Phytoplankton growth dynamics in offshore Lake Erie during mid-winter

Abstract

The phytoplankton community in offshore Lake Erie in mid-winter was active but little net growth was occurring which suggests that high reported accumulations of phytoplankton in this lake in February are likely the product of previous bloom conditions. We measured phytoplankton dynamics as size-specific growth and loss rates of phytoplankton using dilution assays and antibiotic assays in ice-covered offshore waters of Lake Erie during the mid-winter period in 2008, 2009, and 2010. Total chlorophyll-a specific rates (average±standard deviation) measured using dilution assays for growth ([0.72±0.35/d]) and loss ([0.98±0.36/d]) were closely matched. Growth and loss rates of picocyanobacteria determined using an antibiotic technique ranged from −0.10 to 1.22/d and −0.11 to −2.35/d, respectively. The results indicate a trend of higher grazing rate than growth rate but that this difference is not significantly different from zero, suggesting a state of phytoplankton population size equilibrium at this time of year in the waters sampled.