{{Short description|Small island formed on the surface of a coral reef}} {{Redirect2|Sand cay|Cayes|the South China Sea island|Sand Cay|the city in Haiti|Les Cayes}} {{Distinguish|Quay}} {{Other uses}}
[[File:Heron Island, Australia - View of Island from helicopter.JPG|thumb|Heron Island, Australia]]
A '''cay''' ({{IPAc-en|k|iː|,_|k|eɪ}} {{respell|KEE|,_|KAY}}), 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 Lucayan word for "island", {{Lang|tnq|cairi}}, became {{Lang|es|cayo}} in Spanish and "cay" {{IPAc-en|ˈ|k|iː}} in English (spelled "key" in American English).<ref name=Albury1975/><ref name=Craton1986/><ref name=Keegan1992/>
==Formation and composition== thumb|Cay sand under an optical microscope
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''.<ref name=Hopley1981/><ref name=Gourlay1988/> 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.<ref name=Hopley1982/> If the accumulated sediments are predominantly biogenic sand, then the island is called a ''cay''; if they are predominantly gravel, geological sediments, the island is called a ''motu''.
Cay sediments are largely composed of calcium carbonate (CaCO{{sub|3}}), 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.<ref name=Chave1964/><ref name=Folk1964/><ref name= Scoffin1987/><ref name=Yamano2000/> 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: * the extent of reef surface sand accumulations, * changes in ocean waves, currents, tides, sea levels, and weather conditions, * the shape of the underlying reef, * the types and abundance of carbonate producing biota and other organisms such as binders, bioeroders, and bioturbators (creatures that bind, erode, and mix sediments) living in surrounding reef ecosystems.<ref name=Harney2003/><ref name=Hart2007/>
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.<ref name=Scoffin1993/><ref name=Woodroffe2003/>
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.<ref name=Kench2002/><ref name=Hart2003/> 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.<ref name= Woodroffe2007/>
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. Debate around the future of cays has resulted in a consensus that these island environments are very complex and fairly fragile.{{cn|date=September 2025}}
==Examples== [[File:Warraber Island.jpg|thumb|Warraber Island, Torres Strait ]]
Examples of cays include:
* A few of the Florida Keys, such as Sand Key, are "cays" as defined above. (Most of the Florida Keys are exposed ancient coral reefs, and the oolite beds that formed behind reefs.) * Heron Island, Australia, a coral cay on the southern Great Barrier Reef * Prickly Pear Cays, Anguilla * Rama Cay, Nicaragua * Tobacco Caye, Dangriga, Belize * Warraber Island, Torres Strait, Australia, * Elbow Cays, Bahamas * Great Goat Island, Jamaica * Ocean Cay, Bahamas * The Cays of Morrocoy, Venezuela
==See also== {{portal|Islands}} * Archipelago
==References== {{reflist|25em|refs=
<ref name=Albury1975> {{cite book |author=Albury, Paul |year=1975 |title=The Story of the Bahamas |publisher=MacMillan Caribbean |isbn=0-333-17131-4 |pages=5, 13–14 }} </ref>
<ref name=Chave1964> {{cite book |author=Chave, K. |year=1964 |section=Skeletal durability and preservation |editor1=Imbrie, J. |editor2=Newell, N. |title=Approaches to Palaeoecology |publisher=John Wiley and Sons Inc. |place=Sydney, AU }} </ref>
<ref name=Craton1986> {{cite book |author=Craton, Michael |year=1986 |title=A History of the Bahamas |publisher=San Salvador Press |isbn=0-9692568-0-9 |page=17 }} </ref>
<ref name=Folk1964> {{cite journal |author1=Folk, R. |author2=Robles, P. |year=1964 |title=Carbonate sands of Isla Perez, Alacran Reef Complex, Yucatan |journal=Journal of Geology |volume=72 |issue=3 |pages=255–292 |doi=10.1086/626986 |jstor=30075161 |bibcode=1964JG.....72..255F |s2cid=129407952 }} </ref>
<ref name=Gourlay1988> {{cite conference |author=Gourlay, M.R. |year=1988 |title=Coral cays: Products of wave action and geological processes in a biogenic environment |pages=497–502 |editor1=Choat, J.H. |display-editors=etal |book-title=Proceedings of the 6th International Coral Reef Symposium: Vol. 2: Contributed Papers |place=Townsville, Australia }} </ref>
