The distributions of natural stable isotopes of carbon and nitrogen have been extensively investigated in a variety of primary producers such as vascular plants and algae to provide baseline information of the trophic structure of various ecosystems (Currin et al. 1995). However, there have been few attempts to use this ecological approach to characterize lichens which frequently constitute the principal vegetation in many rocky habitats (Gilbert 2000). Rocky sea shores are characterized by a vertical zonation of biological communities which fall into three major zones: supralittoral, mediolittoral and infralittoral. The supralittoral zone is rarely submerged and is typically covered by a vegetation of lichens and cyanobacteria (Lewis 1964; Russel 1991).