Mangrove expansion onto mudflats leaves benthic food webs energetically decoupled

Mangrove reforestation projects are increasingly being expanded onto historically unvegetated tidal flats, raising critical questions about how such habitat conversion alters the structure and functioning of the original ecosystem. Here, we investigated how mangrove afforestation reshapes benthic trophic structure and energy pathways in mudflat ecosystems of Yanpu Bay, China, using stable isotope (δ¹³C and δ¹⁵N) analyses. Trophic levels and food-chain length were comparable between habitats, indicating that afforestation reconfigured energy pathways without fundamentally altering vertical trophic structure. MixSIAR modeling further revealed that, despite the introduction of mangrove litter, microphytobenthos (MPB) remained the dominant energy source supporting macrobenthic consumers. Conversely, mangrove-derived organic matter provided a negligible contribution to macrobenthic diets, serving instead as a localized carbon sink or entering the sediment pool after microbial conditioning. Isotopic niche analyses demonstrated habitat-specific responses among feeding guilds: filter feeders shifted from a reliance on pelagic particulate organic matter in mudflats toward MPB in mangroves, while the broader niches of herbivores in mangroves were driven by taxonomic recruitment rather than dietary diversification. At the community level, total isotopic niche area was larger in mudflats, reflecting greater resource diversity and trophic heterogeneity in the open habitat. Overall, while mangrove establishment on unvegetated tidal flats enhanced habitat complexity, it did not lead to substantial functional integration of mangrove-derived production into benthic food webs. Given the multifaceted ecological value of mudflats, including their roles in biodiversity conservation, migratory shorebird foraging, and carbon storage, their conversion to mangroves requires careful justification. Our study provides a food-web perspective on the ecological consequences of such afforestation, highlighting the importance of prioritizing site-specific ecosystem functions over generalized tree-planting targets.