Understanding coral reef connectivity important to focus conservation efforts

Coral reef in Fiji.
Photo credit: Joao Paulo Krajewski

Scientific Frontline: "At a Glance" Summary

• Main Discovery: Larval connectivity between coral reefs significantly influences their biodiversity and biomass, with "sink" reefs (which receive larvae) showing greater resilience and biomass compared to "source" reefs.
• Methodology: Researchers utilized ocean biophysical models to simulate fish larval dispersal across coral reefs globally, combining ocean current movement data with biological characteristics of four distinct fish groups.
• Key Data: Reefs functioning as larval "sinks" contain approximately twice as much biomass as larval "sources," and 70% of reefs identified as functionally important for biodiversity and fisheries currently lack protection.
• Significance: The study provides the first global-scale simulation of coral reef larval connectivity, revealing that a reef's role as a source, sink, or corridor is a critical determinant of its ability to support fisheries and maintain biodiversity.
• Future Application: These findings offer a science-based framework for strategically positioning future Marine Protected Areas (MPAs) and Other Effective area-based Conservation Measures (OECMs) to maximize conservation outcomes by 2030.
• Branch of Science: Marine Ecology and Conservation Biology
• Additional Detail: While "sink" reefs are potential "sweet spots" for local subsistence fisheries due to high biomass, they still require managed fishing restrictions to maintain their ecological function.

Local fisheries and their associated biodiversity benefit from the transfer of larvae between reefs, with some benefitting more than others, prompting recommendations to protect larval connectivity among coral reefs. A team of international researchers, led in part by the Hawaiʻi Institute of Marine Biology (HIMB) within the University of Hawaiʻi at Mānoa, emphasize that coral reef connectivity is crucial to supporting the benefits coral reefs provide. Their study is published in Science.

Researchers identified significant gaps and opportunities for positioning marine protected areas (MPAs) and other effective area-based conservation measures (OECMs) strategically on coral reefs.

The findings indicate fundamental differences in the relative importance of coral reefs’ connectivity characteristics and their role in maintaining biodiversity and supporting local fisheries. That’s according to the study’s lead author, Luisa Fontoura, a postdoctoral researcher from Macquarie University’s School of Natural Sciences in Australia and recently-graduated doctoral student and UH Mānoa faculty Elizabeth Madin.

Coral reef and colorful fish.
Photo credit: Joao Paulo Krajewski

The global-scale research indicates that reefs receiving larvae from highly interconnected larval dispersal corridors harbor a greater number of fish species. Reefs primarily serving as larval “sinks,” where larvae end up after traveling on ocean currents, contain roughly twice as much biomass as larval “sources,” or the reefs where those larvae originate. When protected, these sink reefs are more resilient to human pressure. By identifying the distinct, yet complementary, roles that sinks, sources and dispersal corridors play on ecosystem services—as measured by fish species and biomass—an informed decision can be made about where MPAs and OECMs should be located to maximize biodiversity persistence and fisheries benefits.

“Scientists have known for decades that larval connectivity is critical for maintaining fish and invertebrate populations in the ocean, but this study shows that whether a reef is a sink, source or a corridor for larvae can clearly influence effectiveness of a conservation area,” said co-author Madin, an assistant researcher at HIMB in UH Mānoa’s School of Ocean and Earth Science and Technology.

Revealing connections

By combining ocean current movement and the biological characteristics of larvae, ocean biophysical models were used to model fish larval dispersal across coral reefs around the world. Even though these methods have been widely used in marine ecology and conservation, this study was the first to simulate coral reef larval connectivity at this spatial scale and resolution and for four distinct fish groups with contrasting life-histories.

Fontoura said, “On coral reefs, different types of fish species may contribute to different ecosystem services—for example, whereas large, carnivorous fish with a relatively short spawning season may make a substantial contribution to local fisheries, small reef fishes that reproduce more frequently during the year are responsible for much of the stunning fish diversity we observe on healthy coral reefs. Understanding the role of larval connectivity patterns from different species in sustaining ecosystem services can provide insights into the optimal design of protected areas based on their conservation and sustainability goals.”

In this study, one of the novelties is the combination of spatial information on larval dispersal networks and human pressure levels to test the importance of connectivity characteristics for supporting ecosystem services. Study results support the importance of larval source-sink systems for local fisheries persistence.

Reef connectivity informs conservation strategies

However, this new research demonstrates that the greater potential of larval sinks to contribute to local fisheries varies by management level and human pressure. Identifying larval sinks can be helpful in identifying OECMs’ “sweet spots” aimed at local fisheries subsistence, however, fishing restrictions remain necessary to protect the role these locations play in providing fisheries benefits to local coastal populations.

Despite their importance, 70% of coral reefs classified by this study as functionally important for biodiversity and fisheries conservation are not protected. To address this current gap and inform the proposed expansion of MPAs and OECMs by 2030, the study proposes a science-based, policy-relevant framework that incorporates coral reef connectivity characteristics in the strategic placement of future marine protected areas.

Published in journal: Science

Title: Protecting connectivity promotes successful biodiversity and fisheries conservation

Authors: Luisa Fontoura, Stephanie D’Agata, Majambo Gamoyo, Diego R. Barneche, Osmar J. Luiz, Elizabeth M. P. Madin, Linda Eggertsen, and Joseph M. Maina

Source/Credit: University of Hawaiʻi

Reference Number: en013122_02

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