were also influenced by depth- and site-specific dynamics in biomass. The high respiration of the benthic community did largely outbalance the productivity of the seagrass plants, probably as an effect of fast turnover rates. This resulted in an overall yearly low positive carbon balance of the entire seagrass system. Overall, the findings show that seagrass plants contribute substantially to the carbon capture in temperate seagrass habitats, but also that the rate of community respiration appears to be highly dependent on the degree of how much detritus material that is retained within the system. Thus, even though these seagrass systems are highly productive and may contain a large carbon stock, seagrass productivity per se seems not to be the most important determining factor for their carbon sink function.

  • 15.
    Deyanova, Diana
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Lyimo, Liberatus D.
    Dahl, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hamisi, Mariam I.
    Mtolera, Matern S. P.
    Björk, Mats
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Contribution of seagrass plants to CO2 capture in a tropical seagrass meadow under experimental disturbance2017In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 12, no 7, article id e0181386Article in journal (Refereed)
    Abstract [en]

    Coastal vegetative habitats are known to be highly productive environments with a high ability to capture and store carbon. During disturbance this important function could be compromised as plant photosynthetic capacity, biomass, and/or growth are reduced. To evaluate effects of disturbance on CO2 capture in plants we performed a five-month manipulative experiment in a tropical seagrass (Thalassia hemprichii) meadow exposed to two intensity levels of shading and simulated grazing. We assessed CO2 capture potential (as net CO2 fixation) using areal productivity calculated from continuous measurements of diel photosynthetic rates, and estimates of plant morphology, biomass and productivity/respiration (P/R) ratios (from the literature). To better understand the plant capacity to coping with level of disturbance we also measured plant growth and resource allocation. We observed substantial reductions in seagrass areal productivity, biomass, and leaf area that together resulted in a negative daily carbon balance in the two shading treatments as well as in the high-intensity simulated grazing treatment. Additionally, based on the concentrations of soluble carbohydrates and starch in the rhizomes, we found that the main reserve sources for plant growth were reduced in all treatments except for the low-intensity simulated grazing treatment. If permanent, these combined adverse effects will reduce the plants' resilience and capacity to recover after disturbance. This might in turn have long-lasting and devastating effects on important ecosystem functions, including the carbon sequestration capacity of the seagrass system.

  • 16.
    Deyanova, Diana
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Lyimo, Liberatus D.
    Sköld, Helen N.
    Bjök, Mats
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Effects of ageing on the photosynthetic capacity of the seagrass Zostera marina LinnaeusManuscript (preprint) (Other academic)
    Abstract [en]

    The effect of tissue age and light stress on seagrass productivity was examined on three scale levels by comparisons among: (i) different parts of a leaf (i.e. the base middle and top), (ii) leaves of different ages, and (iii) shoots of different development stages on the same genet, in the temperate species Zostera marina L. Rapid light curves were performed to estimate chlorophyll fluorescence and to determine the maximal photosynthetic rate (ETRmax), the photosynthetic efficiency (the alpha slope) and the maximal quantum yield (both as Fv/Fm and as the more sensible Fv/F0). The plants were also exposed to inhibiting light stress with measurements performed during the following recovery and non-photochemical quenching (NPQ). The results suggest that seagrass tissue age has an effect on the photosynthetic performance of the plant and that the level of strength varies among different parts of a single shoot and also among shoots of different development stages along the same genet. Younger and senescing tissues generally had lower photosynthetic capacity than mature tissues. It appeared that very young tissues tolerate light stress better than mature and senescing tissues, as the NPQ values of the very young tissue were higher, and they also showed a lower recovery to initial Fv/F0 values. A clear difference was also found in photosynthetic performance and recovery capacity of the youngest shoot compared to the rest of the shoots belonging to the same genet. The leaves of young shoots appeared to better tolerate light stress than leaves of old shoots. These findings provide new insight on seagrass ageing and expand the understanding of ageing effects on photosynthesis on a population level.

  • 17.
    Deyanova, Diana
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Lyimo, Liberatus Dominick
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. University of Dodoma, Tanzania.
    Dahl, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hamis, Mariam
    Mtolera, Marten SP
    Björk, Mats
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Productivity of a tropical seagrass meadow under stress: effects of prolonged shading and simulated grazingManuscript (preprint) (Other academic)
  • 18.
    Eggertsen, Linda
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Federal University of Rio de Janeiro, Brazil; Federal University Fluminense, Brazil.
    Ferreira, Carlos E. L.
    Fontoura, Luisa
    Kautsky, Nils
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Berkström, Charlotte
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Swedish University of Agricultural Sciences, Sweden.
    Seaweed beds support more juvenile reef fish than seagrass beds in a south-western Atlantic tropical seascape2017In: Estuarine, Coastal and Shelf Science, ISSN 0272-7714, E-ISSN 1096-0015, Vol. 196, no 5, p. 97-108Article in journal (Refereed)
    Abstract [en]

    Seascape connectivity is regarded essential for healthy reef fish communities in tropical shallow systems. A number of reef fish species use separate adult and nursery habitats, and hence contribute to nutrient and energy transfer between habitats. Seagrass beds and mangroves often constitute important nursery habitats, with high structural complexity and protection from predation. Here, we investigated if reef fish assemblages in the tropical south-western Atlantic demonstrate ontogenetic habitat connectivity and identify possible nurseries on three reef systems along the eastern Brazilian coast. Fish were surveyed in fore reef, back reef, Halodule wrightii seagrass beds and seaweed beds. Seagrass beds contained lower abundances and species richness of fish than expected, while Sargassum-dominated seaweed beds contained significantly more juveniles than all other habitats (average juvenile fish densities: 32.6 per 40 m2 in Sargassum beds, 11.2 per 40 m2 in back reef, 10.1 per 40 m2 in fore reef, and 5.04 per 40 m2 in seagrass beds), including several species that are found in the reef habitats as adults. Species that in other regions worldwide (e.g. the Caribbean) utilise seagrass beds as nursery habitats were here instead observed in Sargassum beds or back reef habitats. Coral cover was not correlated to adult fish distribution patterns; instead, type of turf was an important variable. Connectivity, and thus pathways of nutrient transfer, seems to function differently in east Brazil compared to many tropical regions. Sargassum-dominated beds might be more important as nurseries for a larger number of fish species than seagrass beds. Due to the low abundance of structurally complex seagrass beds we suggest that seaweed beds might influence adult reef fish abundances, being essential for several keystone species of reef fish in the tropical south-western Atlantic.

