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- Jephson, Therese, et al.
(författare)
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Species- and stratification-dependent diel vertical migration behaviour of three dinoflagellate species in a laboratory study
- 2009
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Ingår i: Journal of Plankton Research. - : Oxford University Press (OUP). - 0142-7873 .- 1464-3774. ; 31:11, s. 1353-1362
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Tidskriftsartikel (refereegranskat)abstract
- This study shows that different species of the same genus can behave differently in relation to a salinity gradient and suggests that a halocline can act as a barrier to the diel vertical migration (DVM) of dinoflagellate species. In a laboratory study, we found that the dinoflagellates Ceratium furca, C. tripos and Dinophysis acuta did not cross a salinity gradient of 5 psu, but instead exhibited DVM exclusively below and above the halocline. Furthermore, C. tripos aggregated in the halocline during the night and migrated to the surface at midday, whereas C. furca aggregated in the halocline at midday and migrated downwards to the bottom during the dark period. Dinophysis acuta was found exclusively above the halocline, with the highest density in the surface water at midday. The present results suggest that different dinoflagellate species display unique DVM behaviours in stratified waters. The species-specific DVM strategies revealed in this study are of central importance for understanding the ecology of these taxa and to further elucidate both the ecological significance and the mechanisms of DVM.
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| 2. |
- Jephson, Therese, et al.
(författare)
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Trophic interactions in Zostera marina beds along the Swedish coast
- 2008
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Ingår i: Marine Ecology - Progress Series. - : Inter-Research Science Center. - 1616-1599 .- 0171-8630. ; 369, s. 63-76
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Tidskriftsartikel (refereegranskat)abstract
- We compared eelgrass Zostera marina communities in 3 regions in Sweden believed to be affected by eutrophication and overfishing, to determine whether bottom-up or top-down processes control the biomass of epiphytic macroalgae and grazers. Nitrogen and carbon isotope signatures were analyzed to explore the food webs and to identify the grazing species feeding on filamentous algae and/or eelgrass. Mixing model (IsoSource version 1.3.1) analysis of the isotope signatures indicated that the amphipods Gammarus locusta and Microdeutopus gryllotalpa fed primarily on filamentous algae and that only 2 small gastropod species consumed eelgrass. Moreover, the grass shrimp Palaemon elegans and F adspersus were ca. 1 trophic level above amphipods and algae, but according to the mixing model played different trophic roles in the different areas. The highest biomass of filamentous algae was found in the west coast beds housing grazers with the lowest biomass and mean size (predominantly G. locusta and M. gryllotalpa, 0.5 to 3 mm). In contrast, the Baltic Sea beds had low algal biomass, but the grazers (mostly G. locusta and Idotea baltica) had higher biomass and were significantly larger (mean size ca. 10 mm). An overall negative correlation was found between grazer biomass and biomass of filamentous algae. The significantly smaller grazers and absence of isopod grazers on the west coast may be due to substantial consumption by small predatory fish. This supports the suggestions that, in Swedish eelgrass beds, grazers are top-down controlled, and overexploitation. of large predators and eutrophication play an important role in the recent increases in algal biomass.
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