By Derek Manzello
As a research oceanographer with the National Oceanic and Atmospheric Administration in Miami, Manzello discusses how ocean acidification and changes in water temperature are threatening coral reef ecosystems.
MIAMI -- Reef-building corals that create the structures well-known to divers and snorkelers live very near their upper temperature limits. Small increases in temperature during summer months can cause coral to expel an algae that is vital to their survival.
This process is known as coral bleaching, because it turns corals -- that are usually vibrant in color -- stark white. Not a single coral reef region on the planet has escaped the impact of warn water bleaching. And the incidents have increased dramatically over the past 30 years.
The Florida Keys are no exception. There have been five widespread, warm-water bleaching events spanning the entire region from 1987 to 2005. By the end of July 2014, it was clear that Florida's coral reefs were in danger of yet another event.
Long-term temperature data collected offshore of Key Largo, near Molasses Reef, show this summer was the warmest on record. And this year's bleaching event may be the worst ever in the Florida Keys.
Because warm water impairs coral immune systems, the incidence of disease was already elevated throughout the Keys.
For instance, during a recent field survey, scientists noted many coral colonies had black-band disease. It appears as narrow, black line attacking healthy tissue, and then leaves the dead skeleton behind. Disease outbreaks are a major cause of coral decline across the Caribbean.
It can take corals several months to recover from a bleached state if the heat-stress does not persist for too long. But even if they survive and recover, they will suffer depressed growth, reduced reproductive ability, and remain prone to disease for a few years.
Elkhorn and Staghorn coral once dominated shallow coral reef environments across the Caribbean, but now are only rarely found.
While the implications of climate change continue to be studied, coral reefs around the globe and in our own backyard are, and have been, suffering the consequences of an increasingly "hot and sour" ocean.
Since the industrial revolution, the oceans have absorbed between one-quarter to one-third of all carbon dioxide released into the atmosphere. This uptake causes ocean acidification.
Scientists were taking surveys to determine the extent of the bleaching and will be documenting incidence of disease and mortality when the heat-stress subsides. This will take several months.
"With future warming of the planet, coral bleaching will likely represent the single greatest threat to the continued existence of coral reefs over this century."