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As much of the world grapples with historic heat waves exacerbated by climate change and the ongoing El Nino event, ocean temperatures are also on the rise.


Coral showing signs of bleaching
Boulder star coral about 15 feet deep near the shore of Key West, Florida water are bleaching due to recent extreme water temperatures. Photo take July 18, 2023, by Lauren Toth, USGS.

U.S. Geological Survey experts recently captured images showing how the high water temperatures are impacting one of the most important building blocks of underwater ecosystems: coral.

Coral provide shelter for many marine species and directly support most of Florida’s multibillion dollar recreation and fishing industries. They also provide coastal communities shoreline protection from storms and waves by helping to break up waves and dissipate energy.

Coral are vulnerable to high water temperatures and as temperatures increase coral can become stressed, often resulting in them expelling the colorful algae that live within them in a process known as coral bleaching. While this desperate act protects the coral in the short term, it is detrimental to the coral’s long-term survival because most coral species obtain more than 75% of their nutrients from the symbiotic relationship they share with algae.

From the Florida Keys to Dry Tortugas National Park in the Gulf of Mexico, USGS scientists have recently observed many coral communities are currently experiencing unprecedented bleaching events due to extreme water temperatures.

“What’s most concerning about this bleaching is the fact it’s happening much sooner in the season than what’s normal,” said Lauren Toth, a USGS research physical scientist and coral expert. “We typically see bleaching events toward the end of summer. The cooler water temperatures in the fall can help coral survive late summer bleaching. However, with this bleaching occurring almost two months before what’s typical it’s unlikely some of these coral will be able to survive unless the waters cool off soon.”

Coral showing signs of bleaching
A colony of fire coral about 5 feet underwater in Dry Tortugas National Park in the Gulf of Mexico shows signs of bleaching from recent extreme water temperatures. Photo taken July 26, 2023, by Lauren Toth, USGS.



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