Marine bivalve shell geochemistry and ultrastructure from modern low pH environments: environmental effect versus experimental bias

摘要

Bivalve shells can provide excellent archives of past environmental changebut have not been used to interpret ocean acidification events. Weinvestigated carbon, oxygen and trace element records from different shelllayers in the mussels Mytilus galloprovincialis combined with detailed investigations of the shellultrastructure. Mussels from the harbour of Ischia (Mediterranean, Italy)were transplanted and grown in water with mean pH_T 7.3 and meanpH_T 8.1 near CO₂ vents on the east coast of the island. Mostprominently, the shells recorded the shock of transplantation, both in theirshell ultrastructure, textural and geochemical record. Shell calcite,precipitated subsequently under acidified seawater responded to the pHgradient by an in part disturbed ultrastructure. Geochemical data from alltest sites show a strong metabolic effect that exceeds the influence of thelow-pH environment. These field experiments showed that care is needed wheninterpreting potential ocean acidification signals because variousparameters affect shell chemistry and ultrastructure. Besides metabolicprocesses, seawater pH, factors such as salinity, water temperature, foodavailability and population density all affect the biogenic carbonate shellarchive.