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Coral (Anthozoa) - Reef Reality Episode 4

Reef Reality Episode Voice Over

There are 260 species of coral on the Great Barrier Reef alone. This coral is at the very heart and soul of all reef life. Most corals depend on sunlight and grow in clear and shallow waters. The world’s first coral reefs occurred about 500 million years ago. Some coral have a symbiotic or mutual relationship with algae as well, and both form wonderful habitats for other reef life.

Species Health / Vulnerability

50% could die by 2030.

Description

Corals are marine organisms from the class Anthozoa. A coral "head” is formed from many individual but genetically identical polyps, each measuring only a few millimetres in diameter. These coral polyps lay down a skeleton over thousands of generations, with each species having its own distinctive skeleton characteristics. Reef building coral secretes calcium carbonate to form a hard skeleton.

Regions & Habitat

Coral reefs are estimated to cover just under 1% of the surface area of the world’s oceans – an estimate 284,300 square kilometres, or half the area of France. This 1% is home to 25% of all marine species, leading to coral reefs being called “rainforests of the sea”.  Most of the world’s coral reefs are found throughout the Indo-Pacific region (92%), with Atlantic and Caribbean coral reefs accounting for 8%. Corals exist in temperate and tropical waters, with the optimum temperature for most reefs being 26 – 27 °C. Shallow-water reefs form only in a zone extending from 30° N to 30° S of the equator.

Feeding

Some corals are able to catch plankton and small fish by means of stinging cells on their tentacles. These animals, however obtain most of their nutrients from zooxanthellae, which are  photosynthetic unicellular algae. As a result, most corals depend on sunlight and therefore grow in clear water shallower than 60 metres. A coral polyp normally harbours one particular species of algae, with which it has a symbiotic relationship. The algae provide energy for the coral via photosynthesis, and aid in calcification of the coral skeleton. In return, the algae benefit from a safe environment, and use the carbon dioxide and nitrogenous waste produced by the polyp.

Biggest Threats

Corals are highly sensitive to environmental changes. Scientists have predicted that over 50% of the world's coral reefs may be destroyed by the year 2030. The following environmental factors can threaten coral:
1) Algae – this can grow prolifically if too many nutrients are present in the water, thus overwhelming a coral reef. Harmful land-use practices threaten coral reefs when runoff from agricultural areas contains high levels of nutrients, which encourage excess algae growth;
2) Water temperature changes - changes of more than a degree or two beyond a coral species’ normal range can kill the coral;
3) Ocean acidification –The narrow niche that coral occupies, and the stony corals' reliance on calcium carbonate deposition, means they are susceptible to changes in water pH. Dissolving CO2 in seawater increases the hydrogen ion (H+) concentration in the ocean, and thus decreases ocean pH. Lowered pH reduces the ability of corals to produce calcium carbonate, can even dissolve those skeletons, in extreme cases. Without deep and immediate cuts in anthropogenic CO2, many scientists fear that ocean acidification will result in the severe degradation or destruction of coral species and ecosystems.  Between 1751 and 1994 surface ocean pH is estimated to have decreased from approximately 8.179 to 8.104.

An early symptom of environmental stress is known as coral bleaching. This is where corals expel their zooxanthellae - without their symbiotic unicellular algae, coral tissues become colorless as they reveal the white of their calcium carbonate skeletons. Ejecting the algae increases the corals’ chances of surviving stressful periods – they can regain the algae at a later time. The corals eventually die if the stressful conditions persisit.

Other human activity also threatens coral reefs, by damaging them through mooring, blast fishing, cyanide fishing for aquarium fish, diving, mining and construction.

How to Help

1) Learn more about coral reefs. How many different species live in reefs? What new medicines have been discovered in reef organisms? Participate in training or educational programs that focus on reef ecology. When you further your own education, you can help others understand the fragility and value of the world's coral reefs.
2) Conserve water. The less water you use, the less runoff and wastewater that eventually finds its way back into our oceans.
3) Don't anchor on the reef. If you go boating near a coral reef, use mooring buoy systems when they are available.
4) If you dive, don't touch! Keep your fins, gear and hands away from the coral, as this contact can hurt you and will damage the delicate coral animals. Stay off the bottom because stirred-up sediment can settle on coral and smother it.
5) Volunteer. Volunteer and community coral reef monitoring programs are very important. If you do not live near a coast, get involved in your local save the river (bay, lake, or other estuarine environment) program. Remember, all watersheds affect the oceans and eventually the coral reefs.
6) Be a wastewater crusader! Make sure that sewage from your boat, from others' boats, and from land is correctly treated. The nutrients from sewage feed growing algae that can smother and kill corals.
7) Link to Article: 25 Ways to Protect our Oceans & Reefs