Reproduction and survival of the calanoid copepod Eurytemora affinis fed with toxic and non-toxic cyanobacteria

Reproduction (egg production and hatching success) and maintenance (mortality and carbon and nitrogen content) of the calanoid copepod Eurytemora affinis were measured at 5 concentrations (ca 50, 100, 200, 400 and 600 mu g C l(-1)) of toxic and non-toxic strains of the cyanobacterium Nodularia sp. and the green alga Brachiomonas submarina, and in 3 different mixtures of these species (1:1, 8:1 and 1:8). In addition, females with egg-sacs were collected from the sea and exposed to different concentrations of Nodularia sp., to find out whether cyanobacterial exudates disturb hatching of eggs produced in natural food conditions. With the B. submarina diet copepod egg production was high (maximum ca 7 eggs female(-1) d(-1)), and increased with increasing food concentration, whereas with both toxic and non-toxic Nodularia sp. diet egg production was comparable to that in filtered sea water (0 to 2 eggs female(-1) d(-1)), irrespective of food concentration. With both toxic and non-toxic Nodularia sp., copepods produced deformed egg-sacs, and hatching success was low, while eggs produced in natural food conditions hatched well, with the exception of those exposed to a high concentration of toxic Nodularia sp. Mortality of E. affinis fed with toxic Nodularia sp. was high, whereas high concentrations of non-toxic Nodularia sp. kept copepods alive. No beneficial effects of Nodularia sp. in mixtures with B. submarina were observed. However, mortality in mixtures with toxic Nodularia sp. was low, hatching success generally high and no deformed egg-sacs were produced, which indicated that copepods were able to avoid feeding on toxic algae. Our results suggest that, in addition to its toxic effect, Nodularia sp, lacks certain essential elements needed for copepod reproduction. However, the non-toxic strain is sufficiently high in food quality to sustain maintenance of E. affinis, if offered in large quantities.