Changes in cyanobacterial dominance following the invasion of the zebra mussel Dreissena polymorpha:: Long-term results from the Hudson River Estuary

The introduction of invasive bivalves such as the zebra mussel (Dreissena polymorpha) can have profound effects on aquatic ecosystems, including decreases in phytoplankton biomass and changes in the taxonomic composition of phytoplankton. Zebra mussel introductions have been associated with increased dominance of cyanobacteria, especially Microeystis, but this change may depend on interacting physical, chemical, or biotic conditions. We used a 12-yr record in the Hudson River to explore the relationship between phytoplankton composition and zebra mussel filtration. During this period (1993-2005), the mean July-September filtration rate of the zebra mussel (ZMF) varied by 8-fold, and the mean biovolume of cyanobacteria, which was dominated by Microcystis, varied from 0 to 4.2 mm(3) l(-1) and comprised up to 52% of total phytoplankton biovolume. There was a tendency for high cyanobacterial biomass to be associated with low rather than high ZMF. Neither the absolute nor the relative amounts of either total cyanobacteria or Microeystis were significantly correlated to ZMF alone or in combination with total phosphorus or any other physical or chemical parameters that we measured. Cyanobacterial dominance and abundance were both strongly correlated to temperature, and over 80% of the among year variance in cyanobacterial dominance could be explained by temperature in a linear model. Temperature in combination with dissolved SiO3 explained 90% of the variation in cyanobacterial dominance. At higher temperatures and lower dissolved SiO3, cyanobacterial abundance increased at the expense of diatoms that dominated at lower temperatures and in higher SiO3 years. The high explanatory value of temperature is surprising as the variation in temperature among years was relatively low (24.0-26.8 degrees C). The results suggest that even slightly increased temperatures could lead to higher biomass and dominance of cyanobacteria in some aquatic systems.