Ändra sökning
Avgränsa sökresultatet
1 - 32 av 32
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Träffar per sida
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
Markera
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 1. Enge, Swantje
    et al.
    Sagerman, Josefin
    Stockholms universitet, Naturvetenskapliga fakulteten, Stockholms universitets Östersjöcentrum.
    Wikström, Sofia A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Stockholms universitets Östersjöcentrum.
    Pavia, Henrik
    A Review of Herbivore Effects on Seaweed Invasions2017Ingår i: Oceanography and Marine Biology: An Annual Review, Volume 55 / [ed] S. J. Hawkins, A. J. Evans, A.C. Dale, L. B. Firth, D. J. Hughes, I. P. Smith, BOCA RATON: CRC PRESS-TAYLOR & FRANCIS GROUP , 2017, Vol. 55, s. 421-440Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    Almost 300 non-native seaweeds are identified worldwide and an increasing number of these are classified as invasive with potential negative effects on the diversity and functioning of native ecosystems. Marine herbivores affect seaweed biomass and community structure in marine habitats across the globe. Consequently, herbivore-seaweed interactions are expected to be important for the establishment and invasion success of non-native seaweeds. To synthesize current knowledge of consumer effects on non-native seaweeds, we performed a meta-analysis on feeding preferences of native herbivores for non-native versus native seaweeds. Data were included from 35 studies, published from 1992-2015 and comprising 18 non-native seaweeds. Results showed that overall, native herbivores tended to prefer to feed on native rather than non-native seaweeds. Preferences were, however, variable across studies with significant differences between taxonomic and functional groups of seaweeds. In particular, filamentous red non-native seaweeds were of low palatability to native herbivores. No general feeding preferences were apparent between natives and non-natives for brown and green seaweeds, or for leathery and corticated seaweeds. In addition, we reviewed the existing studies on the effects of consumers on the performance of native and non-native seaweeds in invaded communities. This indicated that non-native seaweeds performed better than their native competitors in the presence of grazers, but in many cases had superior competitive abilities also in the absence of herbivory. To achieve a comprehensive evaluation of consumers' role in seaweed invasion success, future research should have a larger focus on manipulative community experiments, ideally on time scales that include seasonal changes and complete life cycles of the seaweeds.

  • 2.
    Forslund, Helena
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Botaniska institutionen.
    Wikström, Sofia A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Systemekologiska institutionen.
    Pavia, Henrik
    Higher resistance to herbivory in introduced compared to native populations of a seaweed2010Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 164, nr 3, s. 833-840Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Non-indigenous species (NIS) are important components of global change, and in order to manage such species it is important to understand which factors affect their success. Interactions with enemies in the new range have been shown to be important for the outcome of introductions, but thus far most studies on NIS-enemy interactions have considered only specialist herbivores in terrestrial systems. Here we present the results from the first biogeographic study that compares herbivore resistance between populations in the native and new region of a non-indigenous seaweed. We show that low consumption of the non-indigenous seaweed by a generalist herbivore is caused by higher chemical defence levels and herbivore resistance in the new range-and not by the failure of the herbivore to recognise the non-indigenous seaweed as a suitable host. Since most seaweed-herbivore interactions are dominated by generalist herbivores, this pattern could be common in marine communities. Our results also reveal that traits used to predict the invasive potential of species, such as their resistance to enemies, can change during the invasion process, but not always in the way predicted by dominant theories.

  • 3.
    Halling, Christina
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Tano, Stina
    Eggertsen, Maria
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Buriyo, Amelia
    Msuya, Flower
    Wikström, Sofia
    Stockholms universitet, Naturvetenskapliga fakulteten, Stockholms universitets Östersjöcentrum.
    The introduction of South East Asian seaweed and its ecological implications; Can native East African Eucheuma denticulatum and Kappaphycus alvarezii be a potential alternative for farming?Manuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    The seaweed farming of eucheumoids in East Africa is solely based on introduced South East Asian (SEA) haplotypes of the carrageenophytes Eucheuma and Kappaphycus. As overexploitation of natural seaweed resources lead to a decline in harvest and export, commercial seaweed farming was started using highly productive SEA strains of the same genus introduced from the Philippines to Zanzibar in 1989.  Initially, productivity was high, the sector grew rapidly and seaweed farming soon became an important livelihood. Today, the industry faces various challenges such as decreased productivity and high rates of diseases and epiphytic infestations. Continuous introduction of foreign stock for cultivation vitalization might not be the solution, as escapees of SEA Eucheuma denticulatum have been found spreading into natural environments around Zanzibar with uncertain ecological consequences.  We suggest that indigenous haplotypes of E. denticulatum and Kappaphycus alvarezii should be re-evaluated for farming potential,  for increasing the genetic diversity and hence resilience within stocks.

    This study is a first step towards a reassessment of farming potential of East African (EA) haplotypes. Molecularly identified haplotypes of E. denticulatum and K. alvarezii were tested in in-situ farming conditions in Zanzibar, and growth rates, grazing and epiphytes were compared between EA and SEA haplotypes. Results show, except for an overall decreased growth compared to previous studies, that growth rate was site dependent and that SEA Eucheuma haplotypes have a higher growth rate (1.3 ±1.8 - 3.6 ±1.9% per day) compared to EA haplotypes (0.2 ±1.0 - 2.0 ±0.4% per day). No significant differences were found in grazing rate between native and introduced Eucheuma haplotypes, while native Kappaphycus was more prone to grazing. 

    In conclusion the farming potential for native E. denticulatum, is not rejected but underlines that there is an urgent need of continued search for native East African seaweed resources and a further identification of their desirable traits. If successful, this would enable East African seaweed industry to further expansion and secure its ecological and economical sustainability.

