Taxonomic and functional diversity reveal contrasting crab community dynamics under artificial and natural pond to mangrove restoration

Mangrove restoration is critical for the resilience of coastal ecosystems, yet there remains insufficient research on the ecological effects of artificial versus natural restoration, especially regarding their impacts on faunal communities and ecosystem functions. This study used a space-for-time substitution approach to investigate the taxonomic and functional diversity of crab communities along a 27-year pond-to-mangrove restoration chronosequence in Dongzhaigang Bay, southern China. We analyzed temporal changes in community composition and functional traits under artificial and natural restoration approaches, compared alpha diversity and the components of beta diversity across sites, and explored the influence of environmental variables on variations in crab community structure. A total of 3,700 crabs representing 24 species were recorded. Artificial restoration sites exhibited rapid early colonization, with species richness reaching 1.5 times that of natural restoration sites by year 4. However, by year 27, both artificial and natural restoration sites showed no significant differences in crab taxonomic and functional diversity compared to natural mangroves. The results indicate that species composition in both restoration types underwent a typical successional process, beginning with dominance by filter-feeding Ocypodidae crabs in the early stages and gradually shifting to dominance by herbivorous and omnivorous crabs of the Grapsoidea family in later stages. Nevertheless, the proportion of functional groups in naturally restored sites was closer to that of natural mangroves. Soil pH and salinity were identified as the primary environmental drivers shaping both taxonomic and functional community patterns. Based on these findings, we emphasize the importance of incorporating functional traits and successional dynamics alongside taxonomic metrics to more accurately assess the ecological recovery of mangrove restoration efforts.