Temporal dynamics and network drivers of coral reef structural-functional relationships in the Nansha Islands, South China Sea.

Abstract

For the conservation of coral reefs through resilience-based management, elucidating the evolutionary mechanisms underlying ecosystem functionality and stability emerges as a critical scientific priority. We employed energy flux network analysis to investigate the functional-structural dynamics of the Nansha Islands coral reef ecosystem after the El Niño event. Based on fieldwork (2016-2020), an array of food-web metrics was evaluated at both the entire ecosystem level and the individual taxa level. Simulated and δ¹⁵N-based trophic levels agreed (<i>r</i> ² = 0.83, <i>P</i> < 0.0001), validating model robustness. As the coral coverage increased from 14.1% to 42.1%, there was a corresponding increase in total system throughput (TST), net primary production (NPP), transfer efficiency (TE), and ascendency/capacity (A/C) by factors of 1.10, 1.43, 0.52, and 0.22, respectively, while the overhead/capacity (O/C) decreased by 0.11, indicating an increase in ecosystem maturity. Despite these changes, the relatively low connectance index (CI, 0.15) and omnivory index (OI, 0.18) suggested that the system was still at an immature stage. A low A/C (40.21%) coupled with a high O/C (59.79%) indicated the higher resilience of the ecosystem, with more than half of the energy allocated to buffering El Niño. By integrating informational flexibility with throughput, fish primarily enhance resilience, whereas benthic consumers mainly contribute to increased throughput. Acanthuridae appeared to play a crucial role in actively boosting the resilience of the ecosystem. Overall, the Nansha Islands coral reef ecosystem is evolving towards a more stable and mature state, warranting continued monitoring as a potential model system for ecological restoration.