  • 4.
    Halling, Christina
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Systemekologiska institutionen.
    Wikström, Sofia A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Systemekologiska institutionen.
    Lilliesköld-Sjöö, Gustaf
    Stockholms universitet, Naturvetenskapliga fakulteten, Systemekologiska institutionen.
    Mörk, Erik
    Stockholms universitet, Naturvetenskapliga fakulteten, Systemekologiska institutionen.
    Lundsor, Elisabeth
    Zuccarello, Giuseppe C.
    Introduction of Asian strains and low genetic variation in farmed seaweeds: indications for new management practices2013Ingår i: Journal of Applied Phycology, ISSN 0921-8971, E-ISSN 1573-5176, Vol. 25, nr 1, s. 89-95Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Seaweed farming has a crucial role in the development of future sustainable mariculture. In the same time, spreading of introduced species or genotypes from farms may threaten local ecosystems. We analyzed a molecular marker (mitochondrial cox2-3 spacers) from cultivated and wild specimen of the widely farmed seaweeds Eucheuma and Kappaphycus, collected in Zanzibar on the African east coast where commercial farming was introduced in 1989. Genotypes of presumed Asian origin were found growing on coral reefs and drifting in seagrass meadows, indicating that genotypes introduced for farming have established successfully in the wild in Zanzibar. Only a very low number of genotypes, all of Asian origin, were found in the farms. This indicates a low accessible gene pool, which can limit the capacity for adaptation to changed conditions and disease resistance in the farming system. African genotypes were found in a few sites, showing the potential for future farming of native strains. The ecological effects of the Asian genotypes introduced to coral reefs should also be further investigated in order to evaluate the risk connected with further introductions of new foreign strains.

  • 5.
    Hansen, Joakim
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Botaniska institutionen.
    Sagerman, Josefin
    Stockholms universitet, Naturvetenskapliga fakulteten, Systemekologiska institutionen.
    Sofia, Wikström
    Stockholms universitet, Naturvetenskapliga fakulteten, Systemekologiska institutionen.
    Effects of plant morphology on small-scale distribution of invertebrates2010Ingår i: Marine Biology, ISSN 0025-3162, E-ISSN 1432-1793, Vol. 157, nr 10, s. 2143-2155Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Habitat structure influences organism communities by mediating interactions between individuals and species, affecting abundance and species richness. We examined whether variations in the morphology of soft-bottom plants affect their function as habitat and whether complex structured plants support higher macroinvertebrate abundance and species richness. Three Baltic Sea plant species were studied, together with artificial plants resembling each species. In a field collection, we found higher invertebrate abundance on the morphologically more complex plants Myriophyllum spicatum and Chara baltica than on the structurally simpler plant Potamogeton perfoliatus. In a colonization experiment, we found the highest invertebrate abundance on artificial M. spicatum but found no difference between natural plants. Invertebrate taxon richness displayed no consistent relationship with plant structural complexity. The results imply that plant morphology influences small-scale invertebrate distribution, partly supporting the hypothesis that structurally complex plants harbour higher invertebrate abundance.

  • 6.
    Hansen, Joakim
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Botaniska institutionen.
    Wikström, Sofia
    Stockholms universitet, Naturvetenskapliga fakulteten, Systemekologiska institutionen.
    Axemar, Hanna
    Stockholms universitet, Naturvetenskapliga fakulteten, Botaniska institutionen.
    Kautsky, Lena
    Stockholms universitet, Naturvetenskapliga fakulteten, Botaniska institutionen.
    Distribution differences and active habitat choices of invertebrates between macrophytes of different morphological complexity2011Ingår i: Aquatic Ecology, ISSN 1386-2588, E-ISSN 1573-5125, Vol. 45, nr 1, s. 11-22Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This study explores: (1) whether the abundance of macroinvertebrates differs between macrophytes differing in both morphological complexity and tolerance to nutrient enrichment; (2) whether the distribution of invertebrates between macrophytes is due to active habitat choice; and (3) whether invertebrates prefer structurally complex to simple macrophytes. Macroinvertebrate abundance was compared between two common soft-bottom plants in the Baltic Sea that are tolerant to eutrophication, Myriophyllum spicatum and Potamogeton pectinatus, and one common plant that is sensitive to eutrophication, Chara baltica. Both field sampling and habitat choice experiments were conducted. We recorded higher total macroinvertebrate abundance on the structurally complex M. spicatum than on the more simply structured P. pectinatus and C. baltica, but found no difference in macroinvertebrate abundance between P. pectinatus and C. baltica. In accordance with the field results, our experiment indicated that the crustacean Gammarus oceanicus actively chose M. spicatum over the other macrophytes. Besides, we found that G. oceanicus actively preferred complex to simply structured artificial plants, indicating that the animal distribution was at least partly driven by differences in morphological complexity between plant species. In contrast, the gastropod Theodoxus fluviatilis did not make an active habitat choice between the plants. Our findings suggest that human-induced changes in vegetation composition can affect the faunal community. Increased abundance of structurally complex macrophytes, for example, M. spicatum, can result in increased abundance of macroinvertebrates, particularly mobile arthropods that may actively choose a more structurally complex macrophyte.

  • 7.
    Hansen, Joakim
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Botaniska institutionen.
    Wikström, Sofia
    Kautsky, Lena
    Stockholms universitet, Naturvetenskapliga fakulteten, Botaniska institutionen.
    Effects of water exchange and vegetation on the macroinvertebrate fauna composition of shallow land-uplift bays in the Baltic Sea2008Ingår i: Estuarine, Coastal and Shelf Science, ISSN 0272-7714, E-ISSN 1096-0015, Vol. 77, nr 3, s. 535-547Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Shallow bays with soft sediment bottoms are common habitats along the Swedish and Finnish Baltic Sea coastline. These bays undergo a process of geomorphometric evolution with the natural isostatic land-uplift process, whereby open bays and sounds decrease in depth and are gradually isolated from the sea, forming bays with narrow openings. This study tested the relationship between the morphometric isolation of the bays from the sea and the macroinvertebrate fauna community of these bays. Additionally, we tested the specific role of the submerged vegetation as an indicator of the macroinvertebrate fauna community. We chose two environmental factors for the analyses, water exchange of the bays and the taxon richness of the macroflora in the bays. We found a hierarchical relationship between water exchange, flora taxon richness, and fauna biomass and taxon richness using structural equation modelling: decreased biomass and taxon richness of fauna were related to decreased flora taxon richness, which in turn was related to decreased water exchange. Using multivariate redundancy analysis, the two environmental factors included in the model were found to explain 47.7% of the variation in the fauna taxon composition and 57.5% of the variation in the functional feeding groups of the fauna. Along the morphometric isolation gradient of the bays, the fauna assemblages changed from a community dominated by gastropods, bivalves, and crustaceans, to a community mainly consisting of a few insect taxa. Moreover, the proportion of predators, gathering collectors, and shredders increased while that of filtering collectors and scrapers decreased. Our results indicate that the density and taxon richness of macroinvertebrate fauna are higher in less morphometrically isolated bays than in more isolated bays in the Baltic Sea. Furthermore, we suggest that the taxon richness of macroflora can serve as an indicator of the fauna community.

