Reconstructing Environmental Stresses in Bivalves in Tokyo Bay Using Stable Isotope Records and Growth Pattern Matching in Shells

Abstract

This study focuses on the hard clam (Mercenaria mercenaria), an introduced species in Tokyo Bay, to evaluate the effects of summer hypoxia and high temperature on shell growth by integrating stable carbon and oxygen isotope analysis of biogenic carbonate and shell growth pattern matching. Both delta¹⁸O and delta¹³C profiles showed clear seasonal variation and consistent trends among individuals, with growth cessations during summer. By combining manual date matching and a custom-developed automatic sliding-window fitting method, individual growth chronologies were successfully reconstructed, and shell growth interruptions were precisely linked to hypoxia-related disturbances. This study demonstrates the potential of bivalve shells as sensitive archives of environmental stress and provides insights contributing to coastal ecosystem monitoring and resource management.