Abstract: Estuary and nearshore waters have complicated environment, where plankton community has a frequent feedback regulation and a very unstable particle size structure. In this paper, an investigation was made on the particle size structure of plankton in the turbidity zone of nearshore and port area waters in Liaoning Province of Northeast China. In the waters with high concentration inorganic nitrogen, phytoplankton biomass was mainly of small particle sizes, with the equivalent sphere diameter (ESD) being primarily 20-100 μm, while in low nutrient waters, the phytoplankton biomass was mainly of larger size particles, with the ESD>100 μm, indicating that the phytoplankton feedback regulation caused the phytoplankton community to be comprised of small sized organisms as part of the biological responses to high concentration suspended solids, which reduced the individual number of larger organisms such as Coscinodiscus sp. and other species, and in turn, directly affected the fisheries resources, including a variety of fish and shrimp larvae fed on phytoplankton. A normalized biomass size spectrum with the characteristics of nearshore shallow aquatic oceanic ecosystems exhibiting eutrophication was constructed. The spectrum slope indicated that the plankton community biomass would gradually increase in size. The feasibility of using dinoflagellates and cladocerans as the bio-indicators for eutrophication was discussed.

Key words: normalized biomass size spectra, plankton, size structure, stress response, turbidity zone of nearshore water.