  • 8.
    Hansen, Joakim
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Botaniska institutionen.
    Wikström, Sofia
    Stockholms universitet, Naturvetenskapliga fakulteten, Systemekologiska institutionen.
    Kautsky, Lena
    Stockholms universitet, Naturvetenskapliga fakulteten, Botaniska institutionen.
    Taxon composition and food-web structure in a morphometric gradient of Baltic Sea land-uplift bays2012Ingår i: Boreal environment research, ISSN 1239-6095, E-ISSN 1797-2469, Vol. 17, nr 1, s. 1-20Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Shallow Baltic Sea bays undergo a process of morphometric isolation from the sea due to post-glacial land uplift. Recent studies have documented that both flora and fauna communities change along this gradient. Changes in taxon composition may in turn alter feeding ecology and trophic relationships. In addition, the relative importance of carbon from terrestrial sources may increase with bay isolation. In accordance with previous studies, we found a change in the community composition of both flora and fauna with bay isolation. Results of stable isotope analysis (δ13C, δ15N) suggested that epiphytes and periphyton are the major carbon sources for most benthic primary consumers, but that their importance in relation to angiosperms and charophytes decreased with bay isolation. The results also indicated that filter feeders utilize terrestrially derived carbon, but its importance could not be critically related to bay isolation. Trophic positions of the consumers were similar across the bay isolation gradient.

  • 9.
    Nyström Sandman, Antonia
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Systemekologiska institutionen.
    Wikström, Sofia A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Systemekologiska institutionen.
    Blomqvist, Mats
    Kautsky, Hans
    Stockholms universitet, Naturvetenskapliga fakulteten, Systemekologiska institutionen.
    Isaeus, Martin
    Scale-dependent influence of environmental factors on species distribution: a case study on five benthic species in the Baltic SeaManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    Statistical modelling can be used to relate biological survey data to environmental factors, thereby providing a basis for predictive mapping of species or communities. However, there has been little discussion about the effect of scale on the predictive power of the variables used for species prediction. In this study, we analysed if the relative importance of environmental factors for the distribution of aquatic species was scale dependent, using data on the cover of five common benthic species (four macrophytes and one animal), from 1731 sites along the Swedish Baltic Sea coast. We modelled the cover and distribution of the five species in relation to salinity, depth, slope, wave exposure and substrate in scale steps from 25 to 1500 km, and analysed the relative contribution of the environmental variables to each species model. The average total deviance explained by the models was generally quite high, and decreased with increasing scale for all macrophyte species, while it increased for the animal, the Baltic Sea blue mussel, Mytilus edulis. The average contribution of salinity increased for all species when moving from local to Baltic Sea scale, and for the Baltic Sea blue mussel it was the single most important factor at the Baltic Sea scale. The average contribution of depth decreased with increasing scale for all species. However, regardless of scale, depth was the most important environmental factor to explain the distribution of all but one of the investigated macrophyte species. The relative contribution of different environmental variables changed with scale, and responses also differed between species. Factors measured on a fine scale, and thus describing local conditions were more influential at the local scale, whereas the large scale salinity gradient increased in importance with scale.

  • 10.
    Sagerman, Josefin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Marine seaweed invasions: Impacts and biotic resistance in native ecosystems2015Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Marine seaweeds constitute one of the most productive plant systems known on Earth and a rich fauna including juvenile fish and crustaceans is dependent on the habitats they form. Human influence on marine costal ecosystems has resulted in large scale changes to the abundance and distribution of species, where species introductions constitute an obvious part. The aims of this thesis were to 1) explore how non-native seaweeds impact on ecosystem functions (primary production and decomposition), and 2) study how interactions between non-native seaweeds and native communities affect invasion success. I used a combination of laboratory assays, outdoor mesocosms and field experiments.

    Paper I and II revealed that the impact on ecosystem functions were substantially different depending on the identity of the invader. The highly successful non-native red alga Heterosiphonia japonica had a large effect on community productivity. Due to the rapid growth of the invader, the primary production increased by more than four times in mixed species communities with the invader compared to  communities with only native species. In contrast, the morphologically similar and equally successful non-native red alga Bonnemaisonia hamifera grew slowly and had no effect on community production. But B. hamifera produces a potent defense compound that deters native herbivores and reduces the growth of micro-organisms. As a direct or indirect effect of this chemical defense, the litter from B. hamifera decomposed considerably slower compared to native seaweed litter. Rapid growth and defense against predation are likely important in explaining how the two invaders have become successful in the invaded range. These results show that traits related to invasion success may determine impacts on native communities.

    Paper III shows that the rapidly growing invader H. japonica is avoided as food by native herbivores, which likely enables the invader to survive during colder seasons with sub-optimal growth conditions. 

    In paper IV I found that competition from the native brown alga Fucus vesiculosus decreased growth of the non-native congener Fucus evanescens. Native herbivores caused more damage to the native competitor but it did not relieve F. evanescens from competitive pressure. Several native brown algae grow in the niche of F. evanescens, which may explain why the species only is growing sparingly in the invaded range. The results indicate that competition with native seaweeds have potential to reduce the success of non-native seaweeds in the new range.

    In summary, this thesis shows that non-native seaweeds differ strongly in their effect on ecosystem functions. Knowledge of which traits are present among abundant non-native species and how these traits relates to different effects may enable us to gain a better understanding of invasion impacts on native communities. The thesis also highlights that competitive interactions can be of importance for invasion success in seaweed communities.

