Isolation of incubation chambers during brooding: effect of reduced pH on protoconch development in the estuarine gastropod Crepipatella dilatata (Calyptraeidae)

The sedentary gastropod Crepipatella dilatata encapsulates its embryos and incubates them in the pallial cavity. Females Can deliberately isolate their embryos from the external environment for many hours at a time by pressing their shells tightly against the substrate. We documented the effects of such isolation on pH in the pallial cavity and the effects of reduced pH on changes in shell thickness and the proportion of calcium in embryonic shells. We also quantified the concentration of calcium in the water retained in the pallial cavity during isolation, as well as the growth of encapsulated veligers. Average protoconch thickness decreased by as much as 50% at reduced pH (pH = 6 to 3). During 24 h of exposure to water at the different pHs, calcium was lost from shells, but in swine proportion as the loss of other components. Calcium in the pallial fluid increased during the first 5 h of isolation for both brooding and non-brooding females, suggesting shell dissolution. The calcium content of pallial cavity fluid for brooding females differed from that of non-brooding females, but did not differ from that in the intracapsular fluid, suggesting that calcium diffuses freely through the egg capsule wall. Isolation of the incubatory chamber impeded embryonic shell growth, possibly because the calcium was acting as a 'buffer' to regulate pH changes in the pallial fluid. The isolation of embryos by incubating females, usually viewed as an adaptive benefit of brooding, can cause pronounced negative effects on embryonic development during the period of shell formation.