1. Between-individual variation in behavioural phenotype, termed personality, is an important determinant of how populations cope with acute environmental fluctuation related to climate change. 2. Personality in the beadlet sea anemone (Actinia equina) is linked to genetically distinct morphotypes, which are associated with different heights on the shore. In the intertidal zone, high-shore environments experience more environmental fluctuation due to longer periods of exposure, and animals adapted to live in these environments are predicted to deal more effectively with environmental perturbation than their low-shore counterparts. 3. We collected beadlet anemones of two different morphotypes from three different shore-heights. We investigated variation in two behaviours at three different temperatures and in a temporal control treatment where the temperature was not changed: startle response-time, the time it took an anemone to re-extend its tentacles after a threatening stimulus, and immersion response-time, the time to re-extend tentacles after simulated tidal immersion. These behaviours reflect risk taking and allow individuals to be categorised as bold, shy or intermediate based upon response-times. 4. Both behaviours showed significant changes as the temperature increased. For immersion-response, the morphotype associated with the low-shore lengthened response-times at high temperatures. For startle-response, all animals lengthened their response-times at high temperatures but animals collected from the low-shore lengthened theirs to the greatest degree. At the individual level, although control individuals exhibited temporal changes in their response-times, a clear effect of temperature was present in both behaviours. Shy and bold individuals became more intermediate at higher temperatures in immersion-response (this effect was present to a lesser degree in control individuals), while intermediate individuals raised their response-times at higher temperatures for startle-response. 5. Given that prolonged tentacle retraction reduces foraging opportunities and can negatively impact respiratory efficiency, our data suggest that some individuals within a single population of A.equina, particularly those associated with the lower-shore, may exhibit less effective behavioural responses to temperature-shifts than others. These findings demonstrate that acute temperature changes influence risk-taking, and could have profound short and long-term implications for survival in the face of climate change. 16-Jun-2020