Intensive fish farming in the Philippines is detrimental to the reef-building coral Pocillopora damicornis

Abstract

To determine the effects of fish farm effluent on the reef-building species Pocillopora damicornis, we exposed different life stages of the coral to a gradient of effluent concentrations. After 81 d no juvenile coral survived at the Fish Farm site or at the site receiving intermediate concentra- tions, and survival rates were low (<20%) at the site receiving minimal effluent concentrations and at the reference site. At the Fish Farm site, juveniles (on terracotta tiles) were completely overgrown by barnacles. Coral nubbins and mature colonies displayed similar survivorship trends along the efflu- ent gradient, i.e. higher mortality with higher effluent concentrations. At the site of intermediate exposure, surviving nubbins had skeletal growth rates half of those from the site of minimal influence and from the reference site. The mean gross photosynthesis to respiration ratio of coral branches deployed at the fish farm was below the physiological compensatory value of 1, whereas values of about 1 were attained at the sites of diminishing effluent influence. Reduced larval output in mature colonies exposed to intermediate and minimal concentrations of fish farm effluent were observed as compared to those from the reference site. No reproductive measurements could be conducted for colonies at the Fish Farm site, due to high mortality. At the larval stage, metamorphosis was dimin- ished both on substrates collected from, and tiles conditioned in, the Fish Farm environment, com- pared to those from sites of diminishing effluent influence. Hence, many aspects of coral biology are impaired by exposure to effluent from intensive fish farming.