Historical nautical charts show true extent of reef loss in Florida

By on 7 September, 2017

 

Nautical chart from the Florida Keys, 1775. Image source: the authors.

 

Researchers at UQ and Colby College have been using historical nautical charts, originally intended for seafaring navigation, to study reef loss in the Florida Keys.

A new US and Australian study – including research from The University of Queensland and the Australian Research Council Centre of Excellence in Coral Reef Studies –compared early British charts to modern coral habitat maps to understand changes to reef environments.

UQ’s Professor John Pandolfi said the study used information from surprisingly accurate 18th century nautical charts and satellite data to understand coral loss over more than two centuries in the Florida Keys.

“We found that some reefs had completely disappeared,” Professor Pandolfi said.

The study was led by Loren McClenachan, Assistant Professor at Colby College, in Waterville, Maine, USA.

The team obtained nautical charts dating to 1773 from UK Hydrographic Office archives for the study. The charts contain a wealth of information in addition to depth, including substrate type and descriptions of the ecology. From these charts, the scientists were able to reconstruct a picture of the reefs of the Florida Keys prior to the large-scale detrimental effects of European settlement and industrialisation.

Professor McClenachan said more than half of the coral reef habitat mapped in the 1770s was no longer there. In some areas, particularly near land, coral loss was closer to 90 per cent.

“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,” she said.

This estimate of change over centuries is an important contribution to the study of reef conservation. While most studies look more closely at the loss of living coral from smaller sections of the reef, these marine scientists measured the loss of coral reef habitats across a large geographic area. The study also offers a temporal component that is otherwise only available from more expensive and time consuming methods, such as obtaining drill core.

“We found that reef used to exist in areas that today are not even classified as reef habitat anymore,” Professor Pandolfi said.

“When you add this to the 75 per cent loss of living coral in the Keys at that finer scale, the magnitude of change is much greater than anyone thought.”

This work was undertaken while Professor McClenachan was a visiting researcher in Professor Pandolfi’s lab at UQ’s School of Biological Sciences in Brisbane, Australia, while on sabbatical from Colby College.

The research revealed the precision of the early maps. Postdoctoral researcher at the Bigelow Laboratory for Ocean Sciences in East Boothbay, Maine Dr Benjamin Neal said the early chart makers represented the “Silicon Valley of their time”.

Compared to nautical charts from the century following, these 18th Century charts are much more detailed. In many cases the cartographer included information such as the depth, shape, and colour of the shallow water corals, and distinguishes them from other hard surfaces such as rocks.

“The maps were essential to expansion of the British Empire, and luckily for us, they also included a lot of useful ecological information.”

Professor McClenachan said the findings had important conservation implications and pointed to a shifted spatial baseline.

“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?” she said.

The authors said when large-scale changes like this were overlooked, scientists could lose sight of past abundance, lowering expectations for conservation and recovery.

The study, which also involved authors from Columbia University, National Museum of Natural History, Smithsonian Institution and the University of California San Diego, all in the U.S.,  is published in Science Advances (doi: 10.1126/sciadv.1603155)

 

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