Coral Reef in Timor. Photograph courtesy of Nick Hobgood.
By Frances Hall
Coral reefs provide a number of services to humans beyond colorful aquarium accessories: they protect coastlines from storms, provide an enormous variety of unique medicinal compounds, and support the economy of many developing countries through tourism. Furthermore, the fish that the coral reefs support are a source of vital income and calories: one study estimated that a quarter of the food of 1 billion Asians is reef-supported fish. It will come as no great shock that human activities imperil these reefs in a number of ways,
Carbon dioxide, the primary greenhouse gas, does more than trap heat in the atmosphere. About one quarter of all Carbon dioxide emissions are dissolved into the ocean, where they trigger a reaction that ultimately reduces the available carbonate in ocean water. While this may not sound dire out of context, calcium carbonate forms the skeletons of reef-building coral as well as shelled marine animals, such as urchins and oysters. (Coral refers to the living organism and reef refers to the rocky structure they live on, primarily formed by the skeletons of coral). The lack of it leaves these animals unable to excrete a shell, making them unlikely to survive, and can cause the structure supporting a coral reef, comprised of coral skeletons, to collapse.
Bleached Musifi Coral. Photograph courtesy of Bruno de Guisti.
Corals also respond poorly to rising sea level temperatures. Many corals have living within them: the corals provide shelter, and the dinoflagellates convert sunlight into as much as 95 per cent of the energy its host requires. Often, in a misinformed stress response to heat, corals expel their dinoflagellates, the equivalent of kicking out all your renters the same day you lose your job. This leads to the often-pictured “coral bleaching” because corals without their boarders are pale and usually dying. If this heat stress is mild, corals can often regain their dinoflagellates before irreparable harm is done. Regrettably, climate change is rapidly reaching a point where “mild” will no longer describe the resulting temperature changes.
These findings beg the question: are coral reefs even capable of recovering from such damage? Natural weather events give scientists an excellent opportunity to study this. El Niño happens every two to seven years and is characterized by warmer waters in certain areas, with far reaching effects on both land and sea. In both 1982 and 1997 there were unusually severe El Niño cycles, characterized by temperature fluctuations greater than two degrees Celsius, that lasted for months. This forces corals to exist temporarily under conditions that climate change may one day make permanent. A 2004 study looked at sections of a coral reef in the Cocos Island that had been severely impacted by the 1982 El Niño to the point that certain sections only had three per cent live coral cover. The heat stress of the El Niño had bleached and ultimately killed most of the live coral on the reef.
Coral at Palmyra Atoll. Photograph courtesy of Jim Maragos of the US Fish and Wildlife Service.
In 2004 scientists calculated live coral cover on these same reefs. Some reefs collapsed and one showed no measurable recovery at all. However, others exhibited and average live coral cover of 18 to 21 per cent, an enormous gain in only twenty years. One coral reef had increased to 50 per cent live cover. Furthermore, in some reefs coral diversity, arguably a good measure of reef health, had increased with the appearance of three coral species that hadn’t previously been seen off the Cocos Island. These findings led the scientists to conclude that reefs “have the capacity to recover from severe disturbances” and even increase diversity in the face of them.
Florida Coral Reef. Photograph courtesy of Jerry Reid of the Fish and Wildlife Service.
To accept the conclusions of one study as absolute truth is to live in a desert and assume you’ve seen every kind of plant. Still, even if these findings only apply to the Cocos Islands, or certain kinds of coral, they are cause for celebration. Previous studies estimated that coral reefs would need lifetimes or even centuries to recover. It’s not too late, and as long as there are even patches of healthy corals it probably won’t be. We can still fix this, so of course it’s worth it to try.
Francis has just joined the team at The Ecotone Exchange. She currently works as an outdoor educator at the Pali Institute in Running Springs, California. She graduated earlier this year from Earlham College with a B.A. in biology. In her spare time she hikes, runs, sings, cooks, and reads many, many books.