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Reproduction strategies and distribution of larvae and juveniles of benthic soft-bottom invertebrates in the Kara Sea (Russian Arctic)

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Fetzer, I. (2004): Reproduction strategies and distribution of larvae and juveniles of benthic soft-bottom invertebrates in the Kara Sea (Russian Arctic) , PhD thesis, University of Bremen.
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Abstract:

The main aims of this work are to determine the reproductive patterns of benthic invertebrates in the Kara Sea and to analyse possible adaptations of reproduction strategies to polar conditions. The Kara Sea is a shallow shelf sea located in the Russian Arctic. Hydrography and ecosystems are strongly affected by the immense freshwater input of the two adjacent rivers Ob and Yenisei. Their outflows create a pronounced bilayered pelagic habitat with a confined pycnocline.During the investigation period 44 larval and 54 juvenile species were identified in plankton net and multicorer samples. For 23 of the larval species adults were present in benthos samples. For the remaining 21, adults were reported from the adjacent Barents and Petchora Sea, indicating a strong larval input from the neighbouring seas. Most larvae were found in all water levels, although highest abundances were present in the upper low salinity layer, revealing a high acclimatisation potential of most larvae to low salinities. The pycnocline seemed to act as a physical barrier for most larvae. Meroplankton densities of individual species were generally less than 1 ind. m-3, but brittle star larvae reached densities of 200 ind. m-3. The importance of retention in the study area varied strongly between species.Most benthic species show an Arctic zoogeographic distribution, but considerable numbers of boreal species were also found. The river run-off may not only foster the survival of euryhaline species but through its thermal input may also create favourable conditions for boreal species. Most invertebrate species seem to reproduce directly (without pelagic larvae), which can be explained partly by the high share of peracarid crustaceans. Contrary to other taxa, which display a huge spectrum of reproduction modes within species and geographic regions, peracarids show a direct reproduction trait all over the world. Their elimination from the dataset reveals a larger share of indirect reproducing species. It is assumed that due to the Kara Seas high environmental variability unfavourable conditions for benthic species often occur. Species with pelagic larvae or highly mobile peracarid crustaceans may have an advantage in reoccupying devastated habitats.The numerous larval types found indicate that planktonic development is important in the Kara Sea ecosystem.

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