Coral reef habitats are found around all islands and cays of the USVI, with shallow reefs covering an estimated area of 297.9 km² (Catanzaro et al. 2002). Deep reefs extending past 30 meters depth, also known as mesophotic coral reefs, have recently been mapped and, in the northern USVI, are more extensive than shallow reefs (T. Smith, pers. comm., 2017). USVI coral habitats are made up of at least 57 species of living corals (Wilkinson 2004). Corals are sessile marine invertebrates, which are composed of identical polyps forming a colony system. These corals can be of two types, stony (scleractinian) or soft (alcyonacea), defined by the arrangement and number of tentacles, arrangement of skeletons, and the needs of zooxanthellae. Stony corals grow by drawing calcium from surrounding water and using it to build a calcium carbonate structure to house polyps. These reef-building corals are largely responsible for creating the exceptional living reefs that ring the USVI, protecting coastlines, nurturing fisheries species, creating sandy beaches, and providing the aesthetic beauty that increases tourism.
Coral reefs of the U.S. Virgin Islands were estimated at a value of $210,000,000 in 2012 (Edwards 2013) and are the most economically valuable wildlife feature of the USVI (Beukering et al 2011). Coral reefs provide many ecological and economic benefits for coastal communities (Moberg and Folke 1999, Barker and Roberts 2004). Coral reefs provide an extremely biodiverse habitat supporting numerous coral species, algae, and seagrasses for invertebrates, fish, zooplankton, phytoplankton, and sponges. Many species of plants and animals that inhabit coral reefs are being prospected for human medical uses, such as easing labor, cancer, arthritis, asthma, ulcers, heart diseases, and much more (Erwin et al. 2010, Shah 2013). These habitats offer opportunities for foraging, spawning, breeding, nursery, and refuge for many organisms (Reaka-Kudla 1997). It is estimated that coral reefs house a third of all fish species found in the oceans (Moberg and Folke 1999). These habitats aid in shoreline protection by acting as a buffer against storm surges to protect against loss of life, property damage, and coastal erosion (NOAA 2008, Shah 2013). Lastly, many tourists visit the USVI because of the opportunities for recreation (diving and snorkeling) on the coral reefs.
The main causes of coral reef degradation are believed to be from global factors, such as increasing sea surface temperatures, and local factors, such as overfishing of ecologically important species and increasing deposition of sediments and pollutants from land-based activities (Jackson et al. 2014). Global stressors include natural factors, such as hurricanes, and anthropogenically influenced factors, such as ocean acidification, sea level rise, and increasing ocean temperatures. Coral disease has emerged as a significant threat to the coral reefs of the USVI. Diseases amplify the negative impacts of other stressors. Coral diseases affect many coral species in the USVI (Calnan et al. 2008) and some can be transmitted from colony to colony through the water (Clemens and Brandt 2015). Corals are also more susceptible to disease when impacted by other stressors, such as coral bleaching (Muller et al. 2008, Brandt and McManus 2009).