Salinity in Coral Reefs

Made up of corals, algae, mollusks, sponges and a wide variety of other species, facstaff.gpc.edu defines coral reefs as underwater mounds that home entire ecosystems. Because coral reefs require specific levels of salinity, light, temperature and sedimentation to survive, global warming and recent salinity changes in oceans may threaten existing coral reefs and their formation.

Identification

• As explained on the OceanWorld website, coral reefs start out small and grow slowly at about half an inch per year. Coral reefs grow upward on the accumulation of exoskeletons from past generations of corals. If they are left undisturbed, coral reefs may grow quite large, such as the Great Barrier Reef on the northeast coast of Australia, measuring as much as 93 miles wide and 1,242 miles long.

  Three main types of coral reefs exist. Fringing reefs are located close to the shore and are not separated from land by much water. Barrier reefs are located farther offshore and are separated from land by deep lagoons. Atolls, also called coral islands, are ring-shaped reefs that enclose circular lagoons and are more usually seen around islands.

Formation

• According to the Florida Museum of Natural History, coral reef development requires four main factors: salinity, light, temperature and sedimentation. Salinity refers to the concentration of total salts dissolved in water and is generally measured in parts per thousand (ppt). Coral reefs can tolerate salinities between 30 and 40 ppt. Light is also critical to the development of coral reefs because of their symbiotic association with algae, aquatic plants that require sunlight to survive. Optimal temperatures for coral growth are between 73 and 77 degrees Fahrenheit, which can only be found in tropical waters. Because coral reefs need light to survive, areas of excessive sedimentation can make it difficult for them to grow.

Ideal Environment

• As pointed out on facstaff.gpc.edu, coral reefs are very sensitive to environmental changes. High rainfall, for example, can kill reefs by increasing the amount of sediment in the water and decreasing salinity. The absence of waves and currents is also dangerous since silt can accumulate in muddy patches and suffocate the coral. Thus, only tropical waters along the eastern coast of continents that are salty, sunny, shallow and clear are ideal to the formation and survival of coral reefs.

Why are oceans salty?

• According to the National Ocean Service, salt mainly comes from rocks on land. Because the rain that falls on those rocks is slightly acidic, it erodes the rocks and creates salty ions, or electrically charged particles, that are carried away by streams and rivers to the oceans. The most prevalent ions in ocean water are chloride and sodium. The average concentration of salt in the oceans is of 35 ppt. Interestingly, the National Ocean Service asserts that in a cubic mile of seawater, the weight of the salt is an astronomical 120 million tons.

Salinity Changes in Oceans

• Unfortunately, a study from Ruth Curry of the Woods Hole Oceanographic Institution; Bob Dickson of the Center for Environment, Fisheries, and Aquaculture Science, and Igor Yashayaev of the Bedford Institute of Oceanography, as written on scienceagogo.com, has shown that, as of 2010, ocean waters have become dramatically saltier in the last 40 years. This change in salinity may be partly due to global warming and may be altering the fundamental planetary system that regulates the Earth's water processes such as evaporation and precipitation. Because coral reefs require precise concentrations of salt, light, temperature and sedimentation, salinity changes in oceans may threaten their development and survival.