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.
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.
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.
This effort is an example of UH Mānoa’s goal of Excellence in Research: Advancing the Research and Creative Work Enterprise (PDF), one of four goals identified in the 2015–25 Strategic Plan (PDF), updated in December 2020.