Tropical ectotherms are predicted to be especially vulnerable to climate change because their thermal tolerance limits generally lie close to current maximum air temperatures. This prediction derives primarily from studies on insects and lizards and remains untested for other taxa with contrasting ecologies. We studied the HCT (heat coma temperatures) and ULT (upper lethal temperatures) of 40 species of tropical eulittoral snails (Littorinidae and Neritidae) inhabiting exposed rocky shores and shaded mangrove forests in Oceania, Africa, Asia and North America. We also estimated extremes in animal body temperature at each site using a simple heat budget model and historical (20 years) air temperature and solar radiation data. Phylogenetic analyses suggest that HCT and ULT exhibit limited adaptive variation across habitats (mangroves vs. rocky shores) or geographic locations despite their contrasting thermal regimes. Instead, the elevated heat tolerance of these species (HCT = 44.5 ± 1.8°C and ULT = 52.1 ± 2.2°C) seems to reflect the extreme temperature variability of intertidal systems. Sensitivity to climate warming, which was quantified as the difference between HCT or ULT and maximum body temperature, differed greatly between snails from sunny (rocky shore; Thermal Safety Margin, TSM = −14.8 ± 3.3°C and −6.2 ± 4.4°C for HCT and ULT, respectively) and shaded (mangrove) habitats (TSM = 5.1 ± 3.6°C and 12.5 ± 3.6°C). Negative TSMs in rocky shore animals suggest that mortality is likely ameliorated during extreme climatic events by behavioral thermoregulation. Given the low variability in heat tolerance across species, habitat and geographic location account for most of the variation in TSM and may adequately predict the vulnerability to climate change. These findings caution against generalizations on the impact of global warming across ectothermic taxa and highlight how the consideration of nonmodel animals, ecological transitions, and behavioral responses may alter predictions of studies that ignore these biological details.

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Neritid snails are diverse and conspicuous in tropical coastal environments. They can serve as indicators of environmental change and can provide conservation information. In the present review of the neritid species of Brunei Darussalam, we report sixteen species, including seven new records from estuarine, mangrove and rocky-shore habitats. These records update distributions across the Central Indo-Pacific realm, specifically the Palawan/North Borneo ecoregion. Under-sampling, species misidentifications and locally-rare species undermine the accuracy of records in previous studies for the region. Three of the rocky-shore and two of the mangrove species collected here are represented by single specimens; these rocky-shore species are possible colonizers from neighbouring regions and the scarcity of the mangrove species likely refers to under-sampling. We present novel shell characteristics that readily distinguish between Neripteron violaceum and Nerip. cornucopia. We describe the ecology and habitat use of the Brunei species and discuss conservation issues.