Maintaining Reef Connectivity is Crucial to Protect Reefs Worldwide
Ariel Greiner
Center for Infectious Disease Dynamics, Pennsylvania State University, State College, PA, USA; Department of Biology, University of Oxford, Oxford, UK
Emily Darling
Marine Program, Wildlife Conservation Society, Bronx, New York, USA; Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada
Marco Andrello
Institute for the study of Anthropic impacts and Sustainability in the marine environment, National Research Council, CNR-IAS, Rome, Italy
Marie-Josée Fortin
Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada
“Understanding which reefs are most important to conserve to preserve global coral connectivity is key to maintaining marine biodiversity worldwide and by extension ensuring a crucial source of food and livelihood to close to a billion people”
Coral reefs are one of the most endangered and important ecosystems on the planet and saving them is crucial to preserving the livelihoods, food security, and coastal protection of nearly one billion people (Wong et al. 2022) and preserving marine biodiversity worldwide (a crucial planetary boundary). Coral reefs are an essential source of food and income for many who live near reefs, as they support many local fisheries and tourism industries. Coral reefs also protect coastal inhabitants by reducing the impact of storms. Coral reefs face many interacting stressors, but the largest and most pressing issue is climate change-induced bleaching (loss of algae that live within the coral, leading to coral degradation and sometimes death), which is degrading coral reef habitat worldwide at alarming rates. However, not all coral reefs are bleaching at the same rate. Hence, reefs that have a lower risk of being bleached may be able to help rescue those reefs that have a higher risk of being bleached. The lower-risk reefs may be able to do this because reefs worldwide are connected, forming networks of reefs through coral larval dispersal – i.e., coral larvae (young coral) are released into the water column and move along ocean currents. These coral larvae can land on degraded reefs and help repopulate them with living coral, rescuing those reefs. However, it is unclear which reefs are connected to which and how that might change due to bleaching-induced reef habitat degradation. Therefore, understanding the effectiveness of global coral connectivity in lessening the impact of bleaching, and identifying which reefs are crucial to uphold to preserve overall global reef connectivity, is an important research question. Understanding the answers to these questions is crucial for prioritizing which reefs are most important to maintain worldwide.
Greiner et al. (2022)—The winning article for Canada of the Inaugural Frontiers Planet Prize—mapped and quantified which reefs are in the same networks as other reefs worldwide to determine how those networks could change as reefs become degraded due to climate change-induced bleaching and which degraded reefs could be rescued by low-risk reefs through coral larval dispersal. Our focus on reefs at a lower risk of bleaching was informed by an influential study led by coral reef experts in 2018 that has guided coral reef conservation priorities (Beyer et al. 2018, the ’50 Reefs’ study). We found that reefs are connected into six large reef networks and many smaller networks, where a network is a group of reefs that are connected by larval dispersal. We also found that these networks will be largely maintained under a climate-resilient scenario where only the low-risk reefs remain. However, we also found that these low-risk reefs are not able to send coral larvae to the majority of the world’s reefs, suggesting the need for complementary coral conservation and restoration actions across the global distribution of coral reefs.
Our study greatly improves the understanding and puts a renewed focus on global coral reef connectivity, which had previously been understudied. It has motivated international conservation organizations to focus their conservation efforts on connected networks of reefs, as opposed to prioritizing individual reef locations of low climate risk. In particular, since 2022, we have been working with the Wildlife Conservation Society (WCS) to extend the framework pioneered by Greiner et al. (2022) to search for ideal stepping-stone reefs that are key connectors across a global coral network of low-risk climate-resilient reefs. If these reefs are maintained, they will help ensure that as many reefs as possible have sources of new larvae and will preserve a connected network of climate-resilient coral reefs critical for biodiversity and the livelihoods of nearly one billion people worldwide (Wong et al. 2022). Our first findings indicate that if we focus on just 10 key 'stepping-stone' reefs, we can help connect over 1 million square kilometers of low-risk reefs to other low-risk reefs. Therefore, if nations and conservation groups worldwide prioritize looking after these 'stepping-stone' reefs, it could significantly boost our efforts to preserve coral reefs globally.
Our next steps are to extend this framework to local and regional levels, to identify key reefs in particular areas for conservation. The challenges we face are that local coral larval connectivity is not well-resolved—more money and time needs to be put into reducing our uncertainty in coral connectivity at smaller scales. This should be accomplished through further studies on genetic relatedness of corals living in nearby reefs; improved models of ocean currents, and a better understanding of coral larvae behaviour and movement with ocean currents and climate impacts; and, ultimately, improved species-specific connectivity models. Finding priority reefs at local and regional levels will help individual countries and regions within countries determine which of their reefs are best to prioritize to ensure that the most additional reefs have sources of larvae.
In addition to their crucial role in maintaining biodiversity worldwide and ensuring the survival of nearly one billion people, coral reefs are also often thought of as ‘canaries in the coal mine’ for ecosystem destruction due to climate change. Therefore, any methods that we pioneer to help preserve them can help us design management plans for other similar marine ecosystems, such as temperate rocky reefs. Due to studies like Greiner et al. (2022), more and more ecologists and conservation biologists are studying how ecosystems are connected and how they can use those connections to design smarter conservation management plans. Conservation actions informed by this research will help us conserve biodiversity and mitigate the effects of climate change worldwide, ensuring that we remain in a safe operating space away from crucial planetary boundary tipping points.
Photo 1. Aerial photo of coral reefs in the Great Barrier Reef. Photo Credit: Katerina Katopis, Ocean Image Bank.
Photo 2. From Top Left - Ariel Greiner (credit: Katie Jane Yan), Marco Andrello (credit: Marta Carboni), Emily Darling (credit: Kristine Cofsky), Martin Krkošek (credit: Brian Summers), Marie-Josée Fortin (credit: Diana Tyszko).
References
Greiner, A., Andrello, M., Darling, E., Krkošek, M., & Fortin, M. J. (2022). Limited spatial rescue potential for coral reefs lost to future climate warming. Global Ecology and Biogeography, 31(11), 2245-2258.
Beyer, H. L., Kennedy, E. V., Beger, M., Chen, C. A., Cinner, J. E., Darling, E. S., ... & Hoegh‐Guldberg, O. (2018). Risk‐sensitive planning for conserving coral reefs under rapid climate change. Conservation Letters, 11(6), e12587.
Sing Wong, A., Vrontos, S., & Taylor, M. L. (2022). An assessment of people living by coral reefs over space and time. Global Change Biology, 28(23), 7139-7153.
