Benthic Diatom Blooms of Blue spp. in the Mediterranean Sea.

Blue species are marine benthic pennate diatoms able to synthesize a blue-green water-soluble pigment, like marennine produced by Simonsen. New species of synthetizing blue pigments were recently described (, , and ). Their marennine-like pigments have allelopathic, antioxidative, antiviral and antibacterial properties, which have been demonstrated in laboratory conditions. Marennine is also responsible for the greening of oysters, for example, in the Marennes Oléron area (France), a phenomenon that has economical and patrimonial values. While blue spp. blooms have been episodically observed in natural environments (e.g., France, Croatia, USA), their dynamics have only been investigated in oyster ponds. This work is the first description of blue spp. benthic blooms that develop in open environments on the periphyton, covering turf and some macroalgae-like . Different sites were monitored in the Mediterranean Sea (Corsica, France and Croatia) and two different blue species involved in these blooms were identified: and . A non-blue species was also occasionally encountered. The benthic blooms of blue followed the phytoplankton spring bloom and occurred in shallow calm waters, possibly indicating a prominent role of light to initiate the blooms. In the absence of very strong winds and water currents that can possibly disaggregate the blue biofilm, the end of blooms coincided with the warming of the upper water masses, which might be profitable for other microorganisms and ultimately lead to a shift in the biofilm community.