  • 19. Eggertsen, Linda
    et al.
    Hammar, Linus
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Effects of tidal current-induced flow on reef fish behaviour and function on a subtropical rocky reef2016In: Marine Ecology Progress Series, ISSN 0171-8630, E-ISSN 1616-1599, Vol. 559, p. 175-192Article in journal (Refereed)
    Abstract [en]

    Tidal currents are important features in reef environments with high tidal range. Such current-influenced areas can be attractive for fish due to transport of nutrients and food items. Biological sampling, however, is difficult in these environments and it remains poorly understood to what degree strong currents actually shape tropical and subtropical reef fish communities. We used remote underwater video to investigate effects of flow velocity on fish across the tidal cycle at a rocky reef in southern Mozambique. Fish were recorded during flow velocities ranging from 0 to 1.44 m s(-1). Current flow velocity had no significant effect on the benthic fish assemblage, while increasing flow velocity had a negative effect on pelagic fish abundance and influenced trophic group composition. Limits for tolerated flow velocity on the pelagic assemblage were species-specific, with the highest resistance for larger predatory fish using subcarangiform swimming. Flow velocity had significant positive effects on size of Caranx spp., showing that smaller individuals had lower tolerance to flow than larger conspecifics. Planktivorous pomacentrids and monodactylids were very abundant in flows up to 0.5 m s(-1), suggesting that the area functions as an important foraging ground for planktivorous fish up to this flow velocity, while abundance of barracudas Sphyraena spp. was higher in moderate currents compared to slack water. For the benthic assemblage, benthic structures seemed to provide sufficient flow refuge for fish throughout the tidal cycle, highlighting the importance of structural complexity for benthic fish in this environment. Fish assemblages on reefs subjected to strong tidal currents might therefore be sensitive to habitat modifications. The ecological importance of tidal currents should be considered in marine management.

  • 20.
    Eklöf, J.S.
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    de la Torre-Castro, M.
    Stockholm University, Faculty of Science, Department of Systems Ecology. Stockholm University, Stockholm Resilience Centre.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Zoology.
    Uku, J.
    Muthiga, N.
    Lyimo, T.
    Bandeira, S.O.
    Sea urchin overgrazing of seagrasses: A review of current knowledge on causes, consequences and management2008In: Estuarine, Coastal and Shelf Science, ISSN 0272-7714, E-ISSN 1096-0015, Vol. 79, no 4, p. 569-580Article in journal (Refereed)
    Abstract [en]

    Sea urchins are one of the most common seagrass macro-grazers in contemporary seagrass systems. Occasionally their grazing rates exceed seagrass growth rates, a phenomenon sometimes referred to as overgrazing. Because of a reported increasing frequency of overgrazing events, concomitant with loss of seagrass-associated ecosystem services, it has been suggested that overgrazing is one of the key threats to tropical and subtropical seagrasses. In light of this, we review the current knowledge on causes, consequences. and management of sea urchin overgrazing of seagrasses. Initially we argue that the definition of overgrazing must include scale and impairment of ecosystem services, since this is the de facto definition used in the literature, and will highlight the potential societal costs of seagrass overgrazing. A review of 16 identified cases suggests that urchin overgrazing is a global phenomenon, ranging from temperate to tropical coastal waters and involving at least 11 seagrass and 7 urchin species. Even though most overgrazing events Seem to affect areas of <0.5 km(2), and recovery often occurs within a few years, overgrazing can have a range of large, long-term indirect effects such as loss of associated fauna and decreased sediment stabilization. A range of drivers behind overgrazing have been suggested, including bottom-up (nutrient enrichment). top-down (reduced predation control due to e.g. overfishing), "side-in" mechanisms (e.g. changes in water temperature) and natural population fluctuations. Based on recent studies, there seems to be fairly strong support for the top-down and bottom-up hypotheses. However, many potential drivers often co-occur and interact, especially in areas with high anthropogenic pressure, suggesting that multiple disturbances-by simultaneously reducing predation control, increasing urchin recruitment and reducing the resistance of seagrasses-could pave the way for overgrazing. In management, the most common response to overgrazing has been to remove urchins, but limited knowledge of direct and indirect effects makes it difficult to assess the applicability and sustainability of this method. Based on the wide knowledge gaps, which severely limits management, we suggest that future research should focus on (1) identification and quantification of ecosystem and societal scale effects of overgrazing; (2) assessment of the relative importance and interactions of different drivers; and (3) development of a holistic proactive and reactive long-term management agenda.

  • 21.
    Eklöf, J.S.
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Gullström, Martin
    Department of Zoology. Ekologi.
    Björk, Mats
    Department of Botany.
    Asplund, M.E.
    Hammar, L.
    Dahlgren, A.
    Öhman, Marcus
    Department of Zoology. Ekologi.
    The importance of grazing intensity and frequency for physiological responses of the tropical seagrass Thalassia hemprichii2008In: Aquatic botany, Vol. 89, p. 337-340Article in journal (Refereed)
    Abstract [en]

    Seagrass grazing is an intrinsic disturbance in primarily tropical and subtropical areas. While there is a general parabolic response in seagrass growth to grazing intensity, there is less knowledge on the role of grazing frequency, as well as potential interactions between grazing intensity and frequency. This study experimentally investigated physiological responses in Thalassia hemprichii to simulated (leaf cutting) grazing regimes with different intensities (25% vs. 75%) and frequencies (I times vs. 3 times) over 35 days in Chwaka Bay (Zanzibar, Tanzania). The results showed that the two high-intensity treatments (75% removal) had 37-41% lower growth rate than the low-intensity/low-frequency treatment, and rhizome sugar and starch content were both affected in a similar way. A 36% lower starch content in the simulated low-intensity/high-frequency regime (25% x 3) compared to the one of low-intensity/low-frequency (25% x I) also shows an interaction between grazing intensity and frequency. This suggests that high-intensity (and to some extent frequency) grazing regimes, in comparison to low-intensity regimes, could negatively affect T. hemprichii growth, energy reserves, and thereby the ability to deal with additional stress like light limitation or grazing.

  • 22.
    George, Rushingisha
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Tanzania Fisheries Research Institute (TAFIRI), Tanzania .
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Mangora, Mwita M.
    Mtolera, Matern S. P.
    Björk, Mats
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    High midday temperature stress has stronger effects on biomass than on photosynthesis: A mesocosm experiment on four tropical seagrass species2018In: Ecology and Evolution, ISSN 2045-7758, E-ISSN 2045-7758, Vol. 8, no 9, p. 4508-4517Article in journal (Refereed)
    Abstract [en]

    The effect of repeated midday temperature stress on the photosynthetic performance and biomass production of seagrass was studied in a mesocosm setup with four common tropical species, including Thalassia hemprichii, Cymodocea serrulata, Enhalus acoroides, and Thalassodendron ciliatum. To mimic natural conditions during low tides, the plants were exposed to temperature spikes of different maximal temperatures, that is, ambient (29-33 degrees C), 34, 36, 40, and 45 degrees C, during three midday hours for seven consecutive days. At temperatures of up to 36 degrees C, all species could maintain full photosynthetic rates (measured as the electron transport rate, ETR) throughout the experiment without displaying any obvious photosynthetic stress responses (measured as declining maximal quantum yield, Fv/Fm). All species except T.ciliatum could also withstand 40 degrees C, and only at 45 degrees C did all species display significantly lower photosynthetic rates and declining Fv/Fm. Biomass estimation, however, revealed a different pattern, where significant losses of both above- and belowground seagrass biomass occurred in all species at both 40 and 45 degrees C (except for C.serrulata in the 40 degrees C treatment). Biomass losses were clearly higher in the shoots than in the belowground root-rhizome complex. The findings indicate that, although tropical seagrasses presently can cope with high midday temperature stress, a few degrees increase in maximum daily temperature could cause significant losses in seagrass biomass and productivity.

