Seawater turbidity and fish communities on coral reefs of Puerto Rico

We investigated the variations of reef fish assemblages on coral reefs that experience different turbidity regimes, by assessing the association between the vertical extinction coefficient for photosynthetically active radiation (K d PAR) and communities of fishes and corals at 21 reef sites in La Parguera, southwest Puerto Rico. Statistical correlations and non-metric multidimensional scaling (NMS) identified turbidity as an important environmental parameter affecting ecological processes on coral reefs, as reflected by changes in the composition and abundance of reef fishes and benthic communities. Lower fish density and species richness was found at turbid sites. Turbidity was also negatively correlated to percent coral cover, which together with rugosity, were additional habitat parameters shaping reef fish assemblages. Bluehead wrasse Thalassoma bifasciatum and yellowtail damselfish Microspathodon chrysurus were species rarely present at turbid sites and abundant at clear ones. The yellowtail hamlet Hypoplectrus chlorurus and sharknose goby Elacatinus evelynae had the opposite distribution along the turbidity gradient. We identified seawater turbidity as an additional predictor of the reef fish community structure in La Parguera, in addition to live coral cover and reef rugosity. Because coral reefs and reef fishes were less complex (lower rugosity, less species richness, less diversity) in more turbid sites, managing for clear water conditions within the coastal area of La Parguera should lead to improved ecosystem resilience and stability, and should become a primary goal of management.