The Natural Selection of Coral Reefs

3 07 2007

Hurricanes are among the most devastating of weather events, and coral reefs are often damaged when in the path of a hurricane. It is quite surprising, then, to consider the possibility that hurricanes might actually be helping some coral communities reverse the “great bleaching” that has been destroying so many reefs. While it’s easy to think of corals are a primarily warm-water creature, they are actually quite sensitive to water temperature, and increased ocean temperatures (caused by the current warming trend) has caused the algae that live inside coral and are vital to the existence of coral to either die or be expelled, the coral then taking on a stark white appearance (hence, “bleached”). A new PNAS paper by Manzello, et al. suggests that the local cooling trend that follows hurricanes may benefit some reefs, however, thus giving us a look at a very strange selection process.

What the researchers found when looking at the intensity of coral bleaching at several sites in Florida and the occurrance of tropical storms and hurricanes was a suggestive correlation; as the storms passed within 400 km of the reefs, the high winds cooled water temperature, making it much easier for the reefs to rebound from bleaching. Sites that did not experience such cooling effects (high water temperatures plus no relief until the winter) had as much as 90% of the coral bleached with no notable recovery until a seasonal drop in temperature. The storms can damage the reefs however, and it seems that the reefs have to be close enough to receive the benefits of the cooled water, but not too close to actually be damaged by the storm, and the number of given storms in a year (as well as the path they take) will help to determine what reefs will be favored over others. If there is indeed a real correlation between warming sea temperatures and the occurrence of hurricanes (I suppose I should read Storm World and then talk it over with a prestigious meteorologist friend of mine), then coral reefs around Florida and other southern states may be able to recover despite the overall warming trend. This is certainly an area of research to keep our eyes on if we are concerned about coral conservation, and if the frequency of storms happens enough, it would be interesting if there was a “storm-resistant” variety of reef (keep in mind that a reef is not made up of just one species) that was selected for in this odd fashion.


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