Characterized extracts of the tropical red seaweed Acanthophora spicifera protect Ostrea edulis larvae against Vibrio coralliilyticus

Abstract

Vibriosis is one of the most common bacterial diseases affecting bivalve mollusk hatcheries, especially during their early life stages, leading to high mortality rates and significant economic losses worldwide. Bivalves are more susceptible to diseases because they are filter-feeding organisms capable of accumulating a wide diversity of microorganisms, antibiotic residues, and other contaminants present in the marine environment. In the present study, we evaluated the in vitro and in vivo bioactivity of the aqueous and ethanolic (10, 25, 50, 75, and 100%) extracts of the tropical red seaweed Acanthophora spicifera against Vibrio coralliilyticus which affects the larvae of the European oyster Ostrea edulis. The aqueous extract displayed 43.1% inhibition of V. coralliilyticus growth at 100 mg/L after 46 h (regrowth performance). During the toxicity test, O. edulis larvae showed a survival rate of 91.1 ± 5.8% and 84.6 ± 5.2% at aqueous extract concentrations of 1 and 5 mg/L, respectively. In the challenge test with V. coralliilyticus at a cell density of 105 cells/mL, the aqueous and 10, 25, and 50% ethanol (v/v) extracts at 1 mg/mL resulted in significantly higher survival rates (99.2 ± 1.0%, 93.3 ± 8.8%, 96.5 ± 0.9%, and 95.8 ± 1.9%, respectively) at 48 h post-challenge compared to only 0.6 ± 1.1% for the larvae challenged with Vibrio without seaweed extract (positive control). Chemical characterization of aqueous and 25% ethanol extracts, showing the highest bioactivity based on the challenge test, revealed the presence of succinic acid and the heterosides floridoside and digeneaside as major components in both extracts. This is the first report of the presence of digeneaside in A. spicifera. These findings suggest that aqueous and 25% ethanolic extracts from Acanthophora spicifera provide a natural alternative for disease management in O. edulis hatcheries.