  • 11.
    Sagerman, Josefin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Enge, Swantje
    Pavia, Henrik
    Wikström, Sofia
    Stockholms universitet, Naturvetenskapliga fakulteten, Stockholms universitets Östersjöcentrum. Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Low feeding preference of native herbivores for the successful non-native seaweed Heterosiphonia japonicaManuskript (preprint) (Övrigt vetenskapligt)
  • 12.
    Sagerman, Josefin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Enge, Swantje
    Pavia, Henrik
    Wikström, Sofia A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik. AquaBiota Water Research, Sweden.
    Divergent ecological strategies determine different impacts on community production by two successful non-native seaweeds2014Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 175, nr 3, s. 937-946Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The consequences of plant introductions into ecosystems are frequently reported from terrestrial environments, but little is known about the effects on ecosystem functioning caused by non-native primary producers in marine systems. In this study we explored the effects of the invasion by the two filamentous red algae Heterosiphonia japonica and Bonnemaisonia hamifera on the primary production of seaweed communities by using single and mixed cultures of non-native and native red algae. The experiments were conducted both in the presence and absence of herbivores. Biomass production of the invaded community increased more than four times in mixed cultures with H. japonica, while introduction by B. hamifera had no significant effect. The different impact on community production could be explained by differences in life history strategies between the invaders; H. japonica grew considerably faster than the native seaweeds which directly increased the community production, while B. hamifera showed a relatively slow growth rate and therefore had no effect. From previous studies it is known that B. hamifera produces a highly deterrent, but also costly, chemical defence. The assessment of survival and growth of a native generalist herbivore further corroborated that the biomass produced by B. hamifera constitutes a very low-quality food, whereas the performance of herbivores on a diet of H. japonica was comparable to that on native algal diets. In summary, this study demonstrates that successful invaders belonging to the same functional group (filamentous red algae) may have distinctly different impacts on productivity in the recipient community, depending on their specific life history traits.

  • 13.
    Sagerman, Josefin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Enge, Swantje
    Pavia, Henrik
    Wikström, Sofia A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik. Stockholms universitet, Naturvetenskapliga fakulteten, Stockholms universitets Östersjöcentrum.
    Low feeding preference of native herbivores for the successful non-native seaweed Heterosiphonia japonica2015Ingår i: Marine Biology, ISSN 0025-3162, E-ISSN 1432-1793, Vol. 162, nr 12, s. 2471-2479Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Non-native seaweeds constitute a conspicuous component of many benthic coastal communities. Seaweed invaders are known to significantly affect invaded communities, but relatively little is known about the mechanisms underlying their success. In this study, we explored the feeding preferences of three generalist herbivores for the successful non-native red alga Heterosiphonia japonica and native seaweed competitors. The experiments were conducted on the Swedish Skagerrak coast (58A degrees 52'N, 11A degrees 08'E) from July to August. Additionally, chemical and physical traits of the seaweeds were assessed to mechanistically explain herbivore preferences. The results showed that H. japonica was of low preference to native herbivores and that this was most likely explained by chemical properties of the invader. We were, however, not able to determine whether the low preference was caused by deterrent metabolites or low nutritional quality. We conclude that herbivore avoidance may be important for the survival and success of H. japonica in the introduced range and that efficient means of escaping herbivory may be a common feature of invaders in seaweed communities.

  • 14.
    Sagerman, Josefin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Pavia, Henrik
    Wikström, Sofia
    Stockholms universitet, Naturvetenskapliga fakulteten, Stockholms universitets Östersjöcentrum. Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Competition between the non-native Fucus evanescens and the native congener Fucus vesiculosusManuskript (preprint) (Övrigt vetenskapligt)
  • 15.
    Sagerman, Josefin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Staberg, Nichlas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Pavia, Henrik
    Wikström, Sofia
    Stockholms universitet, Naturvetenskapliga fakulteten, Stockholms universitets Östersjöcentrum. Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Decomposition rates differ between two seaweed invaders with different ecophysiological traitsManuskript (preprint) (Övrigt vetenskapligt)
  • 16.
    Staveley, Thomas
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Hernvall, Patrick
    Stjärnkvist, Nellie
    van der Meijs, Felix
    Wikström, Sofia
    Stockholms universitet, Naturvetenskapliga fakulteten, Stockholms universitets Östersjöcentrum.
    Gullström, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Exploring seagrass fish assemblages in relation to the habitat patch mosaic in the brackish Baltic SeaManuskript (preprint) (Övrigt vetenskapligt)
  • 17.
    Tano, Stina
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik. Stockholms universitetsbibliotek.
    Seaweed in the tropical seascape: Importance, problems and potential2016Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The increasing demand for seaweed extracts has led to the introduction of non-native seaweeds for farming purposes in many tropical regions. Such intentional introductions can lead to spread of non-native seaweeds from farming areas, which can become established in and alter the dynamics of the recipient ecosystems. While tropical seaweeds are of great interest for aquaculture, and have received much attention as pests in the coral reef literature, little is known about the problems and potential of natural populations, or the role of natural seaweed beds in the tropical seascape.

    This thesis aims to investigate the spread of non-native genetic strains of the tropical macroalga Eucheuma denticulatum, which have been intentionally introduced for seaweed farming purposes in East Africa, and to evaluate the state of the genetically distinct but morphologically similar native populations. Additionally it aims to investigate the ecological role of seaweed beds in terms of the habitat utilization by fish and mobile invertebrate epifauna. The thesis also aims to evaluate the potential of native populations of eucheumoid seaweeds in regard to seaweed farming.

    The initial results showed that non-native E. denticulatum is the dominating form of wild eucheumoid, not only in areas in close proximity to seaweed farms, but also in areas where farming has never occurred, while native eucheumoids are now scarce (Paper I). The low frequency of native E. denticulatum in seaweed beds, coupled with a low occurrence of reproductive structures, indicates that the effective population size may be low, which in turn may be a threat under changing environmental conditions. These results, combined with indications that seaweeds may be declining in East Africa, illustrates the need for attaining a better understanding of the ecological role of tropical seaweed habitats. The studies on the faunal communities of seaweed beds showed that they are species rich habitats, with high abundances of juvenile fish and mobile epifauna (Paper II and III), strongly indicating that these habitats should be considered for future seascape studies and management actions. Productivity in East African seaweed farming is decreasing, and as the current cultivation is based on a single non-indigenous haplotype, a more diverse genetic base has been suggested as a means to achieve a more productive and sustainable seaweed farming. Although our results show that East African E. denticulatum has a lower growth rate than the currently used cultivar (Paper IV), the several native haplotypes that are present in wild populations illustrates that, though a demanding endeavour, there is potential for strain selection within native populations.

