THE IMPACT OF HIGH-ENERGY STORMS ON SHALLOW-WATER NAUTILUS (CEPHALOPODA) TAPHONOMY, LIFOU (LOYALTY ISLANDS)

摘要

Shells of the cephalopod Nautilus macromphalus were collected in 2011 from three bays on the island of Lifou in the South Pacific six months after a tropical cyclone passed over the island. All three bays were on the east side of the island; Bays 1 and 2 were 200 m apart whereas Bay 3 was 25 km to the north. Nautilus shells in Bays 1 and 2 were studied in 2008 after six years without tropical cyclones. Greatest damage occurred in shells from Bay 1 and the least from Bay 3. Shell encrustation was lowest in Bay 1. In comparison to the 2008 assemblage, Bay 1 had significantly higher levels of damage and lower levels of encrustation whereas Bay 2 had a higher abundance of severe damage. The Bay 3 assemblage, however, was statistically similar to the 2008 assemblage. An exposed beach cut at Bay 3 revealed a recently buried Nautilus deposit. Nautilus specimens from this deposit displayed damage and encrustation levels similar to shells from Bay 1. Previously buried shells are likely being exposed, damaged, and redeposited in the bays. Spatial variability indicates that, on a short time scale, this is a localized phenomenon. Use of cephalopod fossils as tools in paleoenvironmental reconstruction requires an understanding of the processes that affect their shells. Using the Lifou deposits as analogs, fossil cephalopod shells deposited in shallow water near beaches and where intense storms are periodically present will have extensive breakage. Cephalopod shells would, therefore, be unlikely to survive similar beach conditions unless they were completely buried and not periodically reexhumed by storm events.