  • 23.
    George, Rushingisha
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Tanzania Fisheries Research Institute (TAFIRI), Tanzania.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Mtolera, Matern
    Björk, Mats
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Seagrass cover reduces emissions of methane, nitrous oxide and sulphide levels in organic rich tropical seagrass sediments during daytimeManuscript (preprint) (Other academic)
  • 24.
    George, Rushingisha
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Tanzania Fisheries Research Institute (TAFIRI), Tanzania.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Mtolera, Matern
    Lyimo, Thomas
    Björk, Mats
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Methane emission and sulphide levels increase in tropical seagrass sediments during temperature stress: a mesocosm experimentManuscript (preprint) (Other academic)
  • 25.
    Gullström, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Baden, Susanne
    Lindegarth, Mats
    Spatial patterns and environmental correlates in leaf-associated epifaunal assemblages of temperate seagrass (Zostera marina) meadows2012In: Marine Biology, ISSN 0025-3162, E-ISSN 1432-1793, Vol. 159, no 2, p. 413-425Article in journal (Refereed)
    Abstract [en]

    We estimated and tested variability of seagrass leaf-associated epifaunal assemblages at a range of scales. Sampling was performed in 36 seagrass (Zostera marina) meadows within three regions along the Swedish west coast following a hierarchical design (samples separated by 10 s m, km or 100 km). Results showed strongest variability (43-81%) at the intermediate amongst-meadow (km) scale using biomass of functional categories, while considering taxa composition the within-meadow (10 s m) scale contributed most to variability (60%). Using functional categories, we found that embayment exposure and seagrass shoot density were the most important predictor variables explaining part of the variability in biomass of suspension feeders (bivalves and barnacles) and grazers. In contrast, variability in epifaunal taxa composition was predicted mainly by sediment chemistry, substratum coverage and geographical positioning. Our findings suggest that models to develop predictive power and mechanistic understanding should focus on variables and processes varying at small and intermediate scales rather than those varying at larger scales.

  • 26.
    Gullström, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology. Stockholm University, Faculty of Science, Department of Zoology.
    Berkström, Charlotte
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Öhman, Marcus C.
    Stockholm University, Faculty of Science, Department of Zoology.
    Bodin, Maria
    Dahlberg, Mattis
    Stockholm University, Faculty of Science, Department of Zoology.
    Scale-dependent patterns of variability of a grazing parrotfish (Leptoscarus vaigiensis) in a tropical seagrass-dominated seascape2011In: Marine Biology, ISSN 0025-3162, E-ISSN 1432-1793, Vol. 158, no 7, p. 1483-1495Article in journal (Refereed)
    Abstract [en]

    Although herbivorous fish form critical linkages between primary producers and higher trophic levels, the major factors regulating their spatial structure in seagrass systems remain poorly understood. The present study examined the parrotfish Leptoscarus vaigiensis in seagrass meadows of a tropical embayment in the western Indian Ocean. Stomach content analysis and direct field observations showed that L. vaigiensis is an efficient grazer, feeding almost exclusively on seagrass leaves. Seagrass shoot density was highly correlated to all density variables (total, juvenile and subadult) and juvenile biomass of L. vaigiensis, while subadult biomass was predicted by distance to neighbouring coral habitat. Moreover, density and biomass of predatory fish (piscivores) were predicted by seagrass canopy height and the distribution patterns of predators followed those of L. vaigiensis. Hence, factors at local (seagrass structural complexity and feeding mode) and landscape scale levels (seascape context and distribution of piscivores) likely mutually structure herbivorous fish communities. The findings underscore the importance of incorporating multiple scale-dependent factors when managing coastal seagrass ecosystems and their associated key species.

  • 27.
    Gullström, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Zoology. Ekologi.
    Bodin, Maria
    Nilsson, Per G.
    Öhman, Marcus
    Stockholm University, Faculty of Science, Department of Zoology. Ekologi.
    Seagrass structural complexity and landscape configuration as determinants of tropical fish assemblage composition2008In: Marine ecology - progress series, Vol. 363, p. 241-255Article in journal (Refereed)
    Abstract [en]

    Seagrass meadows are regularly used by fish as resident, transient, or nursery habitat. However, there is a long-standing debate on how spatial variability of seagrass fish assemblages is determined. We examined the influence of seagrass structural complexity, physical water conditions, and proximity of neighboring shallow-water habitats on tropical fish assemblage composition in a shallow seagrass-dominated embayment at Zanzibar Island in the western Indian Ocean. Sampling of fish assemblages was carried out in seagrass meadows dominated by Enhalus acoroides or Thalassia hemprichii (3 localities each), 1 mixed meadow, and 1 unvegetated area. Overall, the density and biomass of fish were dominated by juvenile and subadult herbivores, either stationary seagrass residents or fish associated with coral reef and seagrass habitats. In terms of number of fish species, the majority were either carnivorous or omnivorous, and mainly coral-seagrass-associated. Multiple regression analysis indicated that canopy height was the foremost predictor for density, biomass, and species richness of juvenile fish, whereas adult and subadult fish densities were predicted by water depth. Moreover, distance-based correlation analyses revealed that fish assemblage structure was significantly correlated with the distance to neighboring mangrove and coral-reef habitats, shoot density, and (although weaker) canopy height. Based on these findings, attributes of seagrass structure and the location of a seagrass habitat within the seascape context appear to be important determinants of spatial patterns and variability of seagrass fish assemblages. This kind of information is important for spatial coastal management and for the selection of marine protected areas.

