FEEDING RATE OF CALANUS FINMARCHICUS IN RELATION TO ENVIRONMENTAL CONDITIONS

¹ From the Woods Hole Oceanographic Institution and the Biological Laboratories, Clark University

(1) The filtering rate of Calanus finmarchicus on the diatom, Nitzschia closterium, was measured under different conditions of diatom concentration, light and temperature, by observing the reduction in concentration of the diatoms. Change in diatom concentration had no effect on the rate of filtration. There was some evidence of a diurnal feeding rhythm with greater activity at night. Feeding was most rapid at 8° C., slower at 13° and 3°.

(2) Studies on the growth of Calanus supplied with different concentrations of diatoms indicated that the food requirement is less than has been calculated from oxygen consumption measurements. This is also borne out by comparing the amount of particulate organic matter in the sea with the rate of feeding measured in the laboratory.

(3) The view that the feeding activity of Calanus is automatic filtering is favored by these experiments.

(4) Approximately one-half the organic nitrogen content of Nitzschia is in a form available to Calanus.

(5) These results are correlated with the ecology of Calanus as studied in the field.