Salt ponds are small bodies of saltwater that form into intertidal basins. Originally open to the sea as bays or inlets, they become isolated from the marine environment over time as storm-deposited materials form a berm. The resulting enclosed or mostly enclosed water bodies surrounded by coastal mangroves maintain an influx of salt water either through tidal seepage or periodic breaching of the berm by the sea. Salt ponds are typically hypersaline, with water salinities often in excess of 50 parts per thousand (sea water is generally 35 ppt), although this fluctuates according to freshwater input. Water salinity, oxygen content, and temperature are highly variable and dependent on rainfall and evaporative processes, and influence the fauna of these wetlands (Jarecki 2003). These saline habitats contain invertebrates that form an important prey base for shorebirds and other waterbirds. These ponds, often situated at the base of steep hills, also act as catchment basins for runoff, debris, and pollutants, thus protecting coral and seagrass beds in the marine environment.
Salt flats are level areas associated with mangroves, coastal ponds, or beaches that are seasonally or tidally flooded. These are often mature salt ponds that have infilled with muddy or sandy 42 sediment and are often associated with black mangroves (Avicenna germinans), which have a high salt tolerance. Other plant cover is sparse if at all present, and typically only salt tolerant species such as sea purslane (Sesuvium portulacastrum) persist, although there may also be some alga cover. Salt flats are important feeding and breeding sites for shorebirds, particularly Least Terns and Wilson’s Plovers.
Salt ponds and the specialized salt-tolerant vegetation communities that they support perform a variety of biological, hydrologic and water quality functions. Capturing and retaining sediments is an important water quality function of wetlands (Jarecki 2003, Rennis et al. 2006), helping to protect sensitive coastal resources, such as coral reefs and seagrasses, which can be adversely impacted from siltation. The indirect functions of salt ponds and their associated mangrove systems include the provision of storm protection, flood mitigation, shoreline stabilization, and shoreline erosion control (Jarecki 2003). Salt ponds and mangrove wetlands are the primary habitat for the great land crab (Cardisoma guanhumi), an economically important Caribbean species. These saline coastal wetlands provide an essential habitat for indigenous and migratory birds, many of which are either locally or federally threatened or endangered (Wauer and Sladen 1992). It is estimated that 90% of the resident and migratory birds in the USVI are dependent on wetlands for feeding, nesting or roosting (Philibosian and Yntema 1977). Salt ponds have always held high value to local people. Areas around such ponds and swamps often show evidence of prehistoric habitation, and historic Danish plantation ruins are also frequently located in these low-lying areas.
Reclamation has been the greatest threat to salt pond systems within the USVI prior to strict regulations implemented by the EPA and CZM. Economic success and the burgeoning tourist industry has driven the construction of hotels, marinas, condominiums, and other developments in coastal areas. The infilling of salt ponds and associated wetlands was a common practice. During the economic growth period of the 1960s and 1970s, approximately 14 wetland sites were altered on St. Thomas and St. John (U.S. Geological Survey 1994). The Southgate pond in St. Croix was cut in half by the construction of Green Cay Marina. The largest mangrove system in the USVI, Krause Lagoon, was filled in for the construction of the oil refinery on St. Croix.