Abstract
Zoning to prevent fishing on 30% of the Great Barrier Reef yields 50% more larvae and biomass of coral grouper on fished reefs.
As concerns grow over ecosystem declines, the focus on solutions has intensified. Groups such as the International Union for the Conservation of Nature have advocated protecting 30% of Earth’s ecosystems by the year 2030. In recent years, this idea became the “30 by 30” mantra. As attractive as that slogan may be, it remains the most challenging and largely untested management approach for large marine ecosystems until now, as demonstrated by Bode et al. in this issue of Science Advances (1).
The Great Barrier Reef (GBR) is the world’s largest coral reef ecosystem spanning 2300 km and covering an area over 340,000 km2. After years of study and debate, the entire reef ecosystem was subdivided into seven zones with about 33% being classified as a “Marine National Park Zone” in which almost all extraction of fish is banned (2). Unlike many other no-take reserves in marine ecosystems, the GBR has both good enforcement and compliance. With this zoning began what may be the world’s largest experiment in marine conservation.
No-take marine reserves invariably result in more and larger fish, but the question remains: does this protection go beyond the reserve boundaries? Large fish are known to swim beyond reserves (called “spillover”), but evidence of demographically important baby fish (called larval subsidies) from outside the reserve has been elusive.
Without empirical data, several different concepts took root over the past several decades. In the 1990s, larval source-sink ideas assumed that larvae replenish populations via long-distance transport driven by ocean currents (3, 4). This concept of “open marine populations” gave way to studies showing that larval fish recruitment is unexpectedly local (5). Some reviewers of this topic threw up their hands and admitted “... the almost total absence of studies addressing even the most elemental questions of recruitment in the specific context of [Marine Protected Areas or] MPAs” (6). However, the field progressed, and current research has since turned to new tools such as stable isotopes and genetics to reassess the question of where baby fish come from, also known as “connectivity” (7).
Connectivity research reported by Bode et al., in this issue of Science Advances (1), applied high-resolution biophysical dispersal models around fish spawning periods. The models were validated using a large genetic parentage dataset that gave the researchers a good idea where the fish larvae had originated. The research spanned 18 reefs across 200 km—no other study has scaled up to this size and produced such clear results.
Beyond the obvious advantages for biodiversity of having unfished areas, Bode et al. (1) provides stunning evidence of the benefits of preserving “30 by 30”. Specifically, the authors demonstrated for the first time that the no-take marine reserves comprising 33% of the GBR provided half of all the larvae of coral grouper, which is the region’s most valued coral reef fish (Fig. 1).
Fig. 1. Coral reef protection increases yields.
More than 30% distributed no-take reserves on the GBR result in 50% more coral grouper throughout the reef ecosystem.
Illustration credit: A. Fisher/Science Advances.
This study also demonstrates the success of what is perhaps the world’s biggest experiment in marine conservation. It shows the conservation value of a network of no-take reserves for sustaining highly valued fished species that would otherwise be depleted. It also demonstrates the remarkable result for the fishing community in that every second fish caught resulted from the GBR zoning network of no-take reserves.
Fishing communities worldwide hesitate adopting management plans that restrict fishing, especially when their fishing grounds became no-fishing zones. However, on the basis of this study, the fishing community, managers, and policy makers may see the advantages of such no-take reserves as a “win-win” solution. For both fisheries and conservation, a small area of protection can result in protracted and sustainable increases in biodiversity and improved fishery yields throughout the ecosystem. After all, such sustainability is also job security for those who fish.
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