Yeso scallop population under climatic and anthropogenic changes of environment in Amursky bay of the Sea of Japan

At the study area of industrial and domestic sewages into Amursky Bay at the coasts of Vladivostok city, three main stages in a development of the scallop Mizuhopecten yessoensis population and community of endo- and epibionts of its shell were revealed for 1981–2016. During the first stage lasting until the beginning of 90th, the scallop growth rates and lifetime had decreased, but scallop mortality and degree of the shell bioerosion performed by endolithic polychaeta Polydora brevipalpa had increased. It was a period of an intensification of anthropogenic pollution of Amursky Bay. Further, at the middle of 90th, at a transitional period, the decline in the scallop growth rates had stopped. It was a period of a reduction of the pollution of the water and bottom sediments related to the decrease of sewages due to degradation of industry. During the second stage lasting until the middle of 2000th, the scallop growth rates had increased, but the degree of bioerosion and abundance of epibionts of the scallop shells had decreased. It was a period of the gradual natural depuration of the Bay. Later, during the third stage, which goes on to present day, the scallop growth rates declined again due to an increase of the water euthrophication resulting in the decline of the water oxygen saturation. This was most pronounced for periodic rises of the water temperature caused by quasi-biennial and 7–8-year periodicities of temperature fluctuations. Poaching became one of the negative anthropogenic factors entailing the substantial decline of the scallop population density.