Comparison of coral reef communities in proximity to ocean effluent pipes off the north coast of Puerto Rico

Coral reefs are declining globally as a result of multiple stressors, including land-based stressors, such as sedimentation and pollution, and those that are related to a changing climate, such as increases in ocean acidification. Degradation of US Caribbean coral reef biota has been associated with exposure to sewage effluent from wastewater treatment plants (WWTPs). The Puerto Rico Aqueduct and Sewer Authority (PRASA) maintains WWTPs on the north coast of Puerto Rico, which release effluent into the marine environment in the vicinity of coral reefs. Using data collected by PRASA surveys conducted from 1999 to 2013, we examined coral reef condition at survey sites to identify potential changes or differences in reefs with respect to their proximity to the WWTP effluent pipes (e.g., upstream, downstream). The proportion of coverage represented by all coral, sensitive taxa, and tolerant taxa were compared across sites located upstream and downstream of WWTP effluent pipes using multivariate approaches and analysis of variance. The proportion of healthy, sensitive coral species and invasive or tolerant coral species were not different at sites downstream of the WWTP effluent pipe compared to upstream. These results are caveated by the limited sampling design, highly variable communities across WWTP locations, and the sparsity or absence of well-developed coral reef communities at most stations. We evaluate the strengths and weaknesses of the survey design and provide recommendations for future coral reef surveys investigating potential impacts of WWTP effluent.