Can the blue diatom Haslea ostrearia with strong biological activity be considered as a harmful alga?Charlotte Falaise1, Réjean Tremblay2, Patrick Cormier3, Cyrille François4, Adèle James3, Andreas Seger5, Aiko Hayashi5, Gustaaf Hallegraeff5, Jean-Luc Mouget1

1 Laboratoire Mer Molécule Santé (EA 2160, FR CNRS 3473 IUML), Le Mans Université, Le Mans, France;

2 Institut des Sciences de la Mer, Université du Québec à Rimouski, Rimouski, Canada;

3 Sorbonne Universités (UPMC Paris 06, CNRS, UMR 8227) Integrative Biology of Marine Models, Station Biologique de Roscoff, Roscoff;

4 Ifremer (SG2M-LGPM), Laboratoire de Génétique et de Pathologie des Mollusques Marins, La Tremblade, France;

5 Institute for Marine and Antarctic Studies (IMAS), University of Tasmania, Hobart, Australia



Marennine is the water soluble blue pigment produced by the marine diatom Haslea ostrearia. Blooms in oyster ponds are not associated with mortality events and oyster lovers have been eating “green” oysters for centuries without any record of harmful impacts.

Although the blue diatom and its pigment have been described centuries ago little is known about the ecological significance of marennine. This compound has previously been shown to display allelopathical, antioxidant or antibacterial activities in vitro, but no evidence has emerged for its possible ecological advantage. The application of marennine has been considered in aquaculture to limit bacterial growth or improve physiological condition of farmed shellfish. A prophylactic effect has been observed at low concentration, improving mussel larval survival when exposed to pathogenic Vibrio. Other studies showed larval mortalities at high concentrations or modification of shellfish behavior.

To assess if marennine is a biologically active substance or can be classified as a “natural toxin”, we investigated its activity against marine bacteria, echinoderms, bivalves, human gut epithelial and fish gill cell lines, with acute and sublethal effects sometimes observed depending on the target organism, and marennine concentration. Marennine can cause mortality or embryonic developmental delays in various marine organisms. The biological activity of marennine is compared with that of various algal toxins and similarities and differences are pointed out.