Long‐Term Variation in Mesozooplankton Biomass Caused by Top‐Down Effects: A Case Study in the Coastal Sea of Japan

Abstract

AbstractMesozooplankton is a key group for the recruitment of fish and global biogeochemical cycles. Four decadal observations in the coastal Sea of Japan, the marginal sea of the North Pacific, indicate that wet weight‐based mesozooplankton biomass is controlled by both environment‐induced bottom‐up and predatory‐induced top‐down processes. Interannual variations in mesozooplankton biomass using a generalized linear model approach showed a decrease in biomass during the 1980s, followed by a rapid increase in the early 1990s, and a gradual decrease in the 2010s. These interannual variations were the mirror image of those seen small pelagic planktivorous fish biomass. The difference in zooplankton biomass from the previous year was positively correlated with that of the Pacific decadal oscillation index and negatively with that of fish biomass. The latter was supported by a Granger causality analysis. Therefore, top‐down control is one of the main causes of long‐term variations of zooplankton biomass in the ocean.