When more mangroves mean fewer molluscs: Biodiversity relationships mediated by salinity in tropical coastal wetlands of Hainan Island, China

Résumé fourni par la source

Although positive aboveground-belowground biodiversity linkages are well-established, these relationships are context-dependent in natural communities, particularly in highly dynamic ecotones like mangrove ecosystems where plant-animal interactions remain poorly understood. This study aims to elucidate the complex relationship between plant and mollusc diversity in mangrove ecosystems, challenging the conventional paradigm that higher plant diversity invariably promotes faunal diversity. We focus on investigating how environmental factors mediate these relationships. Mangrove forests of Hainan Island, China—a representative tropical wetland system exhibiting conspicuous east-west plant-mollusc diversity mismatches. A multi-model approach (random forests, linear regression, and structural equation modeling) was used to analyze cross-shore diversity patterns, incorporating climatic, sedimentary, and landscape drivers along eastern (high-plant/low-mollusc) and western (low-plant/high-mollusc) coasts. (1) Significant east-west divergence: the eastern coast had significantly higher plant richness but lower mollusc richness than the western coast; (2) Salinity as critical mediator: plant richness enhanced mollusc diversity indirectly by reducing interstitial water salinity; (3) Environmental threshold effects: stronger negative plant-mollusc correlations occurred under low-stress conditions (average annual temperature < 24.8 °C, aridity index < 0.8, interstitial water salinity < 1.8%). This study quantified threshold effects in mangrove plant-animal relationships along environmental gradients. We propose a novel zone-specific conservation strategy: prioritizing vegetation protection on the eastern coast while emphasizing mollusc conservation on the western coast. These findings provide both theoretical foundations and practical pathways for precision management of mangrove ecosystems, offering valuable insights for coastal wetland conservation in the region.

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