Corals die off the coast of Miami. Why? Due to a 16-month project to expand the port channel. A new study shows how the project killed over half a million coral between 2013 and 2015.
The study, published in the journal Marine Pollution Bulletin Thursday, included observations of the corals on site in conjunction with satellite imagery to see how much sedimentation the dredging of the project threw itself into the water – and how all of that sediment ended up affected the health of corals. The authors found that nearly 2,000 pounds of sediment suffocated the reefs about one and a half miles from the site of dredging.
"If we want to preserve these ecosystems for future generations It is important that we do everything we can to preserve the remaining coral. "
The authors found that up to 74 percent of the coral near the canal died in the months following the start of dredging the shipping channel. Even two years later, the researchers found that the coral density had suffered from sedimentation at a distance of 65 feet from the canal.
Corals are quite fragile organisms. If the water gets too warm, they may begin to die if they expel the algae they need for food production. Too much acid in the water (as a result of carbon dioxide) and coral become weaker and can shrink. As sand and sediment accumulate on corals, they lose access to light, which helps their algae to produce food, and they can use a lot of energy to remove all of this sediment. In short, all these things can kill corals that are already dying in masses around the world because of climate change.
"If we want to preserve these ecosystems for future generations, it is imperative that we do everything we can to preserve the remaining coral," said lead author Andrew Baker, associate professor of marine biology and ecology at the University of Miami, in a scientific publication. "These climate survivors may have the key to understanding how some corals can survive global change."
In Miami, the study found that more than 560,000 coral were killed in the immediate vicinity of the excavator. The authors were able to see where the sediment clouds hit satellite images to estimate the distance of the impact. It turned out that they probably felt more than ten kilometers from the place where the dredging had taken place. Before the start of the project, only one coral had been identified as partially spilled by sediments. After the project, the reefs were completely redesigned.
An independent consulting firm commissioned by the Port of Miami and the Army Corps of Engineers to carry out environmental monitoring for the project previously reported the death of mass corals as an outbreak. However, this study controlled this and investigated how corals closest to dredging developed during this period. The results of the study contradict the findings of the consulting firm and have shown that satellite images, on-site observations and sediment data are the cause of the harmful corals.
"It was important to differentiate these multiple impacts on the reefs to understand the direct effects of dredging," said senior author Ross Cunning, a research biologist at the Shedd Aquarium in Chicago, in the press release. "We have combined all available data from satellites, sediment traps and hundreds of underwater surveys. Taken together, the numerous independent data sets clearly show that dredging has caused the greatest damage to these reefs.
The results are heartbreaking: the endangered staghorn coral protected under the Endangered Species Act was one of those affected. So is Elkhorn coral, another endangered species. These corals need all the protection they can get. And development projects that kill them certainly do not help the threats they are already exposed to from the warming of the oceans.