Heterotrophic protozoa and small metazoa: feeding rates and prey-consumer interactions

• Published in: Journal of Plankton Research
• Main Author: Paffenhöfer, G.-A.
• Format: Text
• Language: English
• Published: Oxford University Press 1998
• Subjects: ORIGINAL ARTICLES; North Atlantic
• Online Access: http://plankt.oxfordjournals.org/cgi/content/short/20/1/121; https://doi.org/10.1093/plankt/20.1.121

A common approach to divide zooplankton into groups has been by size or size fractionation (micro-, meso- and macrozooplankton). Whereas almost all zooplankton retained by 200 μm mesh are metazoa, those not retained are proto- and metazoa. Even so, the variability of major taxa among those retained by 200 μm mesh can range widely between samples, that of passing 200 pm can vary even more when considering the grazing impact. If heavily weighted towards protozoa, the <200 μm community feeding rate on small phytoplankton could be several times the rate when most animals would be metazoa. Also, the interaction between proto- and metazooplankton passing 200 μm mesh ought to be considered, as should be that among protozoa. Using published data from the North Atlantic Ocean, the potential impact of small metazooplankton on the chlorophyll standing stock and primary productivity as well as on protozooplankton was evaluated. It was found that metazoo plankton passing <200 μm mesh removed a much larger part of the primary productivity than those retained by 200 μm mesh. Although the biomass of the 200 μm mesh metazoa was close to that of protozoa passing the same mesh, their ration was only a relatively small part of the primary productivity ingested by the latter. Yet, due to their unusually high abundance in these oceanic waters, the overall metazooplankton appeared to come close to controlling protozooplankton >50 μm3 in volume, i.e. those which could be actively perceived. It is hypothesized that in the absence of control by meta zooplankton, protozoa control their own abundance by predation/cannibalism.