In search of the last refuges of coral biodiversity
The goal of the PRISTINE project, led by an international team of marine biologists, is to conduct an unprecedented survey of marine biodiversity in the last coral reefs in the South Pacific that are untouched, or virtually untouched, by human impact.
Laurent Vigliola, Research Institute for Development (IRD) and David Mouillot, University of Montpellier
After an initial oceanographic campaign on the Astrolabe Reefs in New Caledonia, scientists explored the Acteon Islands in Polynesia, the Minerva Reefs in Tonga, and then the Entrecasteaux, Petri, and Chesterfields Reefs in New Caledonia. The results of this study of some of the most isolated reefs on the planet were presented in Nouméa at the end of February 2016. They are enlightening.
Knowing the original state of an ecosystem
In science, and in ecology in particular, understanding the evolution of a marine ecosystem and assessing the impact of human activity or natural disturbances requires knowledge of the ecosystem's original state. This knowledge takes the form of benchmarks for comparative studies. Reports by naturalists written before the20th century, such as those by James Cook, are too few and too vague to allow for a scientific assessment of the degradation of today's coral ecosystems. For most of them, the pristine state no longer exists, with many areas being exploited by fishing, for example. The reference states are therefore mostly derived from marine reserves, established to meet the objectives of protecting and restoring ecosystems.
However, are these reserves large enough, old enough, and well-preserved enough to be used as a reference? And if not, what objectives should be set for managers wishing to achieve a genuine reference state, without human impact? This is the context for the PRISTINE project: to redefine the reference state of coral systems in different Pacific countries by sampling the most remote areas. These data will provide a benchmark for assessing anthropogenic impacts, as well as the effectiveness of marine reserves. The sites chosen are therefore isolated, uninhabited, and unexploited: here, human impact has been minimal.
The discovery of an unexpected heritage
During expeditions to the isolated reefs of New Caledonia, Tonga, and French Polynesia, biologists encountered a wealth of marine life: sharks, groupers, tuna, napoleon fish, humphead parrotfish... species that are usually very rare but particularly abundant in these areas.
L. Vigliola/IRD, Author provided
87% of dives resulted in shark sightings, compared to an average of 17% on Pacific reefs frequented by humans, 0% outside reserves near large cities, 6% in urban reserves, 15% in small rural reserves, and 55% in strictly protected reserves. Beyond this specific example, scientists from the PRISTINE project have revealed the unaltered functional structure of remote Pacific reefs, indicating that only large no-take reserves can restore the fauna that ensures the "natural" functioning of coral ecosystems.
At a safe distance
After sailing for 40 hours on the open sea aboard an oceanographic vessel to reach the Chesterfields Reefs, halfway between Australia's Great Barrier Reef and New Caledonia's Grande Terre, scientists realized that the travel time for human populations, rather than the simple distance as the crow flies, could be used to measure the degree of reef degradation. Using a new method to estimate the travel time between reefs and human settlements, scientists have revealed the existence of thresholds below which reefs are severely degraded, and above which they reach reference levels.
For example, fish abundance falls by 44% in peri-urban areas compared to isolated reefs, but recovers after a travel time of 6.5 hours. The presence of large predators declines by 69% but recovers after a travel time of 12 hours. For sharks, the decline is 90%. As for functional diversity—that is, the diversity of roles performed by species for the proper functioning of the ecosystem—the decline is 61%; recovery is only visible after 4:30 p.m. travel time. The baseline appears to be around 20 hours. At such a distance, it would seem that the reefs have, for the time being, been relatively spared from human activities such as fishing... even if this isolation offers no protection against global phenomena such as climate change.
L. Vigliola/IRD, Author provided
First global map of reef accessibility
Are there many of these reference reefs? Where are they located? To answer this question, scientists working on the PRISTINE project calculated the travel time between reefs and human populations for all of the world's coral reefs. The study thus provides the first global map of accessibility. The first finding, which came as a surprise, is that reefs are closer to human activities than previously thought. More than half of the world's coral reefs are located less than 30 minutes away from humans. This close coexistence is easily explained: human communities have always tended to colonize these resource-rich sites.
Reefs located more than 20 hours away are very rare, representing only 1.5% of the world's reefs. This is the other major finding of the study: the rarity of these "remnants of the past." These last refuges for marine wildlife are mainly found in the middle of the Indian Ocean and in the Pacific, particularly off the coast of New Caledonia. This archipelago is home to one-third of the planet's isolated reefs. This highlights the responsibility of New Caledonians and France to protect these areas located in the heart of the Mer de Corail Natural Park, one of the largest protected areas in the world.
L. Vigliola/IRD, Author provided
A reservoir of biodiversity, coral ecosystems are currently in decline. The latest balance sheets The scientific findings are alarming, with 75% of the world's reefs currently under threat, 60% of which are under direct and immediate threat, and 100% by 2050. Yet these unique ecosystems directly provide for the food (fishing) and economic (tourism) needs of a large part of the island populations. They offer physical protection from the elements, with reef barriers making many islands habitable.
Coral reefs are also a mythical paradise and a major economic resource: Australia's Great Barrier Reef alone generates nearly €1 billion in revenue for the tourism sector. The conservation and sustainable use of this natural heritage requires an accurate assessment of its condition, which is what the PRISTINE project has set out to do. The project shows that most coral reefs are on a downward trajectory; only a very few reefs are virtually intact. It is now essential to take strong protective measures on a global scale—going well beyond Aichi targets – before it's too late.
Laurent Vigliola, Researcher, Research Institute for Development (IRD) and David Mouillot, Professor of Ecology, MARBEC Laboratory, University of Montpellier
The original version of this article was published on The Conversation.