CayCay Cay A cay ( ), also spelled caye or key, is a small, low-elevation, sandy island on the surface of a coral reef. Cays occur in tropical environments throughout the Pacific, Atlantic, and Indian Oceans, including in the Caribbean and on the Great Barrier Reef and Belize Barrier Reef. Etymology. The 1492 indigenous people of the Bahamas were called "Lucayan", an Anglicization of the Spanish "Lucayos", derived in turn from the Taíno "Lukku-Cairi" (which the people used for themselves), meaning "people of the islands". The Taíno word for "island", "cairi", became "cayo" in Spanish and "cay" in English (spelled "key  in American English, caye" in Belizean English). Formation and composition. A cay forms when ocean currents transport loose sediment across the surface of a reef to where the current slows or converges with another current, releasing its sediment load. Gradually, layers of deposited sediment build up on the reef surface – a ‘depositional node’. Such nodes occur in windward or leeward areas of reefs, where flat surfaces sometimes rise around an emergent outcrop of old reef or beach rock. The island resulting from sediment accumulation is made up almost entirely of the skeletal remains of plants and animals – “biogenic sediment” – from  the surrounding reef ecosystems. If the accumulated sediments are predominantly sand, then the island is called a ‘cay’; if they are predominantly gravel, the island is called a ‘motu’. Cay sediments are largely composed of calcium carbonate (CaCO), primarily of aragonite, calcite, and high-magnesium calcite. They are produced by myriad plants (e.g., coralline algae, species of the green algae Halimeda) and animals (e.g., coral, molluscs, foraminifera). Small amounts of silicate sediment are also contributed by sponges and other creatures. Over time, soil and vegetation may develop on a cay surface, assisted by the deposition of sea bird guano. Development  and stability. A range of physical, biological and chemical influences determines the ongoing development or erosion of cay environments. These influences include: Significant changes in cays and their surrounding ecosystems can result from natural phenomena such as severe El Niño–Southern Oscillation (ENSO) cycles. Also, tropical cyclones can either help build up or tear down these islands. There is much debate and concern over the future stability of cays in the face of growing human populations and pressures on reef ecosystems, and predicted climate changes and sea level rise. There is also debate around whether these islands are relict features  that effectively stopped expanding two thousand years ago during the late Holocene or, as recent research suggests, they are still growing, with significant new accumulation of reef sediments. Understanding the potential for change in the sediment sources and supply of cay beaches with environmental change is an important key to predicting their stability. Despite, or perhaps because of, all the debate around the future of cays there is consensus that these island environments are very complex and fairly fragile. Examples. Examples of cays include: Cay A cay ( ), also spelled caye or key, is a small, low-elevation, sandy island on