Microhabitat analyses of Silurian stromatoporoids as substrata for epibionts

Stromatoporoids associated with a Hoburgen-type reef (Upper Ludlovian, Hamra Beds) on the island of Gotland provided living space for a variety of encrusting epibionts and endoliths. The stromatoporoids were inhabited by some 32 species, including cyclostome, cystoporate, and trepostome bryozoans, tabulates, rugosans, pelmatozoans, brachiopods, spirorbids, cornulitids, tentaculitids, and endolithic organisms. Specialist organisms adapted to the cryptic niche were present and the functional make-up, as well as skeletonized coverage, of this community resembled that of extant cryptic communities. Lower and upper surfaces exhibit similar diversities (H'log e=2.33, 2.43, respectively), although their percent coverages (13.0%, 9.9%) and taxonomic compositions differ, indicating an upper-lower surface polarity. Both lower and upper surfaces exhibit a zonation with diversity and percent coverage decreasing significantly from the outer edge to the interior. Both surfaces also exhibit compositional differences between outer and interior zones