Some considerations on calcium homeostasis in semi-terrestrial crabs

Calcium (Ca), deposited as CaCO₃ after molting events take place, indicates that Ca levels in semi-terrestrial crabs should be regulated at the dietary level as well as through whole animal net Ca flux. Two semi-terrestrial crabs found in salt marsh environments (Sesarma rectum and Chasmagnathus granulata) were fed purified diets with variable Ca concentrations (0%, 2.22% and 6.66% Ca). Both animals displayed similar feeding strategies through consumption of higher amounts of the diet containing more Ca (6.66% Ca). Sesarma, a predominantly herbivore crab, ate more quantities of all the diets offered when compared to Chasmagnathus, a more carnivorous crab. Whole animal net fluxes of Ca over 5 days in Sesarma show that fluxes vary from 2.5 to 1.5 mmol kg^-1 h^-1, similar to values found earlier for a crayfish, Procambarus clarkii. However, the fluxes over 5 days did not decrease significantly compared to fluxes for the first day postmolt. Overall, semi-terrestrial crabs seem to maximize Ca influx through the gills and through dietary intake, a mineral that is known to have great importance for biomineralization in crustaceans.