Mid-intertidal mangrove belts concentrate ecosystem multifunctionality in a semi-enclosed estuary

Mangrove ecosystems are dynamic coastal interfaces that play important roles in nutrient cycling, carbon sequestration, and biodiversity conservation. However, how their multifunctionality responds to spatial gradients in tidal regimes remains poorly understood. Here we assessed plant communities, soil properties, microbial community structure, greenhouse-gas (GHG) fluxes, and ecosystem multifunctionality (EMF) across three mangrove zones in Qinglan Bay, Hainan, China (marine-influenced ≈60 m, mid-intertidal ≈400 m, and terrestrial-edge ≈600 m from the coastline). EMF integrated 33 indicators spanning vegetation, soil, microbial, and GHG attributes. Results showed that the Site Ⅱ showed significantly higher plant diversity (Shannon index: 1.29 ± 0.06; p < 0.05) and evenness (0.34 ± 0.00) than the other two sites. Site II showed the highest soil organic carbon (37.8 ± 3.28 g kg^-1), total nitrogen (1.48 ± 0.11 g kg^-1), available nitrogen (124 ± 15.1 mg kg^-1), and available potassium (261 ± 26.6 mg kg^-1) among the three sites. Microbial α-diversity did not differ significantly across sites; however, microbial co-occurrence networks at Site II showed higher modularity and lower average connectivity (modularity = 0.827; avgK = 2.65), indicating a more compartmentalized configuration of microbial interactions. Ecosystem multifunctionality (EMF) was quantified using 33 indicators spanning plant, soil, microbial, and greenhouse gas (GHG) attributes. Each indicator was first min-max normalized to the [0,1] range, after which a weighted mean was calculated for each plot. EMF peaked at Site II and was positively correlated with key soil nutrient indicators (e.g., TOC, TN, AK). A combination of moderate tidal activity creates favorable conditions for soil nutrient dynamics. In comparison, Sites I and III showed comparatively lower EMF, in line with distinct environmental constraints: Site I experienced stronger marine forcing due to its proximity to the coastline, whereas Site III was characterized by phosphorus enrichment. The highest EMF occurred in the mid-intertidal zone, highlighting the ecological importance of intermediate tidal positions. The mid-intertidal mangrove zones can support higher functional diversity, because hydrological conditions at intermediate tidal elevations balance relative stability with ecological complexity, thereby promoting the maintenance of multiple functions. Our results support zoning strategies that balance ecosystem services with land-use needs. This applies to coastlines supporting aquaculture and coastal agriculture.