Abstract

Although periods of severely reduced oxygen concentration are occurring with increasing frequency in coastal marine ecosystems, the effects of such exposures on early development have not been extensively explored. Brooding females of the gastropod Crepipatella dilatata expose their embryos to such hypoxic conditions (< 1 mg O-2 l(-1)) naturally during periods of intense seasonal rains, when they isolate their brood chambers from the external environment for long periods. We investigated the effects of such reduced oxygen availability on the encapsulated embryos and also looked for delayed (` latent') effects on juveniles after their emergence from the mothers. After 24, 48 or 72 h at oxygen levels <1 mg O-2 l(-1), at 12 degrees C and 30 psu salinity, females were transferred to aerated seawater. Many females selectively evicted some of their egg capsules, particularly those containing advanced embryos. Also, juvenile emergence was de layed, although those individuals emerging later had the same mean size as those derived from non-stressed embryos. Latent effects were also observed: the hypoxia experienced during embryonic development reduced the number of juveniles successfully emerging per female and severely compromised juvenile growth and survival over the next 30 d. Our results show that extended periods of severe hypoxic conditions can have a dramatic impact on early development and reproductive fitness, with some effects not appearing until long after normoxic conditions have been restored and the juveniles have emerged into the natural environment. The study also shows that brooding can in some situations expose embryos to severe stresses, even while protecting embryos from other stresses.