MEPS 406:19-31 (2010)  -  DOI: https://doi.org/10.3354/meps08537

ABSTRACT: The toxic dinoflagellate Cochlodinium polykrikoides forms harmful algal blooms in coastal ecosystems around the world, to the great detriment of fisheries. Here we describe the allelopathic effects of C. polykrikoides blooms and strains isolated from east coast estuaries of the United States on natural communities and cultured phytoplankton. The allelopathic effects of C. poly-krikoides cultures and blooms on the target microalgal cells included loss of motility, distortion of cell morphology, and 60 to 100% cell mortality within minutes to 24 h. Allelopathy by C. polykrikoides on target microalgae was dependent on the relative and absolute cell abundance of each species as well as exposure time. The ability of C. polykrikoides cultures to kill target algae connected through a 5 µm mesh nylon membrane indicated that the allelopathic agents were extracellular and that direct cellular contact with target cells was not required for C. polykrikoides to exhibit allelopathy. Freezing, heating, sonication, and filtration of C. polykrikoides cells led to the complete loss of their allelopathic effect, suggesting that the allelopathic agents were short-lived and dependent on cell viability. Additions of the reactive oxygen species (ROS)-scavenging enzymes peroxidase and catalase into C. polykrikoides cultures eliminated or lessened their allelopathic effects, suggesting ROS-like chemical(s) were responsible for the allelopathy. These results are consistent with bioassays of fish and shellfish larvae with C. polykrikoides, suggesting that its toxicity to fish and shellfish larvae and its allelopathic effects on algae are caused by the same agents. The rapid and strong allelopathic effects exhibited by C. polykrikoides suggest allelopathy may facilitate blooms by eliminating competing species.

KEY WORDS: Allelopathy · Cochlodinium polykrikoides · Harmful algal blooms · Reactive oxygen species · Toxicity · Physiology · Ecology · Phytoplankton