Major controlling factors for spatio-temporal variations in the macromolecular composition and primary production by phytoplankton in Garolim and Asan bays in the Yellow Sea

Abstract

Little information on phytoplankton is currently available for Garolim and Asan bays, which are important spawning and nursery grounds for various commercial fish. The objectives of this study were to investigate the spatial and seasonal variations in the biochemical components (carbohydrates, proteins, and lipids) and primary production by phytoplankton and to determine the major environmental factors controlling the variations in Garolim and Asan bays. All major inorganic nutrients were seasonally available to phytoplankton although PO4 concentrations were relatively lower than those of other nutrients. The chlorophyll-a (chl-a) concentration measured in this study was within the range reported previously and the phytoplankton community was mostly dominated by micro- and nano-phytoplankton (approximately 80 %). Among the different biochemical compositions, carbohydrates were the most dominant throughout our observation period. As a nitrogen source for phytoplankton growth, ammonium was more important compared to nitrate in Garolim and Asan bays because of a significantly high uptake rate of the ammonium observed in this study. The overall mean areal daily carbon uptake rate (238.8 ± 393.3 mg C m−2 d−1) measured in this study is within the range in various bays and coastal waters in Korea. The concentrations of SiO2, NO2+NO3 and micro-sized chl-a were found to be major factors for the variation in the biochemical compositions of phytoplankton. By comparison, the nano-sized chl-a concentration, NH4 concentration and temperature were observed to be major factors in the variation in the carbon uptake rate of phytoplankton in Garolim and Asan bays during our observation period. Further studies on macromolecular compositions and primary production from different cell-sized phytoplankton are warranted for a better understanding their potential effects on marine ecosystems.