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 tem perature and starvation time on egg production rates of the calanoid c opepod Acartia grani were experimentally determined. Spawning rates os cillated according the frequencies of food fluctuations. For high freq uencies 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 maxim um egg production rates, and the length of the starvation period deter mined the time required to reach normal (control) egg productions afte r restarting feeding. The tight coupling between food abundance and eg g production in A. grani (i.e. the incapacity to buffer oscillations i n food abundance) is discussed in relation to its dominance in marine areas where the scales of temporal and spatial variability of food abu ndance allow the species to outcompete other representatives of the sa me genus.