Influence of diet on copepod survival in the laboratory

The mortality rate of female calanoid copepodsTemora longicornisandPseudocalanus elongatuswas measured in relation to the concentration of different algae as a food source. Female copepods were fed either good-quality food (Rhodomonassp.) or nutritionally poor food (Dunaliellasp.,Amphidiniumsp.,Chrysochromulina polylepisandSynechococcussp.) in high (>300 μg C l–1) or low (<100 μg C l–1) concentrations and survival was monitored.

Both copepod species had low mortality rates (≤5% d–1) when fed with a high concentration ofRhodomonassp. orDunaliellasp., 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. elongatussurvived in filtered water nearly twice as long asT. 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.