Landing on one's foot: small-scale topographic features of habitat and the dispersion of juvenile intertidal gastropods

Abstract

The associations of densities of very early recruits of mobile intertidal species with fea- tures of their habitat have rarely been examined in the field. Here, experimental manipulation of local topography (by provision of cracks, grooves and pits of various sizes) demonstrated species-specific re- sponses by animals naturally recruiting into experimental plots. Densities of small (< 3 mm) juvenile snails (Austrocochlea porcata, Bembicium nanum and Nerita atramentosa) and limpets (Cellana tramoserica and Patelloida latistrigata) varied among experimental topographies in consistent ways. Although local densities were influenced by appropriate topographic features, only N. atramentosa and P. latistrigata showed increased density per area of shore with alteration of topography. For the former species, provision of grooves and large pits also caused enhanced densities on open surfaces. P. latistrigata had decreased densities on open surfaces, but very much enhanced densities in grooves and other features, thus increasing total numbers in an area. Experimental transplantation and subse- quent movements of small juveniles demonstrated very similar patterns to those shown after natural recruitment, indicating behavioural responses to local topography. Responses to small-scale topo- graphy can explain small-scale variation in numbers of very early recruits of intertidal gastropods.