Changes in Spatial Pattern of an Intertidal Population of the Nudibranch Mollusc Onchidoris muricata in Relation to Life-Cycle, Mortality and Environmental Heterogeneity

Abstract

The dynamics and changes in spatial patterns of intertidal populations of O. muricata (Mueller) were examined and related to the biological and ecological demands on the individuals. Recruitment of the benthic phase of the life cycle occurs in late June-early July with settlement and metamorphosis of the planktotrophic veliger. The post-metamorph juveniles exhibit an overdispersed distribution, which is an expression of environmental heterogeneity. An apparent change in behavioral response of the individuals was detected by following changes of patchiness, and mortality was of an all-or-none type operating on clumps of individuals. The predator, as yet unknown, has adopted the strategy of seeking out the high-density clumps of the nudibranch. Mortality is viewed as a mechanism inadvertantly easing the energetic stress placed on the individuals of the population in seeking resources, this stress arising from the aggregated nature of their spatial dispersion.