Does allelopathy affect co-culturing with other microalgae relevant to aquaculture?

is a marine diatom known to produce marennine, a water-soluble blue-green pigment responsible for the greening of oysters in ponds along the French Atlantic coast. This phenomenon occurs seasonally when blooms in oyster ponds, and it increases the economic value of cultured oysters. From an ecological perspective, blooms are accompanied by a decrease in the abundance of other microalgae, suggesting that this diatom produces allelochemicals. Recent studies showed that purified marennine has other biological activities, for instance antioxidant, antibacterial, and antiviral activities, which could be used in aquaculture to promote this pigment as a natural antipathogen agent. One important issue regarding the possible use of in aquaculture as a mixed algal diet, however, is the importance of marennine allelopathy. In this study, we investigated the allelopathic effect of on the growth of five microalgal species relevant to aquaculture: , , , , and . Allelopathic tests were realized by co-culturing these microalgae with in batch and in semi-continuous mode, based on initial biovolume ratios. Our findings showed that inhibition of the growth of microalgae due to the presence of and marennine was species dependent. , , and were significantly more sensitive, whereas and appeared to be more resistant. Growth irradiance significantly influenced the allelopathic effect against the sensitive species , and the production of marennine increases with irradiance. Data presented in this study partly support the hypothesis that marennine released into the culture medium possibly acts as an allelochemical compound, thus explaining the dominance of and the loss of sensitive algae in oyster ponds, but also that some species are insensitive, which allows co-culturing and use in a mixed algal diet in aquaculture.