MODERN REEFAL BRYOZOAN SPECIES ASSEMBLAGES IN THE LOWER VERSUS UPPER FLORIDA KEYS -- REGIONAL TRENDS FOR PALEOECOLOGIC ANALYSES

Although reef-dwelling bryozoans have long been known to be significant constituents in the modern Florida reef tract, only now are enough distributional data becoming available to detect possible regional trends or differences of the kind which might be detectable in fossil reef complexes such as in the Great Lakes Silurian. Identification of bryozoan species from several outer reefs in the Lower Keys (Looe Key, Eastern Sambo, Middle Sambo) makes possible for the first time comparison/contrast with species recorded from the Upper Keys (Long Reef, Elliott Key; Choi & Ginsburg '83).

     Seven species occur abundantly in both Lower and Upper Keys reefs: Cleidochasma porcellana, Exechonella antillea, Hippopodina feegeensis, Reptadeonella violacea, Smittipora americana, Steginoporella magnilabris, Trematooecia turrita. These are the forms most likely to be encountered in limited sampling, which could result in oversimplification of the entire fauna as regionally homogeneous.

     Other numerous species are restricted to either part of the keys, and thereby could be used as paleoecologic indicators. Eight characterize the Lower Keys: Cellepora? coronata, Crassimarginatella crassimarginata, Cribrilaria radiata, Floridinella typica, Parasmittina signata, P. spathulata, Smittina smittiella, Stylopoma spongites. Two distinguish the Upper Keys: Parellisina latirostris, Thalamoporella mayori.

     Many more rare species were also identified in our studies, resulting in total observed bryodiversity of 79 species in the Lower Keys reefs and of 24 in the Upper. Such a sizeable contrast may reflect long-term natural influences (latitude, Everglades run-off) or recent anthropogenic impacts (urban and agricultural pollution) affecting the reefs' water quality.