High-density Tegillarca granosa improves water quality and reduces greenhouse gas emissions in sulfamethoxazole-exposed mangrove microcosms.

Anthropogenic activities have led to increasing antibiotic contamination in mangrove wetlands, posing a potential threat to their ecosystem functioning. As ecosystem engineers, benthic fauna may regulate water purification and greenhouse gas (GHG) emissions in a density-dependent manner, but their ecological roles under antibiotic exposure remain poorly understood. Here, a two-factor microcosm experiment combining antibiotic addition with three densities of Tegillarca granosa was conducted to investigate effluent nutrient concentrations, CH4, N2O, and CO2 emissions, sediment enzyme activities, and microbial community structure. The results showed that (1) in the absence of antibiotics, high-density T. granosa reduced effluent TP concentrations and was associated with enhanced acid phosphatase (ACP) activity, whereas T. granosa density had limited effects on effluent nutrient concentrations under antibiotic exposure; (2) T. granosa density had no significant effect on GHG emissions in the absence of antibiotics, but the high-density treatment significantly reduced cumulative N2O and CH4 emissions under antibiotic exposure; (3) under antibiotic exposure, high-density T. granosa also altered the activities of nitrification- and denitrification-related enzymes, suggesting enhanced microbial nitrogen transformation; (4) T. granosa density exerted little influence on microbial community structure in the absence of antibiotics but induced shifts in microbial taxa putatively linked to nitrogen transformation and methane oxidation under antibiotic exposure. These findings highlight the context-dependent role of benthic fauna in regulating mangrove ecosystem functions and suggest that maintaining appropriate densities of native benthic fauna may represent a nature-based strategy for reducing GHG emissions in antibiotic-contaminated mangrove wetlands.