Boring and encrusting communities associated with oysters from Cretaceous-Paleogene boundary, northern Patagonia

BREZINA, S.; ROMERO, M. V.; CASADIO, SILVIO

Mar del Plata

Otro; Reunión de Comunicaciones de la Asociación Paleontológica Argentina; 2015

Universidad Nacional de Mar del Plata

Oysters are hard substrates with high potential for preservation and provide a very good fossil record of its sclerobiotic fauna. Little is known about the changes in these communities during episodes of extinction like those that occurred during the Cretaceous/Paleogene (K-Pg) boundary. The aim of this work is compare the diversity, abundance, distribution and ecological relationships of encrusting and boring communities associated with oysters during K-Pg transition at mid-latitude from Southern Hemisphere. Nine oyster species from Roca and Jagüel Formation in the Neuquén basin were analyzed. The identified encrusters included oysters and other bivalves, polychaetes, bryozoans and verrucids cirripeds. Among encrusting bryozoans, 35 species were identified. The identified borers included sponges, polychaetes, bivalves, cirripeds, ctenostomes bryozoans, phoronids, algae and fungi. In vivo and post mortem colonization of the sclerobionts were inferred from the study of the distribution between valves (left and right), and its surfaces (external and internal). Several factors that influenced the settlement of sclerobionts on the valves were considered (e.g. availability and texture of the exposed surface, the time exposure, sedimentation rate, availability of light and nutrients, currents, competition for space like overgrowth, predation or symbiosis, between others). Sclerobiotic communities are represented mostly by the same groups before and after the K-Pg boundary. But during the late Danian, higher diversity and abundance is registered, especially in bryozoans. This change after the earliest Danian correlates with an increase in the number of species of corals, mollusks, echinoids and crabs derived from low latitudes, reflecting higher seawater temperatures spreading south.