Radio tracking detects behavioral thermoregulation at a snail's pace

The dynamic ebb and flood of tides makes the marine intertidal zone a habitat with temperatures that fluctuate rapidly in both space and time. This is problematic for slow intertidal organisms that cannot move at the speed of tidal fluctuations. The timing of low tides determines which days organisms may experience extreme body temperatures, controlling microclimate to a greater degree than weather patterns. When low tides occur midday, temperatures can exceed critical thermal maxima for many species. Although high shore areas experience the greatest environmental extremes, they often harbor untapped food resources. The periodicity of low tide timing creates a predictable cycle that marine animals can use to obtain food in risky areas while minimizing exposure to thermal extremes. Here, we use a two-part approach to assess whether the snail, Nucella ostrina, uses the predictability of the tidal cycle to obtain food in risky areas while minimizing exposure to thermal extremes. Radio tracking detected the presence/absence of snails in high shore feeding areas continuously for 14 weeks and physical thermal models approximated snail body temperature in those high shore areas. Snails were absent when extreme low tides occurred at times of high solar irradiance (midday). Comparing the subset of physical model body temperatures foraging snails experienced to all available body temperatures in the high shore environment showed snails in foraging areas disproportionately at 9-12 °C and absent at body temperatures > 31 °C, suggesting that N. ostrina is not present when and where thermal risk is greatest. These patterns demonstrate that censusing only at low tide yields an adequate picture of foraging behavior of this species in its natural habitat, and that migratory foraging behavior effectively moderates snail experience of environmental temperature in nature and may buffer this species from aerial warming.