Unraveling Short-Term Coral Connectivity: The Dominant Influence of Tides on Larval Retention in the Great Barrier Reef

Abstract

The Great Barrier Reef (GBR) is the world's largest coral reef system, stretching 2,000 km along Australia's north-east continental shelf, where it experiences complex and intricate tidal dynamics. Despite being one of the most studied reef systems, the extent to which local hydrodynamic processes drive local retention, where larvae return to the natal reef they were released from, as a key mechanism underpinning coral connectivity, remains poorly understood. This study examines how tidal dynamics and wind dynamics influence coral connectivity across the GBR, focusing on short-term larval local retention. High-resolution unstructured mesh hydrodynamic modeling (250–20,000 m) was used to drive Lagrangian particle tracking to assess differences between wind driven connectivity, tidally driven connectivity and combined connectivity. Results show that tides, particularly tight, asymmetric, tidal ellipses, play a critical role in driving larval retention, whereas wind disrupts local retention and drives dispersal away from natal reefs. Reef location within the GBR heavily dictates whether tides or wind are the dominant driver of larvae transportation. These findings help quantify the relative contributions of the physical drivers of coral connectivity, with implications for understanding reef resilience, forecasting connectivity and informing management.