Coral reefs

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Coral reefs are rigid wave-resistant structures made from calcium carbonate deposited by corals and other plants and animals. These fragile ecosystems are found all over the world.

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Understanding Coral reefs

In 1842 with the publication of his book "The Structure and Distribution of Coral Reefs" Charles Darwin became the first scientist to provide a rigorous explanation for the formation of coral reefs. Darwin recognised three types of reef, fringing reefs, barrier reefs and attols. The differences between the reefs was how they formed and how long they had been growing for. Coral reefs grow in water with an almost constant temperature. Need to differentiate between a reef (like those in the depths of the North Sea are they coral) and tropical reefs.

Corals are animals. Hundreds of individual animals grow together to form a colony. Some corals are predatory but most rely on small unicellular photosynthetic organisms (dinoflagellates) that live symbiotically within their cells. This is mutually beneficial. The corals get a steady supply of food and the Coral animals are loosely categorised as to whether they form a hard endoskeleton (hard or stony corals) or soft flexible skeletons (the eponymous soft corals). There are hard or stony and soft corals.

Corals immobility and reliance on sensitive symbionts for nutrition means they are very vulnerable to rapid changes in their environment. Changes such as a rise or fall in sea level, which will affect sea temperature, salinity and intensity of light corals' symbionts recieve affects their growth. Tropical coral reefs grow in nutrient deficient seas - because if there were lots of nutrients in the water there would be lots of unicellular algae and free swimming protozoans eating algae. Lots of unicellular organisms in the water would reduce the amount of light reaching the corals - because corals can't move rapidly to changing light conditions corals die out if there is an unexpected algal bloom. Such alagal blooms have been known to occur in tropical regions where there has been agricultural run-off. That is excess fertililser has contamininated the waterways, ended up in the sea and caused an alagal bloom (eutrophication).

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