Keeping coral reefs connected

| January 21, 2022

Coral reefs connected by larvae dispersal networks have been found to benefit local fisheries and biodiversity conservation, prompting recommendations to increase the protection of connected reefs. In a new study, a team of international researchers, led by Macquarie University, have identified key characteristics of coral reef connectivity that are crucial to supporting the benefits coral reefs provide.

The study, published in Science, identified significant gaps and opportunities for positioning marine protected areas (MPAs) and other effective area-based conservation measures (OECMs) strategically on coral reefs.

The study’s lead author Dr Luisa Fontoura, a postdoctoral researcher from Macquarie University’s School of Natural Sciences said the findings indicate fundamental differences in the relative importance of coral reefs’ connectivity characteristics and their role in biodiversity maintenance and local fisheries.

The globally-conducted research indicates that reefs receiving larvae from highly interconnected dispersal corridors harbour a greater number of fish species. Reefs primarily serving as larval sinks contain roughly twice as much biomass as larval sources, and when protected, are more resilient to human pressure.

“By identifying the distinct yet complementary roles that larval sinks, sources, and dispersal corridors play on ecosystem service provision – as measured by fish species and biomass – we can make informed decisions about where MPAs and OECMs should be located to maximise biodiversity persistence and fisheries benefits,” said Dr Fontoura.

“Although technical guidelines and tools for protecting connectivity exist, empirical studies are needed to determine how different connectivity attributes, for instance, whether the reef is a sink, source, or a corridor for larvae, influence the desired outcomes of a conservation area,” said the senior author Dr Joseph Maina from Macquarie University.

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 the methods have been widely used to study ecology and conservation, this study was the first to simulate coral reef connectivity at this spatial scale and resolution and for four distinct fish groups with contrasting life-histories.

“In coral reefs, different types of fishspecies 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 diversity of fish we observe on tropical coral reefs today,” said Dr Fontoura.

“Understanding the role of 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.”

A key outtake of the study investigates the combination of spatial information on larval dispersal networks and human pressure to test the importance of connectivity characteristics for supporting ecosystem services.

Study results support the importance of larval source-sink systems for local fisheries. Identifying larval ‘sinks’ can be helpful in identifying OECMs sweet spots aimed at subsistence fisheries, however, fishing restrictions remain necessary to protect local coastal populations.

“Getting the local context right is crucial. A deeper understanding of the interactions between human activities and the local environment is necessary to tailor management and support the continuity of ecosystem services to maximise the contributions of larval sinks to sustainable fisheries,” said co-author Dr Stephane D’agata from The French National Institute of Sustainable Development (IRD).

70 per cent of coral reefs classified as critical larval sinks, sources and dispersal corridors, and therefore functionally important for biodiversity and fisheries conservation, are not protected. To address these current gaps 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 protected areas.

“The priority now is to understand the influence of climate change on coral reef connectivity to forecast potential impacts on coastal communities worldwide that rely on coral reef ecosystem services.” Dr Fontoura said.