Kill your enemies and eat them with the help of your toxins: an algal strategy

Abstract

Prymnesium spp. have been shown to kill both their grazers and other algal species, by producing allelopathic compounds. Killing nutrient-competing phytoplankton species enables Prymnesium to freely utilise limiting resources. Mixotrophy, i.e. the ability to ingest bacteria, other algae, and potential grazers, also contributes to the bloom-forming ability of Prymnesium spp. Allelopathy, mixotrophy and grazer deterrence increase when cells of Prymnesium spp. are grown under N- or P-deficiency, as does toxicity. However, the opposite holds if cells are grown with excess N and P in proportions balanced to the needs of the alga. Prymnesium filtrates from nutrient-deficient cultures also exhibit strong allelopathy against other algal species and grazer deterrence. It seems that toxin production in Prymnesium spp. functions not only as a defence mechanism, but also serves to kill competitors, thereby increasing the ability to compete under conditions of nutrient depletion. A consequence of increasing the input of either N or P into aquatic ecosystems is an unbalanced nutrient environment, which favours the production of toxins/allelochemicals by Prymnesium species.