Biomass and estimated production properties of size-fractionated zooplankton in the Yellow Sea, China

The size-fractionated zooplankton biomass, taxonomic composition, and production calculated by formulas basing on Ikeda–Motoda's physiological methods were studied on the basis of samples taken from six cruises in the Yellow Sea. Zooplankton was size-fractionated using sieves into ~ 2 mm, 1–2 mm, 0.5–1 mm, 0.25–0.5 mm and 0.16–0.25 mm groups. The results showed that the average zooplankton biomass was 84.03 mg DM m− 3 in May, followed in order by September, June, March, August and December with 42.34, 38.36, 32.37, 27.17 and 21.83 mg DM m− 3, respectively. The contribution of ~ 2 mm, 1–2 mm, 0.5–1 mm, 0.25–0.5 mm and 0.16–0.25 mm groups to the total biomass was in the range of 15.2–27.4%, 13.2–29.4%, 14.7–18.2%, 15.8–22.6% and 16.3–34.2%, respectively, during the investigating period. The biomass of all size groups was all highest in May, and except that the biomass of 0.16–0.25 mm group was lowest in August, the biomass of other size groups was lowest in December. The dominant zooplankton species (or taxa) in each group were similar between six cruises. The estimated zooplankton production was highest in May with 1.97 mg C m− 3 d− 1, and was lowest in December with 0.51 mg C m− 3 d− 1, and was in the range of 0.67–1.44 mg C m− 3 d− 1 in other investigating months. The estimated annual zooplankton production was 0.37 g C m− 3 y− 1. The two smallest groups aggregately comprised 59–84% of the net-zooplankton production in the Yellow Sea. The geographical distribution of size-fractionated zooplankton biomass and production was significantly affected by the complex physical features of the Yellow Sea. When the Yellow Sea Cold Bottom Water appeared from June to September, the biomass and production of zooplankton larger than 1 mm were higher inside the cold water mass area than outside it, while the zooplankton smaller than 1 mm showed contrary results. The higher biomass and production of all zooplankton groups occurred in the southern part of the study area in December due to the intrusion of the Yellow Sea Warm Current. And in March, the higher zooplankton biomass and production, especially for small size zooplankton, occurred at the coastal waters resulting from complex physical properties. Results of the present paper showed the biomass and production properties of size-fractionated zooplankton, which is very important for “parameterization” of food web structure models of the Yellow Sea.

► The size-fractionated zooplankton biomass was determined in the Yellow Sea.
► The size-fractionated zooplankton production was evaluated based on physiological method in the Yellow Sea.
► The zooplankton biomass and production distributions were affected by complex physical properties of the Yellow Sea.