ИСТИНА

Adaptation of benthic invertebrates to seasonal ice cover. Life cycles of widely distributed polychaete species in White and Barents Seas. Alexander Tzetlin, Nikolai Pertsov White Sea Biological Station, Faculty of Biology, M.V. Lomonosov Moscow State University, Leninskie gory, GSP-1, Moscow 119991, Russia. The White Sea is a semi-isolated region of the Arctic Ocean with the seasonal ice cover. In comparison to Barents Sea, White Sea characterized by low yearly temperature, low salinities (24–25‰) and depressed photosynthesis. Due to low concentration of phytoplankton during polar winters, benthic fauna, especially filter-feeders survive practically without food from November to April. In some species it leads to slow growth, dwarfism or to the change of reproduction mode. We’ve investigated life-cycle transformations in three polychaete species – deposit feeders Maldane sarsi, Nicomache minor (Maldanidae) and filter-feeder Pseudopotamilla reniformis (Sabellidae), widely distributed in North-Atlantic and Arctic. These species are the very common and often form dense settlements in subtidal of the studied area. Asexual reproduction was noted for M. sarsi, N. minor and P. reniformis in Barents Sea. In the White Sea it is regular and frequent. According to previous data, asexual reproduction was not described for them in the other studied parts of their distribution. The sexual reproduction of these species in the Whit Sea is sporadic and takes place not every year; in both of M. sarsi and P. reniformis spawning was not found during last 5 years. We suppose that in the White Sea the failure to spawn in some seasons may be a consequence of poor nutritional condition of adults. Sexual reproduction with swimming larvae is used mainly for the new substrata searching, whereas the asexual one is less energy-intensive and it allows quick occupying of the new substratum. Perhaps, this reproduction mode is common for benthic filter- and deposit-feeders living in seasonal ice ecosystems. Therefore, life-cycle transformations in studied polychaete species seems very interesting in spite of the global thinning of the ice cover in Arctic and the extension of the seasonal-ice cover in Arctic seas.