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Precipitation of Reefs

Coral reefs need to be strong enough to stand up to harsh waves and currents. Mineral precipitation (especially calcium precipitation) in the ocean forms the strong, rocky bones of a coral reef. Coral reefs are a little like humans in this way: we both require calcium for survival. While humans get our calcium from drinking milk, coral reefs absorb it from the ocean's salty water. Reefs are so rocky due to the available calcium, and this helps keep the reefs strong.

Definition
- The most common type of precipitation in a reef system is calcification.
  
  Precipitation is a chemical reaction that occurs when solids suspended in a liquid settle out of solution. The solid that results from a precipitation reaction is called a "precipitate." The precipitation of calcium carbonate (known as "calcification") forms the limestone that creates the base of the reef. The most common type of precipitation in a reef system is calcification. According to NOAA, "calcium carbonate is the building block of coral reefs. As corals produce calcium carbonate they slowly add on to their existing reef structure allowing the reef to grow in size."
Chemistry
- The chemical reaction of precipitation only occurs under precise conditions. For example, water temperature and salt content (referred to as "salinity") must be high and carbon dioxide levels must be low for calcification to occur. Such conditions are typical of warm and shallow coastal waters where coral reefs are most commonly found (SeaWorld). High levels of carbon dioxide in the ocean prevent the precipitation reaction in coral reefs. Carbon dioxide is known to weaken the structure of calcium carbonate (NOAA).
History
- Scientists believe limestone coral reefs began forming approximately 570 million years ago.
  
  Scientists believe limestone coral reefs began forming approximately 570 million years ago during a period of low carbon dioxide levels in the Earth's atmosphere. The low carbon dioxide levels enabled the ocean water to become saturated with calcium carbonate and other minerals. The water became so saturated that the minerals began precipitating out of the water and settling on land masses in shallow waters (USF). Since the calcium precipitate was so strong, species began colonizing the structures for protection.
Purpose
- Corals made of calcium carbonate are strong enough to withstand violent storms.
  
  The precipitation of calcium in reef environments protects reefs by making them strong enough to withstand waves. The calcium carbonate precipitate is stronger than cement and holds sessile stony corals securely in place (Coral Reef Alliance). Scientists also hypothesize that precipitation of calcium aids in the photosynthetic processes of symbiotic algae living within the tissue of coral. One byproduct of the calcium precipitation is carbon dioxide, which is required for photosynthesis (USF).
Concerns
- Rising carbon dioxide levels in the atmosphere could have dramatic effects on stony coral reefs.
  
  Scientists worry that increased carbon dioxide levels in the atmosphere will adversely affect the formation of coral reefs. Increased levels of carbon dioxide can slow the rate of precipitation. The rate of mineral precipitation in coral reefs is slow and any reduction in current reef precipitation rates could lead to a total collapse of stony reef ecosystems. If the rate of precipitation slows too much, corals will not be able to grow strong enough to stand up to ocean currents and waves.

Rocks & Minerals