MEGAVERTEBRATE ACTIVITY ALONG OCEANIC COASTS: SPANNING THE ICHNOLOGICAL-ZOOGEOMORPHIC CONTINUUM

The impact of large reptiles (sea turtles), birds (penguins), and mammals (pinnipeds) on coasts ranges from ephemeral traces to landform scales. Pinniturbation is proposed as a general term for substrate reworking by flipper action. Building on pioneering work along Georgia barrier islands, a suite of sea turtle traces (polychresichnia) is expected to include approach/exit crawlways (repichnia), a compound body pit/egg chamber/cover pit structure (calichnia), as well as hatchling escape (fugichnia/taphichnia) and associated predation (praedichnia/mordichnia) traces. Each nest structure may affect >2 m³ of sediment, with philopatry ensuring that many nesting sites remain preserved in prograded coastal sequences (swales within strandplains) where they may be misinterpreted as storm-surge scour structures. Beyond sediment advection on feet and bodies, burrow excavation (domichnia/calichnia) by several penguin species generates new landforms in coastal peatlands and other soft substrates. Pinnipeds cause the greatest impact on mid-high latitude rocky coasts, with dramatic disturbance of terrestrial ecosystems, especially trampling of native insular vegetation. During haul-outs on beaches, >150 m³ of sediment can be reworked by a herd of 1,000 individuals. Locomotion traces of true seals (phocids) distinguish them from more upright tread-like trackways of fur seals, sea lions, and walruses. On mixed sand-gravel beaches, pinniped interaction and wallowing may reactivate deflation basins. The microtopography produced by animal activity locally affects sediment dynamics and wave focusing along upper berm and dune sites. On the beachface, trace preservation is reduced due to tidal processes. During the past century, the scale of pinniturbation was likely at its minimum, compared to that prior to hunting campaigns and following recent population rebounds. Surficial (LiDAR) and subsurface (georadar) imaging are emerging as effective means of identifying, mapping, and monitoring megavertebrate structures. Future research will focus on paleogeography (shoreline position and trend, paleo-water table), ichnology (ichnotaxonomy and ichnocoenoses), geophysics (geoclutter), geoarchaeology (resource exploitation by maritime cultures), and conservation of protected species.