Feeding of Zooplankton in Diluted Sea-water

Abstract

THE production of fæcal pellets in the sea can be used as evidence that the phytoplankton is being grazed down by zooplanktonic herbivores¹. In the laboratory, results obtainedfrom the copepods Calanus^2–4 and Acartia⁴ suggest that fæcal pellet production may be taken as an approximate measure of the amount of food which is eaten, a larger number of pellets being voided by animals with the greatest feeding activity. The number of fæcal pellets rises with increasing food concentration, but the relationship is not linear, as copepods appear unable to ingest excessive quantities of food and void waste material beyond a certain rate³. Fæcal pellets consist of waste material surrounded by peritrophic membranes⁵ and vary in both shape and size depending on the food³. Preliminary observations on Calanus helgolandicus Claus indicate that major changes in the grazing rate of copepods exposed to sea-water of reduced salinity containing food cells can be detected by measuring the rate of fæcal pellet production⁴. Similar conclusions have since been made from preliminary experiments in which the green flagellate Dunaliella was fed to Acartia bifilosa (Giesbrecht) and A. discaudata (Giesbrecht).