CASADIO Silvio Alberto
congresos y reuniones científicas
Communities associated to Tertiary oyster reefs: changes in space and time
Puerto Madryn
Otro; Reunión Anual de la Asociación Paleontológica Argentina; 2005
Institución organizadora:
Oysters are amongst the most conspicuous members of the marine mollusc faunas of Argentina because of their abundance and diversity. Since the Oligocene and up to the Miocene some very large and thick-shelled taxa [i.e. Crassostrea? hatcheri (Ortmann, 1897)] – in adult specimens the left valve may weigh over 3.5 kg – built reefs in shallow shelf environments. These reefs constitute a high-diversity ecosystem and the oyster valves played an important role in the establishment of very diverse communities that used the shells as a substrate. In this study we compared the communities recorded in two different sets of oyster reefs, from widely separate areas of Patagonia, and of different ages. The first one comprised reefs of Crassostrea? hatcheri from the San Julián (late Oligocene) and Centinela (early Miocene) formations exposed in the area surrounding Puerto San Julián (49º12’S; 67º39’W) and south of Calafate (50º30’S; 72º15’W) respectively. The other one, included reefs of “Ostrea” patagonica d’Orbigny, 1842, from the Puerto Madryn Formation (late Miocene), exposed at Puerto Pirámide (42º35’48’’S; 64º15’27’’W). Presence/absence and relative abundance cluster analyses based on the taxa associated with the reefs showed differences among the three. The analyses rendered two clearly distinctive groups, i.e., from the San Julián and Centinela formations on one side, and from the Puerto Madryn Formation on the other. The difference between the two groups lies rather in the taxonomic composition of the associated fauna, than in the biodiversity observed in each of them. While in the late Oligocene and early Miocene reefs it is boring and encrusting polychaetes and the boring bivalves Hiatella sp. and Pholadidea patagonica (Philippi, 1887) that are dominant, in the late Miocene reefs the dominant taxa are barnacles, encrusting bryozoans, and the boring bivalve Lithophaga sp.