French Polynesia: a climate refuge for the survival of coral reefs in the future?

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A new model predicts that French Polynesia will serve as a climate refuge for the survival of coral reefs in the future

  • New climate model projections of the world’s coral reefs reveal which reefs will be hit first by annual coral bleaching, an event that poses the gravest threat to one of the Earth’s most important ecosystems.
  • These high-resolution projections, based on global climate models, predict when and where annual coral bleaching will occur. The projections show that reefs in Taiwan and around the Turks and Caicos archipelago will be among the world’s first to experience annual bleaching. Other reefs, like those off the coast of Bahrain, in Chile and in French Polynesia, will be hit decades later, according to research recently published in the journal Nature Scientific Reports.

Coral reefs are the marine ecosystem most vulnerable to climate change. Severe coral bleaching events are among the greatest threats to coral reefs posed by climate change. Coral reefs around the world vary in their vulnerability to future bleaching. Vulnerability is a function of exposure to a stressor, such as the warm temperatures that cause bleaching, and the system’s resilience. Resilience refers to the capacity of the system to resist and recover. The aim of this project was to use climate models to learn how future exposure to the warm temperatures that cause bleaching will vary among reefs globally.

 

We produced climate model projections at 4-km resolution that suggested all coral reefs will experience severe bleaching annually this century. Once reefs experience bleaching stress this frequently, corals will struggle to recover, and many reefs are likely to become dominated by fleshy algae. Algae-covered reefs provide less goods and services to human communities – they harbor less biodiversity and represent lower quality habitat for reef and reef-associated fish. On average, annual severe bleaching is projected by the current generation of climate models to occur in 2043. However, there is great spatial variation in when the climate models project annual severe bleaching to occur. Reefs that experience such levels of stress much later than others represent conservation priorities. These ‘refugia’ are locations likely to provide goods and services for decades longer than locations projected to experience annual severe bleaching soon. French Polynesia, especially the southern areas where Tahiti and Moorea Islands are located, are one of the projected ‘climate refugia’.

 

We also examined how coral reef futures may change given the Paris Agreement on climate policy was recently ratified. Under the Paris Agreement, most countries in the world have made pledges to reduce greenhouse gas emissions. Most coral reefs will still experience annual severe bleaching this century if these emissions reductions pledges become reality. However, the planned emissions reductions may buy many reefs decades of extra time before sea temperatures warm enough to cause severe annual bleaching. French Polynesia is one of the locations, along with the NW Hawaiian Islands, that will benefit the most from countries making good on their commitment to reduce emissions. Indeed, many reefs in southern French Polynesia, such as near the Islands of Tahiti and Moorea, are not projected to experience annual severe bleaching this century. French Polynesia is a globally significant climate refuge for coral reefs and may potentially be among the few healthy coral reefs late this century.

 

“These predictions are a treasure trove for those who are fighting to protect one of the world’s most magnificent and important ecosystems from the ravages of climate change” said Erik Solheim, head of UN Environment.

“They allow conservationists and governments to prioritize the protection of reefs that may still have time to acclimatize to our warming seas. The projections show us where we still have time to act before it’s too late.”

 

Figure 1. Global projections of the year annual bleaching conditions start for all reef locations, under the emissions scenario that assumes climate policy will not be enacted or complied with. The median year is 2043. Green locations represent globally significant climate refugia.

Figure 2. Map of the number of additional years reefs will have before annual bleaching conditions start if emissions reductions pledges made under the Paris Agreement become reality. In this case, French Polynesia, along with the Gulf of Oman in the Middle East, are the only reef areas that are not projected to see annual bleaching conditions this century. This map suggests French Polynesia is a globally significant climate refuge for coral reefs.

 

 

The projections we developed are available as interactive map-based tools on the UNEP and NOAA Coral Reef Watch websites. This project represented a collaboration between UNEP, WWF, NOAA-PIFSC, USGS-PICSC, US-NFWF, ERC and EPHE-CNRS and CRIOBE.