Seawater temperature records from stable isotopic profiles in the shell of Modiolus modiolus

The hypothesis that the sea urchin disease, which devastated populations along the Atlantic coast of Nova Scotia in 1980–83, is temperature related requires a record of bottom seawater temperatures over this period. A time series of δ¹⁸O values from two Modiolus shells, collected in a cove in Nova Scotia, were used to reconstruct bottom water temperatures and as an independent method to age the mussels. A fine scale of resolution was achieved, with up to 15 discrete samples per year of shell deposition. Records from two shells showed similar trends. The δ¹⁸O values of the shells clearly tracked seasonal temperatures. They suggested that bottom seawater temperatures were not unusually warm at this site in 1980, the year in which the sea urchin disease was first noticed. Ages of mussels determined from the oxygen isotope record were consistent with those estimated from annual growth lines on the shells.