Nurse egg consumption and intracapsular development in the common whelk Buccinum undatum (Linnaeus 1758)

Abstract

Intracapsular development is common in marine gastropods. In many species embryos develop alongside nurse eggs, which provide nutrition during ontogeny. The Common Whelk Buccinum undatum is a commercially important North Atlantic shallow-water gastropod, which undergoes this type of development, with individuals hatching as crawling juveniles. While its reproductive cycle has been well documented, past observations on the encapsulated development in this species do not match our observations and nurse egg partitioning within a capsule has not previously been discussed. Here, using laboratory reared B. undatum egg masses from the south coast of England, intracapsular development at 6°C is described including nurse egg partitioning, timing of nurse egg consumption and intracapsular size differences through development. Number of eggs, veligers and juveniles per capsule were also compared. Development took 133 to 140 days, over which 7 ontogenetic stages were identified. Numbers of both eggs and veligers were significantly related to capsule volume. Initial development was asynchronous within each capsule. In total approximately 1% of eggs developed per capsule. Each embryo consumed nurse eggs rapidly over just 3 to 7 days. No evidence for cannibalism was found during development but large size differences between embryos developing within each capsule were observed, and occasionally ‘empty’ veligers were seen which had not successfully consumed any nurse eggs. These results indicate high competition for nurse eggs within each capsule during development in the common whelk. The initial differences observed in embryo size may affect individual predisposition in later life.

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