Coral reef connectivity is crucial for conservation

With an ambitious global push underway to protect a third of the world’s ocean environments by 2030, the race to distinguish which areas to safeguard is picking up pace.

A new study published in Science by a team of international researchers has made significant headway on the issue, zeroing in on key attributes required for the successful conservation of coral reefs, and identifying reef connectivity as a prime characteristic.

The research team, led by Macquarie University, found that the best biodiversity outcomes and flow-on benefits to local fisheries come from reefs that are connected to each other through larval dispersal networks – corridors that transport larval fish over vast distances, shuffling the gene pool and helping to build resilience.

Oceanic ecosystems such as coral reefs are connected to each other to a greater extent than their terrestrial counterparts, thanks to the ‘global conveyor belt’ of currents driven by temperature and salinity gradients. But not all marine ecosystems are equally connected – while the Great Barrier Reef is more or less contiguous for is entire length, some reefs form isolated patches separated by enormous stretches of inhospitable ocean. For these patches, the connection to other reefs via ocean currents allows resident fish populations to be topped up, and the gene pool refreshed.

To better understand the importance of connectivity and how to build it into conservation recommendations, the team broke the concept down into the distinct yet complementary roles of larval sinks, sources and dispersal corridors.

The study’s lead author, Dr Luisa Fontoura, a postdoctoral researcher from Macquarie University’s School of Natural Sciences, said the globally conducted research indicates that 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 combining ocean current movement and the biological characteristics of larvae, the team modelled larval dispersal across coral reefs around the world. They then grouped fish into four categories with contrasting life histories to get a better picture of the ecosystem services arising from different reef populations.

“In coral reefs, different types of fish species may contribute to different ecosystem services,” says Fontoura.

“Large carnivorous fish with a relatively short spawning season may make a substantial contribution to local fisheries, whereas 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.”

Seventy per cent of coral reefs that the study identified as critical larval sinks, sources and dispersal corridors – making them functionally important for biodiversity and fisheries conservation – are not protected.

The team suggests this new understanding for the importance of protecting connectivity should be used to better inform the design and placement of protected areas.

“Getting the local context right is crucial,” says co-author Dr Stephane D’agata from the French National Institute of Sustainable Development.

“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 and maximise the contributions of larval sinks to sustainable fisheries.”

Fontoura says that “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.”