Coral reefs around the world are declining because of human activities such as overfishing, land-based pollution, and climate change, but new research finds that strategic local management can make a significant difference in their capacity to sustain biodiversity, including that of fish populations, and perform other ecological functions.
The study, led by 2015 Pew marine fellow Josh Cinner, a professorial research fellow at the ARC Centre of Excellence for Coral Reef Studies at James Cook University in Australia, looked at nearly 1,800 tropical coral reefs distributed across the Caribbean Sea and the Indian and Pacific oceans. It found that local management efforts such as establishment of marine protected areas (MPAs) and restrictions on certain types of fishing are essential for maintaining the combined goals of supporting fisheries, boosting biodiversity, and maintaining ecological functions, but that the effectiveness of those measures changes as the amount of human pressure in the seascape increases.
Specifically, the researchers found that the greatest benefits from local management occur in areas where human pressures on the reefs are low to intermediate. However, local management efforts are unlikely to make much of a difference in places where human pressure is most extreme; in these locations, ecosystem degradation is typically too severe, and reefs are unlikely to recover.
“Our findings highlight the challenges and opportunities for supporting coral reefs in increasingly human-dominated seascapes,” says Cinner. “And with this research, we hope to show what can be realistically achieved through various approaches to local management.”
Rashid Sumaila, a 2008 Pew marine fellow who is a professor at the University of British Columbia, and Tim McClanahan, a 1996 Pew marine fellow who is a senior conservation zoologist at the Wildlife Conservation Society, co-authored the study.
The authors compiled data from reef sites from 41 countries and territories. Using this information, they developed a series of computer models to examine the conditions under which reefs met three key goals for healthy coral ecosystems: supporting fisheries; maintaining important ecological functions, such as parrotfish scraping—in which the fish essentially grind their teeth on coral—which suppresses algae growth and creates habitat for baby corals to settle on; and boosting biodiversity, or the variability of marine life supported by the reef.
The team members developed reference points—standards that could be used to judge success—for each goal based on measurements of healthy reefs. They then calculated the probability of achieving these goals at various levels of human pressure and under different types of local management.
Human pressure was assessed in terms of the size of the local human population and the accessibility of reef sites to people. Previous research has demonstrated this metric to be a useful way of understanding the impacts of human activities on surrounding ecosystems.
The researchers found that openly fished reefs, or places where there no conservation measures in place, were extremely unlikely to meet all three goals—productive fisheries, key ecosystem functions, and high levels of biodiversity—unless they were located in remote areas of the ocean where human impacts are very low. This finding underscores the importance of local management in areas that are accessible to people, as well as the significance of human pressure as a key determinant of reef health.
When the team members looked at the likelihood of meeting the goals individually, however, they found important differences in the effects of human pressure and the effectiveness of local management. For example, key ecological functions could be maintained even under high human pressure in areas with regulated fishing or within MPAs. By contrast, high levels of reef biodiversity were unlikely to be maintained under high or moderate levels of human pressure, regardless of the conservation measures in place.
The study found that fisheries restrictions provide a similar, but often weaker, pattern of conservation gains compared with fully protected MPAs, though restrictions are nearly as effective as MPAs for maintaining key ecological functions. This finding suggests that in areas where full protection may not be desirable or politically feasible, fishing regulations can still benefit reef health by creating conditions that support the settlement of new coral colonies and increases in coral cover.
The results of this research have implications for the design and placement of new marine reserves, as well as broader conservation decision-making in the increasingly human-dominated ocean.
Polita Glynn is a director and Nate Fedrizzi is a senior associate with the Pew Fellows Program in Marine Conservation.