  • 18.
    Tano, Stina A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Eggertsen, Maria
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Wikström, Sofia A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Stockholms universitets Östersjöcentrum.
    Berkström, Charlotte
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Buriyo, A. S.
    Halling, Christina
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Tropical seaweed beds as important habitats for juvenile fish2017Ingår i: Marine and Freshwater Research, ISSN 1323-1650, E-ISSN 1448-6059, Vol. 68, nr 10, s. 1921-1934Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Seaweed beds within tropical seascapes have received little attention as potential fish habitat, despite other vegetated habitats, such as seagrass meadows and mangroves, commonly being recognised as important nurseries for numerous fish species. In addition, studies of vegetated habitats rarely investigate fish assemblages across different macrophyte communities. Therefore, the aim of the present study was to investigate the role of tropical seaweed beds as fish habitat, particularly for juvenile fish, by comparing their fish assemblages with those of closely situated seagrass beds. Fish assemblages were assessed by visual census in belt transects, where fish were identified and their length estimated, and habitat variables were estimated for each transect. The abundance of juvenile fish in seaweed beds was twice as high as that in seagrass meadows, whereas there was no difference in total, subadult or adult fish abundance. In addition, the abundance of commercially important and coral reef-associated juveniles was higher in seaweed beds, as was fish species richness. Fish assemblages differed between habitats, with siganids being more common in seagrass meadows and juvenile Labridae and Serranidae more common in seaweed beds. These results highlight that tropical seaweed beds are important juvenile fish habitats and underscore the need to widen the view of the shallow tropical seascape.

  • 19.
    Tano, Stina A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Halling, Christina
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Lind, Emma
    Buriyo, Amelia
    Wikström, Sofia A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Extensive spread of farmed seaweeds causes a shift from native to non-native haplotypes in natural seaweed beds2015Ingår i: Marine Biology, ISSN 0025-3162, E-ISSN 1432-1793, Vol. 162, nr 10, s. 1983-1992Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Seaweed farming has been the cause of introductions of non-indigenous seaweed species and genotypes throughout the world. In Zanzibar, Tanzania, foreign genotypes of Eucheuma denticulatum were introduced for farming purposes in 1989, and in recent years a spread of non-indigenous haplotypes has been reported. The current study aimed to investigate the presence and extent of introduced and native haplotypes of E. denticulatum as well as their relative frequencies, to obtain the severity of the spread of cultivated seaweed and the current state of the native populations. The results show that all investigated sites are dominated by the introduced South-east Asian haplotypes, even where seaweed farming has never occurred. As the frequencies of East African haplotypes are remarkably low, this shows a shift from native to introduced E. denticulatum. This shift may, at least in part, be caused by earlier overharvest of natural seaweed populations, and indicates a cryptic invasion of the introduced haplotypes at the potential cost of the recovery of the native haplotype populations.

  • 20.
    Tano, Stina
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Eggertsen, Maria
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Wikström, Sofia A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Stockholms universitets Östersjöcentrum.
    Berkström, Charlotte
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Buriyo, A. S.
    Hailing, Christina
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Tropical seaweed beds are important habitats for mobile invertebrate epifauna2016Ingår i: Estuarine, Coastal and Shelf Science, ISSN 0272-7714, E-ISSN 1096-0015, Vol. 183, s. 1-12Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Marine macrophyte habitats in temperate regions provide productive habitats for numerous organisms, with their abundant and diverse invertebrate epifaunal assemblages constituting important linkages between benthic primary production and higher trophic levels. While it is commonly also recognized that certain vegetated habitats in the tropics, such as seagrass meadows, can harbour diverse epifaunal assemblages and may constitute important feeding grounds to fish, little is known about the epifaunal assemblages associated with tropical seaweed beds. We investigated the abundance, biomass and taxon richness of the mobile epifaunal community (>= 1 mm) of tropical East African seaweed beds, as well as the abundance of invertivorous fishes, and compared it with that of closely situated seagrass meadows, to establish the ecological role of seaweed beds as habitat for epifauna as well as potential feeding grounds for fish. The results showed that seaweed beds had a higher abundance of mobile epifauna (mean SD: 10,600 +/- 6000 vs 3700 +/- 2800 per m(2)) than seagrass meadows, as well as a higher invertebrate biomass (35.9 +/- 46.8 vs 1.9 +/- 2.1 g per m(2)) and taxon richness (32.7 +/- 11.8 vs 19.1 +/- 6.3 taxa per sample), despite having a lower macrophyte biomass. Additionally, the high abundance of invertivorous fishes found in seaweed beds indicates that they act as important feeding grounds to several fish species in the region.

  • 21.
    Tano, Stina
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Eggertsen, Maria
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Wikström, Sofia
    Stockholms universitet, Naturvetenskapliga fakulteten, Stockholms universitets Östersjöcentrum.
    Berkström, Charlotte
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Buriyo, Amelia
    Halling, Christina
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Tropical seaweed beds are important habitats for mobile invertebrate epifaunaManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    Marine macrophyte habitats in temperate regions are known to provide productive habitats for numerous organisms, with their abundant and diverse invertebrate epifaunal assemblages constituting important linkages between benthic primary production and higher trophic levels. While it is commonly also recognized that certain vegetated habitats in the tropics, such as seagrass meadows, can harbour diverse epifaunal assemblages and may constitute important feeding grounds to fish, little is known about the epifaunal assemblages associated with tropical seaweed beds.

    We investigated the abundance, biomass and taxon richness of the mobile epifaunal community of tropical East African seaweed beds, as well as the abundance of invertivorous fish, and compared it with that of closely situated seagrass meadows, to establish the ecological role of seaweed beds as habitat for epifauna as well as potential feeding grounds for fish. The results showed that seaweed beds had a higher abundance of mobile epifauna (10565±5954 vs 3742±2788 per m2) than seagrass meadows, as well as a higher biomass (35.9±46.8 vs 1.9±2.1 g per m2) and taxon richness (32.7±11.8 vs 19.1±6.3 taxa per sample). Additionally, the high abundance of invertivorous fish found in seaweed beds indicates that they act as important feeding grounds to several fish species in the region.

