Marine predator movements create seascape connectivity in remote coral reef ecosystems

Movement of marine predators can connect different habitats and create links that are key for maintaining metapopulation dynamics, genetic diversity, energy flow and trophic links within and between systems. This key ecological process is known as ecological connectivity.

We used a combination of acoustic telemetry data, network analysis (graph theory), habitat modelling and machine learning methods to quantify movement patterns and habitat use of three coral reef predators (grey reef shark Carcharhinus amblyrhynchos, silvertip shark Carcharhinus albimarginatus and red bass Lutjanus bohar). We also assessed how movements and habitat preference influence connectivity in two remote reef systems (Rowley Shoals and Scott Reef) off Northwest Australia.

Grey reef shark movements created more substantial connections within reef systems, greater than silvertip sharks and red bass, with occasional long-ranging movement linking distant atolls. Core use areas (nodes with high degree centrality) were represented by low complexity habitats in shallow areas near passages in the reef crest, but varied among species, time of the day and sex. Overall, female sharks had larger networks with greater movement extent than males indicating potential sex-specific patterns in movement and connectivity of sharks at both local (within an atoll) and regional (within reef system) spatial scales. Red bass movements resulted in local-scale connectivity between the lagoon and nearby forereef areas, whereas reef shark connectivity operated at broader scales with movement along the forereef creating stronger connections across distant areas within the reef systems.

The combination of animal tracking data, network analyses and machine learning allowed us to describe complex patterns of movement and habitat use within and between remote coral reef ecosystems and how they influence ecological connectivity over local and regional scales. Importantly, we suggest that the existing spatial protection across these remote coral reefs is effective in protecting the local-scale connectivity of mesopredators, yet broad-scale protection is required to effectively encompass the seascape connectivity of large predators which is crucial for the long-term health and stability of coral reef ecosystems.