MEPS 275:199-210 (2004)  -  doi:10.3354/meps275199

ABSTRACT: Many marine invertebrate larvae have the capacity to reject or accept settlement sites based on a broad range of cues. Species-specific settlement responses to different cues are often inferred from final settlement choice in the field. Little is known about species-specific larval behaviour in response to different cues and, in particular, how the behaviour is linked to final settlement. Rejection of unsuitable substrata may be an important driving force that leads to aggregated settlement patterns. This study examines rejection responses in relation to surface attractiveness for settlement under field and laboratory conditions in the barnacle Balanus improvisus. The attractiveness for settlement was manipulated by varying surface texture in combination with crude extract from conspecific adults. Active rejection behaviour was examined as a function of surface texture and conspecific pheromones in the field and then related to behavioural responses under static and flowing conditions in the laboratory. Recruitment was heavily reduced on substrata with ribbed microtexture compared to smooth substrata and unaffected by crude extract from conspecific adults. On average, 28% of the cyprids that encountered smooth settlement panels recruited. The proportion of cyprids recruiting on 2 microtextured substrata after encounter was 5 and 1% respectively. In behavioural experiments cyprids showed higher motion speed and dispersal rate on textured substrata, which indicated less exploratory behaviour than on smooth substrata, while an addition of conspecific extract increased intensities of surface exploration on all types of substrata. Flume experiments further demonstrated that cyprids are more prone to leave textured substrata and that the rejection rate was independent of conspecific extract. This work emphasises the role of larval behaviour as a potentially powerful mechanism determining final recruitment pattern. It is concluded that the choice of settlement site is an important factor in the settlement process of B. improvisus, and the results suggest that surface topography may be a stronger cue for settlement than chemical attraction by conspecific adults in this species. This study presents an example whereby rejection of unsuitable substrata leads to an increased larval pool on adjacent substrata that are suitable for settlement, and indicates that this process may drive aggregated settlement in the barnacle B. improvisus.

KEY WORDS: Balanus improvisus · Barnacle · Cyprid · Larval behaviour · Settlement · Recruitment · Surface texture · Larval ecology