Smith et al. 2019

scientific chapter |

The United States Virgin Islands

Smith TB, Brandt ME, Brandtneris VW, Ennis RS, Groves SH, Habtes S, Holstein DM, Kadison E, Nemeth RS


Mesophotic coral ecosystems (MCEs) at 30–100 m depth are the dominant hard bottom habitat in the US Virgin Islands of the northeastern Caribbean Sea. Well- developed MCEs surpass the extent of shallow coral reefs by almost a factor of three. These habitats range from high coral cover structural reefs to low coral cover hard bottoms on banks, slopes, and walls. The most common communities in the United States Virgin Islands (USVI) are star coral (Orbicella franksi) banks that are concentrated in a relatively large area (187 km2) south and southwest of St. Thomas in depths of 30–43 m. Wall and slope coral communities in upper (30–60 m) and lower MCE (60–100 m) depths are dominated by lettuce corals (Agaricia spp.) Most MCEs are heavily covered in macroalgae, particularly Lobophora variegata. Corals are species rich in many upper MCE habitats (20–28 species) compared with shallow reefs (31), but not in upper and lower MCE slopes and walls (6–8). Sponges are species rich (24–53 species) in the MCEs of the USVI and may contribute much to nutrient cycling. Fishes are also species rich across habitats (45–151 species), but often their biomass is dominated by a few species, particularly on edges with high abundances of planktivores and piscivores. Despite their importance to the ecology and economy of USVI, MCEs are threatened by a variety of local and global stressors and disturbances that are causing declines in coral cover.