Effect of marennine on the rearing medium and microbiota of Mytilus edulis larvae and its protective effect after exposure to the pathogenic Vibrio splendidus

Abstract

ABSTRACT Opportunistic pathogens have been associated with yield-limiting factors in bivalve hatcheries. Numerous natural compounds are being investigated for their beneficial effects and potential to enhance larval resistance without requiring antibiotics. One of those is the use of marennine, a blue pigment, originating from the diatom Haslea ostrearia, which has demonstrated a positive effect on larvae survival. The aim of this study was to highlight the protective effect of marennine on Mytilus edulis larvae during bacterial challenges in relation to a potential modification of the marennine-treated larvae microbiota. D-larvae and post-larvae were exposed for 96 h to Vibrio splendidus (106 cell mL−1) with and without mareninne (500 µg L−1). The presence of marennine increased the survival rate of D-larvae exposed to the pathogen. The molecular analysis of the larvae microbiota diversity indicated a modification in the D-larval microbiota’s richness related to survival rates of larvae. Ultimately, our study sheds light on the importance of the larval microbiota in pathogen resistance during the bivalve rearing process.