The population ecology of Onchidoris bilamellata (L.) (Gastropoda: Nudibranchia)

Christopher D. Todd*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

27 Citations (Scopus)

Abstract

Onchidoris bilamellata (L.) appears to be largely intertidal in distribution although it does not extend as high up the shore as Balanus balanoides (L.), the major prey organism. Local distribution of the nudibranch is largely determined by desiccation and is, therefore, an expression of the coincidence of certain prerequisite physical (shade and dampness) and biological (presence of Balanus) factors. Mortality has been shown to be density-dependent, resulting in breeding populations of similar size and structure from year to year, in spite of widely differing levels of annual recruitment. Although as yet not proved, it seems probable that most mortality, in lower level populations, will be due to predation and intraspecific competition, with physical control being of secondary importance. Intraspecific competition for food does, however, exert a considerable constraint on the growth rates of these local populations. The highest growth rates in the field, equating those observed in the laboratory, are found at higher levels where there are abundant barnacles. In view of the increased rigour of these latter habitats physical factors are the major cause of mortality, particularly at the juvenile stage during the summer months, with the result that only few individuals survive to reproduce the following winter. Intraspecific competition for food is also reflected in reproductive output, which increases allometrically with body size. Observations that the planktotrophic veliger larva will only metamorphose in the presence of live barnacles, and that recruitment is only detectable in June (after B. balanoides has settled) suggests that successful establishment of the benthic phase of the life cycle depends upon the coincidence of pediveligers competent to settle, and the presence of young barnacle spat. No evidence for an intermediate diet can be found, and it is probably the extent to which the larval settlement of both predator and prey coincide which is the major factor determining the absolute level of recruitment of Onchidoris bilamellata for any one year. In consequence, wide fluctuations in recruitment over the three generations studied were both anticipated and observed. Post-spawning mortality is generally complete by April, although a few individuals may survive into June, at which time recruitment of the succeeding generation begins. With peak spawning in mid-January, the bulk of the larvae will hatch around late February spending some 2 1 2-3 months feeding and growing in the plankton before settling amongst the barnacles. Pediveligers settling too early will be subjected to starvation through an absence of barnacle spat, while those settling too late will be liable to food shortage due to juvenile barnacles having outgrown the prey size-range of the post-metamorph nudi-branchs. It is of particular interest that some rapidly-growing individuals in certain habitats undergo precocious maturation with spawning and death in August. In view of the necessary gearing of the predator and prey life-cycles it is unlikely that there will be recruitment from such spawnings, unless juvenile Balanus crenatus Brug., or other species with more extended reproductive periods, are exploited. No evidence could be found to suggest that any nudibranchs survived for more than the normal 9-10 months.

Original languageEnglish
Pages (from-to)213-255
Number of pages43
JournalJournal of Experimental Marine Biology and Ecology
Volume41
Issue number3
DOIs
Publication statusPublished - 17 Dec 1979

Fingerprint

Dive into the research topics of 'The population ecology of Onchidoris bilamellata (L.) (Gastropoda: Nudibranchia)'. Together they form a unique fingerprint.

Cite this