  • 28.
    Gullström, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    de la Torre-Castro, Maricela
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Bandeira, Salomao O.
    Björk, Mats
    Kautsky, Nils
    Rönnbäck, Patrik
    Öhman, Marcus C.
    Stockholm University, Faculty of Science, Department of Zoology.
    Seagrass ecosystems in the Western Indian Ocean2002In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 31, no 7, p. 588-596Article in journal (Refereed)
    Abstract [en]

    Seagrasses are marine angiosperms widely distributed in both tropical and temperate coastal waters creating one of the most productive aquatic ecosystems on earth. In the Western Indian Ocean (WIO) region, with its 13 reported seagrass species, these ecosystems cover wide areas of near-shore soft bottoms through the 12 000 km coastline. Seagrass beds are found intertidally as well as subtidally, sometimes down to about 40 m, and do often occur in close connection to coral reefs and mangroves. Due to the high primary production and a complex habitat structure, seagrass beds support a variety of benthic, demersal and pelagic organisms. Many fish and shellfish species, including those of commercial interest, are attracted to seagrass habitats for foraging and shelter, especially during their juvenile life stages. Examples of abundant and widespread fish species associated to seagrass beds in the WIO belong to the families Apogonidae, Blenniidae, Centriscidae, Gerreidae, Gobiidae, Labridae, Lethrinidae Lutjanidae, Monacanthidae, Scaridae, Scorpaenidae, Siganidae, Syngnathidae and Teraponidae. Consequently, seagrass ecosystems in the WIO are valuable resources for fisheries at both local and regional scales. Still, seagrass research in the WIO is scarce compared to other regions and it is mainly focusing on botanic diversity and ecology. This article reviews the research status of seagrass beds in the WIO with particular emphasis on fish and fisheries. Most research on this topic has been conducted along the East African coast, i.e. in Kenya, Tanzania, Mozambique and eastern South Africa, while less research was carried out in Somalia and the Island States of the WIO (Seychelles, Comoros, Reunion (France), Mauritius and Madagascar). Published papers on seagrass fish ecology in the region are few and mainly descriptive. Hence, there is a need of more scientific knowledge in the form of describing patterns and processes through both field and experimental work. Quantitative seagrass fish community studies in the WIO such as the case study presented in this paper are negligible, but necessitated for the perspective of fisheries management. It is also highlighted that the pressure on seagrass beds in the region is increasing due to growing coastal populations and human disturbance from e.g. pollution, eutrophication, sedimentation, fishing activities and collection of invertebrates, and its effect are little understood. Thus, there is a demand for more research that will generate information useful for sustainable management of seagrass ecosystems in the WIO.

  • 29. Gullström, Martin
    et al.
    Lundén, Bengt
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Bodin, Maria
    Kangwe, Juma W.
    Stockholm University, Faculty of Science, Department of Botany.
    Öhman, Marcus C.
    Stockholm University, Faculty of Science, Department of Zoology.
    Mtolera, Matern S. P.
    Björk, Mats
    Stockholm University, Faculty of Science, Department of Botany.
    Assessment of vegetation changes in seagrass communities of tropical Chwaka Bay (Zanzibar) using satellite remote sensing2006In: Estuarine, Coastal and Shelf Science, ISSN 0272-7714, E-ISSN 1096-0015, Vol. 67, no 3, p. 399-408Article in journal (Refereed)
    Abstract [en]

    Spatial and temporal dynamics of submerged aquatic vegetation (SAV) cover were studied in the relatively pristine and seagrass-dominated area of Chwaka Bay, Zanzibar (Tanzania) by using satellite remote sensing. Through complementary field work the potential of the technique for change detection was verified. The general changes in SAV cover were examined using Landsat images from 1986, 1987, 1998, 2001 and 2003. Two of these images, from 1987 (Landsat TM) and 2003 (Landsat ETM+), were specifically analysed to create a map of the change in SAV cover. Overall, the general distribution of SAV stayed fairly stable over the period investigated, but the result also showed regions where significant alterations, both losses and gains, had occurred between the two years. Based on our findings and anecdotal information from local fishermen and seaweed farmers potential causative factors are discussed. It was concluded that a repeated mapping with satellite remote sensing is a suitable tool to monitor changes of seagrass and seaweed distribution in shallow tropical environments.

  • 30.
    Gullström, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Lyimo, Liberatus D.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. University of Dodoma, Tanzania.
    Dahl, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Samuelsson, Göran S.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Eggertsen, Maria
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Anderberg, Elisabeth
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Rasmusson, Lina M.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Linderholm, Hans W.
    Knudby, Anders
    Bandeira, Salomao
    Mtwana Nordlund, Lina
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Björk, Mats
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Blue Carbon Storage in Tropical Seagrass Meadows Relates to Carbonate Stock Dynamics, Plant–Sediment Processes, and Landscape Context: Insights from the Western Indian Ocean2018In: Ecosystems (New York. Print), ISSN 1432-9840, E-ISSN 1435-0629, Vol. 21, no 3, p. 551-566Article in journal (Refereed)
    Abstract [en]

    Globally, seagrass ecosystems are considered major blue carbon sinks and thus indirect contributors to climate change mitigation. Quantitative estimates and multi-scale appraisals of sources that underlie long-term storage of sedimentary carbon are vital for understanding coastal carbon dynamics. Across a tropical–subtropical coastal continuum in the Western Indian Ocean, we estimated organic (Corg) and inorganic (Ccarb) carbon stocks in seagrass sediment. Quantified levels and variability of the two carbon stocks were evaluated with regard to the relative importance of environmental attributes in terms of plant–sediment properties and landscape configuration. The explored seagrass habitats encompassed low to moderate levels of sedimentary Corg (ranging from 0.20 to 1.44% on average depending on species- and site-specific variability) but higher than unvegetated areas (ranging from 0.09 to 0.33% depending on site-specific variability), suggesting that some of the seagrass areas (at tropical Zanzibar in particular) are potentially important as carbon sinks. The amount of sedimentary inorganic carbon as carbonate (Ccarb) clearly corresponded to Corg levels, and as carbonates may represent a carbon source, this could diminish the strength of seagrass sediments as carbon sinks in the region. Partial least squares modelling indicated that variations in sedimentary Corg and Ccarb stocks in seagrass habitats were primarily predicted by sediment density (indicating a negative relationship with the content of carbon stocks) and landscape configuration (indicating a positive effect of seagrass meadow area, relative to the area of other major coastal habitats, on carbon stocks), while seagrass structural complexity also contributed, though to a lesser extent, to model performance. The findings suggest that accurate carbon sink assessments require an understanding of plant–sediment processes as well as better knowledge of how sedimentary carbon dynamics are driven by cross-habitat links and sink–source relationships in a scale-dependent landscape context, which should be a priority for carbon sink conservation.

  • 31.
    Gullström, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Lyimo, Liberatus Dominick
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. University of Dodoma, Tanzania.
    Samuelsson, Göran
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Dahl, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Eggertsen, Maria
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Anderberg, Elisabeth
    Rasmusson, Lina
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Linderholm, Hans
    Bendeira, Salmão
    Nordlund, Lina
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Knudby, Anders
    Björk, Mats
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Carbon sequestration capacity in tropical and subtropical seagrass meadows of the Western Indian oceanManuscript (preprint) (Other academic)
  • 32.
    Gullström, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Lyimo, Thomas J.
    Eklöf, Johan S.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Björk, Mats
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Semesi, I. Sware
    de la Torre-Castro, Maricela
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Seagrass Meadows in Chwaka Bay: Socio-ecological and Management Aspects2012In: People, Nature and Research in Chwaka Bay, Zanzibar, Tanzania / [ed] Maricela de la Torre-Castro, Thomas J. Lyimo, Zanzibar: Western Indian Ocean Marine Science Associoation (WIOMSA) , 2012, p. 89-110Chapter in book (Refereed)
    Abstract [en]

