1 Laboratoire Mer Molécule Santé (EA 2160, FR CNRS 3473 IUML), Le Mans Université, Le Mans, France;
2 Sorbonne Universités (UPMC Paris 06, CNRS, UMR 8227) Integrative Biology of Marine Models, Station Biologique de Roscoff, Roscoff, France ;
3 Institut des Sciences de la Mer, Université du Québec à Rimouski, Rimouski, Canada.
Keywords: Haslea ostrearia; marennine; natural bioactive compound; Vibrio
Abstract.
Blooms of the marine diatom Haslea ostrearia are recorded worldwide in natural environments and occur frequently in oyster ponds in the Western French coast. This diatom produces marennine, the water soluble blue pigment that turns oyster gills green and provides a higher market value to the bivalves. Although the blue Haslea and its pigment have been described centuries ago, little is known about the ecological significance of marennine. This blue pigment has previously been shown to display allelopathical, antioxidant and antibacterial activities in vitro and applications in aquaculture were considered as some prophylactic effects were demonstrated at low concentrations on farmed shellfish [1,2]. However, other studies showed larval mortalities at higher concentrations or modification of shellfish behavior [3]. The interactions between marennine and embryos and larvae of various marine invertebrates were thus further investigated. We observed an inhibiting effect of marennine at ecologically relevant doses on the fertilization rate and embryonic development of the sea urchin Sphaerechinus granularis and also on the survival and swimming capacity of the mussel Mytilus edulis larvae. Also, we have investigated the effects of the pigment on the growth of bacteria from the genus Vibrio that are known to induce diseases and mass mortality events in shellfish culture. Experiments conducted on 30 Vibrio strains from 10 different species showed differences in sensitivity between species but also between strains of a same species, ranging from growth inhibition to growth stimulation. Moreover, exposure of Vibrio to an increasing concentration of marennine did not systematically lead to a “classic” dose-response curve, and hormetic effects were observed for some strains with growth stimulation at low doses and growth inhibition at higher doses. It thus appears that marennine displays complex interactions with marine organisms and can impair survival or development of various invertebrates and modify growth dynamics of bacteria. Long term studies, mainly in the field, are much needed to really understand the effects of H. ostrearia blooms on marine ecosystems. Finally, our results question also the use of H. ostrearia and its blue pigment as probiotic in aquaculture.
