A team of scientists have discovered that a large area in the Indo-Pacific known as the “Coral Triangle” is surprisingly resistant to thermal stress from climate change, making it a sanctuary for corals amid the ongoing climate crisis. The findings, published in the journal Global Ecology and Biogeography, are a glimmer of hope amid an otherwise dismal outlook for the world’s coral reefs which are declining globally as ocean waters rapidly warm.
The study, conducted by researchers from 19 tropical research institutions, looked at 226 reefs in 12 countries during 2016, one of the Earth’s warmest years on record. They found that coral sensitivity to heat was highly variable across different marine regions, and that climate-warming models overestimated coral destruction in the biodiversity-rich Coral Triangle. The region contains 75 percent of the world’s coral species and ocean biodiversity and its waters extend throughout Indonesia, Malaysia, Papua New Guinea, the Philippines, Solomon Islands, and Timor-Leste.
Marine conservationists, local communities, and governments are deeply concerned about the fate of the world’s corals and the many species that may be lost due to global warming induced bleaching. Finding and protecting potential ocean sanctuaries, regions where environmental conditions provide a buffer against heat waves, is considered among the highest priorities to safeguard marine ecosystems. Until now, such sanctuaries have been difficult to pinpoint.
The research was led by WCS Senior Conservation Scientist Dr. Tim McClanahan who coordinated with a number of marine scientists across tropical countries to share a common method for evaluating thermal stress to corals. This collaborative effort has resulted in one of the world’s first big-picture views of coral sensitivity, revealing wider variations in bleaching patterns than had been previously understood or predicted by climate models.
Said Dr. McClanahan: “This is the first truly hopeful news for some coral reefs in a long time, and these findings suggest many published predictions for corals were overly pessimistic. It gives us a much better insight into where to focus our conservation efforts. The Coral Triangle is a great place to start. WCS is fortunate to have built a global conservation program that covers a large number of these climate resilient reefs. Even in areas where we find reefs suffering with low heat resistance, there are still smaller sanctuaries that can survive if people can reduce other reef threats, such as overfishing and pollution.”
Scientists evaluated both the sensitivity of corals to heat and the relative exposure of reefs to heat stress. Heat-induced loss of colour, known as bleaching, for each coral species was rated by field observers using a standard methodology to estimate the coral’s sensitivity level. Information on heat exposure for each area was taken from satellite data that has been made publicly available daily since the early 1980s and has shown increasing temperatures across the world’s oceans. The study revealed that the highest and broadest-scale resistance of coral reefs to heat stress occurred in the Australian, Indonesian, and Fiji-Caroline Islands. Reefs in East Africa, India, Japan, and Vietnam showed lower heat resistance. Corals that are more resistant to heat stress tend to be located in island environments that have been exposed to repeated and regular heat pulses that occur with the El Nino-La Nina cycles. These island environments seem to buffer the impacts of the most extreme heat and create marine cool pockets that help corals survive. Corals that have been exposed to periodic heat pulses have some resistance to the warming conditions that are creating havoc for many other reefs.
Dr. Joseph Maina, a Professor at Macquire University who developed the study’s exposure metrics, added, “Satellite data has revolutionised our ability to observe heat stress unfolding in the ocean. Now that field scientists are making comparable underwater observations, we have the ability to correlate ocean surface conditions with underwater conditions and greatly improve our understanding of the impacts of climate change”.
These findings will be extremely valuable in helping scientists focus conservation efforts in regions where coral reefs have the best chance of surviving a warming ocean. Understanding ocean heat stress effects on corals allows organisations like WCS and their partners to concentrate their work to protect the Earth’s most diverse marine ecosystems, before the window of opportunity closes.
WCS’s efforts studying the sensitivity of corals in the Indo-Pacific was generously supported by the John D. and Catherine T. MacArthur Foundation and The Tiffany & Co. Foundation. Additional professional and financial contributions were provided by the 19 partnering research institutions and their supporters.
Header image: Yen-Yi Lee/Coral Reef Image Bank.