RAPID-RESPONSE TRACKING: NEOICHNOLOGICAL OBSERVATIONS IN THE WAKE OF HURRICANE JOAQUIN, SAN SALVADOR, THE BAHAMAS

Intense storm events have a swift and pervasive impact on coastal landforms and ecosystems, commonly manifested in a variety of biogenic structures. Small and isolated tropical islands like San Salvador, The Bahamas, are particularly susceptible to rapid shifts in sedimentation and plant cover, and biogenic storm impacts are evident due to the distinct ecotones with diagnostic trace assemblages (ichnocoenoses). Storm surge and wind stresses produced by Hurricane Joaquin (2015) temporarily disrupted the key decapod (land crab) habitats, causing changes in bioturbation style and depth, as well as ichnocoenosis shifts. Four months following the hurricane, the response patterns of three prolific supratidal decapod tracemakers complemented traditional geological assessments of storm impact. Blue land crab burrows (mangrove fringe) did not extend landward and uphill into blackback crab biotope (vegetated dunes), whereas ghost crabs (upper beach) penetrated into de-vegetated backdune areas, as reflected by their fresh double-shaft openings. Along north Pigeon Creek, washovers from the lagoon buried blue crab burrow networks without any subsequent bioturbation through 5-10-cm-thick carbonate sand. In addition to providing a rare blue crab tracking surface, the sandy overwash resulted in a contrasting fill within an organic muddy matrix. Storm sand and phytodetritus that infilled fiddler and blue crab burrows likely entombed some of these organisms, commensal biota, and washed-in intertidal fauna (possibly articulated) in burrow-fill tempestites that may ultimately serve as the clearest record of the event. Ground-penetrating radar allowed rapid imaging of partially collapsed burrows, and provides opportunities for future monitoring of subsurface changes. Along East Beach, a 2-m-high foredune scarp exhibited blackback burrows, potentially overprinting older tunnels truncated by erosion with bioturbation into a newly exposed surface. This scarp also contained ghost crab fragments, introducing exotic skeletal remains into blackback crab habitat. Rapid incipient lithification and fossilization of the foredunes by fair-weather saltspray action, especially along windward shores, creates exceptional preservation potential of storm event surfaces along insular carbonate margins.