Coral bleaching in 2010 was a bad year

Mark Eakin: It’s been a really bad year for coral reefs around the world.

Mark Eakin is coordinator of the National Oceanic and Atmospheric Administration’s Coral Reef Watch. He said high ocean temperatures in 2010 are causing corals to whiten, or bleach.

Mark Eakin: Major bleaching started in the Central Pacific in the early part of this year, then there was bleaching in the Indian Ocean and especially Southeast Asia throughout May and June. And now the big concern is that we may be seeing the worst bleaching ever in the Caribbean, later this year.

Coral gets its food and color from algae that live in its tissues. Eakin explained that coral bleaching happens when ocean temperatures get too warm and stay warm for too long, and the relationship between the coral and the algae gets stressed. This thermal stress to corals, he said, is the highest its been since 1998, when 15% of the world’s coral reefs died.

Mark Eakin: When you have high temperatures, in conjunction with normal high light conditions, the photosynthetic apparatus in the algae starts to poison the coral. They’ll spit them out into the water. When they do this, they lose their color, look white, which is why they’re called bleached. If that persists for a long time, it can cause the corals to die.

Eakin said corals can recover from bleaching, but bleaching has become more frequent over the past decade and reefs have little time to grow back. He said that the unusually high temperatures in 2010 is due to a combination of El Nino followed by La Nina, and an overall warming trend caused by climate change.

Mark Eakin: All throughout this year, temperatures have been above normal in the Caribbean. This has led to a condition that’s made them really susceptible to high temperatures in the summer. Climate change has set us up for a condition where it’s easier for corals to bleach, because the temperatures are already high. So any elevated temperatures can push corals beyond their limit. This year, we have a problem because there was an El Nino that was going on late 2009 to 2010, and now it’s switched into a La Nina.

Eakin explained that the El Nino and La Nina weather pattern brings heat across the seas.

Mark Eakin: When you get a sequence like this, which we don’t see very often – we saw it in ’97 – ’98, we’re seeing it again now – where we go immediately from a moderately strong El Nino directly into La Nina, that exposes a lot of corals to very high temperatures.

He said that coral bleaching has a big impact on the reef, that you would immediately notice if you were to dive at the reef.

Mark Eakin: Normally, diving on a reef is a spectacular thing. These are beautiful, vibrant communities. At the same time you’re seeing a very active system. When you drive on a reef that’s bleached, it’s frightening and depressing. It’s like suddenly walking out and having the entire forest dead. It just changes everything. Some of the fish are even swimming around looking stunned and confused.