EFFECTS OF CONSTANT AND INTERMITTENT FOOD-SUPPLY ON LIFE-HISTORY PARAMETERS IN A MARINE COPEPOD

Laboratory experiments were used to determine effects of long- an short-term food limitation on birth, growth, and death rates in Centropages typicus (Copepoda, Calanoida), a species Previously reported to be sensitive to patchy food resources. Life-history parameters were measured in cohorts from hatching to senescence in a range of constant food treatments (0.2-7 mug Chl a liter-1) and in two pulsed treatments that cycled between 0.5 and 2.0 mug Chl a liter-1 at periods of approximately 0.5 and 1.0 d. A flow-through culture system minimized biochemical and grazing-induced changes in food supply and allowed automated measurement of food levels (fluorescence). Particulate carbon, nitrogen, lipid, carbohydrate, and protein were measured also. Results show that even the ''food-sensitive'' copepod, C. typicus, can integrate daily fluctuations in food supply at amplitudes comparable to patchiness levels observed in the field. This finding has important implications for field and laboratory studies that relate zooplankton growth and fertility to ambient food supply. Additional new findings include exponential growth in body length, sustained high fertility with age, ingestion of large algal and animal prey, and low contribution of carnivory to the diet. Comparisons with field data suggest that C. typicus is restricted to shelf regions due to food limitation, but that on the shelf it is a major contributor to total copepod production in the fall.