Toxicological effects of biocides on symbiotic and aposymbiotic juveniles of the hermatypic coral Acropora tenuis

Reef-building (or hermatypic) corals harbor the symbiotic dinoflagellates Symbiodinium spp. (Alveolata, Dinophyceae, Gymnodiniales), and contribute to the accretion of coral reefs in tropical and sub-tropical zones. In this study, toxicological effects of three commonly used biocides (dichlorvos (DDVP), a commonly used insecticide; diuron (DCMU), a herbicide; and tributyltin chloride (TBT-Cl), an anti-fouling agent) on the hermatypic coral Acropora tenuis (Anthozoa, Hexacorallia, Scleractinia) were studied using juveniles in both aposymbiotic (symbiont-free) and symbiotic conditions. After exposure to the chemicals, abnormalities such as detachment of soft tissues from the skeleton and/or death were observed, as well as lowered uptake of symbiotic algae (in aposymbiotic juveniles) or reduction of the symbiont population in tentacles (in symbiotic juveniles). Significant reduction of the symbiont population in tentacles of symbiotic juveniles exposed to DDVP, DCMU and TBT-Cl was observed at the concentrations of 100, 10, and 1 μg/l, respectively. Results of this study suggested that symbiotic juveniles of A. tenuis are more sensitive than in the aposymbiotic condition to DDVP and DCMU, but not to TBT-Cl.