Ecosystem restructuring of subtidal oyster reefs responding to a dredged material disposal disturbance revealed by ecological network analysis

Understanding how coastal ecosystems reorganize after abrupt anthropogenic disturbances is fundamental for predicting ecosystem resilience and informing adaptive management strategies. Here, we examined the temporal reorganization of an oyster reef ecosystem responding to an unexpected dredged material dumping event using a before-after assessment framework. Four annual Ecopath models (2017-2020) were constructed to characterize temporal variations in ecosystem structure, energy pathways, trophic organization, and functional resilience. Ecosystem-level indicators displayed strong temporal fluctuations (p < 0.001), with total system throughput and total biomass decreasing in the order of 2017 > 2020 > 2019 > 2018. Following extensive mortality of oysters and macroalgae, the ecosystem experienced substantial functional reorganization in 2018, characterized by reduced ascendency/development capacity ratio and connectance index, together with increased system omnivory and total primary production/total respiration ratio (p < 0.001). These shifts suggested enhanced trophic flexibility accompanied by reduced ecosystem maturity. Following the disturbance, Finn's cycling index, Finn's mean path length, and the detritivory/herbivory ratio increased and reached their maximum values in 2019, indicating enhanced detritus-based energy pathway. Keystone functional groups gradually shifted from fish-dominated regulation toward invertebrate-mediated control, while oysters consistently remained among the dominant functional groups. Redundancy/ascendency index analysis revealed that top predators played important roles in maintaining ecosystem stability under disturbance, whereas zooplankton functioned as key mediators of trophic connectivity. Collectively, these results demonstrated that ecosystem stability depends on higher functional diversity, trophic connectivity, and ecological redundancy. Maintaining ecosystem engineers and preserving diverse energy pathways may therefore represent essential strategies for sustaining ecosystem resilience and long-term ecological stability.