Abandoned Quaternary gastropod shells: Incrustation, bioerosion, and fragmentation approaches

Abstract

At the beach, death assemblages are constantly reworked by wind and waves. One of the various consequences of this shore dynamic is the constant burial and exhumation of the shells, making them inappropriate for epibionts. However, some gastropod shells collected in the death assemblages arranged on the foreshore of the coastal plain of south Brazil were hardly encrusted. Olivancillaria urceus corresponds to 48.8% of all encrusted taxa, suggesting that some shell species may play a more striking role than others as available bioclasts. Therefore, the research aims to discuss the taphonomic implications for epibionts and bioerosion in gastropod shells. Abandoned gastropod shells were collected on 27 sites along a 150 km coastal strip in southernmost Brazil. Epibionts and bioerosion traces were identified, and their frequency was calculated considering their abundance, which taxa they occurred in, and their settlement on the different parts of the shells. At least 13 of 21 taxa were colonized by epibionts, of which 97% were by bryozoans. Other epibionts recognized were serpulid tubes, bivalves, and balanids. Fifteen taxa were bioeroded, showing traces made by worms (cf. Caulostrepsis), bryozoans (cf. Pennatichnus), balanids (cf. Rogerella), bivalves (cf. Gastrochaenolites), and sponges (cf. Entobia). The results reached in this survey suggest that the bryozoans have an advantage over other epibionts at colonizing the gastropod shells.