BRYOZOAN SPECIES ASSEMBLAGES ON ADJACENT MODERN REEFS IN THE LOWER FLORIDA KEYS -- NATURAL VARIABILITY AND PALEOECOLOGIC IMPLICATIONS

Within large ecosystems, different instances of the same kind of subhabitat can exhibit variations in their biotic composition. Examples from modern environments can clarify the extent of such variability, so that comparable variations in fossil assemblages can be recognized and not confused with possible differences introduced by taphonomic processes or sampling procedures. Bryozoan species from adjacent reefs in the modern outer Florida reef tract illustrate this well, in addition to furnishing new data for understanding both those living reefs and their Pleistocene counterparts fossilized near-by, as well as more ancient reefs as in the Ordovician around Lake Champlain.

Over 150 colonies were identified from shallow (0-10 m) and deep (20-30 m) ecozones on Eastern and Middle Sambo reefs (Lower Florida Keys), and compared with those recognized on Looe Key just to the east. Twelve species occur both shallow and deep on the Sambo reefs; those common are Cleidochasma porcellana and Reptadeonella violacea, both also important on Looe Key. Eight (marked *) of the rarer 10 likewise occur on the latter: Antropora granulifera, Cellepora? coronata*, Crassimarginatella crassimarginata*, Holoporella hemispherica, Parasmittina spathulata*, Rhynchozoon vaughani*, Smittina delicatula, S. smittiella*, Stylopoma spongites*, Trematooecia turrita*. Additionally, 7 more species occur rarely in the Sambo shallows (only 2 also at Looe), and 5 others in the Sambo deeps (all at Looe as well). In contrast, 2 species abundant on Looe Key - Smittipora americana and Exechonella antillea - are conspicuous by their absence from the Sambo reefs, as are a number of rare forms.