Behavioral Response of Hermit Crabs (Clibanarius digueti) to Dissolved Carbon Dioxide

CO₂ induced ocean acidification is currently changing the population dynamics of marine organisms. This can involve increased stress in populations, and alteration in individual physiology, which can eventually be expressed through an organism’s behavior. If sustained, CO₂ induced ocean acidification has the potential to cause major impacts on marine food chains, including on services they provide. The purpose of this study was to understand whether and how ocean acidification affects the behavior of hermit crab Clibanarius digueti, a crustacean inhabiting the littoral zone. We hypothesized that an increase in dissolved carbonic acid would modify grazing and individual movement, because an increase in acidification alters the normal chemical composition of the water and potentially the physiology of C. digueti. A model tidal pool experiment consisting of two tanks (control and treatment) inhabited with seven living C. digueti was set up in the Ocean Biome of Biosphere-2. Each tank was also provided with uninhabited shells: two Turbo fluctuosa and four Cerithium sp. Gaseous CO₂ was dissolved into the treatment tank and measured as dissolved CO₂ by using a NaOH titration method. Additionally, water conditions were characterized for light and temperature. Two trials were run in this experiment with tanks and treatments interchanged in each trial. We found a marked treatment effect on C. digueti behavior. The population experiencing increased CO₂ performed daily shell changes after first day of exposure for each of the 4-day trials, as compared to individuals unexposed to dissolved CO₂, that experienced no shell changes. From this study we conclude that the behavior of C. Digueti can be a good indicator of changes in dissolved CO₂. This would allow us to better interpret patterns in marine animal behavior in response to climate change.