Phytoplankton dynamics in a subtropical tidal creek: influences of rainfall and water residence time on composition and biomass

Abstract

Concerns about global climate change have heightened awareness of the role changing rainfall regimes play in altering plankton communities of coastal ecosystems. In this study spatial and temporal patterns of phytoplankton composition and biomass in a sub-tropical tidal creek in Florida were observed over three wet and dry seasons, which included the major storm year of 2005 and the drought year of 2006. Shifts in rainfall levels were associated with changes in phytoplankton composition and biomass, but the effects varied between the upper and lower reaches of the creek. The upper reach of the creek was fresh throughout the study period. The oligohaline to mesohaline lower creek alternated between fresh and marine species in response to shifts in salinity regimes. Blooms of the freshwater dinoflagellate Peridinium sp., small centric diatoms and nitrogen-fixing cyanobacteria were common in the upper Ten Mile Creek during low rainfall years. The euryhaline marine dinoflagellate Akashiwo sanguinea and centric diatoms (e.g. Leptocylindrus minimus) were observed at bloom levels in the lower creek during low to average rainfall periods. The results are discussed within the context of how variability in rainfall influence water residence times, nutrient concentrations and salinity regimes, which in turn influence phytoplankton composition and biomass.