In search of the last refuges of coral biodiversity

The objective of the PRISTINE project, led by an international team of marine biologists, is to carry out 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, Institut de recherche pour le développement (IRD) and David Mouillot, University of Montpellier

Astrolabe reef, New Caledonia. J.M Boré/IRD

After an initial oceanographic campaign on the Astrolabe reefs in New Caledonia, the scientists explored the Actéon islands in Polynesia, the Minerve 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 edifying.

Knowing the original state of an ecosystem

In science, and in ecology in particular, the evolution of a marine ecosystem and the assessment of the impact of man or natural disturbances requires knowledge of the ecosystem's original state. This knowledge takes the form of benchmarks for comparative studies. Reports drawn up by naturalists before the 20th century, such as those by James Cook, are too few in number and too lacking in detail to enable a scientific assessment of the degradation of today's coral reef ecosystems. For most of them, the pristine state no longer exists, with many areas exploited by fishing, for example. For the most part, reference conditions are therefore derived from marine reserves, set up to meet ecosystem protection and restoration objectives.
But are these reserves large enough, old enough and preserved enough to be taken 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 background to the PRISTINE project, which aims to redefine the reference state of coral reef systems in various Pacific countries by sampling the most remote areas. This data will provide a baseline against which to assess anthropogenic impacts, as well as the effectiveness of marine reserves. The sites chosen are therefore isolated, uninhabited and undeveloped: here, human impact has been minimal.

Discovering an unsuspected heritage

During expeditions to the isolated reefs of New Caledonia, the Tonga Islands and French Polynesia, biologists have come across an abundance of species: sharks, groupers, tunas, humphead wrasse, humphead parrotfish... species that are usually very rare but are particularly abundant here.

Sharks, seen in large numbers on isolated reefs.
L. Vigliola/IRD, Author provided

Sharks were observed on 87% of dives, compared with an average of 17% on Pacific reefs frequented by humans, 0% off-reserve near major cities, 6% in reserves in urban areas, 15% in small reserves in rural areas and 55% in strict reserves, where access is forbidden. Beyond this specific example, PRISTINE scientists have revealed the unaltered functional structure of remote reefs in the Pacific, indicating that only large integral reserves can re-establish a fauna that ensures the "natural" functioning of coral ecosystems.

From a safe distance

By sailing for 40 hours on 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 of human populations, more than just the distance as the crow flies, could measure the degree of reef degradation. Using a new method for estimating the travel time between reefs and human settlements, scientists have revealed the existence of thresholds below which reefs are severely degraded, and beyond which they reach reference levels.
For example, fish numbers fall by 44% in peri-urban areas, compared with isolated reefs, but recover after 6.5 hours' travel time. The presence of large predators falls by 69%, recovering after 12 hours' travel time. For sharks, the drop is 90%. As for functional diversity - i.e. the diversity of roles played by species in the proper functioning of the ecosystem - the drop is 61%, with recovery only visible after 16h30 of travel time. The reference state seems to be established at around 20 hours. At such a distance, it would seem that the reefs have, for the time being, been relatively unaffected by human activities such as fishing... even if this isolation offers no protection against global phenomena such as climate change.

The Alis ocean-going vessel on which scientists carry out their oceanographic missions.
L. Vigliola/IRD, Author provided

World's first reef accessibility map

How many reference reefs are there? Where are they located? To answer this question, PRISTINE scientists have calculated the travel time between reefs and human populations for all the world's coral reefs. The result is the world's first accessibility map. The first surprising finding is that reefs are closer to human activities than previously thought. More than half of the world's coral reefs are less than 30 minutes from human activity. This strong 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 just 1.5% of the planet's reefs. This is the other major finding of the study: the rarity of these "relics of the past". These last refuges of marine fauna are found mainly in the middle of the Indian Ocean and in the Pacific, notably off the coast of New Caledonia. This archipelago is home to a third of the planet's isolated reefs. Caledonians and France alike have a responsibility to protect these areas, which lie at the heart of the Coral Sea Natural Park, one of the world's largest protected areas.

Human communities, never far from the reef.
L. Vigliola/IRD, Author provided

Coral ecosystems are a reservoir of biodiversity, but are currently in decline. Visit latest balance sheets Scientific evidence is 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 support the food (fishing) and economic (tourism) needs of a large proportion of island populations. They also provide physical protection from the elements, with reef barriers keeping many islands habitable.
The ConversationCoral reefs also represent a mythical paradise and a major economic resource: Australia's Great Barrier Reef alone generates almost a billion euros in sales for the tourism sector. The conservation and sustainable use of this natural heritage requires a precise diagnosis of its condition, which is what the PRISTINE project is all about. The PRISTINE project shows that most coral reefs are in a negative trajectory, with only a very few remaining virtually intact. It is now essential to take strong protection measures on a global scale - going far beyond the Aichi targets - before it's too late.
Laurent VigliolaResearcher, Institute of Research for Development (IRD) and David MouillotProfessor of Ecology, MARBEC laboratory, University of Montpellier
Visit original version of this article was published on The Conversation.