The toxic dinoflagellate Alexandrium minutum impairs the performance of oyster embryos and larvae

Justine Castrec (1) , Helene Hegaret (1) , Matthias Huber (1) , Jacqueline Le Grand (1) , Arnaud Huvet (2) , Kevin Tallec (2) , Myrina Boulais (1) , Philippe Soudant (1) , Caroline Fabioux (1)

1 LEMAR - Laboratoire des Sciences de l'Environnement Marin (LEMAR)
2 IFREMER - Institut Français de Recherche pour l'Exploitation de la Mer

The dinoflagellate genus Alexandrium comprises species that produce highly potent neurotoxins known as paralytic shellfish toxins (PST), and bioactive extracellular compounds (BEC) of unknown structure and ecological significance. The toxic bloom-forming species, Alexandrium minutum, is distributed worldwide and adversely affects many bivalves including the commercially and ecologically important Pacific oyster, Crassostrea gigas. In France, recurrent A. minutum blooms can co-occur with C. gigas spawning and larval development, and may endanger recruitment and population renewal. The present study explores how A. minutum affects early-oyster development by exposing embryos and larvae, under controlled laboratory conditions, to two strains of A. minutum, producing only BEC or both PST and BEC. Results highlight the major role of BEC in A. minutum toxicity upon oyster development. The BEC strain caused lysis of embryos, the most sensitive stage to A. minutum toxicity among planktonic life-stages. In addition, the non-PST-producing A. minutum strain inhibited hatching, disrupted larval swimming behavior, feeding, growth, and induced drastic decreases in survival and settlement of umbonate and eyed larvae (9 and 68 %, respectively). The findings indicated PST accumulation in oyster larvae (e.g. umbonate stages), possibly impairing development and settlement of larvae in response to the PST-producing strain. This work provides evidences that A. minutum blooms could hamper settlement of shellfish.

Mots clés: Harmful Algal Bloom (HAB); Bioactive Extracellular Compounds (BEC); Paralytic Shellfish Toxin (PST); Crassostrea gigas; embryo; larvae; bivalve

Domaines: Ecotoxicologie; Médecine vétérinaire et santé animale; Océanographie

Justine Castrec, Helene Hegaret, Matthias Huber, Jacqueline Le Grand, Arnaud Huvet, et al.. The toxic dinoflagellate Alexandrium minutum impairs the performance of oyster embryos and larvae. Harmful Algae, 2020, 92, pp.101744. ⟨10.1016/j.hal.2020.101744⟩. ⟨hal-02879884⟩