ABSTRACT

" SOME PERSPECTIVES ON REPRODUCTION AND LARVAL ECOLOGY OF NUDIBRANCH MOLLUSCS "

Our perspective of the life cycles and life histories amongst nudibranch molluscs is perhaps biased toward the prevalence of annual or sub-annual life cycles and the semelparous reproductive strategy. In the British Isles there are several species (including Archidoris pseudoargus (Rapp)) which are biennial and semelparous, reproducing only in their second year. Relatively large body size, and specialist predation on long-lived and seemingly stable prey species populations, appear to be co-adaptive traits displayed by these biennials. More unusual is the relatively small dorid, Cadlina laevis (L.): field and laboraotory observations have shown that this species is exceptional in being relatively small and very slow-growing. Individuals reproduce for the first time only when two years old and they are iteroparous, surviving to spawn for up to perhaps three or four further years. A further unusual feature is that only the one spawn mass is produced by reproductive individuals in any one year. Data concerning the growth, respiration and reproductive energetics of Cadlina laevis will be discussed. Consideration also will be given to egg size variation, and possible implications thereof, on the evolution of lecithotrophic larval forms amongst nudibranch molluscs. Finally, from laboratory observations of larval metamorphic behaviour, population genetic analyses and field transplant experiments between genetically distinct populations, the dispersal and colonising abilities of pelagic lecithotrophic larvae will be considered.

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