A Yesso Scallop Population Exposed to Climate-Induced and Anthropogenic Habitat Changes in Amur Bay, Sea of Japan

Abstract

In the study area, located in the coastal waters of Amur Bay off Vladivostok, which is exposed to industrial and domestic sewage effluents, the population of the Yesso scallop Mizuhopecten (=Patinopecten) yessoensis and the community of the endo- and epibiosis of its shell underwent major changes during the period 1981–2016, in which three main stages can be identified. During the first stage, which lasted until the early 1990s, the growth rate and lifespan of the scallop decreased, but the mortality rate and the degree of shell bioerosion grew. This stage coincided with the period of increased anthropogenic pollution in Amur Bay. In the mid-1990s, which was a transitional period, the decline in the scallop growth rate ceased. At that time environmental pollution decreased due to reduced sewage discharge as industrial production fell. During the second stage, which lasted until the mid-2000s, the scallop growth rate increased, but the degree of bioerosion and abundance of epibionts on the scallop shell reduced. That was a period when the bay underwent gradual natural self-purification. During the third stage, which continues until present, the scallop growth rate has declined again due to increased eutrophication, which leads to lower oxygen saturation of water. This is most evident during periodic increases in water temperature associated with the quasi-biennial and 7- to 8-year temperature fluctuation cycles. Poaching is a negative anthropogenic that has caused a substantial reduction in scallop population density.