A 16-month dredging project in the Port of Miami may have resulted in the death of over half a million corals despite environmental reports saying otherwise, according to a new study published in Marine Pollution Bulletin.

The “devastating story of loss” was told by researchers at the University of Miami who reanalyzed multiple independent data from satellites, sediment traps, and underwater surveys originally collected by consultants under an environmental monitoring program. Initial findings indicated that widespread loss of coral was attributed to the outbreak of coral disease at the same time. However, when controlling for the impacts of bleaching and disease loss, researchers found that corals near the dredge site were more likely to die than those further away.

Areas closer to dredging saw higher build-ups of sediment coverage. So much so, that divers measured sediment burying between 50 percent and up to 90 percent of nearby reefs, hindering corals’ ability to feed, reproduce, and attach to a hard substrate, causing widespread coral death.

“Coral reefs worldwide are facing severe declines from climate change,” said study author Andrew Baker in a statement. “If we want to conserve these ecosystems for the generations that come after us, it’s essential that we do all we can to conserve the corals we still have left. These climate survivors may hold the key to understanding how some corals can survive global changes. We have to start locally by doing all we can to protect our remaining corals from impacts, like dredging, that we have the ability to control or prevent.” 

Researchers also observed that satellite images of suspended sediment, known collectively as sediment plumes, were highly correlated with negative impacts on the seafloor as a result of dredging.

“This connection allowed us to predict impacts beyond where ship-based monitoring was taking place, and showed that dredging likely damaged this reef several kilometers away,” said study co-author Brian Barnes. “While this same relationship may not apply in all projects, this is a remarkable finding that further establishes Earth-observing satellites as independent monitoring tools to fill in gaps where data are otherwise not available.”

Port of Miami’s shipping channel bisects the Florida Reef Tract, the only nearshore coral reef in the continental US. It is surrounded by areas designated under the Endangered Species Act as critical habitat for hundreds of colonies of endangered shallow-water staghorn and elkhorn corals, some of which have declined by as much as 98 percent. As dredging continues across the world, the researchers suggest that associated activities could threaten the livelihood of fragile coral systems and result in widespread decline.