Allelopathic effects and mechanisms of Cochlodinium geminatum isolated from the Pearl River Estuary

The dinoflagellate Cochlodinium geminatum can form near-monospecific blooms which have occurred at the same location in the South China Sea repeatedly in the last decade. Here, we demonstrate the allelopathic effects of C. geminatum isolated from the bloom waters of the Pearl River Estuary, South China Sea, in August 2011, which inhibited four of six co-occurring phytoplankton species tested. Inhibition increased with rising cell density and reached a maximum in the declining growth stage. Four different C. geminatum culture components negatively affected growth of Akashiwo sanguinea in order of decreasing percent inhibition: sonicated culture, filtrate of sonicated culture, whole-cell culture and filtrate of whole-cell culture. The highest inhibition was at 25 °С and salinities of 30 PSU and light intensities of 100 μmol photons m−2 s−1. Overall, our study showed that C. geminatum could inhibit growth of phytoplankton competitors during succession of phytoplankton community, achieving nearly monospecific blooms, and the allelopathic effects were regulated by environmental factors.