Seasonal life history phenomena were monitored through 1978 for two sublittoral cheilostome bryozoans from souther Britain: Chartella papyracea (Ellis and Solander), a non-placental brooder, and Bugula flabellata (Thompson in Gray), which is placental. The intracolonial relationships between growth by zooid budding, polypide recycling, and sexual reproduction, were analysed for both species — quantitatively in the case of C. papyracea. Although both species grow only in summer, their life histories differ. C. papyracea is more of a K-strategist, producing perennial fronds that release larvae in several successive years, most being liberated in winter months. The reduced need for maximization of the larval productivity rate is reflected in the intracolonial configuration of polypide and sexual recycling. B. flabellata is more of an r-strategist. The larvae are produced by the ephemeral fronds of two successive colony generations each summer. Colonies are dormant in winter. The need to maximize the larval productivity rate in this species is reflected in the polypide/sexual recycling configuration. It is believed that embryonic placentation contributes to the maximization of the larval productivity rate in this and other placental brooders. |
