In the first study of its kind, A connectivity portfolio effect stabilizes marine reserve performance demonstrates that a network of no-take zones ensures a consistent supply of replenished fish stocks across marine reserve habitats. No-take zones are marine protected areas (MPAs) where fishing activities are not allowed in order to preserve biodiversity.

Begun in 2007, and drawing on a body of research spanning 20 years, the study centers on genotyping and tracking the movements of larval coral grouper in the Keppel Islands within the Great Barrier Reef of Australia. Findings are published in the September 2020 issue of the Proceedings of the National Academy of Sciences of the United States of America, the official journal of the National Academy of Sciences.

KAUST Red Sea Research Center Director Dr. Michael Berumen is among the lead contributors, with additional experts based at the Australian Institute of Marine Science, Australian Research Council Centre of Excellence for Coral Reef Studies, James Cook University, and the Queensland University of Technology.

Larval dispersal findings

Established research shows that fish in no-take zones grow much bigger than those in fished zones, and females produce more eggs during spawning, which increases fish populations across the ecosystem. However, prior studies had not systematically tracked the distribution of baby fish in relation to the overall ecosystem.

Coral grouper (Plectropomus spp.) are a valuable fisheries species throughout the Indo-Pacific region. Total annual harvest on the Great Barrier Reef average 983 metric tons and the majority are exported live to foreign markets. Image courtesy of Tane Sinclair Taylor.

For this study, Berumen and researchers captured (and released) thousands of coral grouper adults and babies. Local fishermen—the long-run beneficiaries of the protection plan—participated by helping the scientists find and catch adult groupers.

By genotyping material snipped from a fragment of their tails, the team learned which babies came from which parents, and used the information to map their journeys. Some of the babies stayed in the no-take zones. Others traveled to near and distant areas, seeding populations and contributing to biodiversity both inside and outside the protected reserve.

Coral grouper (Plectropomus spp.) are an important predatory fish on coral reefs. Image courtesy of Tane Sinclair Taylor.

Relating research to marine conservation management

The findings provide information about larval dispersal patterns that fishing authorities can use to design effective marine reserves and assure fishing communities that no-take zones are smart investments for replenishing fish stocks.

Berumen said the advantage of conducting a multi-year study in the same area is that they have comprehensive measurements that they can then use to assess how the dispersal patterns vary and affect the network through the years. In this way, the study is unique from others for the scale of data that is collected and applied to conservation management.

"For a long time people made educated guesses about the movements of larval fish after spawning," said Berumen. "We now have empirical data about where they come from and where they end up as adults that we can use to track their movements through time—at present going back six years. With this quantitative information, we can appropriately scale where to focus protection based on how much exchange is occurring between places."

Much in the same way that a stock market portfolio buffers variable market conditions, the findings show that an aggregate of diversified no-take zones stabilizes fish populations across the whole despite fluctuating or volatile conditions of individual reserves, allowing marine populations to recover and rebuild.

"If you were only counting on one of these reserves to seed the whole system, you would have some really bad years, but by protecting multiple zones, the ones that do well help support the whole system. The no-take zones represent a small percentage of the total reef area—in this case, 20-30%—so a small investment of protection yields big benefits."

In addition to groupers, the team has sampled different species, including clownfish, snappers, butterflyfish, and parrotfish. The team looks forward to applying their research to more commercial species and in more locations in the future.

No-take marine reserves generate many benefits to ocean ecosystems and coastal communities. Inside reserves, coral grouper are bigger and more abundant, which generates important larval subsidies beyond their boundaries to sustain fish stocks. Connectivity across marine seascapes is highly variable but a network of reserves can create a safety net to ensure reliable replenishment of fish stocks. In the Keppel Island of the Great Barrier Reef, reserves generate half of all fish on the reef. Image courtesy of Hugo Harrison / Arc Centre of Excellence for Coral Reef Studies.