Immunomodulatory and Antiviral Effects of Macroalgae Sulphated Polysaccharides: Case Studies Extend Knowledge on Their Importance in Enhancing Shellfish Health, and the Control of a Global Viral Pathogen Ostreid Herpesvirus-1 microVar

Abstract

Macroalgae are the primary source of non-animal sulphated polysaccharides (SPs) in the marine environment with fucoidans derived from brown algae (Phaeophyta) and carrageenans from red algae (Rhodophyta). Much research has been carried out on SP effects on Asian shrimp species (genera Penaeus and Metapenaeus) but their effect on commercially important bivalve mollusc species is limited and in Pacific oyster Crassostrea gigas is unknown. Knowledge of their impact on bivalve pathogens and Palaemon shrimp is unknown. The objectives of this study were to assess the effects of Fucus vesiculosus (Phaeophyta), Mastocarpus stellatus (Rhodophyta) and algal derivatives (fucoidan and κ-carrageenan) on C. gigas performance, and on ostreid herpesvirus-1 microvar (OsHV-1 μVar) and bacteria Vibrio spp. development. Both pathogens have been associated with significant oyster mortalities and economic losses globally. The effects of sulphated galactan from Gracilaria fisheri (Rhodophyta) on European common prawn Palaemon serratus, an important fishery species, was also assessed. Findings indicate a rapid and prolonged increase in total blood cell count, lysozyme (enzyme that destroys pathogens), and a difference in the ratio of blood cell types in treated individuals compared to their control counterparts. A significantly lower OsHV-1 μVar prevalence was observed in treated oysters and κ-carrageenan was found to suppress viral replication (loads), while OsHV-1 μVar was not detected in the fucoidan treated oysters from Day 8 of the 26-day trial. No antibacterial effect was observed however, the oysters did not succumb to vibriosis. These findings contribute further knowledge to macroalgae sulphated polysaccharide biotherapeutic properties, their twofold effect on animal health and viral suppression.