Perhaps the single most breathtaking aquatic sight on Earth, the Great Barrier Reef, has been named one of the seven wonders of the natural world. Stretching 3,000 km along Australia’s coast, the reef is home to more than 1,500 species of tropical fish. It also serves as a habitat for coral sponges, mollusks, rays, dolphins, more than 200 different bird species and at least 20 species of reptiles. In addition, the reef serves as a breeding ground for the humpback whale and a habitat for endangered species such as the dugong and the green sea turtle. Over 400 species of coral inhabit the Great Barrier Reef, making it an ideal habitat for marine life. Now, however, the well-being of the Great Barrier Reef is under threat from coral bleaching.
Coral tissue is not colored, but clear. The colors of coral reefs come from the algae that live within the coral bodies. These photosynthetic algae help to nourish the coral and enhance calcification in a symbiotic relationship. During elongated periods of high temperatures, the algae lose their pigmentation and their ability to nourish the coral. Unable to obtain the nourishment it needs, the coral cannot recover from the effects of erosion. Since 1950, global warming has raised average ocean temperatures around the world by one degree Fahrenheit.
Eight instances of coral bleaching have been recorded in the Great Barrier Reef since 1979, and the time between these occurrences has been far too short for the reef to recover fully. Annual bleaching is predicted to occur by the middle of this century if the emission of carbon dioxide and other heat-trapping gases continues to rise. This may not sound threatening, but the fact is that carbon dioxide released into the atmosphere is absorbed by oceans and increases the acidity of the water. The acidified water increases erosion of the already weakened coral skeletons, and can actually be fatal to coral reefs. The disappearance of coral from the Great Barrier Reef could in turn be fatal to the animals that depend on it, causing many species that are exclusive to the reef to go extinct.
The good news is that there may be a way to save the Great Barrier Reef and the species that inhabit it from extinction. Scientists at the University of Sydney’s One Tree Island research facility say that the answer to combating ocean acidification and its effects is the sea cucumber. Many sea cucumber species are detritivores that feed on the dead matter that falls to the ocean floor. As they feed, sea cucumbers cannot help but ingest a small amount of sand. One of the by-products of sea cucumbers that have ingested sand is calcium carbonate. Calcium carbonate is a major component in coral skeletons, and increased levels of it may give coral populations like the Great Barrier Reef a greater ability to recover from the effects of bleaching and acidification.
According to One Tree Island deputy director Maria Byrne, coral reefs require a rate of accumulation of calcium carbonate greater than or equal to the rate at which they are eroded by factors like acidification to remain healthy. Research has shown that deposits of the compound by sea cucumbers, as well as other detritivores, can contribute significantly to the overall health of coral reefs. Sea cucumbers also help coral reefs in another way. According to researchers, the natural digestive process of the sea cucumber increases pH levels in the area where the sea cucumber defecates. An increase in pH has the effect of neutralizing the acidity of the surrounding ocean water, making it more likely that a coral population will survive in the wake of a bleaching event.
In light of the recent discovery of the sea cucumber’s ability to mitigate the effects of climate change, experts argue that more careful consideration should be given to the commercial harvesting of these animals. Approximately 30 species of sea cucumber are commercially harvested by fisheries throughout the tropics. They are considered a delicacy in many cultures, and a ton of dried sea cucumbers can bring one million dollars. Currently, sea cucumbers are protected in many parts of the world. However, if the species that do not play a role in climate change reversal happen to go extinct, it could lead to illegal harvesting of those species that are vital to reversing the effects of climate change. If that happens, it would only be a matter of time before populations like the Great Barrier Reef are entirely destroyed.