Seasonal variations in phytoplankton composition and transparent exopolymer particles in a eutrophicated coastal environment

Annual variations in phytoplankton composition and concentrations of transparent exopolymer particles (TEP) were studied in Tokyo Bay, one of the most eutrophicated coastal environments in central Japan, This study aimed at evaluating the influence of anthropogenic input on phytoplankton composition, bloom formations and their subsequent impact on TEP concentrations. Phytoplankton composition was dominated by diatoms, particularly Skeletonema costatum, during most of the year. However, raphidophytes represented by Heterosigma akashiwo became abundant from late spring to summer. TEP concentrations varied between 14 and 1774 mug Xanthan equiv. 1(-1), with higher values in the inner bay (169 182 mug Xanthan equiv. 1-1, which in terms of carbon is equivalent to 118 +/- 127 mug 1(-1)) than the bay mouth (112 +/- 70 mug Xanthan equiv. 1(-1), equivalent to 78 +/- 49 mug C 1(-1)). TEP concentrations followed an empirical relationship with chlorophyll a. In addition, peak TEP coincided with the peak chlorophyll a and raphidophyte abundance. Multivariate analysis between TEP and the different groups of phytoplankton indicated a predominant influence of diatoms and raphidophytes. TEP-carbon percent of chlorophyll-carbon tended to be higher during winter, which coincided with low bacterial counts and implied low or no utilization of TEP and hence an accumulation during such periods. Laboratory experiments were conducted with cultures of,S. costatum and H. akashiwo to test the species-specific variation, if any, in total organic carbon (TOC) production and TEP formation. The consistently higher chlorophyll equivalent TEP production in H, akashiwo confirmed our hypothesis that, in addition to well-known contributions by diatoms, groups like the raphidophytes contribute substantially to TEP as well as organic matter production in eutrophicated coastal regions. TOC and TOC equivalent TEP production revealed that, in addition to the biomass and composition, the growth stage(s) of the phytoplankton is an important factor controlling the C-rich TEP concentrations in aquatic ecosystems subjected to anthropogenic perturbances.