Broward County

Climate change shrinking South Florida reefs sooner than expected

In 1976, staghorn coral grew thick on the Carysfort reef east of Key Largo. By 2016, the same area was sandy bottom.
In 1976, staghorn coral grew thick on the Carysfort reef east of Key Largo. By 2016, the same area was sandy bottom. University of Miami Rosenstiel School of Marine and Atmospheric Research

South Florida’s shrinking reefs may be vanishing faster than expected.

In a new study published Monday in the journal Global Biogeochemical Cycles, researchers found that climate-related coral erosion projected to start between 2050 and 2060 has already started near Miami. The situation is better moving south and away from Miami’s dense coast, where pollution may be worsening conditions. But researchers say Miami could serve as a glimpse of things to come for the Florida reef tract.

“We tend to think we have a lot of time and this study shows we have maybe 30 years less time,” said lead author Chris Langdon, a University of Miami marine biologist. “We need to get serious sooner rather than later.”

Monday’s report comes just days after another study concluded a reef tract near Miami took a hit from another unlikely threat: the U.S. government.

In its first assessment of a $205 million dredging of PortMiami, the National Marine Fisheries Service last week concluded that sediment stirred up by the work smothered and killed many of the coral near the Government Cut channel. The report contradicts findings earlier this year by the U.S. Corps of Engineers, which managed the project and blamed the deaths for an outbreak of white plague disease.

The findings follow months of warnings from NMFS and environmentalists, including the Miami Waterkeeper, that dredging the channel to 50 feet, and then barging that sediment to an offshore dump site, was spreading a plume of sand damaging far more coral than anticipated, including some threatened species.

NMFS divers surveyed more than 165 acres north of the channel that was hardest hit by the work and found sediment on about 158 acres, the report said. Sand piled up on more than six acres so thickly that the habitat is no longer functioning as a reef and likely won’t until the sand is removed. Divers also found severe to moderate damage from sediment on about 120 more acres.

Corps officials, however, defended their assessment that included over 7,000 dives covering 252 acres and concluded white plague, not dredging work, killed 85 percent of the coral.

The Corps “performed significant mitigation for the Miami Harbor deepening up-front and also during the project. Those efforts have been very successful and will lead to a net increase in the amount of listed staghorn coral colonies and seagrass beds,” spokeswoman Susan Jackson said in an email. “Completed mitigation features of the project include the creation of 17 acres of new seagrass beds and more than 11 acres of new artificial reef with thousands of coral relocations.”

In environmental circles, the debate over damage has sometimes turned bitter, with the Waterkeepers suing over management of the project and Corps’ contractors crying foul. Ecologist Bill Precht, who supervised the Corps’ assessment, plans on making a presentation later this month at a Coconut Grove restaurant to debunk what he described in an email as “dramatic statements by project opponents.”

Florida’s reef tract once stretched from the Dry Tortugas north to Palm Beach County but has shrunk to just a fraction of that historic range, pounded by pollution, over-fishing and damage from anchors.

A year ago, National Oceanic and Atmospheric Science researchers warned that warming temperatures could cause an increase in bleaching events for the region a dozen years sooner than expected.

Langdon’s findings are even more alarming: Fowey Rocks, a popular dive spot in Biscayne National Park off Key Biscayne, is disappearing today, he said.

Typically reefs flourish in the summertime, when temperatures rise and plants grow, soaking up carbon making conditions just right for tropical coral to grow. In winter, the opposite can happen. Langdon said. Seagrass and other marine life dies, putting carbon back into the water. Historically, summer growth outpaced winter die-offs. But increasing acidification is expected to start slowing summer growth and worsening winter erosion.

Langdon’s team found patterns both seasonal and geographic. Reefs closer to Miami’s polluted coast did the worst with reefs getting progressively better heading south. That trend may reflect pollution, he said, as well as its unique position: most reefs are tropical and South Florida’s set on a gradient range of sub-tropical.

The study also found that transplanting corals or finding hardier species won’t be enough to protect a $7.6 billion asset estimated at creating 70,000 South Florida jobs.

“Those will have short-term benefits. But if the reef framework is dissolving under them, that’s not going to be a solution. So we really need to get serious about the carbon solution,” he said. “We have a real financial stake in trying to keep this ecosystem healthy.”

An earlier version of this story misstated the number of jobs supported by coral reefs in South Florida and Bill Precht’s position on the Corps’ reef assessment.