Having lived in the hurricane zone for most of the last decade, I have developed a bit of an addiction to The Weather Channel this time of year. Until recently, the general feeling around hurricane coverage and anticipation of hurricane season in the United States has been a fear of “the big one.” Now, and especially this summer, I am surprised to find I am hoping for a hurricane. Not a big one, of course. But as far as the health of coral reefs is concerned, a few minor ones would do the trick.
It may surprise you to know that, given the warming trends in the ocean and the fact that El Niño seems to be setting up for this winter, a hurricane is just what coral reefs need to avoid a mass bleaching event.
Don’t get me wrong: Big hurricanes can cause serious damage to coral reefs. But generally, storms are something they have adapted to and as long as they are in good health, will be able to recover from.
But why are hurricanes good for coral reefs?
The combination of still hot water and radiation stress from cloud-free summer days is a deadly duo for corals. But with hurricanes, you get lots and lots of wind, and the ocean gets all stirred up. The clouds come in and darken the sky and cool things off with lots of rainfall. This is just what a reef needs to keep from bleaching when they have been cooking in the sun, getting stressed from the heat.
Here’s why: When corals are stressed, they expel the tiny algae cells that live in their tissues, turning the corals white. This bleaching (the appearance of “whitened” coral where there was once-colorful coral) is a symptom of stress in corals and other reef animals with symbiotic algae. These tiny algae are known as zooxanthellae and are present in most healthy reef-building corals. Zooxanthellae provide nutrients and oxygen to the coral through photosynthetic activities, allowing their host to direct more energy toward growth and constructing its calcium carbonate skeleton.
The host coral polyp in return provides zooxanthellae with a protected environment and a constant supply of carbon dioxide needed for photosynthesis. When sea temperatures become too warm (above 28 C), the photosythetic system of the zooxanthellae can not effectively process incoming light. This results in production of “superoxides,” such as hydrogen peroxide, toxic byproducts of this process. These toxins contribute to coral stress reactions, which lead to bleaching. In extreme cases of bleaching, corals die.
I tend to think about the hurricane season in terms of the alphabet — if we are in August and have gotten past the letter “G,” it usually means a pretty active year. Remember the hurricane season of 2005, when we used up all the letters and started using Greek letters?
Now, here at the height of this year’s hurricane season, we’ve barely reached “E,” with only one hurricane in the bunch. With Hurricane Bill avoiding the Caribbean pretty much, we can only hope to see a few small storms this month that would cool things off in the Lesser Antilles and Northern Caribbean. That’s good news, because NOAA’s Coral Reef Watch Program has predicted these areas will be hit the hardest by mass bleaching, based on the current sea surface temperature models derived from satellite data.
Right now, Florida reefs are under watch for bleaching due to persistent warm water that doesn’t seem to be going away. This isn’t good news — but unfortunately, it gets worse. Because it is the beginning of an El Niño year that is typically characterized by warming seas, we can expect to see even more extreme conditions for Caribbean reefs next year.
Scientists have identified a trend that usually goes something like this: The first part of the El Niño cycle brings some bleaching to the Caribbean, and then in the later part of the El Niño cycle the sustained sea warming trend makes Caribbean reefs even more likely to experience mass bleaching. So, we may get a teaser now that will hopefully prepare coral reef managers for what is to come next summer.
One of the tools The Nature Conservancy and partners such as NOAA are encouraging reef managers to develop and use is a bleaching response plan. These plans help managers to be prepared for the impending event by:
Making decisions about bleaching monitoring protocols;
Coordinating monitoring teams among many different agencies;
Communicating about the event;
Discussing how to implement management interventions.