    The shallow-water seascape of Chwaka Bay consists of diverse habitats including coral reefs, sand/mud flats, algal belts and mangrove forests, but the embayment is primarily characterized by its widespread and highly productive seagrass beds. The Bay is a unique seagrass diversity “hotspot”, with eleven species observed, from small, fast-growing and thin-leaved “pioneer” species like Halophila ovalis and H. stipulacea to large, slower-growing “climax species” with thick and long leaves like Thalassodendron ciliatum and Enhalus acoroides. Consequently, it is not surprising that the small-scale subsistence fishery of Chwaka Bay can be seen as a seagrass fishery, with catches consisting primarily of species intimately associated with the seagrass meadows (de la Torre-Castro and Rönnbäck 2004; de la Torre-Castro 2006).Seagrasses are a polyphyletic group of marine vascular, rhizomal plants (den Hartog 1970, 12-13), which form stands of varying sizes usually called “beds” or “meadows” in intertidal and subtidal coastal waters across the globe. Seagrass meadows typically occur on nearshore soft bottoms (although some species are found on rocky bottoms) in single- or mixed-species assemblages, with the typical wide range from tropical to boreal margins of coastal waters (Green and Short 2003, 21-22). They form one of the most productive aquatic ecosystems on Earth (Duarte and Chiscano 1999) and in most areas occur intermixed with other large primary producers like macroalgae. Seagrass ecosystems support multiple ecological functions, including nursery grounds, food and refuge for many benthic,

  • 33. Hammar, Linus
    et al.
    Andersson, Sandra
    Eggertsen, Linda
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Haglund, Johan
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Ehnberg, Jimmy
    Molander, Sverker
    Hydrokinetic Turbine Effects on Fish Swimming Behaviour2013In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 8, no 12, p. e84141-Article in journal (Refereed)
    Abstract [en]

    Hydrokinetic turbines, targeting the kinetic energy of fast-flowing currents, are under development with some turbines already deployed at ocean sites around the world. It remains virtually unknown as to how these technologies affect fish, and rotor collisions have been postulated as a major concern. In this study the effects of a vertical axis hydrokinetic rotor with rotational speeds up to 70 rpm were tested on the swimming patterns of naturally occurring fish in a subtropical tidal channel. Fish movements were recorded with and without the rotor in place. Results showed that no fish collided with the rotor and only a few specimens passed through rotor blades. Overall, fish reduced their movements through the area when the rotor was present. This deterrent effect on fish increased with current speed. Fish that passed the rotor avoided the near-field, about 0.3 m from the rotor for benthic reef fish. Large predatory fish were particularly cautious of the rotor and never moved closer than 1.7 m in current speeds above 0.6 ms(-1). The effects of the rotor differed among taxa and feeding guilds and it is suggested that fish boldness and body shape influenced responses. In conclusion, the tested hydrokinetic turbine rotor proved non-hazardous to fish during the investigated conditions. However, the results indicate that arrays comprising multiple turbines may restrict fish movements, particularly for large species, with possible effects on habitat connectivity if migration routes are exploited. Arrays of the investigated turbine type and comparable systems should therefore be designed with gaps of several metres width to allow large fish to pass through. In combination with further research the insights from this study can be used for guiding the design of hydrokinetic turbine arrays where needed, so preventing ecological impacts.

  • 34. Hammar, Linus
    et al.
    Eggertsen, Linda
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Andersson, Sandra
    Ehnberg, Jimmy
    Arvidsson, Rickard
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Molander, Sverker
    A Probabilistic Model for Hydrokinetic Turbine Collision Risks: Exploring Impacts on Fish2015In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 10, no 3, article id e0117756Article in journal (Refereed)
    Abstract [en]

    A variety of hydrokinetic turbines are currently under development for power generation in rivers, tidal straits and ocean currents. Because some of these turbines are large, with rapidly moving rotor blades, the risk of collision with aquatic animals has been brought to attention. The behavior and fate of animals that approach such large hydrokinetic turbines have not yet been monitored at any detail. In this paper, we conduct a synthesis of the current knowledge and understanding of hydrokinetic turbine collision risks. The outcome is a generic fault tree based probabilistic model suitable for estimating population-level ecological risks. New video-based data on fish behavior in strong currents are provided and models describing fish avoidance behaviors are presented. The findings indicate low risk for small-sized fish. However, at large turbines (>= 5 m), bigger fish seem to have high probability of collision, mostly because rotor detection and avoidance is difficult in low visibility. Risks can therefore be substantial for vulnerable populations of large-sized fish, which thrive in strong currents. The suggested collision risk model can be applied to different turbine designs and at a variety of locations as basis for case-specific risk assessments. The structure of the model facilitates successive model validation, refinement and application to other organism groups such as marine mammals.

  • 35. Hammar, Linus
    et al.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Dahlgren, Thomas G.
    Asplund, Maria E.
    Braga Goncalves, Ines
    Molander, Sverker
    Introducing ocean energy industries to a busy marine environment2017In: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 74, p. 178-185Article, review/survey (Refereed)
    Abstract [en]

    The immense energy potential of the oceans is being increasingly recognized the world over, at the same time the integrity of marine ecosystems is challenged by pressure from multiple human activities. For good reasons environmental licensing procedures are precautionary and new industries must declare their detrimental impacts and provide mitigation measures. New ocean energy industries target renewable energy sources thus, on a grand scale, partly mitigating climate change. However, on-site environmental impacts are yet to be established. In this review we compare ocean energy industries with a wide range of conventional, better understood, human activities and outline environmental risks and research priorities. Results show that ocean energy systems are thought to incur many pressures, some familiar and others with yet unknown effects. Particular uncertainties regard ocean thermal energy conversion (OTEC) and large fast-moving turbines. Ocean energy industries should not be considered in isolation because the significance of environmental impacts depend on the full spectra of human activities in each area. Marine spatial planning provides a platform for holistic assessments and may facilitate the establishment of ocean energy industries, as long as risk-related uncertainties are reduced.

  • 36.
    Hedberg, Per
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Rybak, Fanny F.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Jiddawi, Narriman S.
    Winder, Monika
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Fish larvae distribution among different habitats in coastal East Africa2019In: Journal of Fish Biology, ISSN 0022-1112, E-ISSN 1095-8649, Vol. 94, no 1, p. 29-39Article in journal (Refereed)
    Abstract [en]

    Fish larvae abundances, diversity and trophic position across shallow seagrass, coral reef and open water habitats were examined to characterize their distribution in coastal East Africa. Larvae were identified to family and analysed for abundance differences between sites and habitats, trophic level using stable-isotope analysis and parental spawning mode. Abundances differed greatly between sites with the highest numbers of larvae occurring in the open-water and seagrass habitats. Larval fish diversity was high across habitats with 51 families identified with small differences between sites and among habitats. Notably, larvae of abundant large herbivorous fishes present in reef and seagrass habitats were almost completely absent at all sampling locations. In the seagrass, demersal spawned larvae were more abundant compared with the reef and open-water habitats. Stable-isotope analysis revealed that fish larvae have a varied diet, occupying trophic level two to three and utilizing planktonic prey. This study offers new insights into distributional aspects of fish larvae along the East African coast where such information is sparse.

