Does the red tide dinoflagellate Karenia brevis use allelopathy to outcompete other phytoplankton?
Limnol. Oceanogr., 50(3), 2005, 883-895 | DOI: 10.4319/lo.2005.50.3.0883
ABSTRACT: Monospecific blooms of phytoplankton can disrupt pelagic communities and negatively affect human health and economies. Interspecific competition may play an important role in promoting blooms, and so we tested (1) whether the outcome of competition between the red tide dinoflagellate Karenia brevis (ex Gymnodinium breve) and 12 cooccurring phytoplankters could be explained by allelopathic effects of compounds released by K. brevis and (2) whether waterborne, lipophilic molecules, including brevetoxins, are involved. Nine of 12 phytoplankton species were suppressed when grown with live K. brevis at bloom concentrations. K. brevis extracellular filtrates or lipophilic extracts of filtrates inhibited six of these nine species, indicating allelopathy. However, these inhibitory effects were weaker than those experienced by competitors exposed to live K. brevis. Brevetoxins at ecologically reasonable waterborne concentrations accounted for the modest inhibition by K. brevis of only one competitor, Skeletonema costatum. The addition of brevetoxins also caused significant autoinhibition, reducing the maximum concentration of K. brevis. Allelopathy is one mechanism by which K. brevis appears to exhibit competitive advantage over some sympatric phytoplankters, although unidentified compounds other than brevetoxins must be involved, in most cases. K. brevis was also susceptible to competitive exclusion by several species, including Odontella aurita and Prorocentrum minimum, known to thrive during K. brevis blooms. Although field experiments are required to assess whether allelopathy plays a fundamental role in bloom dynamics, our results indicate that allelopathy occurs widely but with species-specific consequences.