Potential connectivity of marginal coral reefs in the northern South China Sea

Marginal coral reefs in the northern South China Sea (NSCS) are increasingly affected by thermal stress and local disturbances, yet their potential larval connectivity remains poorly quantified. Here, we assessed potential larval exchange among 23 reef patches in the NSCS using a Lagrangian particle-tracking model driven by regional ocean circulation data from 2000 to 2025. Connectivity was evaluated under pelagic larval duration (PLD) scenarios of 5, 30, and 120 days. Increasing PLD from 5 to 120 d increased the number of potential inter-patch links from 13 to 29, but mean positive off-diagonal connectivity declined by approximately 62%, indicating that many additional long-PLD pathways were weak. Episodic networks further showed that such low-frequency pathways could extend potential exchange among reef sectors, including the Beibu Gulf-western Hainan sector, the Xisha Islands, and the Vietnam coastal reefs. At the patch level, several Beibu Gulf and Hainan reefs showed self-retentive tendencies, whereas patches in the Xisha Islands and Vietnam coastal sector showed more diverse functional roles. These findings suggest that marginal reefs in the NSCS are linked by a spatially uneven and temporally intermittent network of potential larval exchange, providing testable hypotheses for connectivity-informed conservation assessment that should be evaluated alongside habitat condition, recruitment, and genetic evidence.