Underwater erosion could affect corals

Sea floor erosion is contributing to the declining health of the coral reefs in some areas, according to a new study recently released from the United States Geological Survey.

In the first ecosystemwide study of changing sea depths at five large coral reef tracts in Florida, the Caribbean and Hawaii, U.S. Geological Survey researchers found the sea floor is eroding in all five places, and the reefs cannot keep pace with sea level rise. As a result, coastal communities protected by the reefs are facing increased risks from storms, waves and erosion.

“Our measurements show that seafloor erosion has already caused water depths to increase to levels not predicted to occur until near the year 2100,” said biogeochemist Kimberly Yates of the USGS’ St. Petersburg Coastal and Marine Science Center, the study’s lead author. “At current rates, by 2100 sea floor erosion could increase water depths by two to eight times more than what has been predicted from sea level rise alone.”

In the Florida Keys, the U.S. Virgin Islands and Maui, coral reef degradation has caused sea floor depths to increase as sand and other sea floor materials have eroded over the past few decades, the USGS study found. In the waters around Maui, the sea floor losses amounted to 81 million cubic meters of sand, rock and other material – about what it would take to fill up the Empire State Building 81 times, the researchers calculated.

The team found that overall, sea floor elevation has decreased at all five sites, in amounts ranging from 0.09 meters to 0.8 meters. All five reef tracts also lost large amounts of coral, sand, and other sea floor materials to erosion.

“We saw lower rates of erosion—and even some localized increases in seafloor elevation—in areas that were protected, near refuges, or distant from human population centers,” Yates said. “But these were not significant enough to offset the ecosystem-wide pattern of erosion at each of our study sites.”

Worldwide, more than 200 million people live in coastal communities protected by coral reefs, which serve as natural barriers against storms, waves and erosion. These ecosystems also support jobs, provide about one-quarter of all fish harvests in the tropical oceans, and are important recreation and tourism sites.

“Coral reef systems have long been recognized for their important economic and ecological value,” said John Haines, Program Coordinator of the USGS Coastal and Marine Geology Program. “This study tells us that they have a critical role in building and sustaining the physical structure of the coastal seafloor, which supports healthy ecosystems and protects coastal communities. These important ecosystem services may be lost by the end of this century, and nearby communities may need to find ways to compensate for these losses.”

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