Historical nautical maps show coral loss more extensive than previously believed – “The magnitude of change is much greater than anyone thought”

By Mike Gaworecki
20 September 2017
(Mongabay) – A team of researchers based in Australia and the United States have used historical nautical maps to determine that coral reef loss in the Florida Keys is much more extensive than previously understood.
The British empire began mapping its overseas territories in the 18th century, and coral reefs in particular were quite thoroughly documented given the danger they posed to wooden-hulled ships. In the process, these imperial cartographers unwittingly provided a source of high-resolution spatial data on coastal areas that, as it turns out, can still be useful today in establishing historical baselines for the extent of coral reefs and assessing changes to those reef systems over the ensuing centuries.“The degree of biologically relevant information recorded varied by cartographer, but the best of these British maps describes the depth, shape, and color of shallow-water corals and distinguishes them from other hard structures such as rocks,” the authors of a study published in the journal Science Advances earlier this month wrote. The researchers used nautical charts dating from the 1770s to help quantify changes in the coral reefs of the Florida Keys over the past 240 years.“The maps were essential to expansion of the British Empire, and luckily for us, they also included a lot of useful ecological information,” according to Benjamin Neal, a postdoctoral researcher at the Bigelow Laboratory for Ocean Sciences in East Boothbay, Maine and a co-author of the study. [more]

Historical nautical maps show coral loss more extensive than previously believed

7 September 2017 (UQ News) – Centuries-old nautical charts, mapped by long-deceased sailors to avoid shipwrecks, have been used by modern scientists to study loss of coral reefs.

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 Professor Loren McClenachan, Assistant Professor at Colby College, in Waterville, Maine, USA.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 close 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 added to modern observations of recent loss of living corals.The marine scientists measured the loss of coral reef habitats across a large geographic area, while most studies look more closely at the loss of living coral from smaller sections of the reef.“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”.“They had the best technology and they used it to create new information that conferred a lot of power,” Dr. 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.”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 US, was published in Science Advances (doi: 10.1126/sciadv.1603155)

Contact

Professor John Pandolfi, j.pandolfi@uq.edu.au, +61 7 3365 3050, @JohnPandolfi, @CoralCoE; Professor Loren McClenachan, lemcclen@colby.edu,  Cell: 1 207 509 4419, @LMcClenachan, @Colby.

Eighteenth century nautical charts reveal coral loss

ABSTRACT: Massive declines in population abundances of marine animals have been documented over century-long time scales. However, analogous loss of spatial extent of habitat-forming organisms is less well known because georeferenced data are rare over long time scales, particularly in subtidal, tropical marine regions. We use high-resolution historical nautical charts to quantify changes to benthic structure over 240 years in the Florida Keys, finding an overall loss of 52% (SE, 6.4%) of the area of the seafloor occupied by corals. We find a strong spatial dimension to this decline; the spatial extent of coral in Florida Bay and nearshore declined by 87.5% (SE, 7.2%) and 68.8% (SE, 7.5%), respectively, whereas that of offshore areas of coral remained largely intact. These estimates add to finer-scale loss in live coral cover exceeding 90% in some locations in recent decades. The near-complete elimination of the spatial coverage of nearshore coral represents an underappreciated spatial component of the shifting baseline syndrome, with important lessons for other species and ecosystems. That is, modern surveys are typically designed to assess change only within the species’ known, extant range. For species ranging from corals to sea turtles, this approach may overlook spatial loss over longer time frames, resulting in both overly optimistic views of their current conservation status and underestimates of their restoration potential.

Ghost reefs: Nautical charts document large spatial scale of coral reef loss over 240 years