Examining allelopathic competition of a red tide alga within two different marine communities
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Blooms of the marine dinoflagellate Karenia brevis exist in two distinct habitats: far offshore where blooms initiate at low densities and inshore where dense blooms are driven by wind and water currents. Two competing hypotheses could explain variation seen in competitor species response to K. brevis allelopathy: offshore species are more susceptible to allelopathy because they have not evolved a mechanism to combat allelopathy, or inshore species are more susceptible to allelopathy because K. brevis evolved the allelopathic mechanisms to combat these species specifically. The allelopathic effects of K. brevis were observed on competitor species from each environment. Nine species, four offshore and five inshore, were exposed to K. brevis, but separated by mesh so that no cellular contact occurred between K. brevis and competitors. The growth of one inshore species and one offshore species was significantly inhibited by K. brevis allelopathy. There was no difference between inshore and offshore species response to allelopathy and therefore the hypotheses were rejected. However, treatments from both habitats responded similarly in that there fluorescence was unusually high, indicating K. brevis allelopathy causes sublethal damage to photosystem II.