In 2013, when the Army Corps of Engineers dredged sediment out of the Port of Miami and transported it out to sea, they said the process would have minimal impacts on the reef around the port. But new evidence suggests the dredging may have killed many of the corals that provide the city with natural protection from storm surges.

Many ports along the US Eastern Seaboard are preparing to accommodate larger container ships that will soon pass through a widened Panama Canal. Port Miami was the first port in Florida to undergo a deepening and widening project in order to accept these new ships fully laden.

But unlike other ports, the Port of Miami boasts an unusual and, in this era of sea level rise, important feature: a coral reef just offshore. And despite the assurances of Corps engineers, the project may have done serious damage to this fragile ecosystem.

In December, divers from the southeast fisheries division of the National Oceanic and Atmospheric Administration assessed the impact of the dredging on a particular area of reef.

“We surveyed nine sites north of the channel that were expected to see the greatest impacts, and we were looking at sedimentation as well as any sort of signs of impacts to corals, coral reefs or other species on the reef,” says Andy Strelcheck, the deputy regional administrator.

The NOAA divers found that sediment depths “were greatest nearest the channel where the dredging was occurring and there was mortality of corals associated with sedimentation that occurred over a fairly broad area,” Strelcheck says.

Corals buried by sediment near Port Miami Credit: Miami Waterkeeper

Corals are animals and they can suffocate when covered up by sand, rock, and silt. The NOAA scuba divers found that hundreds of acres of reef had been buried in dredging sediment. At one site as much as 80 percent of the reef was impacted.

A December report commissioned by the Army Corps stated that a bleaching event had been the primary cause of death for corals in Miami. But Rachel Silverstein, head of the Miami Waterkeeper, says the report was an attempt to downplay the role of the port expansion project. “There was bleaching and disease going on the region, but it didn’t explain how corals became buried in half a foot of sediment,” Silverstein notes.

A big part of Silverstein’s job at Miami Waterkeeper is to fight for the protection of the coral reef off the coast of South Florida. Already, the reef has declined by more than 80 percent since the 1970s, she says.

Multiple factors have contributed to that decline, from climate change and ocean acidification to agricultural runoff and disease. But coastal development is also playing a role.

NOAA’S Andy Strelcheck says that he wants to finish surveying other areas around the port and work with the Army Corps of Engineers to begin reef restoration. But Rachel Silverstein also wants to make sure the Corps doesn’t repeat its mistakes. A similar port expansion project is scheduled to begin in Fort Lauderdale next year.

“So far, the Army Corps has made promises that they won’t let the same thing happen again in Fort Lauderdale, but the documents that they’ve sent to Congress to support the authorization of this project were not one bit updated to account for what we know happened at Port Miami,” Silverstein warns.

Miami and Fort Lauderdale are two of the US cities most vulnerable to sea level rise from climate change, and reefs provide natural protection that could help them cope with increased flooding.

“These reefs that were destroyed are directly offshore of the city of Miami Beach, and they were protecting the coastline of the city of Miami Beach at the same time the city is spending hundreds of millions of dollars trying to pump the Atlantic Ocean off of its streets,” Silverstein says.

But she sees a value in South Florida's reefs that goes beyond the protection that they offer.

“This is the only coral reef in the continental United States,” Silverstein explains. "It’s as rare and unique as the geysers of Wyoming or the sequoias or the redwoods in California. I think it deserves the same level of attention and the same level of protection from our government and the public.”

This article is based on a story that aired on PRI’s Living on Earth with Steve Curwood.