About Corals

Where are corals found?  Corals can be found throughout the oceans, from deep, cold waters to shallow, tropical waters.  Shallow coral reefs have optimal growth rates in warm water ranging from 70–85° F (21–29° C). Coral reefs can be found at depths exceeding 91 m (300 ft), but reef-building corals generally grow best at depths shallower than 70 m (230 ft). The most prolific reefs occupy depths of 18–27 m (60–90 ft), though many of these shallow reefs have been degraded. Corals also need salt water to survive, so they also grow poorly near river openings with fresh water runoff. Other factors influencing coral distribution are availability of hard-bottom substrate, the availability of food such as plankton, and the presence of species that help control macroalgae, like urchins and herbivorous fish.

Basic ecology.  Corals are in fact animals (not a plant!) that fall under the phylum Cnidaria and the class Anthozoa. They are relatives of jellyfish and anemones.  Corals can exist as individual polyps, or in colonies and communities that contain hundreds to hundreds of thousands of polyps. For example, brain corals consist of colonies of many individual polyps; each individual polyp averages 1-3 mm in diameter. Corals can be divided into two groups: hard coral and soft coral. Hard corals, also known as stony coral, produce a rigid skeleton made of calcium carbonate (CaCO3) in crystal form called aragonite, with reef-building capabilities. Alternatively, soft corals, including sea fans, do not produce a rigid calcium carbonate skeleton and do not form reefs, though they may be present in a reef ecosystem.
 

Feeding: Most reef-building corals have a mutually beneficial relationship with a microscopic unicellular algae called zooxanthellae that lives within the cells of the coral's gastrodermis. As much as 90 percent of the organic material the algae manufacture photosynthetically is transferred to the host coral tissue. In addition to the symbiotic relationship with algae, most corals capture and consume live prey ranging from microscopic zooplankton to small fish, depending on coral size. Using its tentacles that extend outside it body, the coral with utilize it nematocysts, or stinging cells, to stun and kill  its prey before passing it to its mouth. Once the food has been digested, the waste is expelled from the same opening.
 

Reproduction: Corals are unique in that they are capable of reproducing both sexually and asexually. Sexual reproduction is the more common method and can be performed in two ways: broadcast spawning or brooding. Broadcast spawning consists of both male and female coral expelling massive amounts of gametes (eggs and sperm) into the water column during synchronized events. Brooding is similar to broadcast spawning, except only the male gametes are released into the water column. Coral sperm is negatively buoyant once released and hopefully will be carried by ocean currents to female coral where they will fertilize the egg cells of the female coral.

The Value of Corals

Healthy coral reefs are among the most biologically diverse and economically valuable ecosystems on earth, providing valuable and vital ecosystem services. Coral ecosystems are a source of food for millions; protect coastlines from storms and erosion; provide habitat, spawning and nursery grounds for economically important fish species; provide jobs and income to local economies from fishing, recreation, and tourism; are a source of new medicines, and are hotspots of marine biodiversity.
 

Biodiversity: Coral reefs are essential spawning, nursery, breeding, and feeding grounds for numerous organisms. In terms of biodiversity, the variety of species living on a coral reef is greater than in any other shallow-water marine ecosystems and is one of the most diverse on the planet, yet coral reefs cover less than one tenth of one percent of the ocean floor. Coral reefs support more than 800 hard coral species and more than 4,000 species of fish.
 

Coastal Protection: Healthy coral reefs have rough surfaces and complex structures that dissipate much of the force of incoming waves; this buffers shorelines from currents, waves, and storms, helping to prevent loss of life, property damage, and erosion.  Coastlines protected by reefs are more stable, in terms of erosion, and are also a source of sand in natural beach replenishment
 

Fisheries: The fish that grow and live on coral reefs are a significant food source for over a billion people worldwide—many of whom live far from the reefs that feed them. Approximately half of all federally managed fisheries in the United States depend on coral reefs and related habitats for a portion of their life cycles. The NOAA National Marine Fisheries Service estimates the annual commercial value of US fisheries from coral reefs to be over $100 million. Reef-based recreational fisheries generate over $100 million annually in the US. Globally, one estimate shows fisheries benefits account for $5.7 billion of the total $29.8 billion global net benefit provided by coral reefs. Sustainable coral reef fisheries in Southeast Asia alone are valued at $2.4 billion per year. These numbers do not take into account the value of deep-sea corals, which are themselves home for many commercially valuable species and thus additional fisheries value.
 

Medicine: Many species found in coral ecosystems produce chemical compounds for defense or attack, particularly the slow-moving or stationary species like nudibranchs and sponges. Searching for potential new pharmaceuticals, termed bioprospecting, has been common in terrestrial environments for decades. However, bioprospecting is relatively new in the marine environment and is nowhere close to realizing its full potential. Creatures found in coral ecosystems are important sources of new medicines being developed to induce and ease labor; treat cancer, arthritis, asthma, ulcers, human bacterial infections, heart disease, viruses, and other diseases; as well as sources of nutritional supplements, enzymes, and cosmetics. The medicines and other potentially useful compounds identified to date have led to coral ecosystems being referred to as the medicine cabinets of the 21st century by some, and the list of approved and potential new drugs is ever growing.
 

Tourism and Recreation: Every year, millions of scuba divers and snorkelers visit coral reefs to enjoy their abundant sea life. Even more tourists visit the beaches protected by these reefs. Local economies receive billions of dollars from these visitors to reef regions through diving tours, recreational fishing trips, hotels, restaurants, and other businesses based near reef ecosystems. One estimate places the total global value of coral-reef based recreation and tourism at $9.6 billion of the total global net benefit of coral reefs.

Content borrowed from http://coralreef.noaa.gov/