Acute metabolic responses of two marine brachyuran crabs to dilute seawater: The aerobic cost of hyper regulation.

Hepatus pudibundus ("flecked box crab") is a stenohaline osmoconfomer, and restricted to marine habitats. Callinectes danae ("swimming crab Dana") lives in coastal/estuarine waters and is a weak hyper regulator. There is no consensus on which strategy is more expensive metabolically face salinity challenges: conformation with higher dependence on cell volume regulation, or hyper regulation, alleviating the need for intense cell volume regulation. Crabs were probed for their acute response to dilute seawater through exposures to salinities 35‰, 30‰, 25‰, and 20‰ for 2, 4, and 6 h. Hemolymph osmolality, lactate, and ions (chloride, sodium, magnesium, potassium) were assayed, as well as muscle water content. Water dissolved oxygen, ammonia, and pH levels were also measured. H. pudibundus conformed for osmolality and displayed increase in muscle hydration along the decrease in salinity down to 25‰, while C. danae efficiently maintained hemolymph osmo ionic stability, consumed more oxygen, acidified more the water, and released more ammonia. In 25‰, both species spent energy: H. pudibundus putatively controlling cell volume, and C. danae regulating hemolymph concentrations. In 20‰, H. pudibundus closed itself, avoiding the contact of the interface epithelia with the external environment and producing much lactate, whereas C. danae spent more energy (aerobic) in extracellular osmo ionic stability. Under these conditions, anisosmotic extracellular regulation (together with additional cell volume regulation) is more oxygen consuming than osmoconformation with a putatively more intense challenge to cell volume. The exposure to hyposalinity limits the occupation of estuarine environments by H. pudibundus in short and middle term.

Biomarkers of homeostasis, allostasis, and allostatic overload in decapod crustaceans of distinct habitats and osmoregulatory strategies: an empirical approach.

The term "allostasis", meaning the assumption that homeostasis may not be as static as the term implies, has been vastly employed for mammals, and other vertebrates, for which the degree of internal stability is maximal, according to their higher complexity. We have here investigated how these states of homeostasis, allostasis, and allostatic overload could be diagnosed in decapod crustaceans, upon acute salinity challenges. Decapods of distinct lineages and habitats have been submitted to 3 salinity levels for 6 and 12 h. The first salinity was the habitat salinity (control), considered as the one that allows the homeostatic condition. The next salinity represented a mild challenge, that would potentially lead to allostasis, and the third salinity was intended to represent an overload, albeit not lethal. Species used were: the marine crab Hepatus pudibundus (Hp, osmoconformer, salinities 33, 25, and 20‰), the marine/estuarine swimming crab Callinectes danae (Cd, weak regulator, salinities 30, 20, and 10‰), and the diadromous freshwater prawn Macrobrachium acanthurus (Ma, strong regulator, salinities <0.5, 15, and 30‰). These 3 species follow a sequence of growing regulatory capacity (Hp