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

Abstract

AbstractHepatus 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. pudibundusconformed for osmolality and displayed increase in muscle hydration along the decrease in salinity down to 25‰, whileC. danaeefficiently maintained hemolymph osmo ionic stability, consumed more oxygen, acidified more the water, and released more ammonia. In 25‰, both species spent energy:H. pudibundusputatively controlling cell volume, andC. danaeregulating hemolymph concentrations. In 20‰,H. pudibundusclosed itself, avoiding the contact of the interface epithelia with the external environment and producing much lactate, whereasC. danaespent 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 byH. pudibundusin short and middle term.