CORAL DEATH

WHY CORAL IS DYING

Coral reefs have been dying since the late seventies and are in rapid decline globally due to human-driven climate change. This is vitally important to many species of reef sharks that depend on coral ecosystems, because the death of the coral results in the disappearance of the reef of which it formed the base.

Coral reefs encircle the planet at the tropical and subtropical levels, and are thought to be home to a quarter of the planet's species, comparable to the terrestrial rain forests. Their loss will result in dramatic biodiversity decline, and the extinction of the animals who originally took millions of years to construct this valuable ecological habitat.

Consequences for the health of the biosphere are unknown.

Bleaching events are lasting longer and are becoming more extensive, and this trend is expected to continue in the next decades as oceanic temperatures continue to rise. Warmer waters are also expected to increase the incidence of coral diseases such as black band disease, white band disease, white plague, and white pox, all of which can lead to mass mortality of coral, and subsequently the ecosystem that it supports.

Another threat to coral is that the ocean is becoming more acidic as it absorbs carbon dioxide from the atmosphere, and this increased acidity inhibits the corals’ ability to form their skeletons through calcification. Thus their growth is slowed.

A doubling of atmospheric carbon dioxide will half the rate of coral calcification and if concentrations of 450 to 500 ppm are reached, as are predicted for 2030 to 2050, the rate of erosion of coral reefs will exceed the rate of calcification.

Sea level rise, caused by the melting of the ice caps and the thermal expansion of the oceans, will also result in some reefs becoming too deep to receive adequate sunlight.

An unprecedented ecological disaster is unfolding as a result, all against the background of industrial pollution, over-fishing, and the de-oxygenation of the oceans.

2018

Warming, rising seas, pollution from human settlements and industry, dynamite fishing, and oceanic acidification, have caused increasing numbers of wide-spread bleaching events.

Bleaching results when the stressed coral animals expel the colourful algae that live within them. If the algae is not replaced within a few weeks, the coral will die. Some coral are able to recover, but too often the coral dies, and the entire ecosystem for which it forms the base, virtually disappears.

The dying coral pictured at right has bleached and become diseased.

With so many sources of stress, coral has increasing difficulty in recovering from the damage caused by storms and dynamite fishing. The loss of sharks from reefs resulting from their removal for the shark fin racket, further inhibits the ability of coral to recover from damage and bleaching. The reef at left is dead.