  • 22.
    Tano, Stina
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Eggertsen, Maria
    Stockholms universitet, Naturvetenskapliga fakulteten, Stockholms universitets Östersjöcentrum.
    Wikström, Sofia
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Berkström, Charlotte
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Buriyo, Amelia
    Halling, Christina
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Tropical seaweed beds as important habitats for juvenile fish in an East African seascapeManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    Seaweed beds within tropical seascapes have received little attention as potential fish habitat despite being a prominent feature within these systems. Other tropical shallow-water habitats such as seagrass meadows and mangroves are relatively well studied and are commonly recognised as important nurseries for several species of coral reef fishes. However, there are indications that structural complexity may be more important for the juvenile fish community than the habitat type itself, which implies that other shallow habitats with high structural complexity, like seaweed beds, could also be important for fish recruitment. This study therefore investigated the role of seaweed beds as fish habitat, particularly for juveniles, in the Western Indian Ocean by comparing their fish assemblages to that of closely situated seagrass beds.

    Fish assemblages were assessed by visual census in belt transects, where fish were identified and their length estimated, and habitat variables were estimated for each transect.

    Total fish abundance was found to be similar between seaweed and seagrass habitats, while abundance of juvenile fishes was higher in seaweed beds than in seagrass meadows (25.0±13.7 vs 10.1±10.3 per transect), with no differences in subadult and adult fish abundance. Species richness was higher in seaweed beds than in seagrass meadows (11.2±3.1 vs 8.2±3.9 per transect), and seaweed beds also had higher juvenile abundance of commercially important (19.6±12.3 vs 7.6±8.9 per transect) and coral reef associated fish species (21.1±13.0 vs 3.9±5.3 per transect) than did seagrass meadows. The total fish assemblages, as well as juvenile family communities, differed between seaweed and seagrass habitat, with the fish communities of seaweed beds being less variable than those of seagrass meadows. These results highlight that tropical seaweed beds are important as juvenile fish habitats, and underscore the need to widen the view of the shallow tropical seascape and incorporate seaweed beds in management actions. 

  • 23.
    Wallin, Anders
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Systemekologiska institutionen.
    Nyström Sandman, Antonia
    Stockholms universitet, Naturvetenskapliga fakulteten, Systemekologiska institutionen.
    Wikström, Sofia A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Systemekologiska institutionen.
    Blomqvist, Mats
    Kautsky, Hans
    Stockholms universitet, Naturvetenskapliga fakulteten, Systemekologiska institutionen.
    Spatially dependent relationships between environmental factors and phytobenthic communities along the Swedish coast of the Baltic Sea, a numeric model approachManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    The phytobenthic plant and animal communities are important components in the Baltic Sea ecosystem. In order to properly manage and monitor these communities the knowledge of structuring factors is important. In this study we used multivariate analyses to test the relative importance of environmental variables structuring the phytobenthic communities along the Swedish Baltic Sea coast, how the importance of these factors change with spatial scale and between the three main Baltic Sea sub-basins, the Baltic proper, Bothnian Sea and Bothnian Bay. We also studied the effect of these environmental factors for different species groups. The environmental factors included were salinity, wave exposure, substrate slope, depth and substrate type. For the analysis a large dataset of 1362 diving transects performed with comparable methods was used, describing the phytobenthic plant and animal species depth distribution and coverage. The environmental factors changed in importance at the different scales. The community-environment relationships also differed between the sub-basins, especially in the Bothnian Bay compared to the Baltic proper and Bothnian Sea. In the calculated best combination of factors correlating with the phytobenthic community the depth and the substrate were included in a majority of the analyses, both at different scales and in the different sub-basins. Differences in the correlation between the phytobenthic community and the environmental factors were also found between species groups. The differences between the spatial scales, the sub-basins and the species groups indicate that the criteria for environmental status, and stratification of sampling during local monitoring assessments, have to be area specific.

  • 24.
    Wikstrom, Sofia A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Systemekologiska institutionen.
    Hillebrand, Helmut
    Invasion by mobile aquatic consumers enhances secondary production and increases top-down control of lower trophic levels2012Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 168, nr 1, s. 175-186Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Increased biological diversity due to invasion by non-indigenous species (NIS) is a global phenomenon with potential effects on trophic interactions and ecosystem processes in the invaded habitat. We assessed the effects of resource availability and invasion of three non-indigenous invertebrate grazers (two crustaceans and a snail) on secondary production, relative dominance of NIS grazers and resource depletion in experimental freshwater mesocosms. The relative dominance of NIS grazers increased with increasing initial resource availability, although the effect was largest for one of the three species. The effect was due to the fact that all the included non-indigenous grazers were able to expand their populations quickly in response to resource addition. For the most dominating species, the increased grazer diversity due to invasion in turn resulted in higher production of grazer biomass and a more efficient depletion of the periphyton resource. The effect was largest at high initial resource availability, where NIS dominance was most pronounced. Our results show that an invasion-induced increase in species diversity can increase resource depletion and consequently production, but that the effect depends on identity of the introduced species. The results also suggest that properties of the recipient system, such as resource availability, can modulate ecosystem effects of NIS by affecting invader success and dominance.

  • 25.
    Wikström, Sofia A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Botaniska institutionen.
    Marine Seaweed Invasions: the Ecology of Introduced Fucus evanescens2004Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Biological invasions are an important issue of global change and an increased understanding of invasion processes is of crucial importance for both conservation managers and international trade. In this thesis, I have studied the invasion of the brown seaweed Fucus evanescens, to investigate the fate and effect of a perennial, habitat-forming seaweed introduced to a coastal ecosystem. A long-term study of the spread of F. evanescens in Öresund (southern Sweden) showed that the species was able to expand its range quickly during the first 20 years after the introduction, but that the expansion has been slow during the subsequent 30 years. Both in Öresund and in Skagerrak, the species is largely restricted to sites where native fucoids are scarce. Laboratory experiments showed that the restricted spread of F. evanescens cannot be explained by the investigated abiotic factors (wave exposure and salinity), although salinity restricts the species from spreading into the Baltic Sea. Neither did I find evidence for that herbivores or epibiota provide biotic resistance to the invader. On the contrary, F. evanescens was less consumed by native herbivores, both compared to the native fucoids and to F. evanescens populations in its native range, and little overgrown by epiphytes. Instead, the restricted spread may be due to competition from native seaweeds, probably by pre-occupation of space, and the establishment has probably been facilitated by disturbance.

