The effects of the harmful alga Heterosigma akashiwo on cultures of Schmackeria inopinus (Copepoda, Calanoida)

Harmful effects of red tide dinoflagellates on copepods have gained particular attention in recent years. In this study, monocultures and mixed cultures of the harmful alga Heterosigma akashiwo and the non-harmful alga Isochrysis galbana were utilized as diets to investigate the ingestion, reproduction and recruitment of the copepod Schmackeria inopinus. When compared with a monoculture of I. galbana, a sole diet H. akashiwo apparently inhibited ingestion rates, proportions of gravid female (PGFs), egg production rates (EPRs), gross growth efficiencies (GGEs) and recruitment of S. inopinus. We found that the harmful effects of H. akashiwo on the abundance of S. inopinus were concentration- and time-dependent. S. inopinus exhibited significantly reduced ingestion rates, EPRs and GGEs when they were fed on food mixtures of H. akashiwo (0–75% of I. galbana) in comparison with the control diet (100% of I. galbana). The data on ingestion rates and EPRs in the diet mixtures suggest that H. akashiwo is toxic to S. inopinus, which might be attributable to the glycocalyx structures in the H. akashiwo cell surface. The results in this study indicate that a bloom of H. akashiwo could cause significant stress to S. inopinus.