Feeding rates of appendicularians (Oikopleura spp.) in coastal Newfoundland waters : results of in situ studies

Abstract

Appendicularian populations were observed in Logy Bay, Newfoundland over a two year period to quantify their feeding behavior and to elucidate their role in energy flow in a cold ocean environment. Populations were observed to fluctuate rapidly in apparent response to wind-induced changes in water mass characteristics. Very large individuals of Oikopleura vanhoeffeni dominated very cold waters (< 0°C) while warmer waters (> 8°C) were characterized by higher densities of the smaller Oikopleura labradoriensis. -- Radioactively labelled algae were used to measure in situ ingestion and clearance rates of individual Oikopleura over a wide range of animal sizes, temperatures and ambient food concentrations. Multiple regression analysis indicated that animal body size (measured as tail length) explained 11.3% of the variance in ingestion rate and 46% of the variance in clearance rate. Temperature was not a significant variable, while the biomass concentration of phytoplankton < 2 μm explained an additional 8% of the variation in clearance rate. Animal activity, estimated from tail beat observations, explained 60% of the variation in ingestion rate for a sublet of the data but was not significantly correlated with temperature, body size or ambient food concentrations. Oikopleura populations were estimated to clear a maximum of 2% of the water column per day at observed densities, while literature estimates of densities for nearby Conception Bay yielded clearing estimates up to 64% per day.