  • 37.
    Henricksson, Oskar
    et al.
    Södertörn University College.
    Mwandya, Augustine
    Stockholm University, Faculty of Science, Department of Zoology.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Zoology.
    Population genetics structure of juvenile Mugil cephalus around Zanzibar and Bagamoyo (Tanzania) reveals multiple genetic demesManuscript (Other academic)
    Abstract [en]

    There is a growing demand for wild caught juvenile fish to supply the market for aquaculture. However, little is known about the genetic effects of juvenile collection from wild populations. There are a number of imminent threats to both aquaculture systems and wild populations. Juvenile collection from a single population can for example reduce population’s evolutionary potential as well as the disease resistance within an aquaculture pond. In this study, we investigated the local genetic structure of juvenile Mugil cephalus collected from six sites around Bagamoyo (Tanzanian mainland) and Zanzibar Island, East Africa. Fish were caught in low tide using a seine net. All fish collected were juveniles with a total length ranging between 7 and 14 cm (mean length of about 10 cm). Samples were analyzed using Amplified Fragment Length Polymorphism (AFLP), and the Bayesian assignment test implemented in the STRUCTURE 2.2 software was applied to detect if sites were composed of several genetic demes. Our results indicate that all sites contain several different genetic demes suggesting that juvenile collection from a single site may neither harm the genetic diversity of wild M. cephalus nor reduce its disease resistance within an aquaculture system. By collecting juvenile fish from a single site one will in effect harvest juveniles from several genetic lineages.

  • 38.
    Henriksson, Oskar
    et al.
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology. Södertörns högskola.
    Mwandya, Augustine
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Thorberg, Marika
    Grahn, Mats
    AFLP assisted DNA-Barcoding of mullets (Mugilidae) used in East African aquaculture2012In: Western Indian Ocean journal of marine science, ISSN 0856-860X, Vol. 11, no 1, p. 41-54Article in journal (Refereed)
    Abstract [en]

    There is a growing demand for wild caught juvenile fish to supply the market for aquaculture. However, little is known about the genetic effects of juvenile collection from wild populations. There are a number of imminent threats to both aquaculture systems and wild fish populations. Juvenile collection from a single population can for example reduce population’s evolutionary potential as well as the disease resistance within an aquaculture pond. In this study, we investigated the local genetic structure of juvenile mullets collected from five sites around Bagamoyo (Tanzanian mainland) and Zanzibar Island, East Africa. Fish were caught in low tide using a seine net. The fish were morphologically identified, and then genetically identified using direct sequencing of the CO1 gene with cross referencing with the Barcode of Life Database (BOLD) systems.  Molecular variance analyses were used to infer genetic subdivision based on geographic sampling site as well as inferring population structure through the Bayesian assignment test implemented in STRUCTURE 2.3. Our results showed that samples morphologically identified as Mugil cephalus where in fact Valamugil buchanani and we also found evidence of an introgression genome event, where the gene flow from one species may have affected the general gene pool. The Bayesian analysis revealed a clear genetic population structure among the sampled fish; the main difference was the presence of a unique mainland cluster. Our findings may have important implications for management and conservation of mullet fishes in the region and elsewhere.

  • 39.
    Ismail, Rashid
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Ulanga District Council, Tanzania.
    Asplund, Maria
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. University of Gothenburg, Sweden.
    George, Rushingisha
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Tanzania Fisheries Research Institute (TAFIRI), Tanzania.
    Buriyo, Amelia
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Björk, Mats
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Calcifying algae modify the air-sea flux of CO2 in tropical seagrass meadowsManuscript (preprint) (Other academic)
  • 40. Jahnke, Marlene
    et al.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. University of Gothenburg, Sweden.
    Larsson, Josefine
    Asplund, Maria E.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. University of Gothenburg, Sweden.
    Mgeleka, Said
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Tanzania Fisheries Research Institute (TAFIRI), Tanzania.
    Silas, Mathew Ogalo
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Tanzania Fisheries Research Institute (TAFIRI), Tanzania.
    Hoamby, Arielle
    Mahafina, Jamal
    Mtwana Nordlund, Lina
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Uppsala University, Sweden.
    Population genetic structure and connectivity of the seagrass Thalassia hemprichii in the Western Indian Ocean is influenced by predominant ocean currents2019In: Ecology and Evolution, ISSN 2045-7758, E-ISSN 2045-7758Article in journal (Refereed)
    Abstract [en]

    This study is the first large-scale genetic population study of a widespread climax species of seagrass, Thalassia hemprichii, in the Western Indian Ocean (WIO). The aim was to understand genetic population structure and connectivity of T. hemprichii in relation to hydrodynamic features. We genotyped 205 individual seagrass shoots from 11 sites across the WIO, spanning over a distance of similar to 2,700 km, with twelve microsatellite markers. Seagrass shoots were sampled in Kenya, Tanzania (mainland and Zanzibar), Mozambique, and Madagascar: 4-26 degrees S and 33-48 degrees E. We assessed clonality and visualized genetic diversity and genetic population differentiation. We used Bayesian clustering approaches (TESS) to trace spatial ancestry of populations and used directional migration rates (DivMigrate) to identify sources of gene flow. We identified four genetically differentiated groups: (a) samples from the Zanzibar channel; (b) Mozambique; (c) Madagascar; and (d) the east coast of Zanzibar and Kenya. Significant pairwise population genetic differentiation was found among many sites. Isolation by distance was detected for the estimated magnitude of divergence (D-EST), but the three predominant ocean current systems (i.e., East African Coastal Current, North East Madagascar Current, and the South Equatorial Current) also determine genetic connectivity and genetic structure. Directional migration rates indicate that Madagascar acts as an important source population. Overall, clonality was moderate to high with large differences among sampling sites, indicating relatively low, but spatially variable sexual reproduction rates. The strongest genetic break was identified for three sites in the Zanzibar channel. Although isolation by distance is present, this study suggests that the three regionally predominant ocean current systems (i.e., East African Coastal Current, North East Madagascar Current, and the South Equatorial Current) rather than distance determine genetic connectivity and structure of T. hemprichii in the WIO. If the goal is to maintain genetic connectivity of T. hemprichii within the WIO, conservation planning and implementation of marine protection should be considered at the regional scale-across national borders.

