Trait-based vulnerability and tolerance thresholds of tropical mollusks in light of projected increases in climate-change stressors

Extreme climate conditions increasingly threaten worldwide coastal biodiversity. We applied a trait-based approach to quantify the tolerance thresholds of 13 mollusk species from five tropical coastal habitats, using controlled experiments that simulate extreme temperature, salinity, submersion, and desiccation stress. Survival was analyzed in relation to functional traits, including isolation from ambient conditions (presence/absence of shell closure and/or operculum), respiration mode (branchial or pulmonate), shell thickness, and habitat type. Thermal safety margins (TSMs) were also projected under future climate scenarios. Species that possess isolation traits consistently survived across stress conditions. Bivalves generally tolerated higher temperatures and broader salinity ranges than gastropods, and pulmonate gastropods experienced high mortality under both prolonged submersion and desiccation. Desiccation tolerance was strongly associated with the ability to isolate. Thicker shells provided limited protection against extreme temperatures but did not protect taxa with narrow salinity tolerances. Projected TSMs indicated that species from mangrove and oyster-bank habitats will be subject to temperatures that exceed their upper thermal limits before the end of this century. Vulnerability to climate change arises from a combination of functional traits and habitat context. By addressing multiple climate-related variables, i.e., temperature, salinity, inundation, and desiccation, all of which are shifting with global climate change, this study identified combinations of traits that will confer tolerance to tropical mollusks under future conditions and identified taxa that will likely be at risk. This study fills critical data gaps for tropical habitats worldwide and provides a framework for predicting biotic responses to climate extremes.