Predicting the distribution of threatened orbicellid corals in shallow and mesophotic reef ecosystems

Orbicellid corals are threatened primary reef-building corals throughout the Caribbean in shallow and mesophotic coral ecosystems (MCEs), yet a poor understanding of where they occur limits population monitoring and management. The goals of this study were to predict suitable habitat for orbicellid coral species and to identify how abiotic environmental factors constrain that habitat on the eastern Puerto Rico Shelf. The probability of occurrence for Orbicella annularis and O. faveolata/O. franksi (combined) from shallow to mesophotic depths on the eastern Puerto Rico Shelf was predicted using maximum entropy models. Contributions of abiotic predictors, including bathymetry, seafloor topography, temperature, wave exposure, and bottom velocity, were assessed. Model performance was assessed using area under the receiver operating characteristic curve, standard error of the replicate model runs, and mean absolute error. Both O. annularis and O. faveolata/O. franksi distributions were best predicted by rugosity, temperature, and wave exposure. O. faveolata/O. franksi occurred at shallow and mesophotic depths, and acted as a proxy for identifying the spatial extent of MCEs, contrary to O. annularis, which was predicted at shallow depths. Results for O. faveolata/O. franksi in mesophotic depths indicated potential for large areas of unexplored and unmonitored MCEs along the southeast shelf of St. Thomas, US Virgin Islands and within the Virgin Passage. These spatial predictions of potential mesophotic reef habitats will provide direction for future MCE exploration efforts.