First investigations of blue Haslea blooms in natural environments (Calvi Bay, Corsica, France)Julie Séveno1, Damien Sirjacobs2, Pierre Lejeune3, Denis Baurain2, Sylvie Gobert3,4, Myriam Badawi1, Vincent Leignel1, and Jean-Luc Mouget1

1 Laboratoire Mer Molécule Santé (EA 2160, FR CNRS 3473 IUML), Le Mans Université, 72000 Le Mans, France

2 InBioS–PhytoSYSTEMS, Eukaryotic Phylogenomics, University of Liège, Liège, Belgium

3STARESO Research Station, Revellata Cape, 20260 Calvi, France

4 FOCUS-Oceanology- University of Liège, Liège, Belgium



The pennate diatom Haslea ostrearia is the emblematic and most studied species of the genus Haslea. H. ostrearia is mainly benthic and epiphyte, forming biofilms on sediment and on macroalgae. The cells produce a blue-green water-soluble pigment, the marennine, with allelopathic, antioxidant, antiviral and antibacterial properties, as demonstrated in laboratory conditions. Marennine is also responsible for the greening of oysters in refining ponds in the Marennes Oléron area (France), a phenomenon that has economical and patrimonial values. Recently, new species of blue Haslea that produce marennine-like pigments were described (H. karadagensis, H. nusantara, H. provincialis), thus illustrating an unsuspected biodiversity of the taxon. Based upon the H2020 GHaNA (The Genus Haslea, New marine resources for blue biotechnology and Aquaculture) programme, our research project aims to study the development of blue Haslea blooms in some natural environments.

Benthic blooms of blue Haslea spp. occur regularly in natural environments (e.g., France, USA, Croatia, Australia). For instance, in Calvi Bay, (Corsica France) Haslea spp. was first mentioned in spring 1996 and large biomass developments were observed during the last years. Species of Haslea responsible for the bloom were identified, using morphological and molecular approaches. Their abundances were determined and the cartography of the recent bloom localisations was achieved. The importance and patchiness of Haslea spp. developments were studied within shallow photophilous rocky habitats, in particular on the principal macroalgal hosts (Padina sp., Acetabularia sp., Halopteris sp., and macroalgal turf), which were sampled to study their epiphytic communities. Epiphytic floristic and faunistic inventories are currently compiled to determine if these epiphytic communities are affected by the release of marennine-like pigments. This work represents the first study on the dynamics of the bloom of blue Haslea species in natural environment in open water.



Keywords: bloom, diatom, diversity, epiphytes, Haslea, Mediterranean Sea.