Standing stocks and production rates of phytoplankton and planktonic copepods in the Inland Sea of Japan

Abstract

Standing stocks and production rates of phytoplankton and planktonic copepods were investigated at 15 stations in the Inland Sea of Japan during four cruises in October–November 1979, January, April and June 1980. The overall mean of phytoplankton biomass was relatively constant during the study period, ranging from 2.3 mg chl.a m−3 in April to 3.6 mg chl.a m−3 in October–November. Primary production was low in January (mean: 90 mg C m−2 d−1), but higher than 375 mg C m−2 d−1 on the other occasions. Integrated annual primary production was 122 g C m−2 yr−1. In terms of carbon weight,Paracalanus parvus was the most important copepod species. The variation of the mean copepod biomass (range: 7.6 mg C m−3 in April to 20.2 mg C m−3 in June) was smaller than that of copepod production, which was estimated by the Ikeda-Motoda's physiological method. Copepod producion was low in cold seasons (0.6 and 0.9 mg C m−3 d−1 in January and April, respectively), and increased, following the elevation of primary production, to 4.9 mg C m−3 d−1 in June. Annual copepod production was 33.7 g C m−2 yr−1, of which herbivore (secondary) production was 26.4 g C m−2 yr−1 (21.7% of primary production). The ratios of pelagic planktivorous fish catch and total fish catch to the primary production were 0.82 and 1.8%, respectively, indicating very high efficiency in exploiting fishery resources in the Inland Sea of Japan.