    The studies provided little support for a general enemy release in introduced seaweeds. The low herbivore consumption of F. evanescens in Sweden could not be explained by release from specialist herbivores. Instead, high levels of chemical anti-herbivore defence metabolites (phlorotannins) could explain the pattern of herbivore preference for different fucoids. Likewise, the low epibiotic colonisation of F. evanescens plants could be explained by high resistance to epibiotic survival. This shows that colonisation of invading seaweeds by native herbivores and epibionts depends on properties of the invading species. The large differences between fucoid species in their quality as food and habitat for epibionts and herbivores imply that invasions of such habitat-forming species may have a considerable effect on a number of other species in shallow coastal areas. However, since F. evanescens did not exclude other fucoids in its new range, its effect on the recipient biota is probably small.

  • 26.
    Wikström, Sofia A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Stockholms universitets Östersjöcentrum.
    Carstensen, Jacob
    Blomqvist, Mats
    Krause-Jensen, Dorte
    Cover of coastal vegetation as an indicator of eutrophication along environmental gradients2016Ingår i: Marine Biology, ISSN 0025-3162, E-ISSN 1432-1793, Vol. 163, nr 12, artikel-id 257Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Coastal vegetation communities are important for primary production, biodiversity, coastal protection, carbon and nutrient cycling which, in combination with their sensitivity to eutrophication, render them potential indicators of environmental status for environmental policies like the EU Water and Marine Strategy Framework Directives. We evaluated one potential indicator for coastal vegetation, the cumulative cover at depths where the vegetation is light limited, by investigating its response to eutrophication along gradients in natural conditions. We used a large data set covering the Swedish coastline, spanning broad gradients in nutrient level, water clarity, sea-bed substrate, physical exposure and climate in addition to a salinity gradient from 0.5 to 30.5. Macroalgal cover increased significantly along gradients of declining nutrient concentration and increasing water clarity when we had accounted for diver effects, spatio-temporal sampling variability, salinity gradients, wave exposure and latitude. The developed empirical model explained 79% of the variation in algal cover across 130 areas. Based on this, we identified macroalgal cover as a promising indicator across the Baltic Sea, Kattegat and Skagerrak. A parallel analysis of soft-substrate macrophytes similarly identified significant increases in cover with decreasing concentrations of total nitrogen and increasing salinity, but the resulting empirical model explained only 52% of the variation in cover, probably due to the spatially more variable nature of soft-substrate vegetation. The identified general responses of vegetation cover to gradients of eutrophication across wide ranges in environmental settings may be useful for monitoring and management of marine vegetation in areas with strong environmental gradients.

  • 27.
    Wikström, Sofia A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Botaniska institutionen.
    Kautsky, Lena
    Stockholms universitet, Naturvetenskapliga fakulteten, Botaniska institutionen.
    Invasion of a habitat-forming seaweed: effects on associated biota2004Ingår i: Biological Invasions, ISSN 1387-3547, E-ISSN 1573-1464, Vol. 6, nr 2, s. 141-150Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Fucus evanescens is a brown alga of arctic origin that has invaded European coasts. The epiphytic community of F. evanescens in southern Sweden was compared with that of the native Fucus vesiculosus, to examine to what extent an invading seaweed can modify local biodiversity. F. evanescens was much less fouled than F. vesiculosus, supporting both less biomass and fewer species of epiphytes. Multivariate analysis of the most common epiphyte taxa showed that the epiphytic community composition of F. evanescens was not entirely separated from that of F. vesiculosus, but host species contributed significantly to explain the variation in community composition. The biomass of free-living invertebrates was also lower on F. evanescens, although the pattern differed between taxonomic groups. While the biomass of amphipods was lower on F. evanescens, there was no significant difference in biomass of isopods or gastropods between the Fucus species. The good correlation between biomass of epiphytes and free-living animals suggests that the epiphytes play an important role in providing a suitable habitat for many species of free-living epifauna. The study shows that the invasion of F. evanescens affects the environmental conditions for many species associated with the Fucus community but that the direct effect on biodiversity is probably low.

  • 28.
    Wikström, Sofia A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Botaniska institutionen. Växtekologi.
    Kautsky, Lena
    Stockholms universitet, Naturvetenskapliga fakulteten, Botaniska institutionen. Växtekologi.
    Structure and diversity of invertebrate communities in the presence and absence of canopy-forming Fucus vesiculosus in the Baltic Sea2007Ingår i: Estuarine, Coastal and Shelf Science, Vol. 72, s. 168-176Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Canopy-forming seaweeds are regarded as important habitat-formers in shallow coastal zones and their present decline or disappearance in many coastal areas can potentially affect diversity and abundance of associated species. Here, we evaluate potential effects of large-scale disappearance of the dominant canopy-forming species Fucus vesiculosus L. on vegetation-associated invertebrates in the Baltic Sea. We compare the macroalgal and invertebrate assemblages between sites where F. vesiculosus has disappeared over a larger area and adjacent sites with intact Fucus vegetation. The species richness of animals did not differ between sites with and without F. vesiculosus and no species were clearly confined to sites with Fucus. However, total animal abundance and biomass were generally lower when F. vesiculosus was absent and the animal assemblage at sites without Fucus differed consistently from adjacent Fucus sites. Since the assemblage of epiphytic and turf-forming macroalgae also differed with the presence of Fucus, the differences in invertebrate assemblages can be explained either by direct effects of the Fucus plants or by altered abundance of other macroalgal species. Based on these observations we suggest that large-scale disappearance of F. vesiculosus in the Baltic Sea may result in a changed composition and biomass of vegetation-associated invertebrates, with potential effects on higher trophic levels.

