page_title: Coral island
section_title: Human impacts on coral islands
hierarchical_section_title: Coral island / Human impacts on coral islands
caption_attribution_description: English: Bleached coral, Acoropora sp.
context_page_description: A coral island is a type of island formed from coral detritus and associated organic material. They occur in tropical and sub-tropical areas, typically as part of coral reefs which have grown to cover a far larger area under the sea.
context_section_description: Coral is important for biodiversity and the growth of fish populations, so maintaining coral reefs is important. Coral reefs are threatened by numerous anthropogenic impacts, some of which have already had major effects worldwide. Reefs grow in shallow, warm, nutrient-poor waters where they are not outcompeted by phytoplanktons. By adding fertilizers into the water runoff phytoplankton populations can explode and choke out coral reef systems. Adding too many sediments can cause a similar problem by blocking out the sun, starving the zooxanthellae that live on coral causing it to undergo a process known as coral bleaching. The ocean's acidity is also a factor. Coral is made of calcium carbonate and is dissolved by carbonic acid. With the increase in carbon dioxide from combustion reactions in the atmosphere through precipitation carbon dioxide mixes with water and forms carbonic acid raising the ocean's acidity which slows coral growth. Through chemical and physical changes humans can cause significant harm to reef systems and slow the creation of coral island chains.
caption: Bleached coral due to rising sea temperature, increased acidity, or pollution.
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