Nautical charts mapped in the 18th century are showing modern researchers just how much coral has been lost around the world.
A new U.S. and Australian study has compared early British navigation charts to modern coral habitat maps to determine what changes have taken place over the past three centuries.
The study was led by Professor Loren McClenachan of Colby College in Waterville, Maine, with assistance from the University of Queensland (UQ) in Australia and the Australian Research Council Centre of Excellence in Coral Reef Studies.
Professor John Pandolfi of UQ said that the study used information from “surprisingly accurate” 18th century nautical charts and satellite data to understand coral loss in the Florida Keys.
Professor McClenachan said that more than half of the coral reef habitat mapped in the 1770s was no longer there. In some areas, coral loss was close to 90 percent.
“We found near the shore, entire sections of reef are gone, but in contrast, most coral mapped further from land is still coral reef habitat today,” McClenachan said.
This is one of the first studies where marine scientists have measured the loss of coral reef habitats over a large geographic area. Most studies look more closely at the loss of living coral from smaller sections of reefs.
“We found that reef used to exist in areas that today are not even classified as reef habitat anymore,” Pandolfi said. “When you add to this the 75 percent loss of living coral in the Keys at that finer scale, the magnitude of change is much greater than anyone thought.”
Dr. Benjamin Neal of the Bigelow Laboratory for Ocean Sciences in East Boothbay, Maine, said that the early maps were remarkably precise.
“They had the best technology and they used it to create new information that conferred a lot of power,” Neal said. “The maps were essential to expansion of the British Empire, and luckily for us, they also included a lot of useful ecological information.”
This research has important conservation implications. As the authors said, when large-scale changes like this were overlooked, scientists could miss out on information about past abundance.
“We tend to focus on known areas where we can measure change. That makes sense. Why would you look for coral where you never knew it was?” McClenachan said.