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

• Published in: Geophysical research letters 2022-08, Vol.49 (15), p.n/a
• Main Authors: Kodama, T., Igeta, Y., Iguchi, N.
• Format: Article
• Language: English
• Subjects: anchovy; Annual variations; Biogeochemical cycle; Biogeochemical cycles; Biomass; Coastal waters; Fish; fisheries; Generalized linear models; Interannual variations; Marginal seas; Marine fishes; Oceans; Pacific Decadal Oscillation; Plankton; Prey; sardine; Sea of Japan; Statistical models; top‐down control; Variation; Wet weight; Zooplankton
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2022GL099037

Mesozooplankton 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. Plain Language Summary Zooplankton are the prey of fish and export carbon and nitrogen from the surface ocean to the deep ocean. To identify changes in zooplankton abundance and the reasons for these changes, wet weights of plankton net samples were measured over four decades from 1967 to 2019 in the Sea of Japan, surrounding Japan, Korea, and Russia. Yearly variations of weights were the mirror image of the biomass of sardine, anchovy, and round herring which eat zooplankton. In addition, the increase (or decrease) of plankton weights was also related to the decrease (or increase) of small pelagic planktivorous fish biomass. These results suggested the feeding activity of fish controls zooplankton biomass in this sea. Key Points Over four decadal observations on mesozooplankton biomass were conducted in the Sea of Japan These interannual variations of mesozooplankton were the mirror image of the small pelagic planktivorous fish biomass The first report on top‐down control of zooplankton biomass in their long‐term variations in the ocean