Toxic haptophyte Prymnesium parvum affects grazing, survival, egestion and egg production of the calanoid copepods Eurytemora affinis and Acartia bifilosa

Nitrogen- and phosphorus-depleted or NP-balanced toxic haptophyte Prymnesium parvum was fed to 2 dominant copepod species of the northern Baltic Sea (Eurytemora affinis and Acartia bifflosa), and their ingestion, egg and faecal pellet production rates and mortality were measured. The copepods were incubated in 5 different cell concentrations of P. parvum for 3 consecutive days; the cryptophyte Rhodomonas salina was used as a control for non-toxic, nutritionally high-quality food. Toxicity (haemolytic activity) of P. parvum was measured before and after the incubations. The haemolytic activity of R parvum was the highest in cultures grown under nutrient deficiency. The toxicity decreased after 1 d incubation in all treatments, in both the presence and absence of copepods. Neither of the copepod species ingested R parvum, irrespective of the nutrient treatment (toxicity) or cell concentration, and the pellet and egg production rates were correspondingly low. Although there was no significant increase in mortality in P. parvum treatments, copepods that were exposed to P. parvum in any concentration or nutrient treatment soon became inactive. It was evident that the toxicity of even nutrient-replete P. parvum had an indirect and sublethal influence on copepods, although this could not be measured as short-term increased mortality. Our results suggest a strong reduction in secondary production of copepods in an event of a P. parvum bloom.