The Food of Some Freshwater Cyclopoid Copepods and its Ecological Significance

Abstract

Considering the advanced state of our knowledge of the systematics of the freshwater cyclopoid copepods and the fact that many species are abundant in natural waters it is surprising that practically nothing is known of their food and feeding mechanisms. A few casual and often contradictory statements relating to the food of the group are to be found scattered through the literature but no definite study of the subject appears to have been made. Gurney's statement (1931) that 'it is most difficult to determine the food as it is generally impossible to recognize it from the contents of the gut' is too pessimistic, for by the employment of a very simple technique the nature of the gut contents can usually be revealed. The earliest references to the food of cyclopoids are to be found in writings dating back to the early years of the nineteenth century, but as Klugh (1927), who studied the feeding habits of certain freshwater crustaceans remarks 'the earlier writers on Entomostraca are extremely vague in their statements as to the food of these animals'. However, one of the earliest, Jurine (1820), made the observation, which seems to have been largely ignored by subsequent workers, that Cyclops is carnivorous. Birge (1897) (cited by Klugh 1927, and Gurney 1931) also claimed that Cyclops is partially carnivorous, eating rotifers, nauplii 'and other animals'. He also mentions a Cyclops, presumably a plankton species, feeding on Ceratium. Since these early days references to the food of cyclopoids have been made by Naumann (1918), Klugh (1927) and Vetter (1927a, b), though Vetter was interested in phytoplankton and its fate rather than in the food of cyclopoids. Neither he nor Naumann made specific determinations, a fact which robs their observations of much of their value, and neither added substantially to our knowledge. Klugh's work is still the most comprehensive review of the food of the freshwater Entomostraca, though he studied only two cyclopoid copepods-Macrocyclops fuscus and what would now be called Acanthocyclops bicuspidatus thomasi. The only food which he recorded from the gut of the latter species was the alga Chaetophora elegans, while from the gut of Macrocyclops fuscus he recorded 'palmella forms', a Chlamydomonas, and 'chitin fragments'. However, he also observed Macrocyclops fuscus seizing and partially devouring small specimens of its own species and of Diaptomus birgei. In addition a few casual statements from the literature deserve mention. Babaik (1913), cited by Oliva & Sladacek (1950), reports an attack on the larva of * Present address: East African Fisheries Research Organization, P.O. Box, 343, Jinja, Uganda.