Coral Bleaching Threat Increasing in Western Atlantic and Pacific Oceans

As unusually warm ocean temperatures cover the north Pacific, equatorial Pacific, and western Atlantic oceans, NOAA scientists expect greater bleaching of corals on Northern Hemisphere reefs through October, potentially leading to the death of corals over a wide area and affecting the long-term supply of fish and shellfish. The news comes from the latest NOAA's Coral Reef Watch four-month Coral Bleaching outlook, which is updated weekly.

2015 Jun 30 NOAA 60% Probability Coral Bleaching Thermal Stress for Jul-Oct 2015

While corals can recover from mild bleaching, severe or long-term bleaching can kill corals. Even if corals recover, they are more susceptible to disease. Once corals die, it usually takes decades for the reef to recover -- but recovery is only possible if the reefs are undisturbed. After corals die, reefs degrade and the structures corals build are eroded away, providing less shoreline protection and fewer habitats for fish and shellfish.

"The bleaching that started in June 2014 has been really bad for corals in the western Pacific," said Mark Eakin, NOAA Coral Reef Watch coordinator. "We are worried that bleaching will spread to the western Atlantic and again into Hawaii."

Coral bleaching occurs when corals are stressed by changes in environmental conditions such as temperature, light or nutrients. The coral expels the symbiotic algae living in its tissue, causing the tissue to turn white or pale. Without the algae, the coral loses its major source of food and is more susceptible to disease. Scientists note, however, that only high temperatures can cause bleaching over wide areas like those seen since 2014.

NOAA's bleaching prediction for the upcoming months supports the findings of a paper published in the journal Science last week that examined the threat to marine ecosystems and ecosystem services under two different carbon dioxide emission pathways.

"The paper reports that even if humans limit the Earth's warming to two degrees Celsius (3.8 degrees F), many marine ecosystems, including coral reefs, are still going to suffer," said Eakin, an author on the paper. "The increase we are seeing in the frequency and severity of bleaching events is part of why the climate models in that paper predict a dire future for coral reefs."

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