Species composition and long-term dynamics of coral reef fishes at Meiji Reef, Nansha Islands

Abstract

Meiji Reef, in the east-central Spratly Islands, is a typical coral reef ecosystem with high fish biodiversity. To investigate fish community dynamics, we integrated multiple survey methods (longlining, hand-lining, drift gillnetting, dive fishing, and eDNA) with historical records (1998–1999, 2004, 2012, 2016–2019) and field surveys (2020–2024). The objectives were to characterize community composition, reveal long-term changes from 1998 to 2024, and assess succession following island reclamation. This integrated dataset enabled a systematic analysis of evolutionary trends in fish community structure at Meiji Reef. As of 2024, a total of 353 coral reef fish species have been documented, classified into 162 genera, 61 families, and 14 orders. Small fishes (43.81 %) and carnivorous fishes (74.92 %) dominated the community. We found a marked decline in the number of large carnivorous fish species since the 1998–1999 surveys, alongside an increase in the proportion of small carnivorous fishes and an overall reduction in mean length and weight of carnivorous fishes. The similarity coefficients for carnivorous fish species across different periods were consistently low, categorized as either "very dissimilar" or "dissimilar," indicating substantial community turnover. However, during the 2020–2024 period, the proportions of large carnivorous fishes and reef-dependent taxa, such as the Serranidae family, notably increased compared to 2016–2019, whereas proportions of smaller carnivorous species and taxa less dependent on live coral habitats, such as Sheepfishes (Labridae), decreased significantly. These findings suggest a gradual recovery of fish resources following reef reclamation, with increases in large carnivores and coral-associated taxa, and declines in non-coral-dependent taxa. Continuous long-term monitoring is essential for elucidating fish community succession patterns and is critically important for promoting the health and resilience of coral reef ecosystems.