Effects of Environmental Factors on Reproduction of the Sea Urchin Strongylocentrotus Intermedius

The results of long-term studies (2003–2015) of the reproductive biology of the sea urchin Strongylocentrotus intermedius in wild populations located in the northwestern Sea of Japan along 400 km of the coast of the Primorye region of Russia and differing by the level of anthropogenic pressure are reported. Our analysis showed that since 1970–1980s, the shift in spawning season from autumn to early summer occurred in S. intermedius populations inhabiting anthropogenically polluted areas of Peter the Great Bay, resulting in the appearance of three types of populations that differ from each other in the proportions of individuals with early spawning (the end of May–June) and late spawning (September–early October). Our results indicate that neither photoperiod nor temperature may be considered as the primary external factors determining a shift in S. intermedius temporal patterns of gonad maturation and the timing of spawning and that phytoplankton concentration is the main factor for initiation of sea urchin spawning activity. We hypothesized that the shift in spawning season from autumn to early summer in S. intermedius populations inhabiting polluted areas can be explained by a phenotypic response of this species to environmental changes caused by chronic eutrophication.