Studies on a Calanus Patch III. The quantity of food eaten by Calanus finmarchicus

Abstract

The purpose of this paper is to assess the grazing capacity of Calanus finmar-chicus (Gunner.) in terms of the quantity of food eaten in the sea. The part played in the growth of the animal by the quantity eaten will only be briefly discussed. The parts played by nutrient lack, sinking and diffusion on the algal productive rates will also be discussed, leading to the conclusion that grazing mortality is the most effective controlling agent on algal production.A subsidiary purpose of this paper is to relate changes in the weight of Calanus finmarchicus to changes in food consumed and to changes in water temperature. Measurements of C. finmarchicus have been made by a number of workers (Adler & Jespersen, 1920; Russell, 1928; Marshall, 1933; Stormer, 1929; Bogorov, 1934; Jespersen, 1939; Clarke & Zinn, 1937). It will be shown that in the North Sea, in spring, the greatest changes in weight are most readily related to changes in quantities of food consumed.

Cannibalism by female Calanus finmarchicus on naupliar stages

“…Ingestion rate on algae (ml ind. The clearance and ingestion rates on Thalassiosira weissflogii were relatively high, but in the range of previously observed rates of late Calanus finmarchicus stages feeding on diatoms or on the natural algae community (Cushing & Vucetic 1963, Barthel 1988, MeyerHarms et al 1999, Meyer et al 2002. Clearance rates were also high at algal concentrations below 20 mg C m -3 ; thus no, or only a very low, threshold concentration seems to be associated with the filtering of T. weissflogii cells.…”

Some Observations on the Dependence of Zooplankton Grazing on the Cell Size and Concentration of Phytoplankton Blooms

“…No evidence for "superfluous feeding" (BEKLEMISHEV, 1957;CUSHING and VUCETIC, 1963) was encountered in this series of experiments. However, much of the data presented here are demonstrative of phytoplankton which because of their size or shape were not particularly suited to the zooplankters which were grazing on them.…”

The impact of appendicularian grazing on natural food concentrations in situ1

“…The population densities of 0. dioica, a cosmopolitan, eurythermal species, vary considerably with location and season, Cushing and Vucetic (1963) S tegasoma magnum is known from warmer waters of the Pacific, Atlantic, and Indian Oceans. In the Gulf of California, its densities were considerably lower than those of 0. dioica, reaching a maximum of 63 -rnM3.…”