On Monday the National Oceanic and Atmospheric Administration announced that a third consecutive year of higher-than-normal sea temperatures could lead to an increase in coral bleaching around the world and in the Virgin Islands.
This third global event began in 2014 and is unprecedented in scale. Rising global temperatures and a strong El Nino have combined to make it the longest and most widespread bleaching event ever recorded.
Since the event began, coral reefs in Hawaii, Guam, the Commonwealth of the Northern Mariana Islands, Florida Keys, Puerto Rico and the Virgin Islands have seen above normal temperatures with more than 70 percent of them now at risk of bleaching.
NOAA scientists made the announcement during the 13th International Coral reef Symposium in Honolulu, Hawaii, which runs through this week. The goal of the meeting is to turn scientific findings about coral reefs into effective policy.
When corals bleach, it’s more difficult for them to feed and can lead to their deaths. But corals are resilient organisms. If ocean temperatures return to normal levels relatively quickly and local stressors like wastewater runoff and fishing are kept to a minimum, corals have a better chance of recovering.
Viktor Brandtneris, a coral reef researcher at the University of the Virgin Islands, explained that the best models suggest a La Nina could happen this year. That could mean warmer ocean temperatures in the Caribbean and western Pacific.
“But we don’t know exactly when that switch will happen, so sometime this year or next there’s a reasonable likelihood that we’ll see warm water and possibly bleaching in the Caribbean and Virgin Islands,” Brandtneris said.
Brandtneris, who is attending the symposium in Hawaii, said a number of factors could impact where, when and how strong the bleaching event could be, since things like hurricanes and big rain events can ease thermal stress when ocean temperatures get too hot.
“Ultimately we’re just in a wait-and-see mode,” Brandtneris said. “If things start to ramp up we’ll be ready to go for bleaching monitoring as part of the territorial coral reef monitoring program.”
Following the 2005 and 2010 bleaching events, the territory lost between 50 and 70 percent of its shallow-water corals, while only 5 to ten percent of corals in water deeper than 100 feet died off, Brandtneris said.
Depth and distance from shore greatly affect how corals fare when oceans warm. Reefs in shallow water and near the shore are subject to higher temperatures and other stressors, such as runoff.
“NOAA’s satellite and climate models provide us with the ability to track the high temperatures that are causing this bleaching and alert resource managers and scientists around the world,” said C. Mark Eakin, NOAA’s Coral Reef Watch coordinator.
Because bleached reefs can recover, scientists agree it’s important to reduce over-nutrified local runoff like nitrogen from poorly constructed decentralized wastewater treatment systems, which is relatively common in the territory. Limiting heavy fishing and tourism near struggling reefs can also help.
Effective management can help limit local stressors, but the threat of warming ocean temperatures is a global issue.
“It’s time to shift this conversation to what can be done to conserve these amazing organisms in the face of this unprecedented global bleaching event,” said Jennifer Koss, NOAA’s Coral Reef Conservation Program director. “We have boots on the ground and fins in the water to reduce local stressors.”
Koss added that, “Local conservation buys us time, but it isn’t enough. Globally, we need to better understand what actions we all can take to combat the effects of climate change."