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Fishing for lessons on coral reefs

Nature volume 535, pages 361362 (21 July 2016) | Download Citation

A global study has identified coral reefs with greater fish biomass than would be predicted given human and environmental pressures. These outliers might teach us something about sustainable coral-reef management. See Letter p.416

The human population is expected to reach 9.7 billion by mid-century1, with many of us concentrated in the narrow, coastal zones of the world. The inevitable growing demand for food is of great concern to conservationists. Seafood is a key source of nutrition for people worldwide, yet unsustainable fishing practices have already led to the degradation of many coastal ecosystems2, and these degraded ecosystems have a reduced capacity to support stable fisheries3. Strong fishing restrictions are in place for only 2% of the world's oceans4, leaving the vast majority of marine ecosystems at risk from overfishing and continued degradation. On page 416, Cinner et al.5 provide key insights into the social and economic conditions linked to declines in the biomass of coral-reef fish.

Although there is a well-established link between overfishing and coral-reef health, we know less about the social, cultural and economic conditions that cause some communities to overfish while others fish more sustainably. Understanding the root causes of overfishing may allow individuals and organizations to address, and potentially alleviate, the conditions that contribute to overfishing, and to promote the socio-economic conditions associated with sustainable fisheries.

Cinner et al. compiled ecological and environmental data for some 2,500 coral reefs worldwide, as well as the socio-economic data for the use of these reefs. The authors then compared how the biomass of fish on coral reefs varied with numerous social and economic factors, such as human population growth and levels of tourism, on both local and national scales, while also accounting for some environmental conditions (largely beyond human control) that influence reef fish populations.

The authors find that conventional conservation approaches such as well-enforced reserves (areas that are not fished) generally increase fish biomass, but they also describe other socio-economic factors that lead to reef-fish declines. In particular, there are fewer fish in locations with shorter travel times to large markets where people can sell fish.

The effect of increasing market-based forces on decreasing fish biomass was stronger than the effects of many of the other factors that influence reef-fish biomass, including human population pressures, environmental conditions or local management actions. This result is crucial for coral-reef conservation because it suggests that market forces contribute to overfishing and that market-based interventions — such as eco-labelling or creating markets for sustainably harvested fish — may be necessary to support sustainable fisheries on coral reefs.

The authors also report a second compelling result. They identify 15 reefs that have much greater fish biomass than would be expected given the human and environmental pressures. These reefs constitute what are called 'bright spots' (Fig. 1), and can now be analysed to learn lessons that may point conservationists in new directions.

Figure 1: Bright spots.
Figure 1

Cinner et al.5 carried out a global analysis of fish biomass on coral reefs and identified locations (such as Raja Ampat, Indonesia, shown here) known as bright spots, where fish stocks were higher than expected given local human and environmental pressures. Image: Reinhard Dirscherl/Ullstein Bild/Getty

Identifying and scaling up the lessons learned from individuals or populations that are outperforming those around them has been done successfully in the fields of human health, development (such as agricultural practices or resource use) and business management, but this strategy is not a standard approach in marine-conservation studies. The benefits of understanding the factors that underlie outperformers — whether in coral-reef conservation or human health — are manifold and include the potential to generate local community involvement by identifying proven and practical solutions that can be scaled up in other locations.

“Preliminary analyses suggest that bright spots tend to be associated with communities that are actively engaged in reefmanagement decisions.”

Five of the fifteen bright spots identified by Cinner and colleagues are in unpopulated areas. This leaves only ten other sites with which to explore how different socio-economic conditions might affect decisions to fish sustainably when access to markets is not limiting. The authors' preliminary analyses suggest that bright spots tend to be associated with communities that are actively engaged in reef-management decisions, and which are highly dependent on the resources, or in communities that have customs in place to control usage. On the basis of these results, strategies that promote community engagement and local enforcement may be crucial for sustainable management.

The new results are compelling, but 10 sites out of 2,500 reefs is an extremely limited number for a robust, quantitative analysis of bright spots (although the low number is interesting in its own right, suggesting that there are very few outliers among the world's reefs). More in-depth socio-economic studies are needed to fully understand why these conditions support high reef-fish biomass in some locations but not in others.

One limitation of this study is the tight focus on the market-based causes of coral-reef degradation at a time when coral reefs are increasingly threatened by accelerating environmental changes6. The precarious health of coral reefs was heart-breakingly illustrated in early 2016, when warm ocean temperatures caused severe bleaching (the expulsion of photosynthetic algae from corals, which can result in the death of the coral) of reefs globally7, including at the iconic Great Barrier Reef8. In their study, Cinner et al. also find that coral reefs that have experienced recent environmental shocks, such as bleaching or cyclones, have lower fish biomass than would be expected on the basis of pressures such as market influences. In addition, the coral reefs located near cooler, deeper waters where animals can hide during unfavourable conditions had higher fish biomass.

Lessons can also be learned from the 'dark spots' (reefs that support fewer fish than would be predicted on the basis of human and environmental pressures) that were identified by Cinner and colleagues. Not surprisingly, several of these reefs were recently exposed to environmental disturbances, such as cyclones, highlighting the importance of considering how climate change will continue to affect reefs in the future.

Although analysis of bright spots may help to identify market-based management approaches for sustaining coral-reef fishes, a portfolio of conservation approaches is probably still needed to address the numerous threats to coral-reef ecosystems, including climate change. Without sustainable fisheries, we will not be able to maintain healthy coral reefs. And without healthy coral reefs, we will not be able to sustain the fisheries needed to feed the world's growing population.



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  1. Kristy J. Kroeker is in the Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, Santa Cruz, California 95060, USA.

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Correspondence to Kristy J. Kroeker.

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