Enantiostasis

Enantiostasis is the ability of an open system, especially a living organism, to maintain and conserve its metabolic and physiological functions in response to variations in an unstable environment. Estuarine organisms typically undergo enantiostasis in order to survive with constantly changing salt concentrations. The Australian NSW Board of Studies defines the term in its Biology syllabus as "the maintenance of metabolic and physiological functions in response to variations in the environment".

Enantiostasis is not a form of classical homeostasis, meaning "standing at a similar level," which focused on maintenance of internal body conditions such as pH, oxygen levels, and ion concentrations. Rather than maintaining homeostatic (stable ideal) conditions, enantiostasis involves maintaining only functionality in spite of external fluctuations. However, it can be considered a type of homeostasis in a broader context because functions are kept relatively consistent.

The term enantiostasis was proposed by Mangum and Towle. It is derived from the Greek ἐναντίος (enantio-; opposite, opposing, over against) and στάσις (stasis; to stand, posture).

An example of an organism which undergoes enantiostasis in an estuary environment includes-

• The oxygen binding effectiveness of hemocyanin in the blue crab Callinectes sapidus varies according to the concentration of two factors, calcium ion concentration, and hydrogen ion concentration. When these concentrations are varied in the same direction, they have a counterbalancing effect. To stabilize oxygen binding at low ionic concentrations, the crab increases its internal pH (decreasing the hydrogen ion concentration) to allow the hemocyanin to continue to function efficiently.