ИСТИНА

The White sea is a cold one with large temperature change during the year. The sea is covered by the ice in Winter and Spring months and temperature of the sea surface rises up to 15-20C in Summer months. Twenty hydromedusan species inhabit the White Sea. Most species appear in Spring when the ice is melting and only a few species (mainly Sarsia (Stauridiosarsia) producta and Obelia geniculata) appear during the temperature maximum. In the work I compare the temperature range of medusae appearance in the sea with aquarium experimental observations. Change of the temperature in aquarium is an essential step for realization of seasonality and study of hydrozoan life cycles in the laboratory. In the work I maintained several White Sea hydroids (Catablema vesicarium, Halitholus cirratus, Rathkea octopunctata, Sarsia sp, Sarsia producta, Obelia longissima, Bougainvillia superciliaris) in aquarium with natural or artificial sea water. The change of the experimental temperature encourage the hydroids to produce the medusae buds or gonophores. The hydroids was affected by reduction in temperature (down to 0-2C, 2-4C, 4-6C) or by warming (up to 4-6C, 10-12C). Several species produced medusae buds or gonophores in such condition about a 2-4 weeks after the temperature change. Two species (C. vesicarium and R. octopunctata) produced medusae in the most experiments after decrease the temperature. But the other species vary in their reactions. The food and flow conditions as well as chemical inductors or light may be essential for medusae production in the sea.