Scientists have found that a large dredging project at the port of Miami killed more than half-a-million corals from 2013 to 2015, devastating the only nearshore coral reef in the continental United States. Sediment kicked up by the project buried up to 90 percent of nearby reefs, with the impacts felt as far as 15 miles away, according to a new study published in the journal Marine Pollution Bulletin.
The mass coral death in southeast Florida was previously attributed to a region-wide outbreak of coral disease that occurred at the same time as the $220 million PortMiami project, which widened and deepened the city’s shipping channel to allow larger container vessels to enter the harbor. But a team of researchers, led by scientists at the University of Miami, examined data collected by the port project’s environmental consultants. They found that many of the coral species that died were not susceptible to the disease, and that the closer susceptible corals were to the dredging site, the more likely they were to perish.
Sediment can affect nearly every biological function of corals, from reducing feeding activity to impairing spawning and fertilization. Sedimentation also forces corals to expend energy reserves to remove sediment, and it covers up the hard substrate that coral settle on.
“This study provides a clear and scientifically robust estimate of the impact of this dredging project on Miami’s coral reef resources,” Rachel Silverstein, executive director of Miami Waterkeeper and a co-author of the study, said in a statement. “It tells a devastating story of loss that we cannot afford to ignore any longer.”
Florida’s reef tract has declined by at least 70 percent since the 1970s. Staghorn corals specifically have declined 98 percent. The reef adjacent to the PortMiami project is designated as “critical habitat” under the U.S. Endangered Species Act, as well as “essential fish habitat” for threatened species such as spiny lobster, snapper, and grouper. In all, the PortMiami project dredged more than 148 million cubic feet of material from the harbor, with sediment plumes covering 88 square miles.
The scientists noted that similar dredging projects are happening across the globe as shallow-water ports race to accommodate the larger cargo ships that came into service following the expansion of the Panama canal in 2016. Understanding the impacts of such ventures on already fragile coral reef ecosystems is a “key conservation goal in light of continued dredging activities,” they wrote in the study.