Collapse of Calanus chilensis reproduction in a marine environment with high diatom concentration

Variations of egg production rate (EPR), hatching success (HS), production of abnormal larvae (AL) and histology of gonads have been investigated with Calanus chilensis females sampled weekly, from late November to December 2004, at a station located in the coastal zone off Dichato (Chile), at time diatom concentration in phytoplankton bloom was high. Weekly EPR estimate in nature did not change significantly during this period. It remained close to normal values (25-40 eggs/female/day), whereas HS was constantly low and high proportions of AL were observed. In parallel, bioassays revealed that EPR was strongly depressed by artificially enriched diets, corresponding to natural diatom assemblages (NDA) occurring in the field, while abnormal HS and AL values could not be improved. Ingestion of diatoms by females was estimated by faecal pellet production rates and SEM examination of diatom remains in pellet samples. Low HS and the high amounts of abnormal larvae were not reversible when females were offered a favourable food, the dinoflagellate P. minimum (PM). Minor cell degradations were observed in gonads of females fed NDA diets. In comparison with other environments, present results show that impairment of Calanoid copepod reproductive factors can occur at both high and low diatom concentrations, depending on maternal diets and diatom species in blooms.