Blue diatoms boost shellfish sector

The BIOVADIA (Biodiversity and valorisation of blue diatoms) project investigated the biology and biodiversity of blue diatoms, a form of microalgae. Researchers studied their specific blue pigments as well as their taxonomy, focusing on their position within the genus Haslea.

Haslea ostrearia, the first blue diatom ever described, is well known for its water-soluble blue pigment, marennine, which is responsible for producing green oysters. In addition to changing the oysters' colour, the greening also makes the flesh sweeter and tastier. This phenomenon gives the famous emerald green-tinged oysters of western France, which are of economic importance to the region.

Project partners collected and identified blue diatoms from different geographical areas. New species of marennine-producing diatoms were found and described with the aid of morphometrics (the analysis of their structure) and molecular genetic markers. Researchers also investigated the way in which the diatoms' physiology has adapted to their environment, including their life cycle and reproduction.

After collection and isolation, strains of blue Haslea were characterised by comparing the morphology of their silicified cell wall (frustule), the UV-visible spectrum of their pigments, and the sequences of some genetic markers from their plastid, mitochondrial and nuclear genomes. This information led to the discovery of four new species of blue Haslea, one in the Mediterranean Sea (H. provincialis), two in the Canary Islands (H. silbo sp. nov. and H. acoran sp. nov.), and one in the Java Sea (Haslea sp.).

Methods for extracting and purifying the blue pigments were improved by the consortium. A study of their biological properties (antioxidant, antiproliferative) was also conducted in order to increase understanding of these extraordinary biomolecules and how they can be used economically.

Marennine was shown to inhibit the growth of the pathogenic marine bacteria Vibrio splendidus, and to enhance larval survival of the blue mussel Mytilus edulis and the scallop Placopecten magellanicus exposed to this pathogen. This is of great interest for sustainable aquaculture, by reducing the need for treatment by prophylactic antibiotics, an environmental issue especially pertinent to intensive aquaculture.

BIOVADIA will help scientists gain a better understanding of marennine-type pigments and blue diatoms. This will improve the cultivation of green oysters and their contribution to Europe's economy, while enabling gourmets to continue enjoying their tasty treat.