Growth rates and population dynamics in Crassostrea cf. rarilamella from the Lower Eocene Roda Formation (southern Pyrenees, Spain)

Abstract

An oyster bed of Crassostrea cf. rarilarmella was preserved in life position in muddy estuarine sediments of Lower Eocene age in the Roda Formation, southern Pyrenees, Spain. Its population structure was studied by counting and measuring annual growth increments in the hinge plate of the oyster. The population structure is normal and indicates a time averaged death assemblage. The life table and survivorship curve show that C. cf. rarilamella had a high juvenile mortality and constant adult mortality pattern. The mean yearly decrease of the adult population was very low, as is shown by the regression coefficient. Growth line analysis revealed slower and faster growth. The cumulative growth curve does not show a gradual decrease in inclination, which confirms the interpretation of the functional shell morphology (adaptation to a muddy substrate) of C. cf. rarilamella. C. cf. rarilamella shows characteristics of an equilibrium species or K-strategist, to be expected in this sedimentological setting.