Marine and terrestrial ecosystems meet along the coast, where species composition often overlaps. The USVI coast consists of beaches and rocky shorelines, and makes up a large percentage of total area of the islands. St. Croix has 113 km of shoreline, St. Thomas 85 km, and St. John 80 km, for a total of 278 km. Adding in the shorelines of over 50 cays raises this figure to 376 km. Sandy beaches comprise 80 km, around 21% of the total shoreline (Dammann and Nellis 1992). The beaches in the USVI comprise three types: sand, gravel, or coralline. Sandy beaches are made of a mixture of several materials, including coral particles, shell and urchin fragments, and algal plates. Gravel beaches are made of minerals or rocks that erode from cliffs and are carried to the shore by guts during torrential rainfall. Coralline rubble beaches are covered with pieces of coral skeleton broken by storm action. The remaining coast is comprised of rocky shoreline and mangrove forest. Rocky shorelines generally consist of boulder talus or cliffs and are poorly vegetated. Mangroves, discussed more fully in another section, occur in inundated areas along the coast.
Beaches provide habitat for a wide range of invertebrates, which in turn provide a food source for higher organisms, especially shorebirds. Sandy beaches offer nesting areas for sea turtles, Wilson’s Plovers, Least Terns, and other species. Beaches also buffer coastal areas from storm energy, and filter sedimentation from upland runoff. Littoral plant communities perform the important ecosystem services of dune stabilization and protection of the shoreline from erosion. Intertidal organisms play a role in filtering sediment and improving water quality.
Coastal areas of the USVI are under extreme threat from development for resorts, condominium complexes, and private residences. Many of the mangroves and salt ponds have already been replaced, although these resources are now protected across the territory. Detrimental beach activities include the construction of structures that affect the movement of beach sediments, thereby restricting the supply of new sand and causing beaches to disappear. Beach nourishment, the addition of sand to create man-made beaches by covering beachrock, can have severe impacts by altering sea turtle nesting habitat and reducing water quality through increased sedimentation from erosion of added sand (Peterson and Bishop 2005).