A comprehensive survey for endolithic organisms was undertaken to evaluate the distribution of endolithic algae and cyanobacteria in the structure of ancient cliff ecosystems of the Niagara Escarpment. Rocks were collected at 12 sites along the escarpment. Three rock samples were collected from each of five transects for a total of 180 rock samples. Cryptoendolithic or chasmoendolithic organisms were extracted from freshly cleaved faces under laboratory conditions, and attempts were made to culture, grow, and identify these organisms. Cultures of cryptoendolithic organisms were successfully obtained from between 6.7 and 40 of the culture plates from any one site, whereas chasmoendolithic organisms were obtained from 98 of the attempts. Twenty-two taxa were found, including some Cyanophyta that were present at most sites (Chlorogloea) and others that were found rarely (Schizothrix). Cyanophytes were more common at northern sites than southern sites. Among the Chlorophyta,Stichococcusbacillariswas ubiquitous, butStichococcus exiguuswas restricted to one site. The chlorophytes were evenly found along the Escarpment. No geographical trends were obvious among the Xanthophyceae, but some taxa such asChloridellaneglectawere common and others such asEllipsoidionstichococcoideswere not. These results suggest that endolithic organisms within the rocky limestone cliffs of the Niagara Escarpment are not uniform in abundance or species composition. Consequently, management plans intended to maintain microbial species diversity in the face of different patterns of land use and environmental pollution may have to be location-specific along the escarpment.Key words: terrestrial algae, cryptoendolithic organisms, cliffs, Niagara Escarpment.
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