On the south margin of the reef complex, five assemblages of stromatoporoids are defined in the 500 m thick Frasnian succession. The first, in the lower part of the Flume unit, consists of five species that occupied a platform environment in the initial Devonian sea. The second assemblage, of the upper Flume and upper Cairn interval, contains the greatest number of species and represents a patch reef environment formed as relief between the reef complex and basin developed. The third assemblage, of the lower Pecchee Member, contains few species of dominamly tabular-encrusting stromatoporoids that occupied the complex margin at the time of maximum relief and is contained in a megabreccia bed derived from the edge of the complex. The fourth, in the upper part of the Peechee Member, is associated with the close of reef growth at the complex margin and is found in an upper megabreccia bed and bioherms that grew on its surface. The fifth assemblage, of the Arcs Member, represents the return to a patch reef environment that supplied carbonate sand to form this member. Stromatoporoid diversity is low in assemblage I, increases to a maximum at the bottom of assemblage II, and decreases through the upper parts of assemblages II, III, and IV. It is again high in assemblage V. Low values of diversity are interpreted as reflecting shallow water environments of high unpredictability.Twenty-two species of the stromatoporoid fauna are described or re viewed. The following new taxa are established: Sticlostroma jasperense, Taleastroma steleforme, Hermatostroma haultainense, Stachyodes jonelrayi.