<ref name=Harney2003>{{cite journal |author1=Harney, J.N. |author2=Fletcher, C.H. |year=2003 |title=A budget of carbonate framework and sediment production, Kailua Bay, Oahu, Hawaii |journal=Journal of Sedimentary Research |volume=73 |issue=6 |pages=856–868 |doi=10.1306/051503730856 |bibcode=2003JSedR..73..856H |url=http://www.soest.hawaii.edu/coasts/publications/Harney_Fletcher_JSR_2003.pdf |archive-date=2013-11-06 |access-date=2013-05-31 |archive-url=https://web.archive.org/web/20131106064813/http://www.soest.hawaii.edu/coasts/publications/Harney_Fletcher_JSR_2003.pdf |url-status=dead }}</ref>
<ref name=Hart2003> {{cite conference |author=Hart, D.E. |year=2003 |title=The importance of sea-level in an inter-tidal reef platform system, Warraber Island, Torres Strait |book-title=Proceedings of the 22nd Biennial New Zealand Geographical Society Conference |place=Auckland, NZ |pages=77–81 }} </ref>
<ref name=Hart2007>{{cite journal |author1=Hart, D.E. |author2=Kench, P.S. |year=2006 |title=Carbonate production of an emergent reef platform, Warraber Island, Torres Strait, Australia |journal=Coral Reefs |volume=26 |pages=53–68 |doi=10.1007/s00338-006-0168-8 |hdl=10092/312 |s2cid=11188232 |hdl-access=free |url=http://www.geog.canterbury.ac.nz/department/staff/deirdre/Hart_Kench07.pdf |access-date=2013-05-31 |archive-date=2017-04-07 |archive-url=https://web.archive.org/web/20170407141443/http://www.geog.canterbury.ac.nz/department/staff/deirdre/Hart_Kench07.pdf |url-status=dead }}</ref>
<ref name=Hopley1981> {{cite journal |author=Hopley, D. |year=1981 |title=Sediment movement around a coral cay, Great Barrier Reef, Australia |journal=Pacific Geology |volume=15 |pages=17–36 }} </ref>
<ref name=Hopley1982> {{cite book |author=Hopley, D. |year=1982 |title=The Geomorphology of the Great Barrier Reef – Quaternary Development of Coral Reefs |series=Wiley-Interscience Publication |place=New York, NY |publisher=John Wiley and Sons Ltd. |isbn=0471045624 }} </ref>
<ref name=Keegan1992> {{cite book |author=Keegan, William F. |year=1992 |title=The People Who Discovered Columbus: The Prehistory of the Bahamas |publisher=University Press of Florida |isbn=0-8130-1137-X |page=11 }} </ref>
<ref name=Kench2002> {{cite journal |author1=Kench, P.S. |author2=Cowell, P. |year=2002 |title=Erosion of low-lying reef islands |journal=Tiempo Climate Newswatch |volume=46 |pages=6–12 |url=http://www.tiempocyberclimate.org/newswatch/feature040610.htm |url-status=dead |archive-url=https://web.archive.org/web/20130510001101/http://www.tiempocyberclimate.org/newswatch/feature040610.htm |archive-date=2013-05-10 }} </ref>
<ref name=Scoffin1987> {{cite book |author=Scoffin, T.P. |year=1987 |title=Introduction to Carbonate Sediments and Rocks |place=Glasgow, UK |publisher=Blackwell |isbn=0216917891 }} </ref>
<ref name=Scoffin1993> {{cite journal |author=Scoffin, T.P. |year=1993 |title=The geological effects of hurricanes on coral reefs and the interpretation of storm deposits |journal=Coral Reefs |volume=12 |issue=3–4 |pages=203–221 |doi=10.1007/BF00334480 |bibcode=1993CorRe..12..203S |s2cid=39658794 }} </ref>
<ref name=Woodroffe2003> {{cite book |author=Woodroffe, C.D. |year=2003 |title=Coasts: Form, Process and Evolution |publisher=Cambridge University Press |place=Cambridge, UK |isbn=0521011833 |url=http://catdir.loc.gov/catdir/samples/cam033/2002017418.pdf }} </ref>
<ref name= Woodroffe2007> {{cite journal |last1=Woodroffe |first1=C.D. |last2=Samosorn |first2=B. |last3=Hua |first3=Q. |last4=Hart |first4=D.E. |year=2007 |title=Incremental accretion of a sandy reef island over the past 3000 years indicated by component-specific radiocarbon dating |journal=Geophysical Research Letters |volume=34 |issue=3 |article-number=2006GL028875 |citeseerx=10.1.1.548.8845 |doi=10.1029/2006GL028875 |doi-access=free |bibcode=2007GeoRL..34.3602W }} </ref>
<ref name=Yamano2000> {{cite journal |last1=Yamano |first1=H. |last2=Miyajima |first2=T. |last3=Koike |first3=I. |year=2000 |title=Importance of foraminifera for the formation and maintenance of a coral sand cay: Green Island, Australia |journal=Coral Reefs |volume=19 |pages=51–58 |doi=10.1007/s003380050226 |s2cid=43843977 }} </ref>
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Category:Islands by type