  • 41. Knudby, Anders
    et al.
    Nordlund, Lina Mtwana
    Palmqvist, Gustav
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Wikström, Karolina
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Koliji, Alan
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Lindborg, Regina
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Using multiple Landsat scenes in an ensemble classifier reduces classification error in a stable nearshore environment2014In: International Journal of Applied Earth Observation and Geoinformation, ISSN 0303-2434, Vol. 28, p. 90-101Article in journal (Refereed)
    Abstract [en]

    Medium-scale land cover maps are traditionally created on the basis of a single cloud-free satellite scene, leaving information present in other scenes unused. Using 1309 field observations and 20 cloud- and error-affected Landsat scenes covering Zanzibar Island, this study demonstrates that the use of multiple scenes can both allow complete coverage of the study area in the absence of cloud-free scenes and obtain substantially improved classification accuracy. Automated processing of individual scenes includes derivation of spectral features for use in classification, identification of clouds, shadows and the land/water boundary, and random forest-based land cover classification. An ensemble classifier is then created from the single-scene classifications by voting. The accuracy achieved by the ensemble classifier is 70.4%, compared to an average of 62.9% for the individual scenes, and the ensemble classifier achieves complete coverage of the study area while the maximum coverage for a single scene is 1209 of the 1309 field sites. Given the free availability of Landsat data, these results should encourage increased use of multiple scenes in land cover classification and reduced reliance on the traditional single-scene methodology.

  • 42. Lindegarth, Mats
    et al.
    Bergström, Ulf
    Mattila, Johanna
    Olenin, Sergej
    Ollikainen, Markku
    Downie, Anna-Leena
    Sundblad, Göran
    Bucas, Martynas
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Snickars, Martin
    von Numers, Mikael
    Svensson, J. Robin
    Kosenius, Anna-Kaisa
    Testing the Potential for Predictive Modeling and Mapping and Extending Its Use as a Tool for Evaluating Management Scenarios and Economic Valuation in the Baltic Sea (PREHAB)2014In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 43, no 1, p. 82-93Article in journal (Refereed)
    Abstract [en]

    We evaluated performance of species distribution models for predictive mapping, and how models can be used to integrate human pressures into ecological and economic assessments. A selection of 77 biological variables (species, groups of species, and measures of biodiversity) across the Baltic Sea were modeled. Differences among methods, areas, predictor, and response variables were evaluated. Several methods successfully predicted abundance and occurrence of vegetation, invertebrates, fish, and functional aspects of biodiversity. Depth and substrate were among the most important predictors. Models incorporating water clarity were used to predict increasing cover of the brown alga bladderwrack Fucus vesiculosus and increasing reproduction area of perch Perca fluviatilis, but decreasing reproduction areas for pikeperch Sander lucioperca following successful implementation of the Baltic Sea Action Plan. Despite variability in estimated non-market benefits among countries, such changes were highly valued by citizens in the three Baltic countries investigated. We conclude that predictive models are powerful and useful tools for science-based management of the Baltic Sea.

  • 43.
    Lyimo, Liberatus D.
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. University of Dodoma, Tanzania.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Lyimo, Thomas J.
    Deyanova, Diana
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Dahl, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hamisi, Mariam
    Björk, Mats
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Shading and simulated grazing increase the sulphide pool and methane emission in a tropical seagrass meadow2018In: Marine Pollution Bulletin, ISSN 0025-326X, E-ISSN 1879-3363, Vol. 134, p. 89-93Article in journal (Refereed)
    Abstract [en]

    Though seagrass meadows are among the most productive habitats in the world, contributing substantially to long-term carbon storage, studies of the effects of critical disturbances on the fate of carbon sequestered in the sediment and biomass of these meadows are scarce. In a manipulative in situ experiment, we studied the effects of successive loss of seagrass biomass as a result of shading and simulated grazing at two intensity levels on sulphide (H2S) content and methane (CH4) emission in a tropical seagrass meadow in Zanzibar (Tanzania). In all disturbed treatments, we found a several-fold increase in both the sulphide concentration of the sediment pore-water and the methane emissions from the sediment surface (except for CH4 emissions in the low-shading treatment). This could be due to the ongoing degradation of belowground biomass shed by the seagrass plants, supporting the production of both sulphate-reducing bacteria and methanogens, possibly exacerbated by the loss of downwards oxygen transport via seagrass plants. The worldwide rapid loss of seagrass areas due to anthropogenic activities may therefore have significant effects on carbon sink-source relationships within coastal seas.

  • 44.
    Lyimo, Liberatus Dominick
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. University of Dodoma, Tanzania.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hamis, Mariam
    Lyimo, Thomas J.
    Björk, Mats
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Emission of nitrous oxide and methane from tropical seagrass meadows: effects of gas transport through seagrass plant and eutrophicationManuscript (preprint) (Other academic)
  • 45.
    Lyimo, Liberatus Dominick
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. University of Dodoma, Tanzania.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Lyimo, Thomas J.
    Deyanova, Diana
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Dahl, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hamis, Mariam
    Björk, Mats
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Shading and simulated grazing of seagrass leaves increases sulphide production and methane emission in a tropical seagrass meadowManuscript (preprint) (Other academic)
  • 46. Mazzuca, Silvia
    et al.
    Björk, Mats
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Beer, S.
    Felisberto, P.
    Gobert, S.
    Procaccini, G.
    Runcie, J.
    Silva, J.
    Borges, A. V.
    Brunet, C.
    Buapet, Pimchanok
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Champenois, W.
    Costa, M. M.
    D'Esposito, D.
    Gullström, Martin
    Lejeune, P.
    Lepoint, G.
    Olive, I.
    Rasmusson, Lina M.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Richir, J.
    Ruocco, M.
    Serra, I. A.
    Spadafora, A.
    Santos, Rui
    Establishing research strategies, methodologies and technologies to link genomics and proteomics to seagrass productivity, community metabolism, and ecosystem carbon fluxes2013In: Frontiers in Plant Science, ISSN 1664-462X, E-ISSN 1664-462X, Vol. 4, article id 38Article in journal (Refereed)
    Abstract [en]

    A complete understanding of the mechanistic basis of marine ecosystem functioning is only possible through integrative and interdisciplinary research. This enables the prediction of change and possibly the mitigation of the consequences of anthropogenic impacts. One major aim of the European Cooperation in Science and Technology (COST) Action ES0609 Seagrasses productivity. From genes to ecosystem management, is the calibration and synthesis of various methods and the development of innovative techniques and protocols for studying seagrass ecosystems. During 10 days, 20 researchers representing a range of disciplines (molecular biology, physiology, botany, ecology, oceanography, and underwater acoustics) gathered at The Station de Recherches Sous-marines et Oceanographiques (STARESO, Corsica) to study together the nearby Posidonia oceanica meadow. STARESO is located in an oligotrophic area classified as pristine site where environmental disturbances caused by anthropogenic pressure are exceptionally low. The healthy P. oceanica meadow, which grows in front of the research station, colonizes the sea bottom from the surface to 37 m depth. During the study, genomic and proteomic approaches were integrated with ecophysiological and physical approaches with the aim of understanding changes in seagrass productivity and metabolism at different depths and along daily cycles. In this paper we report details on the approaches utilized and we forecast the potential of the data that will come from this synergistic approach not only for P. oceanica but for seagrasses in general.

