Coral Bleaching Creates a Vicious Cycle of Further Bleaching and Disease
Photo: Rosenstiel School of Marine and Atmospheric Science
Corals just Can't Win...
A new study published in the October issue of the journal Ecology sheds a bit more light on a phenomenon that is becoming more and more common for corals around the world: Bleaching (described as "the whitening of corals, due to stress-induced expulsion or death of symbiotic unicellular algae or due to the loss of pigmentation within the algae"). The paper shows that bleaching can make coral more susceptible to coral diseases, which in turn can lead to more bleaching. It is the interaction of these two things that cause the worst damage, not the bleaching alone (like previously thought).
Healthy coral, something that is becoming harder to find. Photo: Wikipedia, CC
Why is bleaching a problem? Because "Corals rely on algae that live inside each coral polyp to provide nutrients and supplemental oxygen. Bleaching occurs when these colorful algae die out or leave the polyps, often in response to overly warm conditions. Without their brightly colored algae, the coral's skeleton becomes visible through its transparent tissue, making it appear white. Although the tissue remains intact and can recover over time, this stressful condition can cause corals to stop growing and reproducing."
We've already written on how global warming is affecting coral. Well, this new study shows that warmer water also increases the incidence of coral diseases, and that these, unlike simple bleaching, can "cause irreparable loss of coral tissues".
Bleaching coral is under a very stressed state, and so it is not surprising that its resistance to various diseases is lower than in a normal, healthy state. So bleaching and pathogens attack with a double-whammy that can be fatal.
And as we know, coral reefs are some of the most productive marine ecosystems and are home to countless species...