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July 16th 2008

One third of reef-building corals face extinction

The first-ever comprehensive global assessment of reef-building corals has recently been undertaken, with some extremely disconcerting results. The assessment highlighted the widespread plight of coral reefs, revealing that a third of this important group of marine species is threatened with extinction.

The most biologically diverse of marine ecosystems, coral reefs are home to more than 25 percent of marine species. Unfortunately, these remarkable species have been shown to be highly sensitive to changes in their environment, with the results of this particular assessment showing that reef-building corals are vulnerable to the effects of climate change. In addition, corals are threatened by the more localized impacts of destructive fishing, water pollution, and the degradation of coastal habitats.

The death of corals leads to the demise of other plants and animals that depend on coral reefs for food and shelter, which can lead to the collapse of entire ecosystems. With coral reefs harboring fish and other marine resources important for coastal communities, in addition to the protection they provide coastal settlements from erosion and flooding, the loss of the corals will also have profound implications for millions of people.

Here are just a few of the coral species that were included in the assessment; species that may be lost forever if urgent conservation measures are not implemented now.

Staghorn corals (Acropora species) face the highest risk of extinction, with 52 percent of species listed in a threatened category. They are among the fastest growing corals on reefs, making them excellent and important reef-builders. However, their speed of growth (which can be up to 20 centimetres a year) is balanced by the fragility of some of the structures, which are easily damaged in storms.

image: Pocillopora eydouxi surrounded by fish

The hardy, widespread and common cauliflower corals (Pocillopora species) can easily be identified by the presence of wart-like growths, called verrucae, which cover the colonies. Pocillopora is one of four genera that constitute the majority of the dead coral trade, adding to the threats of climate change, pollution and habitat degradation.

Stony corals (Stylophora species) were once named as the 'tramp' species of the coral world, due to their tendency to attach themselves to floating objects on which they travel hundreds of kilometres, reproducing on the way.

Fire corals (Millepora species) get their common name from the painful stings they inflict on divers. Most fire coral species have brittle skeletons that can easily be broken during storms or by divers, when diving for leisure or when collecting fish for the aquarium trade.

The appearance of the pretty flowerpot corals (Goniopora species) belies their aggressive behaviour. They are capable of developing elongated 'sweeper' polyps, which can inflict severe tissue damage on other coral within reach. It is believed that this adaptation benefits flowerpot corals in the intense competition for space on the reef.

image: Organ pipe coral, Tubipora musica, with extended polyps

Unlike most corals, it is not colourful polyps that make organ pipe corals (Tubipora species) attractive, but instead, their dark red coloured skeletons. Unfortunately, the permanently coloured skeletons of organ pipe corals make them an attractive material for ornaments and jewellery, and they are under considerable pressure from over-harvesting.

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