  • 47. Moksnes, Per-Olav
    et al.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Zoology.
    Tryman, Kentaroo
    Baden, Susanne
    Trophic cascades in a temperate seagrass community2008In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 117, no 5, p. 763-777Article in journal (Refereed)
    Abstract [en]

    We assessed the relative importance of bottom-up and top-down processes in structuring an eelgrass community in Sweden, a system impacted both by eutrophication and overfishing. Using artificial seagrass as substrate, we manipulated nutrient levels and predator abundance in a full-factorial cage-experiment.

    The results revealed a seagrass community dominated by strong top-down processes controlling the aggregate biomass of mesograzers and macroalgae. In the absence of predators the large amphipod Gammarus locusta became very abundant resulting in a leaf community with low biomass of algae and smaller mobile fauna. One enclosed gobid fish predator reduced the abundance of adult G. locusta by > 90%, causing a three to six times increase in the biomass of algae, smaller mesograzers and meiofauna. Numerous small predators in uncaged habitats reduced the biomass of G. locusta and other mesograzers by > 95% in comparison to the fish treatment, further increasing the biomass of epiphytic algae and meiofauna. Although water column nutrient enrichment caused a temporal bloom of the filamentous macroalgae Ulva spp., no significant nutrient-effects were found on the algal community at the end of the experiment. The only lasting nutrient-effect was a significant increase in the biomass of G. locusta, but only in the absence of ambient predators.

    These results demonstrate that mesograzers can respond to enhanced food supply, increase their biomass and control the algal growth when predation rates are low. However, in the assessed system, high predation rates appear to make mesograzers functionally extinct, causing a community-wide trophic cascade that promotes the growth of ephemeral algae. This top-down effect could penetrate down, despite a complex food-web because the interaction strength in the community was strongly skewed towards two functionally dominant algal and grazer species that were vulnerable to consumption. These results indicate that overexploitation of gadoid fish may be linked to increased macroalgal blooms and loss of eelgrass in the area through a trophic cascade affecting the abundance of mesograzers.

  • 48.
    Mtwana Nordlund, Lina
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Åbo Akademi University, Finland; WIO CARE, Tanzania.
    de la Torre-Castro, Maricela
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Stockholm University, Faculty of Science, Stockholm Resilience Centre.
    Erlandsson, Johan
    Conand, Chantal
    Muthiga, Nyawira
    Jiddawi, Narriman
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Intertidal Zone Management in the Western Indian Ocean: Assessing Current Status and Future Possibilities Using Expert Opinions2014In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 43, no 8, p. 1006-1019Article in journal (Refereed)
    Abstract [en]

    This expert opinion study examined the current status of the intertidal zone in the Western Indian Ocean (WIO) and ranked and discussed future management approaches. Information was gathered from scientists, practitioners, and managers active in the WIO region through a questionnaire and a workshop. The experts stated that the productive intertidal environment is highly valuable for reasons such as recreation, erosion protection, and provision of edible invertebrates and fish. Several anthropogenic pressures were identified, including pollution, harbor activities, overexploitation, and climate change. The experts considered the WIO intertidal zone as generally understudied, undermanaged, and with poor or no monitoring. The most important management strategies according to the expert opinions are to develop and involve local people in integrated coastal zone management (ICZM), to increase knowledge on species-environment relationships, and to develop awareness campaigns and education programs. To improve coastal environmental management and conservation, we argue that the intertidal zone should be treated as one organizational management unit within the larger framework of ICZM.

  • 49.
    Mtwana Nordlund, Lina
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Unsworth, Richard K. F.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Cullen-Unsworth, Leanne C.
    Global significance of seagrass fishery activity2018In: Fish and Fisheries, ISSN 1467-2960, E-ISSN 1467-2979, Vol. 19, no 3, p. 399-412Article in journal (Refereed)
    Abstract [en]

    Seagrass meadows support fisheries through provision of nursery areas and trophic subsidies to adjacent habitats. As shallow coastal habitats, they also provide key fishing grounds; however, the nature and extent of such exploitation are poorly understood. These productive meadows are being degraded globally at rapid rates. For degradation to cease, there needs to be better appreciation for the value of these habitats in supporting global fisheries. Here, we provide the first global scale study demonstrating the extent, importance and nature of fisheries exploitation of seagrass meadows. Due to a paucity of available data, the study used a global expert survey to demonstrate the widespread significance of seagrass-based fishing activity. Our study finds that seagrass-based fisheries are globally important and present virtually wherever seagrass exists, supporting subsistence, commercial and recreational activity. A wide range of fishing methods and gear is used reflecting the spatial distribution patterns of seagrass meadows, and their depth ranges from intertidal (accessible by foot) to relatively deep water (where commercial trawls can operate). Seagrass meadows are multispecies fishing grounds targeted by fishers for any fish or invertebrate species that can be eaten, sold or used as bait. In the coastal communities of developing countries, the importance of the nearshore seagrass fishery for livelihoods and well-being is irrefutable. In developed countries, the seagrass fishery is often recreational and/or more target species specific. Regardless of location, this study is the first to highlight collectively the indiscriminate nature and global scale of seagrass fisheries and the diversity of exploitative methods employed to extract seagrass-associated resources. Evidence presented emphasizes the need for targeted management to support continued viability of seagrass meadows as a global ecosystem service provider.

  • 50. Mwandya, A. W.
    et al.
    Mgaya, Y. D.
    Öhman, M. C.
    Stockholm University, Faculty of Science, Department of Zoology.
    Bryceson, I.
    Gullström, M.
    Stockholm University, Faculty of Science, Department of Zoology.
    Distribution patterns of striped mullet Mugil cephalus in mangrove creeks, Zanzibar, Tanzania2010In: AFR J MAR SCI, ISSN 1814-232X, Vol. 32, no 1, p. 85-93Article in journal (Refereed)
    Abstract [en]

    Spatial and seasonal variations in density of striped mullet Mugil cephalus were investigated in four mangrove creeks in Zanzibar, Tanzania, during a one-year cycle. Fish were collected monthly in the lower, intermediate and upper reaches of each creek using a beach-seine net. All fish collected were juveniles between 2 and 16 cm standard length. The density of juvenile mullet differed significantly among the creeks, but the spatial patterns within them were consistent with higher densities upstream in three of the creeks. Generally, small mullet (2-10 cm) were more abundant in the upper reaches compared to the lower and intermediate reaches. Seasonal patterns were weak, although mullet densities were high during the period of heavy rains (March-May). Principal component analysis showed that a muddy substrate with microphytobenthos was positively correlated with high mullet densities, although site-specific variables such as shallow water depth and water clarity were also significantly correlated. Our findings suggest that the densities of juvenile striped mullet vary among sites and creeks in response to refuge availability from turbid, shallow water and the accessibility of food from benthic microalgae.

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