Effect of oxygen conditions on intracapsular development in two calyptraeid species with different modes of larval development

Oxygen availability in the aggregation of offspring has been shown to be a critical factor affecting the survival and development of embryos in aquatic systems. It is not yet known, however, to what extent the capacity to provide 02 to embryo aggregations may act on the time of parental protection (here encapsulation), ultimately determining indirect. and direct embryonic development. We assessed 02 conditions during encapsulation, the factors determining those conditions, and the consequences on embryo survival in 2 gastropod species with contrasting developmental modes: Crepidula fornicala, an indirect developer, and Crepidula coquimbensis, a direct developer showing adelphophagy. Results showed that intracapsular 02 conditions decreased to almost hypoxic conditions throughout development in C. fornicala, in contrast to the oxygenated conditions observed in C. coquimbensis during the entire encapsulation period. These contrasting patterns between species were explained by: (1) differences in metabolic rate of the embryos, (2) differences in total metabolizing material per capsule throughout development, and (3) differences in wall thickness and rates of decay throughout development, which may affect 02 diffusion. Moreover, when the low O-2 conditions observed at the end of the encapsulation period were maintained after hatching by artificially extending encapsulation for 2 d, a dramatic negative effect on embryonic survival was observed in the indirect developer. In contrast, no effect on juvenile survival was observed in the direct developer. We suggest that hatching at intermediate stages of embryonic development in C. fornicata may be a response to increased 02 constraints during the encapsulated period.