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Coastal Ecosystems of the Baltic Proper The coastal ecosystems of the Baltic have low diversity compared to those of the Swedish west coast although we can find here a mixture of marine and limnic plants and animals. Among macroalgae the marine species, e.g. bladderwrack (Fucus vesiculosus), are dominating. The bladderwrack is important for structuring the hard-bottom communities down to depths of 6-8 m. The littoral zone is an important feeding ground for many fishes. Physical complexity and spatial patchiness influence the interactions between predatory fishes and their prey. We have choosen to study diffeerent aspects of the bladderwrack community in order to understand what circumstances are responsible for the large changes occurring in later decades. Although bladderwrack is the dominating macroalgae in the Baltic in the southern parts it coexists with saw wrack (F. serratus). This is in contrast to the Swedish west coast where they form seperate belts. Recruitment is a crucial phase in the Fucus life-cycle. In this respect we study the significance of spring and autumn reproduction. Important factors are the existance of filamentous algae and invertebrate grazers. Field observations together with mesocosm and aquarium experiments have shown crustaceans (Idotea and Gammarus) and gastropods (Theodoxus and Lymnea) to be important grazers affecting different life stages of bladderwrack. Population density of grazers vary considerably both temporally and spatially. One possible explanation is varying predation pressure from fish. Sampling of fish with standardized coastal survey nets has been done for one year. During summer roach (Rutilus rutilus) and silver bream (Blicca bjoerkna) dominated replaced by herring (Clupea harengus) and flounder (Platichtys flesus) during autumn and winter. During the summer period the abundance of predatory fish was low, which could explain the high abundances of invertebrate grazers found in early autumn. Herring showed to be an efficient predator on isopods (Idotea baltica) and amphipods (Gammarus sp), and may thus be responsible for the reduced densities of invertebrate grazers found in spring. We try to use our knowledge of the bladderwrack community in a project aiming at finding methods to reestablish bladderwrack in a recipient of a pulp mill plant. (http://www.ng.hik.se/~fucus/Fucrest.htm). In the beach wrack fauna we study amphipods of the superfamily Talitroidea. The four species found in the Baltic all have their distributional limit in our part of the Baltic. The reproductive period of Orchestia gammarellus is somewhat shorter in the Baltic compared to the west coast of Sweden. This is probably due to lower temperatures, especially in spring. One species, Platorchestia platensis, is gaining increased distribution and seems to be able to outcompete O. gammarellus. Another part of our activities is directed towards regional monitoring of the coastal environment. This gives us basic and regular information on the ecosystem. Lars-Eric Persson, PhD,
Associate Professor Persson, L.-E. 1997. Effects of cropping of submerged macro- phytes on coastal benthic and epibenthic animal communities, southeastern Sweden. - In , Biodiversity of the Baltic ecosystem, Proceedings of the 14th BMB- symposium, Tallin 1997, pp 195-204. Persson, L.-E. 1999. Growth and reproduction in two brackish water populations of the amphipod Orchestia gammarellus (Amphipoda, Talitridae) from the Baltic Sea. - Journal of Crustacean Biology. vol. 19:53-59 Malm, T. 1999. Distribution patterns and ecology of Fucus serratus L. and Fucus vesiculosus L. in the Baltic Sea. -Dissertation, Dept. of Botany, University of Stockholm, 32 pp. Malm, T.,R. Engkvist & L. Kautsky. In press. Grazing effects by two fresh- water snails on juvenile Fucus vesiculosus L. in the Baltic Sea. -Mar. Ecol. Progr. Ser. |
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