OREGON SEA STACK: ECOLOGICAL DIVERSITY OF A MODERN TRYPANITES ICHNOFACIES

Rocky intertidal areas provide an analog for hardground substrates within the rock record. Ancient examples of bored hardgrounds, collectively classified as Trypanites ichnofacies, typically possess low diversity and moderate to high abundance in traces, and frequently lack evidence of encrusters, squatters and other soft-bodied organisms. Organisms that are capable of modifying the substrate through bioerosion, or those that can strongly cement themselves to a substrate are most likely to be preserved within the rock record as in situ fossils and trace fossils, which leaves much of the remaining marine community unknown. It is necessary therefore to use modern analogs to help understand and explain the ecological diversity potential of Trypanites ichnofacies. Lion Rock, Arcadia Beach, Oregon consists of a sandstone and basalt substrate, which has been colonized by abundant, albeit low diversity boring taxa and a diverse array of encrusting and squatting organisms as a modern Trypanites ichnofacies. The boring bivalve, Petricola pholadiformis, produces the clavate boring Gastrochaenolites and is limited to sandstone portions of the sea stack. The morphology of occupied and vacant Gastrochaenolites is highly variable due the density of the borings and the erosive nature of the high energy environment. Vertical littoral zonation of non-boring organisms, typical of rocky intertidal shores, is present throughout the sea stack and is dictated by environmental conditions (e.g. wave energy, water depth, exposure time) and biological constrains (e.g. competition, mode of life). Although there have been many studies on ancient and modern hardgrounds, none have tried to compare the two within an ecological scope to help determine the ecological diversity potential of Trypanites ichnofacies throughout time.