By Tim McClanahan and Emily Darling
The longest and strongest El Niño recorded since the introduction of modern instrumentation has produced in 2016 a global heat wave with superheated ocean temperatures that have stressed tropical corals around the world. While it is heartening to see coverage of this phenomena in the news, environmental reporting risks missing the larger picture.
The bleaching events devastating globally important corals in places such as Australia’s Great Barrier Reef and Hawaii have rightly attracted intense media scrutiny, but these areas represent just a small percentage of the world’s reefs that belt the larger tropics, where disastrous heat waves have been reported since 1983.
Over the past several months, a group of scientists led by WCS (Wildlife Conservation Society) with partners from Tanzania, Réunion, Reef Conservation Mauritius, IUCN, Muséum National d’Histoire Naturelle, James Cook University, and the Natural History Museum of Denmark have conducted more than 170 coral bleaching surveys in 10 countries: Fiji, Solomon Islands, Kenya, Tanzania, Maldives, Mauritius, Réunion, Madagascar, Philippines, Japan and Indonesia.
Our goal was to assess the impact of coral bleaching on biodiversity hotspots in the Indo-Pacific and the Western Indian Ocean and to understand how corals are being impacted by this El Niño heat wave. Further, we wanted to know if there are species and locations that are escaping these effects.
First, the good news: Some reefs appear to be escaping the superheated waters or showed limited heat stress or bleaching. The Philippines, Fiji, Solomon Islands, Indonesia and even some locations in Kenya and Madagascar had these hopeful reefs.
Nonetheless, the surveys confirmed that climate change is driving another large global-level crisis in corals. More than half of the roughly 43,000 colonies we looked at, including many undisturbed by past heat waves, showed signs of bleaching. And structurally important species that form the carbonate backbone of coral reefs were among the hardest hit.
It’s a story we know well. Having collected data on a broad number of coral reefs from East Africa across the Indo-Pacific from the past three decades we are building a larger window onto the crisis facing corals today.
Half the corals in the Indian Ocean died in the 1998 El Niño, for example, and yet this disaster – taking place in seascapes that typically attract fewer tourists and media scrutiny – went largely unnoticed despite its implications for climate change policy. We only became aware of this phenomenon through our close contact with colleagues working in Indian Ocean countries and by compiling bits of the local investigations largely unpublished in the scientific literature or reported in popular media.
Jumping forward two decades, we know that coral bleaching in 2016 is widespread throughout the world’s tropical oceans and occurring in developing countries that lack the capacity to monitor their corals. But with the exception of some reporting from popular diving spots like the Maldives and Thailand, the status of most reefs in tropical countries remains largely unknown to the larger population.
Further, despite the ongoing coral crisis, few readers are getting the message that while some reefs are dying off, others are proving to be more resilient. This is a critical outcome. We must identify what are the drivers of resilience in these survivor reefs that have the potential to help the world’s corals adapt to the changing climate.
Only by studying all reefs around the world – and using similar methodologies and sharing data – can scientists learn what determines climate resilience for coral reefs. In the coming months and years, reef scientists will need to evaluate the reasons for this range of responses to stress in and between countries.
Are they attributable to oceanographic conditions that maintain or bring cooler waters to corals or to the histories of temperature stresses at each reef? Or to local management that has controlled fishing or land-based impacts from logging, development or pollution? And how long into the future will these hopeful conditions persist? These questions are critical for policies and priorities for coral reef conservation.
The future of coral reefs depends on the response and adaptation of corals to rising ocean temperatures. Finding reefs that serve as climate refuges and managing them globally is one of the highest priorities for action. To achieve that goal will require funding reef science beyond the borders of wealthy countries and prioritizing the monitoring and reporting of coral reefs around the world.
What we know for certain is that global warming is happening right now, and will have real consequences for the world’s reefs and millions of people who depend on them. El Niño events will certainly repeat, but our response as a society must smartly evolve if we are to secure the future for a healthy marine environment.
Dr. Tim McClanahan and Dr. Emily Darling are conservationists with the Global Marine Program at WCS (Wildlife Conservation Society). They gratefully acknowledge the 24 marine scientists in Fiji, Solomon Islands, Kenya, Tanzania, Maldives, Madagascar, Mauritius, Réunion, Philippines and Indonesia who conducted underwater coral surveys.