Effects of seawater alkalinity on calcium and acid-base regulation in juvenile European lobster (Homarus gammarus) during a moult cycle

Fluxes of NH4+ (acid) and HCO3− (base), and whole body calcium content were measured in European lobster (Homarus gammarus) during intermoult (megalopae stage), and during the first 24 h for postmoult juveniles under control (~ 2000 μeq/L) and low seawater alkalinity (~ 830 μeq/L). Immediately after moulting, animals lost 45% of the total body calcium via the shed exoskeleton (exuvia), and only 11% was retained in the uncalcified body. At 24 h postmoult, exoskeleton calcium increased to ~ 46% of the intermoult stage. Ammonia excretion was not affected by seawater alkalinity. After moulting, bicarbonate excretion was immediately reversed from excretion to uptake (~ 4-6 fold higher rates than intermoult) over the whole 24 h postmoult period, peaking at 3-6 h. These data suggest that exoskeleton calcification is not completed by 24 h postmoult. Low seawater alkalinity reduced postmoult bicarbonate uptake by 29% on average. Net acid-base flux (equivalent to net base uptake) followed the same pattern as HCO3− fluxes, and was 22% lower in low alkalinity seawater over the whole 24 h postmoult period. The common occurrence of low alkalinity in intensive aquaculture systems may slow postmoult calcification in juvenile H. gammarus, increasing the risk of mortalities through cannibalism.