Connection and protection boost health in coral reefs

Coral reefs may seem like paradise, but they are being degraded by a range of global and local factors, including climate change, poor water quality, and overfishing. New research reveals that connections between reefs help stabilise reef health, reducing the risk of collapse, and that a dual approach – improving conditions on both land and sea – may be the best way to protect these crucial ecosystems. The study was a collaboration between the University of Oxford, the University of Toronto, the National Research Council of Italy, and the Wildlife Conservation Society (WCS).

By developing a mathematical model of a network of coral reefs in Fiji, researchers simulated future reef conditions when managed in three different ways: reducing fishing pressure (increasing herbivore grazing), reducing environmental run-off (decreasing coral mortality), and the two interventions combined. Addressing these two local pressures is a focus as many reefs in Fiji are climate refugia with reduced impacts from global warming and coral bleaching, and show natural recovery to acute events like cyclones. When considering local pressures, reducing the combination of fishing and pollution provided the best outcomes for reefs, showing the value of coordinated actions on land and in the ocean. Importantly, this result was robust to uncertainty in important reef conditions, indicating that it may be relevant for real-world decision-making in reef systems in Fiji and beyond.

Image: Emily Darling

They also discovered that fishery closures that improve grazing in less than half of the reef network can lead to increases in coral cover across the entire system due to larval dispersal connections. This result highlights the usefulness of planning conservation around networks of locations connected by coral larval dispersal, rather than isolated reefs – an approach that remains uncommon but proves powerful in revealing how connections between reefs influence long-term outcomes.

Lead researcher Dr Ariel Greiner (Oxford Biology) explains:

“For too long, coral reefs have been managed in isolation. Our research shows that when we account for connections between reefs, we find that they are far more stable than previously thought. Protecting a few key reefs can help sustain high coral cover across the entire network – the key is identifying which ones to protect. We also illustrate that strategies that address both overfishing and land-based pollution together deliver the strongest and most lasting results.”

The study also revealed that the dispersal of juvenile corals likely stabilises long-term reef dynamics, lowering the risk of a coral-dominated reef tipping into a non-coral-dominated state – an indicator of poor reef health. Dr Ariel Greiner says:

“Our study shows that when we include realistic dispersal connectivity between many reefs, the duality of coral- or non-coral-dominated reefs that we see in models of single or pairs of reefs disappears when we consider entire networks of reefs. This is a novel, unexpected, and exciting result with impacts for coral reef management, and for our understanding of coral reef dynamics globally.”

The study used a value of information analysis in combination with a mathematical model, which is novel for marine conservation. This combination of methods can inform more effective conservation planning by allowing modellers and decision-makers to assess the robustness and impact of management actions across large spatial scales and long timeframes, improving our ability to anticipate risks and design resilient strategies for the future.

“This study shows how modelling can help forecast the long-term consequences of today’s conservation decisions and pinpoint the actions that build lasting resilience for reefs facing multiple pressures,” says Dr Emily Darling (Director of Coral Reefs at WCS), a co-author of the study. “What’s powerful about these findings is their practicality: when we focus on climate-resilient coral reefs, coordinated efforts to reduce fishing pressure and improve water quality can generate outsized benefits across entire reef networks. This gives decision-makers a realistic path to protect ecosystems while supporting the communities who depend on them.”

The researchers next plan to look similarly at other coral reef systems around the world and extend the models to more explicitly include human dynamics – for example, exploring the impact of tourism-funded conservation initiatives – and to better understand under what conditions the dispersal of young coral and macroalgae will stabilise local reef dynamics.

To read more about this research, published in Ecological Applications, visit: https://doi.org/10.1002/eap.70156