ABSTRACT: In Barkley Sound, British Columbia, Canada, newly hatched Nucellaemarginata, a direct developing prosobranch gastropod, are almost exclusively located within 3 structurally complex microhabitats: the filamentous algae Cladophoracolumbiana, clusters of mussels Mytilus spp., and dense assemblages of the barnacle Semibalanuscariosus. When exposed to desiccation or predators for 4 to 5 h, mortality of hatchlings located in these microhabitats (1.7 to 36% mortality) was considerably lower than for individuals on open surfaces (99 to 100%). Also, food (prey species) in C.columbiana, mussel clusters, and S. cariosus microhabitats was more abundant but of similar energetic value to that on open rock surfaces. The microhabitats used by early juvenile N.emarginata thus provide the double advantage of a considerably reduced risk of mortality and abundant prey. The means by which hatchlings disperse after emerging from their egg capsules were established by laboratory observations and by deployment of collectors in the field. Hatchlings do not actively initiate dispersal by drifting in the water column. Crawling is the usual means of travelling from the capsule to protective microhabitats, with hatchling crawling speed averaging only 3.7 mm min^-1 on smooth rock surfaces in the laboratory. The abundance and distribution of microhabitats that protect early juveniles could therefore be important determinants of the local abundance and distribution of N.emarginata populations. The use of protective microhabitats may be the key to survival through the vulnerable early juvenile period in many benthic marine organisms.

KEY WORDS: Mortality . Desiccation . Predation . Structural complexity . Drifting

Published in MEPS Vol. 128 (1995) on November 23
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1995