Oregon Sea Stack: Ecological Diversity of a Modern Trypanites Ichnofacies

The paleoecology of rocky substrates in the rock record is commonly interpreted based on ichnology and is frequently associated with a bioeroding community (the Trypanites Ichnofacies) with low ichnological diversity. However, analyses of a modern, siliciclastic, intertidal hardground community at Lion Rock, located at Arcadia Beach State Park, Oregon, reveals a diverse community of boring, encrusting, and squatting/clinging organisms. Through observations and descriptions of organism distribution and abundance, more than 40 species of plants and animals are reported to reside within three littoral zones (upper, middle, and lower littoral zone) on the sea stack. A newly established erosional lower littoral zone is a subdivision of the lower littoral zone, where shifting foreshore sand influences colonization and biotic diversity. Borings are produced by four bivalves, Adula californiensis, Hiatella arctica, Penitella penita, and Zirfaea pilsbryi, and are identified as Gastrochaenolites traces. It is likely that ancient Trypanites Ichnofacies communities had considerably higher diversity and faunal abundance than their ichnological record indicates. It is also likely that Trypanites Ichnofacies are much more dynamic environments, with shifting sediment, wave energy and tidal energy influences. Comparisons with modern assemblages are thus crucial in assessing these environments in ancient succession