coral bleaching

Coral Bleaching, Death, and Recovery

Oculina patagonica

Oculina patagonica Photo Credit: Laura Bori

The past couple of years have not been kind to coral reefs; a global bleaching event has been ongoing since 2014. A large portion of the northern Great Barrier Reef has been devastated, and about 2/3 of the corals there are said to be dead. But what does this mean? Are we doomed to lose all of or most of the remaining coral reefs, as some scientists have asserted?

Bleaching occurs when corals stressed by heat and ocean acidification expel their symbiotic algae, losing both their color and their food source. It appears that there are multiple factors at play here: corals not subjected to changing pH are far better able to withstand higher temperatures, and pollutants and runoff from agriculture may also contribute to coral stress.

Reefs can survive in a bleached condition for a time. If the water temperature drops again relatively quickly, the corals can easily recover. But if too much time passes, they will die, as has happened in many locations around the globe. The current global bleaching event has been ongoing for over two years, and is expected to continue into 2017.

While the situation appears to be grim, there are also some hopeful signs, and scientists are working to find solutions that may at least mitigate the worst of the damage. It turns out that some corals do seem to have the ability to survive bleaching events, and studies are being conducted to determine why, and what this means for the resilience of coral reefs over the long term.  https://www.newscientist.com/article/2113270-bleached-corals-in-the-pacific-have-started-bouncing-back/

The case of Coral Castles, a remote reef located in the Phoenix Islands between Hawaii and Fiji, is particularly intriguing. The reef was declared dead in 2003, and as recently as 2012 had showed few signs of life. But then, in 2015, a research expedition discovered that the reef was rebounding. In August of this year, they discovered that corals there were continuing to recover, even as sea temperatures continued to rise.

phx-islands-coral

A giant clam and Acropora coral in the Phoenix Islands protected area Photo credit: Craig Cook/Undersea Medical

Little is known about how this happened, or what the implications may be for other areas hit hard by bleaching events. But a great deal of research has been done in the past several decades that gives us some clues. Among other things, scientists have discovered that some corals and their algae are genetically better equipped to cope with stressful conditions. When there is massive die-off on a reef, some of the better adapted corals may survive and reproduce, eventually recolonizing the reef. This is, however, a slow process.

In order to try to lend a hand in this, scientists have been experimenting with culturing these more resilient corals and algae, and then transplanting them onto reefs where massive bleaching has occurred. They have had some success with this, and have shown that the increased resilience is passed along when corals reproduce. http://www.sci-news.com/genetics/science-corals-heat-tolerant-genes-02958.html

These and other projects offer some hope that we may be able to help the reefs to survive. But beyond science, it is of utmost importance that we stop those activities that are causing the problem – particularly the use of fossil fuels, but also the use of other pollutants. Each of us can help by considering carefully the choices that we make as consumers, and by trying to leave a smaller footprint on the earth

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