The role of tidal acclimation on the physiological responses of the green shore crab, Carcinus maenas, to thermal stress

Abstract

Animals inhabiting the intertidal zone are exposed to abrupt changes in environmental conditions associated with the rise and fall of the tide. For convenience, the majority of laboratory studies on intertidal organisms have acclimated individuals to permanently submerged conditions, and thus we currently know little about how acclimation to cyclic emersion-immersion influences the ability of intertidal organisms to cope with fluctuations in environmental conditions. In the present study, the green shore crab Carcinus maenas was acclimated to either a simulated tidal regime of continuous emersion-immersion (tidal) or to permanently submerged conditions (non-tidal). Aquatic oxygen consumption was assessed when crabs were exposed to cooling (15 °C - 5 °C) or warming (15 °C - 25 °C) regimes. Tidal crabs had lower levels of oxygen consumption over the 15 °C - 20 °C range. During acute thermal stress, the Q10 values of non-tidal crabs increased as the temperature declined to 5 °C, whereas tidal crabs maintained relatively consistent Q10 values across the temperature range (5 °C–25 C). These changes in oxygen consumption were paralleled by changes in haematological parameters. Tidal crabs had higher levels of haemocyanin which may have augmented oxygen delivery to the tissues and buffered acid-base imbalances. Surprisingly lactate levels were higher in tidal crabs, these appeared unconnected to anaerobic metabolism, but may have been an important metabolic fuel for tidal crabs. These results suggest that acclimation to a simulated tidal cycle may result in different physiological responses to environmental stressors and as such is an important consideration when assessing the responses of intertidal animals in a laboratory setting.