Bouchardia rosea, a vanishing brachiopod species of the Brazilian platform: taphonomy, historical ecology and conservation paleobiology

Abstract

Dead-live faunal comparisons can offer powerful data to detect natural or human-induced population changes in the late Holocene. Here, we document dead–live comparisons for death assemblages of the brachiopod Bouchardia rosea in nearshore (0–45 m) environments along the northern coast of São Paulo State, Brazil. The sampling programme included 30 stations (14 at Ubatuba, 16 at Picinguaba bay). The bottom was sampled via Van Veen grab sampler, and also dredged. Out of 30 stations, 22 yielded brachiopods. The fidelity estimates were obtained by direct comparisons of live biota with dead shells. A total of 6627 brachiopods were recovered, 5339 (80.6%) from Ubatuba and 1288 (19.4%) from Picinguaba. Out of these, 6621 (99.9%) were empty, dead shells, while only six individuals (0.1%) were found alive, all in the Picinguaba Bay. These results suggest extremely poor dead–live compositional fidelity for B. rosea assemblages. The spatial data suggest that the distribution of B. rosea accumulations has been highly patchy in the region, whereas the great scarcity of live brachiopods may point to a recent decline in local populations. Several lines of evidences indicate that changes in water temperature, nutrient availability, population history and even pollution, may have all affected spatio-temporal dynamics of B. rosea populations.

Keywords:

• fidelity
• taphonomy
• paleoecology
• brachiopods
• South Atlantic Ocean
• late Holocene

Acknowledgements

This project was supported by the FAPESP grant 00/12659-7, Petroleum Research Fund grant 40735-AC2 and the National Science Foundation grants EAR-0125149 and OCE-0602375. We thank Dr Adilson Fransozo (UNESP, Botucatu campus) for providing assistance during boat trips, in the study area in the period of 1988–2003. We are also deeply indebted to Karl Flessa and David Dettman (The University of Arizona, Tucson), who provided the isotope geochemistry analysis of some B. rosea shells. The final version of this contribution was substantially improved, thanks to careful and constructive comments of an anonymous reviewer. This is a contribution to the FAPESP (00/12659, 02/13552-7, 06/00169-1, 06/59416-8) and CNPq (3004448/2003-1, 306601/2006-0) projects.