Toxic effects and mechanisms of Prymnesium parvum (Haptophyta) isolated from the Pearl River Estuary, China

Prymnesium (Haptophyta) species form toxic blooms throughout the world resulting in large fish-kills and economic losses. A culture of Prymnesium parvum JX12 was isolated and established from the Pearl River Estuary of China. The toxic characteristics of JX12 to aquatic animals were investigated, considering the effects of temperature, salinity, and nutrients. Cultures of JX12 exhibited significant lethal toxicity to the fish, Mugil sp., M. soiuy, M. cephalus, Ctenogobius sp. and Chrysiptera parasema, and the brine shrimp, Anemia sahna, but no significant effects on the shellfish Ruditapes variegatus and the shrimp Penacus orientalis. The toxicity of JX12 to A. salina increased with growth of the culture. The decline phase displayed the strongest potency, followed by the stationary phase, exponential phase and lag phase. Also, there was a significant difference in toxicity among culture fractions of JX12 compared to whole-cell culture. For example, the toxicity of a cell-free culture filtrate on brine shrimp was reduced by 50% by the end of the experiment, while the sonicated and re-suspended cultures caused near 100% mortality. The toxicity of JX12 was also regulated by environmental factors such as temperature, salinity and nutrients. The strongest toxicities were at moderate water temperature (20-25 degrees C) and salinity (35 psu). The toxicity was reduced significantly at higher or lower temperatures and salinities. Furthermore, the toxicity of JX12 was greatly enhanced when ambient nutrients were deficient. Due to the potent toxicity of JX12 to multiple aquatic animals, especially fish and zooplankton, this species threatens the food web and trophic dynamics of coastal ecosystems. This study suggested that the ability to produce and release toxin(s) is an effective competition strategy for P. parvum to suppress predators and sympatric competitors and thus form blooms.