Abstract:

Aims The Yangtze River Estuary (YRE) faces eutrophication caused by discharge of industrial and agricultural sewage. This leads to frequent harmful algae blooms involving the rapid proliferation of specific toxic species. The aims of our study are to: 1) apply scientific methods and field experiments to clarify the distributional relationship between phytoplankton species and the environment, and 2) provide data on species and environment informative for further research on estuary ecosystem protection.
Methods An interdisciplinary survey of hydrological, chemical and biological resources was conducted in the YRE on August 28 - September 6, 2004. Phytoplankton cell counts and species identification were performed with an inverted microscope at ×100-×400 magnification after sedimentation for 24 h in 25 ml Utermøhl chambers. Temperature, salinity, pH and dissolved oxygen were measured by a pre-calibrated YSI 6000. Other abiotic environmental data were obtained based on protocols of marine investigations. Canonical correspondence analysis (CCA) was applied to explore the relationship between phytoplankton species and environmental parameters using CANOCO4.0.
Important findings Turbidity and nutrient gradient along the Yangtze River runoff were the most important factors influencing the distribution of phytoplankton species. Transparency, nitrate and silicate were major factors affecting the phytoplankton community structure. The dominant phytoplankton species Proboscia alata f. gracillima preferred low nitrate concentration and clear offshore areas, while Skeletonema costatum preferred high nitrate and more turbid waters. CCA can be a useful tool to understand the spatial distribution of phytoplankton species in marine ecosystems.

Key words: phytoplankton, Skeletonema costatum, Proboscia alata f. gracillima, environmental factors, canonical correspondence analysis, Yangtze River Estuary