The Growth Response of Prorocentrum minimum Pavill. (Dinophyta) to Karlotoxin Exposure

Abstract

Extracellular metabolites produced by harmful algae can act as growth-inhibiting agents for other phytoplankton species, influencing species competition and succession and hence affecting structure of the plankton community. Karlodinium veneficum Ballant., a cosmopolitan estuarine dinoflagellate, produces toxic compounds known as karlotoxins that exhibit sterol-dependent, cytotoxic activity and are frequently associated with fish kills. Karlotoxin-sensitive cells tend to have desmethyl sterols as predominant cellular sterols, and karlotoxin-resistant cells have 4-methyl sterols as dominant sterols. The allelopathic effects of karlotoxins on other algae have been described, but the question of whether or not K. veneficum is allelopathic against Prorocentrum minimum, a common co-occurring dinoflagellate, is unknown. We determined the sterol profiles of two different Chesapeake Bay strains (RR4B1 and IB) of P. minimum and also exposed them to different concentrations of karlotoxin extracted from K. veneficum cells. The strains, RR4B1 and IB, experienced mortality at high toxin concentrations, i.e., 256 ng mL -1 . After 24 hours of exposure, cell counts declined resulting in calculated “negative growth rates” of -1.17 (d -1 ) for RR4B1 and