Taxonomic characterization and toxicity assessment of strains of Gambierdiscus belizeanus from Seychelles, southwestern Indian Ocean

Benthic dinoflagellates associated with human ciguatera poisoning are present in the Indian Ocean and species such as Fukuyoa (formerly Gambierdiscus) yasumotoi, G. toxicus and G. belizeanus have been reported since the mid 90s. Even though, very little information is available concerning the occurrence of Gambierdiscus species and toxicity in the Seychelles waters. This study investigates four Gambierdiscus belizeanus strains isolated from Seychelles, focusing on their morphological and genetic characterization, as well as their potential for neurotoxin production. Water samples were collected in Bay Ternay (West Mahé) and around Saint Anne Island. Culture aliquots were fixed for species identification using microscopy and molecular tools (sequencing of D1-D3 and D8-D10 of LSU rDNA) and toxin production analyzed in a 21-day culture using the N2a bioassay. This revealed detectable low CTX activity in only one of the four strains, estimated to 1.7 fg CTX3C equiv/cell, while the other strains were non-cytotoxic. These findings represent the first molecular and toxicological characterization of G. belizeanus strains from the Seychelles, contributing to the understanding of ciguatera poisoning risks in the Indian Ocean and highlighting the variable toxin production capacity within Gambierdiscus species. Expanding this project to areas with high ciguatera occurrence in the Indian Ocean could help in characterizing the responsible toxins.