It is almost impossible to have avoided knowing about the extinction threat facing coral reefs. Though the images of their bright colours and many thriving species contrasted aside the bleak, white empty skeletons they leave behind are certainly memorable, their destruction can easily be brushed to the back of the mind as another inescapable tragedy of climate change. The intricacies of these reefs are lost in an endless torrent of environmental news that no one can hope to comprehend in totality. Yet it is not all cause for despair, with numerous efforts for conservation and new science providing a variety of approaches allowing for a cautious optimism, providing their importance is not forgotten.
Coral reefs are built from one specific subtype of coral which congregates in colonies of thousands to form the familiar sprawling, colourful habitats. This type of coral are called Scleractinia, or ‘hard’ corals, and form reefs out of their hard calcium exoskeletons. They are permanently fixed in one place for the duration of their lives, which in part allows them to create complex, co-dependant ecosystems providing a home and life source to over four thousand species of fish and an estimated 25 percent of all marine life. Reefs primarily rely upon a symbiotic relationship with algae called zooxanthellae, which provide food for the corals through photosynthesis, and in turn the algae is provided with a home. It is this algae which gives the reefs their distinctive rainbow of colour, and its absence leaves them ghoulishly white, giving rise to the term “bleaching”.
Bleaching, easily the most distinctive and infamous threat to coral reefs, occurs when the algae are forced to leave the coral due to rising temperatures. While bleaching is not always unrecoverable damage, it can leave the reef vulnerable to various other types of damage, often too posed by global warming and human interference. Predictably, bleaching events have been increasing in frequency.
Global warming has also contributed to a 30 percent rise in ocean acidity since the 1700s, upsetting a delicate balance of salts for coral exoskeletons and in extreme cases, leading to dissolving. Excess atmospheric carbon dioxide is absorbed into seawater, where it reacts to form carbonic acid and inhibits the formation of healthy reefs.
The list of man-made destruction affecting coral reefs drags on, including issues created by coastal development. The offshore depositing of sediment can smother corals, strangling their symbiotic relationship with photosynthesizing algae. Perhaps counter to expectation, increasing nutrient levels from fertilisers and animal waste are also damaging to corals, which have adapted to low nutrient levels. With such an extensive list, extinction can feel like the only thing on the horizon, however constant new breakthroughs and research do present hope.
Research in February 2021 suggested that probiotics, micro-organisms often found as a diet supplement may be able to help coral reefs become more disease resistant. The probiotic used was able to both decelerate disease progression in sick corals and prevent healthy corals from being infected. Identifying healthy corals with apparent disease resistance or hardiness can provide further clues to emulate.
Hostile conditions can be withstood by certain corals, according to recent research at James Cook University and the Australian Institute of Marine Science. They investigated reefs spanning over 800km, concluding that certain reefs had adapted to survive heat waves, with more frequent exposure leading to better resistance to damage.
The importance of coral reefs are undeniable and go far beyond providing such rich and biodiverse ecosystems for marine creatures. The direct impact on humanity is not only ecological, but economical, providing food and income to over 500 million people. Their contribution to the tourism industry also helps to sustain economies around the world and protect livelihoods. They are also key in preventing erosion and coastal flooding as they reduce the severity of waves, which will become increasingly critical to saving lives as sea levels continue to rise.
