The importance of tidal acclimation when assessing the physiological responses of Carcinus maenas to environmental stressors

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 held these organisms in constant submerged conditions. However, this is not representative of the daily cycle of emersion and immersion that intertidal organisms experience in their natural habitat. In this thesis, I explored whether acclimation of the intertidal green crab Carcinus maenas to a continuous simulated tidal cycle (from herein referred to as ‘tidal’ crabs) resulted in different physiological responses to environmental stressors compared to crabs acclimated to permanently submerged (‘non-tidal’) conditions. Chapter 1 reviews the previous literature on the physiological tolerance of C. maenas to emersion, hypoxia and thermal stress and opens the discussion of the importance of ecological realism in experimental design for accurate physiological responses. Chapter 2 and 3 are experimental research manuscripts that investigates how tidal acclimation influences the physiology behind oxygen delivery and acid base balance during submersion and emersion (Chapter 2), and hypoxia and thermal stress (Chapter 3). Chapter 4 serves as an overall general discussion of Chapters 2 and 3 with suggestions for future research directions. Overall, the findings of my research show that acclimation to a tidal regime produces physiological adjustments such as elevated haemocyanin levels and lower oxygen consumption during submersion that can influence how crabs respond to environmental stressors. Notably, acclimation to a tidal regime allows C. maenas to avoid the metabolic acidosis that occurs in non-tidal crabs during emersion, likely through the buffering effects of elevated hemocyanin. The results of this study suggest that how C. maenas responds to common stressors in the intertidal is complex, and that adaptation to air exposure during low tides may alter their physiological responses to other environmental stressors. In order to gain a better understanding of how intertidal organisms will respond to predicted environmental changes, laboratory experiments should incorporated a tidal regime into their design.