Marine protected areas, or reserves – regions of the ocean where human activities, like fishing, are banned or restricted – are a primary marine conservation tool. Numerous studies have shown their benefits, such as higher amounts of fish, greater biodiversity of fish, and significant contributions to sustainable fisheries.
Networks of marine reserves have the potential to support large-scale ocean connectivity and contribute to global conservation targets, such as the 30×30 initiative. However, it remains a major challenge to prove that the benefits seen within these networks have ecological and economic value to the entire ecosystem, including non-protected waters.
Bode, M., Choukroun, S., Emslie, M.J., Harrison, H.B., Leis, J.M., Mason, L.B., Srinivasan, M., Williamson, D.H. and Jones, G.P., 2025. Marine reserves contribute half of the larval supply to a coral reef fishery. Science Advances, 11(6): eadt0216.
Recent research takes a step forward in understanding the impacts of marine reserves with a large scale assessment along Australia’s Great Barrier Reef, where around 30% of the reef ecosystem is well-protected as no fishing zones. Data from coral groupers – the region’s most valuable coral reef fish – were used to capture information on demography, reproduction, larval connectivity, and commercial harvests over a three-year period. This information was collected or extrapolated over the scale of the entire Great Barrier Reef Marine Park, which includes over 750 no-take marine reserves and over 1,500 reefs open to fishing.
The results provide clear evidence of how the network of no-take marine reserves contributes a larger-than-expected benefit to non-protected reefs. Although no-take marine reserves contain only around 30% of grouper habitat in the region, they support 51% of the total coral grouper biomass. The reserve network is also responsible for 55% of total egg production across the region.
There is significant spillover of larvae as well from protected reefs: reserves are responsible for 50% of all larval settlement across the region, which represents a dominant way that fish populations maintain connectivity. In terms of economic benefits, the marine reserve network is estimated to be the source of 47% (by weight) of the coral grouper caught by the commercial fishery.
This provides the strongest evidence to date about how marine reserves can have outsized benefits: the no-take zones in the region had a disproportionately greater positive effect on the fished reefs. It provides an example of how targets of 30% protected areas could be effective for marine ecosystems such as coral reefs, which have struggled in the face of climate warming, natural disasters, and other ecological changes.
As policy for creating and administering marine protected areas continues to change and develop, empirical evidence of their benefits outside of reserve boundaries can be helpful in making key decisions. The most effective marine reserves are ones that are well-managed, adaptable to climate change, and provide not only high quality habitat but migratory corridors as well. This translates to productive, biodiverse ecosystems both inside and outside reserve networks, making them a win-win situation for both conservation and sustainable fisheries.
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