2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 165-8
Presentation Time: 3:55 PM


CURRAN, H. Allen, Department of Geosciences, Smith College, Northampton, MA 01063 and SEIKE, Koji, Atmosphere and Ocean Research Institute, University of Tokyo, Kashiwa, 277-8564, Japan, acurran@smith.edu

Deep-burrowing callianassid shrimp (Decapoda: Axiidea: Callianassidae) are dominant bioturbators in modern tropical, intertidal to shallow subtidal, sandy carbonate substrates throughout the Bahamas. Nonetheless, callianassids remain poorly known regarding species present, environmental preferences, and burrow forms. Goals of this study are to determine what callianassid species inhabit shallow marine environments around San Salvador Island, their environmental preferences, and burrow characteristics. Four species total have been identified from 4 study sites, with resin casts made of burrows from 3 sites. Callianassid burrows are large, complex, and species specific. Our geological-paleontological goal is to establish matches between modern burrow forms and those of the trace fossil Ophiomorpha, attributed to callianassids and found in marine Pleistocene deposits throughout the Bahamas and beyond. At our Graham’s Harbour site, burrowed, sandy areas are interspersed with seagrass beds. Neocallichirus maryae (formerly N. rathbunae) and N. cacahuate are present in sandy areas. N. maryae casts document a U-shaped form with large, tiered, pouch-like structures. Efforts to cast N. cacahuate burrows were unsuccessful, but hand excavations revealed robust, thickly lined, branching burrows. Two intertidal sites are in the shallow Pigeon Creek lagoon. Muddy-sand flats bordering northern parts of Pigeon Creek are characterized by mounded topography generated by Glypturus acanthochirus. Burrow casts have a distinctive, downward spiraling form. The second Pigeon Creek site is a spit on the lagoon’s south arm, near the inlet to the open Atlantic. Burrows of N. grandimana are common, and casts have a characteristic architecture of multiple robust shafts and tiered branches that end in bulbous chambers stuffed with marine vegetation. Long Bay on the island’s west coast is our second subtidal site; wave energy is greater than in Graham’s Harbour, and grass beds are absent. Burrows of N. cacahuate are common, and hand excavation exposed burrows similar to those in Graham’s Harbour. Future successful matching of modern callianassid burrow architectures with those of Ophiomorpha will aid significantly in differentiating paleoenvironmental settings of ancient tropical, shallow-marine carbonates.