Chapter 9 - Emersion and hypoxia

Abstract

As a common inhabitant of coastal waters and the intertidal zone, Carcinus maenas regularly experiences emersion and aquatic hypoxia. Emersion often occurs in intertidal habitats, where the ebb and flow of the tide results in a predictable transition between an aquatic and aerial environment. While air is oxygen rich, its dehydrating properties can restrict the performance of gas exchange structures. In comparison, aquatic hypoxia is characterized by low levels of dissolved oxygen that can occur naturally in enclosed waterbodies, such as isolated tidepools during low tide, but also in open environments, such as coastal waters, related to increased eutrophication and compounded by climate-induced warming. Emersion and hypoxia may seem to present similar physiological stress through the manifestation of an internal functional hypoxia during prolonged exposure, but initial responses to emersion and hypoxia can initiate a distinct set of behavioural and physiological responses. Over decades of research, C. maenas has played a major role in contributing towards our understanding of how coastal crustaceans respond to both emersion and hypoxia, particularly with regards to respiratory, cardiovascular, and acid-base physiology. For an aquatic decapod, C. maenas is an effective air breather during emersion and exhibits an impressive oxyregulatory capacity during aquatic hypoxia. In habitats where emersion and hypoxia can occur simultaneously (such as the intertidal), C. maenas is able to partially emerge out of hypoxic water to utilize the high oxygen availability in air to reoxygenate internal conditions while maintaining optimal conditions for gas exchange. The ability of C. maenas to tolerate and manipulate such environments contributes towards its widespread distribution and secures its status as a global marine invader.