Warming oceans put corals on the edge
El Niño could be brewing in the Pacific and the consequences could be felt as far away as the Cayman Islands.
Scientists are on alert that the phenomenon – which causes a temporary spike in ocean temperatures – could contribute to widespread bleaching of coral reefs worldwide.
Bleaching occurs when coral suffers heat stress and expels the algae living in their tissues causing the coral to turn completely white, often resulting in disease or coral die-offs.
Opinion is divided on the potential effects of the coming El Niño, and forecasts have varied on whether the meteorological event will actually occur in 2015.
If it does, it will likely be weaker than previous El Niño events. Good news, say scientists.
But the overall diagnosis is not so positive.
Mark Eakin, who coordinates the National Oceanic and Atmospheric Administration’s Coral Reef Watch program, warned last month that generally increasing ocean temperatures mean that corals, which survive within a tight temperature band, are closer than ever to their limit.
He cautioned that it may not take a particularly strong El Niño event to tip them over the edge.
“Overall, the oceans’ waters have warmed so much in recent years that most coral areas are right on the verge of having enough heat stress to cause bleaching and it doesn’t take nearly as much to start one of these global-scale events,” he told the Mother Jones magazine website.
Timothy Austin, deputy director of the Cayman Islands Department of Environment, said reefs around the islands have suffered bleaching as a consequence of previous El Niño events.
A particularly strong El Niño in 1998, estimated to have wiped out almost 20 percent of the world’s coral reefs, was particularly devastating.
“Any predicted increase in ocean temperature poses a real threat for Cayman reefs,” Mr. Austin said.
He said the Department of Environment has been tracking sea surface temperatures around the islands since 2001. Data for January 2015 shows temperatures slightly higher than normal for the time of year. Mr. Austin said the summer months frequently saw temperatures peak close to the upper thermal limit for corals.
“Every summer, we come very close to bleaching events,” he said. “1998 still remains the worst on record. We largely escaped the 2005 event but had significant bleaching in 2010.”
Carrie Manfrino, president of the Central Caribbean Marine Institute, said there are no current signs that reefs around Cayman are stressed, though this will not necessarily be clear until later in the summer. She believes it would likely take a strong El Niño to impact Cayman.
“It is always a possibility that the El Niño might build to a greater extent and result in massive bleaching everywhere. We will be more certain as to what will happen in Cayman by early summer,” she said.
She said the 2005 and 2010 El Niño events caused some bleaching on Cayman’s reefs but little or no coral mortality.
“What Mark Eakin is saying is El Niño is not as strong as it was in 1998. That is good news. He is also saying that whereas in the past a strong El Niño would lead to bleaching today, bleaching may occur due to compounding stress,” she said.
Karsten Shein, a climatologist with NOAA who has worked with CCMI, said bleaching events are notoriously difficult to predict.
According to the most recent forecast from NOAA, there is an approximately 50-60 percent chance of El Niño emerging during the next two months, with neutral conditions favored thereafter.
Mr. Shein said the effects of an El Niño event could be exacerbated because of warming ocean temperatures. But his personal opinion is that the impact of any El Niño in 2015 will be felt more keenly in the Pacific than in the Caribbean.
“It generally takes a fairly strong El Niño event to provide the push that really modifies conditions in the Caribbean. A weak El Niño is less likely to do it,” he said.
He added that rising ocean temperatures mean that corals are closer to the edge of their comfort zone and more susceptible to a number of threats.
“Water temperatures worldwide have been warming, Caribbean included, and other factors not related to El Niño could push them beyond the bleaching threshold,” he said.
Research will be take place at CCMI in the summer to monitor subsurface water temperatures to gain a better understanding of how temperatures on the surface translate to the reef itself.