In Search of the Last Refuges of Coral Biodiversity
To conduct a comprehensive survey of marine biodiversity in the last remaining coral reefs in the South Pacific that are untouched or virtually untouched by human activity: this is the goal of the PRISTINE project, led by an international team of marine biologists.
Laurent Vigliola, French National Research Institute for Sustainable Development (IRD) and David Mouillot, University of Montpellier
Following an initial oceanographic expedition to the Astrolabe Reefs in New Caledonia, scientists explored the Actéon Islands in Polynesia, the Minerve Reefs in Tonga, and then the Entrecasteaux, Pétri, 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 in late February 2016. They are enlightening.
Understanding 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 is then used to create reference points for comparative studies. Reports by naturalists compiled before the20th century, such as those by James Cook, are too few in number and lack sufficient detail to allow for a scientific assessment of the degradation of today’s coral ecosystems. For most of them, the pristine state no longer exists, as many areas are exploited by fishing, for example. Reference states therefore mostly come from marine reserves, established to meet ecosystem protection and restoration objectives.
Are these reserves, however, large enough, old enough, and well-preserved enough to serve as a reference? And if not, what objectives should be provided to managers seeking to achieve an authentic reference state, free from human impact? This is the context of the PRISTINE project: redefining the reference state of coral reef systems in various Pacific nations by sampling the most remote sites. These data will provide a benchmark for assessing anthropogenic impacts, as well as the effectiveness of marine reserves. The selected sites are therefore isolated, uninhabited, and unexploited: here, human impact has been minimal.
The discovery of an unexpected heritage
During expeditions to the remote reefs of New Caledonia, Tonga, and French Polynesia, biologists were treated to a wealth of marine life: sharks, groupers, tuna, wrasse, humphead parrotfish… all species that are usually very rare but are particularly abundant here.
L. Vigliola/IRD, Author provided
Sharks were observed in 87% of dives, compared to an average of 17% on human-visited Pacific reefs, 0% outside reserves near major cities, 6% in urban reserves, 15% in small rural reserves, and 55% in strictly protected reserves where access is prohibited. 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 a fauna capable of ensuring 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 Chesterfield Reefs, located halfway between Australia’s Great Barrier Reef and Grande Terre in New Caledonia, scientists realized that travel time for human populations—rather than simply the distance as the crow flies—could serve as a measure of the degree of reef degradation. Using a new method to estimate travel time between reefs and human settlements, scientists revealed the existence of thresholds below which reefs are severely degraded, and above which they reach baseline levels.
Thus, fish abundance drops by 44% in peri-urban areas compared to isolated reefs; it recovers once travel time exceeds 6.5 hours. The presence of large predators declines by 69% and recovers once travel time exceeds 12 hours. For sharks, this decline is 90%. As for functional diversity—that is, the diversity of roles played by species for the proper functioning of the ecosystem—the decline is 61%; recovery is only visible after 16.5 hours of travel time. The baseline condition appears to be established at 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, Photo courtesy of the author
First global map of reef accessibility
Are there many of these reference reefs? Where are they located? To answer this question, scientists from the PRISTINE project calculated the travel time between reefs and human populations for all of the world’s coral reefs. The study thus presents the first global accessibility map. The first finding—and it comes as a surprise—is that reefs are closer to human activities than previously thought. In fact, more than half of the world’s coral reefs are located within 30 minutes of human settlements. This close coexistence is easily explained: human communities have always tended to settle in these resource-rich areas.
Reefs located more than 20 hours’ travel away are very rare, accounting for only 1.5% of the world’s reefs. This is the study’s other major finding: the rarity of these “relics of the past.” These last refuges for marine wildlife are found primarily in the middle of the Indian Ocean and the Pacific, particularly off the coast of New Caledonia. This archipelago is home to one-third of the world’s isolated reefs. This underscores the responsibility of New Caledonians and France to protect these areas located at the heart of the Coral Sea Natural Park, one of the world’s largest protected areas.
L. Vigliola/IRD, Author provided
As reservoirs of biodiversity, coral ecosystems are currently in decline. The latest reports Scientific findings are alarming: 75% of the world’s coral reefs are currently threatened, with 60% facing a direct and immediate threat, and 100% expected to be threatened by 2050. Yet these unique ecosystems directly support the food (fishing) and economic (tourism) needs of a large portion of island populations. They provide physical protection from the elements, with coral reefs making many islands habitable.
Coral reefs are also a legendary paradise and a major economic resource: Australia’s Great Barrier Reef alone generates nearly one billion euros in revenue for the tourism sector. The conservation and sustainable use of this natural heritage require an accurate assessment of its condition, which is what the PRISTINE project set out to do. The project shows that most coral reefs are on a downward trajectory; only a very few reefs remain 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, French National Research Institute for Sustainable Development (IRD) and David Mouillot, Professor of Ecology, MARBEC Laboratory, University of Montpellier
The original version This article was published on The Conversation.