EFFECTS OF CANOPY COVER, HERBIVORES AND SUBSTRATUM TYPE ON PATTERNS OF CYSTOSEIRA SPP SETTLEMENT AND RECRUITMENT IN LITTORAL ROCKPOOLS

The effects of microhabitat types on patterns of Cystoseira spp. settlement and recruitment in littoral rockpools were examined in this study. Three experiments were carried out from July 1989 to December 1991 on the west coast of Italy (Western Mediterranean). By manipulation of (1) the adult canopy of Cystoseira spp., (2) herbivore density and (3) substratum type, we tested the general null hypothesis that the distribution and abundance of Cystoseira spp. embryos and juveniles were unaffected by microhabitat differences. Settlement was higher in patches of algal turfs than in areas covered by encrusting corallines or dominated by a full canopy of Cystoseira spp. In contrast, recruitment was significantly higher in plots dominated by encrusting and filamentous algae when herbivores were removed. Grazers (essentially limpets), if left at their natural density, greatly reduced the abundance of both Cystoseira spp. embryos and juveniles in these areas. Our results indicated that post-settlement mortality could reverse the patterns of recruit abundance expected from the distribution of settlers among microhabitats. The information gathered in this study will allow more accurate predictions of the spatial and temporal variability of Cystoseira populations in littoral rockpools.