Coral-associated viruses and bacteria in the Ha Long Bay, Vietnam

Abstract

ABSTRACT: Viruses inhabiting the surface mucus layer of scleractinian corals have received littleecological attention so far. Yet they have recently been shown to be highly abundant and couldeven play a pivotal role in coral health. A fundamental aspect that remains unresolved is whethertheir abundance and diversity change with the trophic state of their environment. The presentstudy examined the variability in the abundance of viral and bacterial epibionts on 13 coral spe-cies collected from 2 different sites in the Ha Long Bay, Vietnam: one station heavily affected byanthropogenic activity (Cat Ba Island) and one protected offshore station (Long Chau Island). Ingeneral, viral abundance was significantly higher in coral mucus (mean = 10.6 ± 2.0 × 10 7 virus-like particles ml –1 ) than in the surrounding water (5.2 ± 1.3 × 10 7 virus-like particles ml –1 ). Con-comitantly, the abundance and community diversity (inferred from phylogenetic and morpholog-ical analyses) of their mucosal bacterial hosts strongly differed from their planktonic counterparts.Surprisingly, despite large differences in water quality and nutrient concentrations between CatBa and Long Chau, there were no significant differences in the concentrations of epibiotic virusesand bacteria measured in the only 2 coral species (i.e. Pavona decussata and Lobophyllia flabelli-formis) that were common at both sites. The ability of corals to shed bacteria to compensate fortheir fast growth in nutrient-rich mucus is questioned here.KEY WORDS: Viruses · Coral-associated bacteria · Mucus · Symbionts · Coral reefs