Grazer-induced bioluminescence and toxicity in marine dinoflagellates

Marine copepods are the most abundant type of multicellular zooplankton in the global oceans. They imprint their surrounding waters with a unique bouquet of polar lipids; copepodamides. Copepodamides are recognized by prey organisms, who respond by inducing defensive traits including bioluminescence, toxin production, colony size plasticity and structural modifications. Copepodamides are suggested to act as general alarm-cues, but only a limited number of species have been experimentally exposed to copepodamides to date. Here, we quantify bioluminescence and toxin content in response to increasing concentrations of copepodamides in three additional species of marine dinoflagellates: Alexandrium catenella, Protoceratium reticulatum, and Gymnodinium catenatum. All three species up-regulated their defensive traits in response to copepodamide exposure. Neither bioluminescence nor toxin production was associated with measurable costs in terms of reduced growth rates. The results corroborate the role of copepodamides as general alarm-cues in marine phytoplankton. Moreover, the expression of simultaneous defensive traits in A. catenella may confound studies addressing the costs and benefits of these co-varying traits.