Embryonic encapsulation and maternal incubation: Requirements for survival of the early stages of the estuarine gastropod Crepipatella dilatata

During their reproductive period, females of Crepipatella dilatato deposit their embryos in capsules that they then brood in the pallial cavity until juveniles emerge several weeks later, after passing through a transient veliger larval stage. Artificially excapsulated veligers of this species experimentally exposed to a wide range of salinities (5,10,15, 20, 25, and 30 psu) for six hours showed reduced activity at salinities of 15 and 20 psu, whereas encapsulated veligers exposed to those same salinities showed no reduction of activity. Artificially excapsulated veligers showed high mortality at salinities of 5 and 10 psu; encapsulated embryonic stages also showed high mortalities at 5 psu and serious sublethal effects at 10 psu in tests excluding maternal protection, showing that encapsulation alone does not provide complete protection from low salinity stress. Natural tidal cycles in the Quempillen River estuary also reduced embryonic survival at salinities of :5 10 psu when the capsules were exposed without maternal protection. In contrast, encapsulated embryos protected by their mothers survived well regardless of the salinity to which they were exposed, under both natural and laboratory-simulated estuarine tidal cycles. C dilatata are able to develop in the estuary only because of maternal protection, since salinity levels in this environment sometimes decline to as low as 7 psu. Successful embryonic development in this estuary reflects the capacity of C dilatata adults to detect dangerously low salinity levels and then seal themselves off from the environment for up to 50 hrs (O. Chaparro pers. obs.) when the salinity drops below 22.5 psu, allowing salinity to remain above this level within the pallial cavity despite continued salinity declines in the surrounding seawater. (C) 2008 Elsevier BY. All rights reserved.