Biomass, production and trophic roles of micro- and net-zooplankton in Dokai Inlet, a heavily eutrophic inlet, in summer

We measured the abundance, biomass and production rate of micro- and net-zooplankton in Dokai Inlet, a heavily eutrophic and polluted embayment in northern Kyushu, in August 1996. This inlet nourished a much higher biomass of net-zooplankton (mean: 53.2 μg Cl^-1) than microzooplankton (10.1 μg Cl^-1). Mean contribution of tintinnid ciliates to the total microzooplankton biomass was largest (75%), followed, in order, by copepod nauplii (20%) and naked ciliates (5%). For net-zooplankton, the mean biomass of copepods (i.e. Acartia, Euterpina, Oithona and Paracalanus) was lower (43% of the total net-zooplankton biomass) than non-copepod taxa, such as chaetognaths and the larvae of bivalves and polychaetes. Mean secondary production rates of micro- and net-zooplankton in the inlet were 14.4 and 38.3 mg C m^-3 d^-1, respectively, and the mean tertiary production rate of net-zooplankton was 4.20 mg C m^-3 d^-1. The transfer efficiency from phytoplankton primary production to zooplankton secondary production was 28%, and the efficiency from secondary production to tertiary production was 7.9%. The amount of food required to support zooplankton secondary production was equivalent to 87% of the phytoplankton primary production, indicating that zooplankton, particularly net-zooplankton, are the major phytoplankton grazers in this extremely eutrophic inlet.