Evaluation and forecasting of habitat suitability and thermal growth responses in the mud clam Geloina coaxans under climate change.

The mud clam (Geloina coaxans) is an ecologically important mangrove-associated bivalve. However, its sensitivity to climate warming and future growth responses remain insufficiently understood. By jointly analyzing habitat suitability predictions from an Ensemble Species Distribution Model (ESDM) with growth simulations from a Dynamic Energy Budget (DEB) model, this study provides a comprehensive assessment of the mud clam's thermal sensitivity and growth dynamics under climate change. The ESDM results indicated that suitable habitats are concentrated within Indo-Pacific mangrove regions, including the Beibu Gulf, northern and northeastern Australia, southern Vietnam, southern Indonesian islands and Pacific islands. These habitats are characterized by similar sediment nitrate levels, seasonal precipitation patterns, sediment electrical conductivity, and stable tropical to subtropical thermal regimes. The mud clam exhibited stronger responses to nutrient availability and seasonal precipitation variability than to other environmental factors. DEB simulations under SSP585 indicated that warming significantly reduces growth and induces body size miniaturization: compared to current conditions, grid cells with shell length >5 cm and dry mass >1.2 g decline by 42.9% and 53.3%, respectively. Within major medium- and high-suitability areas, growth reduction is most pronounced along eastern Australia, with maximum decreases of 0.77 cm in shell length and 0.57 g in dry mass. The miniaturization may result from increased maintenance and stress-related metabolic demands under thermal stress, reducing energy available for growth. This study provides a basis for conservation of mud clam resources and improves mechanistic understanding and prediction of warming impacts on mangrove-associated benthic bivalves.