  • 29.
    Wikström, Sofia A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Botaniska institutionen.
    Pavia, Henrik
    Chemical settlement inhibition versus post-settlement mortality as an explanation for differential fouling of two congeneric seaweeds2004Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 138, nr 2, s. 223-230Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It has been proposed that seaweed secondary metabolites, e.g. brown algal phlorotannins, may have an ecologically important function as a chemical defence against epiphytes, by acting against colonisation of epiphytic organisms. We tested whether the low epiphytic abundance on the invasive brown seaweed Fucus evanescens, compared to the congeneric F. vesiculosus, is due to a more effective chemical defence against epiphyte colonisation. A field survey of the distribution of the common fouling organism Balanus improvisus (Cirripedia) showed that the abundance was consistently lower on F. evanescens than on F. vesiculosus. However, contrary to expectations, results from experimental studies indicated that F. vesiculosus has a more effective anti-settlement defence than F. evanescens. In settlement experiments with intact fronds of the two Fucus species, both species deterred settlement by barnacle larvae, but settlement was lower on F. vesiculosus both in choice and no-choice experiments. Phlorotannins from F. vesiculosus also had a stronger negative effect on larval settlement and were active at a lower concentration than those from F. evanescens. The results show that Fucus phlorotannins have the potential to inhibit settlement of invertebrate larvae, but that settlement inhibition cannot explain the lower abundance of the barnacle Balanus improvisus on F. evanescens compared to F. vesiculosus. Assessment of barnacle survival in the laboratory and in the field showed that this pattern could instead be attributed to a higher mortality of newly settled barnacles. Observation suggests that the increased mortality was due to detachment of young barnacles from the seaweed surface. This shows that the antifouling mechanism of F. evanescens acts on post-settlement stages of B. improvisus.

  • 30.
    Wikström, Sofia A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Botaniska institutionen.
    Steinarsdottir, Maria B.
    Kautsky, Lena
    Pavia, Henrik
    Evaluation of the enemy release hypothesis for an invading seaweedManuskript (Övrigt vetenskapligt)
  • 31.
    Wikström, Sofia A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Botaniska institutionen.
    von Wachenfeldt, Torgny
    Kautsky, Lena
    Stockholms universitet, Naturvetenskapliga fakulteten, Botaniska institutionen.
    Establishment of the exotic species Fucus evanescens C. Ag. (Phaeophyceae) in Öresund, Southern Sweden2002Ingår i: Botanica Marina, ISSN 0006-8055, E-ISSN 1437-4323, Vol. 45, nr 6, s. 510-517Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The spread and establishment of the exotic species Fucus evanescens in öresund, Southern Sweden was documented through inventories in 1966–72 and 2000. The species spread fast from the first known introduction in 1955, colonising harbours along the coast. After this expansion the further spread has been limited and the species is still largely confined to harbour areas, where it occurs in the same depth zone as its native relatives, F. vesiculosus, F. serratus and Ascophyllum nodosum. It is more common in the northern part of the area and has not expanded into the Baltic Sea proper. Tests of the attachment strength of F. evanescens plants suggest that the restriction to harbours is not due to the direct effects of wave exposure on adults. In the laboratory, reproductive success of F. evanescens decreased from 99% in 24 psu to 12% in 10 psu and at lower salinity reproduction failed. Growth of embryonic recruits was similarly affected by salinity. Hence, low salinity explains the limited success of F. evanescens in southern Öresund, where the salinity is low and fluctuating, and its failure to colonise the Baltic Sea proper.

  • 32.
    Wikström, Sofia
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Stockholms universitets Östersjöcentrum.
    Blomqvist, Mats
    Svedäng, Henrik
    Effekter av bottentrålning på ekosystemtjänster i svenska hav2018Rapport (Övrigt vetenskapligt)
    Abstract [sv]

    Bottentrålsfiske ger omfattande effekter på marina ekosystem och ekosystemprocesser. I rapporten redovisar vi det kunskapsunderlag som finns vad gäller effekterna av trålning på havets ekosystem och de ekosystemtjänster vi får från havet. Vårt syfte med studien har därför varit att ta fram underlag för att bedöma behovet av ytterligare begränsningar av bottentrålning i inflyttningsområdena innanför trålgränsen och i eller i anslutning till skyddade områden utanför trålgränsen. Vi baserar vårt arbete på publicerade vetenskapliga studier från både Sverige och andra delar av världen. När det gäller den specifika situationen i svenska havsområden hämtas mycket av kunskapen från områden som idag är skyddade från bottentrålning, bland annat från Öresund som är ett stort trålfredningsområde mellan Sverige och Danmark, där större delen av havsområdet har varit skyddat mot aktiva fiskeredskap sedan 1932. Bottentrålningen i svenska hav är framförallt koncentrerad till Västerhavet och södra Östersjön men lokalt finns begränsade områden med bottentrålning även i övriga delar av svenska hav. 

    Effekterna av bottentrålning är dels kopplade till påverkan av havsbottnarna, dels till att bottentrålar är starkt selektiva på så sätt att all fisk över en viss storlek fångas, medan mindre fisk har möjlighet att simma igenom nätmaskorna. Dessa effekter kan innebära att många ekosystemtjänster missgynnas. Exempel på ekosystemtjänster som kan påverkas negativt är biologisk mångfald, livsmiljöer på bottnarna, näringsvävar, produktion av livsmedel och rekreation. Studier från svenska hav visar att den pågående bottentrålningen minskar biologisk mångfald och mångfalden av livsmiljöer i trålade områden. 

    Trålningsbegränsningar i skyddade områden kan därför få positiva effekter på ekosystemtjänsterna biologisk mångfald och livsmiljöer. För övriga ekosystemtjänster saknas den kunskap som skulle behövas för att bedöma hur mycket de påverkas av nuvarande trålning i skyddade områden och innanför trålgränsen. Det finns därför ett behov av ytterligare forskning för att kvantifiera effekten av bottentrålning på många av ekosystemtjänsterna. Speciellt behövs mera systematisk forskning och kunskapssynteser kring utnyttjandet av svenska kustområden för att åstadkomma mer heltäckande utvärderingar av de kulturella ekosystemtjänsterna och hur de påverkas av exempelvis bottentrålning.

    Effekter av tidigare högt fisketryck är mycket tydligt längs hela svenska västkusten norr om Öresund, där lokala rovfiskbestånd, företrädesvis torsk, har försvunnit eller har gått starkt tillbaka, vilket påverkar flera ekosystemtjänster. Det är dock okänt i hur hög grad risttrålfiske efter havskräfta och räka innanför trålgränsen påverkar dessa lokala fiskbestånd idag.

1 - 32 av 32
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf