EGG-PRODUCTION OF CALANUS-FINMARCHICUS - EFFECT OF TEMPERATURE, FOOD AND SEASON

The use of the egg production rate of herbivorous copepods as an impor tant parameter for understanding population dynamics and as an index o f secondary production requires knowledge of the regulatory mechanisms involved and of the response to changes in food concentrations and te mperature. Furthermore, the effects of season and generation on egg pr oduction have to be studied. In this context data are presented for Ca lanus finmarchicus from the northern North Atlantic. Prefed and presta rved females were exposed to different concentrations of the diatom Th alassiosira antarctica over 1 to 2 wk at 0 or 5 degrees C, and egg dep osition was controlled daily. Egg production increased with higher foo d concentrations, but much less when prestarved. The effect of tempera tures between -1.5 and 8 degrees C on egg production was studied in fe males maintained at optimum feeding conditions. Egg production rate in creased exponentially over the whole temperature range by a factor of 5.2, from 14.2 to 73.4 eggs female(-1) d(-1), and carbon-specific egg production by 4, from 2.1 to 8.5% body C d(-1). The response to starva tion was also temperature dependent. In both the temperature and feedi ng experiments egg production rate was regulated mainly by changes of the spawning interval, while changes of clutch size were independent o f experimental conditions. Different responses to optimum feeding cond itions were observed in females collected in monthly intervals on thre e occasions between March and May. The March females deposited more cl utches than the April and May females. In May, >50% of the females did not spawn at all. Maximum egg production rates were never >25% of the rate expected at 5 OC, indicating endogenous control of egg productio n in addition to food and temperature effects.