ECOLOGICAL SUCCESSION WITHIN A HOLOCENE OYSTER REEF: AN INDICATOR OF ESTUARY DEVELOPMENT IN SOUTHWEST FLORIDA

Southwest Florida's coastal geomorphology and estuarine ecology depend upon the proliferation of oyster reefs, yet little is known about timing and environmental detail of coastal development. This study considers the paleontology and taphonomy through the late Holocene development of a vermetiform gastropod to eastern oyster (Crassostrea virginica) reefal succession within an archetypical region of Estero Bay. Six stratigraphic cores, spanning 2700 years of history, were studied stratigraphically and sedimentologically; one core's paleontologic and taphonomic characteristics were analyzed intensively. Reef construction is dominated through much of history (~2700-500 ybp) by sessile vermetiform gastropods; oysters co-occur with gastropods as builders beginning at ~500 ybp; ultimately oysters build reefs exclusively from ~100 ybp until present. Patterns in faunal assemblages and in taphonomy support a shift from more marine, higher energy settings during the vermetiform-only phase to more brackish and protected conditions through the successional change to oyster-only frame building. Assemblages during the oyster-only phase contain numerous euryhaline species, while the vermetiform-only and mixed phases contain stenohaline, marine taxa. The taphonomic grade of vermetiform gastropods improves upsection, supporting a more protected embayment through time. Patterns in oyster taphonomic grade are more equivocal, though here too preservational quality improves upsection. Analysis of biocorrosion and bioencrustation, characteristics indicative of marine conditions, does not support the transition to more estuarine conditions, while those indicative of time averaging (margin loss, coloration, luster) suggest increasingly lower energy conditions through time. Finally, the marine to estuarine transition is supported by the modern distribution of vermetids and C. virginica. A core taken more distally and behind the current barrier island indicates that Estero Bay existed as an open coast in the recent past. The reef succession in the barrier island's wake monitors the timing of estuarine development and perhaps the timing of island formation. This research demonstrates the value of studying proximal depositional settings to infer the history of estuaries.