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  • 1.
    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.

  • 2.
    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.

  • 3.
    Deyanova, Diana
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Seagrass productivity: from plant to system2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Seagrasses form one of the most productive habitats on earth and are recognized as very efficient carbon sinks. The levels and patterns of productivity within and across different seagrass systems vary widely due to natural or human-induced factors. Seagrass plants, being the foundation species of seagrass meadows, have a substitutional role as primary producers to the overall productivity of their habitat. Clarifying the variation in the carbon capture potential of these plants on physiological and ecological levels is essential to understand of the whole system’s carbon balance. In this thesis, the photosynthetic performance and productivity of seagrass plants were studied in relation to factors that have large impact on productivity, such as tissues age, season and water depth. Furthermore, the seagrass response, in terms of capacity to capture and sequester carbon, to human-induced stress factors such as shading and simulated grazing was evaluated in a tropical seagrass meadow. The research has included a multitude of seagrass productivity assessments from plant- to system level.

    The results showed that age has a significant effect on the photosynthetic performance of the temperate seagrass Zostera marina L., both within a single shoot and between shoots. When comparing leaves among the same shoot, the photosynthetic capacity and efficiency were highest in mature tissues and significantly reduced in very young tissues as well as in tissues undergoing senescence. In response to high light stress, very young tissues seemed to cope better with dissipating excess light energy, which was demonstrated by the higher values of non-photochemical quenching (NPQ) observed compared to mature and senescent tissues. Such an effect was also observed when comparing the oldest and youngest shoots from the same genet; the youngest shoot showed higher ability to dissipate excess light energy compared to the oldest one, and might thus be able to better withstand light stress.

    On a larger spatiotemporal scale, the areal productivity of seagrass plants was significantly affected by light availability and temperature, leading to a strong seasonal variation. In addition, depth had a strong site-specific effect on plant productivity in terms of biomass. On a yearly basis, productivity rates varied substantially, reaching up to 20 g C m-2 24h-1 in the summer months. This high carbon capture potential was, however, outbalanced by the high respiration rates of the benthic community. Overall, the whole system had a low but positive yearly carbon balance.

    Both shading and simulated grazing negatively affected seagrass plants and the whole habitat after five months of experimental disturbance. On the plant level, photosynthesis, productivity and growth were all reduced. On the system level, a reduction in community productivity was recorded. The long-term refractory carbon was, however, not affected although erosion was observed in treatments subjected to simulated grazing.

    In summary, this thesis has established that age, season, depth and exposure are factors highly responsible for natural variation in seagrass plant- and habitat productivity, and that seagrasses respond to human-induced stress by significantly reducing their productivity. Even though seagrass plants are generally capable of surviving stress periods, these results suggest that prolonged deteriorating stress conditions will lead to serious harm on the plants as well as the entire habitat, and thereby compromising the carbon burial capacity of the seagrass system.

  • 4.
    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.

  • 5.
    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.

  • 6.
    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.

  • 7.
    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)
  • 8.
    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.

  • 9.
    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)
  • 10. Röhr, Maria Emilia
    et al.
    Holmer, Marianne
    Baum, Julia K.
    Björk, Mats
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Chin, Diana
    Chalifour, Lia
    Cimon, Stephanie
    Cusson, Mathieu
    Dahl, Martin
    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. Bulgarian Academy of Sciences, Bulgaria.
    Duffy, J. Emmet
    Eklöf, Johan S.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Geyer, Julie K.
    Griffin, John N.
    Gullström, Martin
    Hereu, Clara M.
    Hori, Masakazu
    Hovel, Kevin A.
    Hughes, A. Randall
    Jorgensen, Pablo
    Kiriakopolos, Stephanie
    Moksnes, Per-Olav
    Nakaoka, Masahiro
    O'Connor, Mary I.
    Peterson, Bradley
    Reiss, Katrin
    Reynolds, Pamela L.
    Rossi, Francesca
    Ruesink, Jennifer
    Santos, Rui
    Stachowicz, John J.
    Tomas, Fiona
    Lee, Kun-Seop
    Unsworth, Richard K. F.
    Boström, Christoffer
    Blue Carbon Storage Capacity of Temperate Eelgrass (Zostera marina) Meadows2018In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 32, no 10, p. 1457-1475Article in journal (Refereed)
    Abstract [en]

    Despite the importance of coastal ecosystems for the global carbon budgets, knowledge of their carbon storage capacity and the factors driving variability in storage capacity is still limited. Here we provide an estimate on the magnitude and variability of carbon stocks within a widely distributed marine foundation species throughout its distribution area in temperate Northern Hemisphere. We sampled 54 eelgrass (Zostera marina) meadows, spread across eight ocean margins and 36 degrees of latitude, to determine abiotic and biotic factors influencing organic carbon (C-org) stocks in Zostera marina sediments. The C-org stocks (integrated over 25-cm depth) showed a large variability and ranged from 318 to 26,523gC/m(2) with an average of 2,721gC/m(2). The projected C-org stocks obtained by extrapolating over the top 1m of sediment ranged between 23.1 and 351.7MgC/ha, which is in line with estimates for other seagrasses and other blue carbon ecosystems. Most of the variation in C-org stocks was explained by five environmental variables (sediment mud content, dry density and degree of sorting, and salinity and water depth), while plant attributes such as biomass and shoot density were less important to C-org stocks. Carbon isotopic signatures indicated that at most sites <50% of the sediment carbon is derived from seagrass, which is lower than reported previously for seagrass meadows. The high spatial carbon storage variability urges caution in extrapolating carbon storage capacity between geographical areas as well as within and between seagrass species.

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