Multi-scale biophysical modelling explains contrasted coral connectivity and genetic structure in the high-relief basin of the Aruba–Bonaire–Curaçao islands.

Abstract

Coral connectivity plays a fundamental role in the persistence and resilience of reef ecosystems, yet remains challenging to quantify due to the complex interplay between poorly-quantified larval traits and the ocean dynamics. This challenge is amplified in physically intricate regions such as the Aruba-Bonaire-Cura¸cao (ABC) islands, where sharp bathymetric gradients and fine-scale hydrodynamics strongly influence larval transport and recruitment. In this study we apply the multi-scale, GPU-accelerated ocean model SLIM3D to simulate several years of hydrodynamics in the ABC basin, enabling the fine-scale (∼100 m) representation of coastal circulation in reef areas. We then use SLIM’s Lagrangian Particle Tracker (LPT) to simulate the dispersal of millions of virtual larvae including species-specific biological traits, such as competency acquisition/loss, mortality, and settlement behaviour, thereby providing a robust assessment of connectivity pathways at the regional scale. Sensitivity analyses on the LPT’s physical and biological parameters further help us identify the most influential factors shaping connectivity. We analyze dispersal patterns for the broadcast spawner Diploria labyrinthiformis (Dlab) and the brooder Favia fragum (Ffra) and find very contrasted results. While Ffra shows very limited inter-island exchanges due to rapid larval settlement, resulting in largely isolated reef populations, Dlab exhibits broader dispersal enabled by longer pelagic larval durations and advection by the strong northwestward Caribbean Current. Additionally, the formation of (sub)mesoscale eddies in the lee of the islands also promote larval retention and self-recruitment, leading to lower genetic differentiation for the broadcaster than for the brooder. Our findings align with in-situ genetic measurements, revealing numerous distinct genetic groups for Ffra, and only two major groups for Dlab. This study underscores the role of coral larval early-life history traits in self-recruitment and long-distance dispersal, giving insights into how dispersal potential varies with reproductive mode and local hydrodynamics