Effects of constant and fluctuating food supply on egg production rates of Acartia grani (Copepoda: Calanoida)

The effects of fluctuating food concentration and the influence of temperature and starvation time on egg production rates of the calanoid copepod Acartia grani were experimentally determined. Spawning rates oscillated according the frequencies of food fluctuations. For high frequencies of food variability (12 h), the light conditions at which food was available had a quantitative effect, with higher production rates for copepods feeding at high food concentration by night. Alternating 24 h high food-low food concentrations had no effects on the average fecundity. However, lower frequency food fluctuations (>48 h high food-low food) reduced egg production. Temperature seemed to control maximum egg production rates, and the length of the starvation period determined the time required to reach normal (control) egg productions after restarting feeding. The tight coupling between food abundance and egg production in A. grani (i.e. the incapacity to buffer oscillations in food abundance) is discussed in relation to its dominance in marine areas where the scales of temporal and spatial variability of food abundance allow the species to outcompete other representatives of the same genus.