CONICET | Buscador de Institutos y Recursos Humanos

Bioerosion structures are abundant in the shells of Holocene age (5.3 ? 2.1 ky, MIS 1) marine molluscs of Bahia San Blas, south of Buenos Aires Province, Argentina. The aim of our research was to examine the bioerosion structures on the shells of the Holocene and modern benthic communities of Isla Jabali (40º 35´S/62º11´ W) . We analysed ten localities (five Holocene one and five modern one ) and found 44 molluscan species There were 12 species among them which was bearing bioerosion structures.In the Holocene marine deposits (6-3 m thick) four ichnogenera and two ichnospecies were found. The most abundant ichnogenera are Maeandropolydora isp., Entobia isp. and Oichnus isp.. Pinaceocladichnus also occurred on some examined tests. The ichnogenus Maeandropolydora was found in the central area of Ostreola equestris and Entobia covered the umbonal and central region of Glycymeris longior, Amiantis purpurata and Zidona dufresnei shells Oichnus was recognized in Adelomelon brasiliana and in Olivancillaria carcellesi. Maeandropolydora sulcans had been found in the umbonal area of Amiantis purpurata and Oichnus simplex occurred in the last whorl on Heleobia australis. In the modern beach the dominant ichnogenera were Entobia, Oichnus and Maeandropolydora. Entobia occurred in all the shells of Buccinanops globulosus, Zidona dufresnei and Trophon patagonicus and in the umbonal area of Ostrea equestris. Oichnus was present in the last whorl of Olivancillaria carcellesi and in the central area of Ostreola equestris. Meandropolydora covered the central and umbonal area of Ostreola equestris and Amiantis purpurata. We concluded that the main bioeroders of the territory had been polychaete annelids, ctenostomate bryozoans, clionaid sponges, and carnivorous gastropods. (Trophon patagonicus) The dominant of ichnotaxa indicate sandy bottom and high water oxygenation both in the Holocene and both in the modern times. .