Hihg contribution of small phytoplankton to the total primary production in the Yellow Sea during the summer period in 2016

Abstract

Small phytoplankton contributing to the total primary production is getting important in relation to warming sea surface temperature since the marine food web structure as well as the primary production could be changed by increasing small phytoplankton. However, little information on the contribution of small phytoplankton is available in the Yellow Sea to date. Chlorophyll-a concentration and carbon and nitrogen uptakes were measured at 5 stations in the Yellow Sea in August 2016 to determine the contributions of small phytoplankton to total primary production. The daily total carbon uptake rate averaged from the 5 stations was 0.29 g C m-2 d-1 (S.D. = ± 0.17 g C m-2 d-1) in this study, which is approximately 60 % lower than that (0.47 ± 0.29 g C m-2 d- 1) measured in mid - eastern coast of the Yellow Sea during the similar period in 1989 - 1990. The daily total nitrogen uptake rate was 0.15 g N m-2 d-1 (S.D. = ± 0.07 g N m-2 d-1) in this study. The contributions of small phytoplankton to carbon and nitrogen of total phytoplankton were 71.9 % and 63.0 %, respectively, which are relatively higher than small phytoplankton contribution (53.1 %) to the total chlorophyll-a concentration (t-test, p < 0.05). Previous studies showed that the averaged contribution of phytoplankton (< 20 μm) to the total primary production is 55.4 ± 8.0 % which is significantly lower in this study (t-test, p < 0.05). A potential reason for the lower total primary production in this study is believed to the higher contribution of small phytoplankton, which is consistent with the results in the East/Japan Sea. Monitoring small phytoplankton contributions to the total primary production will be warrant for detecting changes in marine ecosystem under ongoing climate change.