Influence of diet on copepod survival in the laboratory

The mortality rate of female calanoid copepods Temora longicornis and Pseudocalanus elongatus was measured in relation to the concentration of different algae as a food source. Female copepods were fed either good-quality food (Rhodomonas sp.) or nutritionally poor food (Dunaliella sp., Amphidinium sp., Chrysochromulina polylepis and Synechococcus sp.) in high (>300 mug C l(-1)) or low (<100 mug C l(-1)) concentrations and survival was monitored. Both copepod species had low mortality rates (less than or equal to5 % d(-1)) when fed with d high concentration of Rhodomonas sp. or Dunaliella sp., somewhat higher rates with the same species at a low concentration (4 to 12 % d(-1)), and highest rates with all the other algae (12 to 18 % d-1), irrespective of the concentration. Hence, some poor-quality algae can supply part or all of the energy required for survival. Diet-specific differences were more pronounced at high than at low food concentrations, suggesting that at low concentrations, qualitative differences of the algal food source decrease. The clearest copepod-specific difference was observed in survival without food: probably due to internal energy reserves, P. elongatus survived in filtered water nearly twice as long as T longicornis. We suggest that, in low food environments, food quantity and species-specific ability to resist starvation might be as important as food quality in determining the success of copepod populations.