Long-term vegetation succession increases aquatic animal structural stability and functional vulnerability following pond-to-mangrove restoration

Abandoned pond-to-mangrove restoration, as a more cost-effective method than mudflat afforestation, would be the primary method of mangrove restoration globally in the future. Comparing the long-term recovery and evolution characteristics of aquatic animal community assembly and key drivers across nutrient levels is essential to systematically assess the ecological benefits and effectiveness of pond-to-mangrove restoration. Here, we carried out long-term monitoring on the aquatic animal species and functional diversity recovery after abandoned ponds converted to mangroves in China’s first pond-to-mangrove restoration area of Southern China. Co-occurrence network model and multivariate statistical analysis were used to compare the aquatic animal community assembly and key drivers across nutrient levels at different succession stages (5 years, 9 years, 28 years). We found that an increase in species and functional diversity of aquatic animals as mangrove succession in pond-to-mangrove restoration sites, but functional diversity recovery lags behind species diversity, which was dominated by changes in soil organic matter, seawater salinity, and plant traits. Greater niche width in crustacean community caused more rapid recovery than the mollusk and fish communities. Although structural stability of aquatic animals increased, functional vulnerability increased as well owing to abiotic-driven functional redundancy decrease. Deterministic processes and stochastic processes have a disproportionate influence on the community assembly of aquatic animals, and biological stochastic processes are dominant. As mangrove succession, the stochastic process always has a higher explanation for fish, and the influence on mollusks gradually decreases, while the influence on crabs gradually increases. Our findings highlight that long-term evolution of species and functional diversity in aquatic animals and different recovery strategy across nutrient levels following the pond-to-mangrove restoration, which provide scientific evidence for the long-term biodiversity conservation and restoration of mangrove forests. • Evolution heterogeneity in structure and function among aquatic animal community after pond-to mangrove restoration was unveiled. • Functional diversity recovered slower than species diversity due to loss of redundancy from abiotic change. • Crustaceans recovered faster than mollusks and fish owing to their broader ecological niche widths. • Aquatic animal community assembly was dominated by vegetation succession and biological stochastic processes.