Caribbean corals exhibit species-specific differences in competitive abilities with an aggressive encrusting alga, Ramicrusta textilis.

Caribbean coral cover has decreased substantially in recent decades, with much of the live coral being replaced by macroalgae. Encrusting red algae in the genus Ramicrusta have become abundant throughout the region and have demonstrated widespread harm to corals by overgrowing living tissue, causing colony mortality, and impairing coral recruitment. In this research, Ramicrusta textilis was identified by morpho-anatomy and DNA sequencing from nine sites around St. Thomas, US Virgin Islands, and 3D photogrammetry was used to measure the rate of algal growth on stony corals. 3D models of individual coral colonies (five species plus controls, N = 72) competing with R. textilis revealed differential competitive abilities among taxa, with Siderastrea siderea being the only species capable of inhibiting overgrowth by the alga (mean linear algal growth − 1.1 mm yr⁻¹). Important reef building coral species such as Orbicella annularis and Orbicella faveolata were poor competitors (mean linear algal growth + 15 mm yr⁻¹ and + 7.7 mm yr⁻¹, respectively), indicating that the emergence of the alga could have significant impacts on Caribbean coral reef species diversity, community composition, and structural complexity. [ABSTRACT FROM AUTHOR]