Zooplankton filtration rates in Lake Huron, Georgian Bay and North Channel

Abstract

On three research cruises in 1981, zooplankton community filtration rates were measured at 4 stations: Saginaw Bay, mid-Lake Huron, Georgian Bay and North Channel. For all four stations, the highest rates were observed during the late-September cruise. The maximum observed rate was 137000 ml d⁻¹ m⁻³, while the lowest rate was 7200 ml d⁻¹ m⁻³. The grazing experiments were performed on three size classes of radioactively labelled algal food (0.45–5 µm, 5–20 µm and 20–64 µm). In 11 of 12 experiments, the smallest size class of food yielded the highest filtration rate. For the late-May cruise we used published data on phytoplankton biomass for the Georgian Bay and North Channel stations to calculate community feeding rates of 0.09 and 0.015 mg C mg Cm⁻³ d⁻¹, respectively, and percent cropping rates of 0.74 and 0.35 per day, respectively. A comparison of our feeding rates to literature values for zooplankton biomass suggests that algal food alone may not be sufficient to sustain zooplankton growth at those stations.