Reproduction strategies and distribution of larvae and juveniles of benthic soft-bottom invertebrates in the Kara Sea (Russian Arctic). The influence of river discharge on the structure of benthic communities: a larval approach

The aims of this work are to determine the reproductive patterns of benthic invertebrates in the Kara Sea and to analyse adaptations of reproduction strategies to polar conditions. Ecosystems of the Kara Sea are strongly affected by the freshwater input of the rivers Ob and Yenisei.Their outflows create a bilayered pelagic habitat with a confined pycnocline. 44 larval and 54 juvenile species were identified in plankton net and multicorer samples.For 23 of the larval species adults were present.For the remaining 21 adults were reported from the Barents and Petchora Sea, indicating larval input from the neighbouring seas.Most larvae were found in all water levels, although highest abundances were present in the upper 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 were generally less than 1 ind. m-3, but brittle star larvae reached densities of 200 ind. m-3.The importance of retention 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 create favourable conditions for boreal species.Most invertebrates seem to reproduce directly (without pelagic larvae), which can be explained partly by the high share of peracarid crustaceans.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 habitatsThe numerous larval types found indicate that planktonic development is important in the Kara Sea ecosystem