Application of dendrochronology techniques to the Pacific geoduck clam (Panopea abrupta) in northern British Columbia, Canada

We applied dendrochronology techniques to develop a 103-year growth increment chronology using geoduck clams (Panopea abrupta) collected from the Tree Nob region of northern British Columbia, Canada. Using acetate peels of the chondrophore region of fifteen geoduck clams, growth increments were photographed under a dissecting microscope and imported into image analysis software. All samples were visually crossdated and growth increment widths measured. A crossdating check in COFECHA calculated an interseries correlation of 0.716 and mean sensitivity of 0.29. We then used negative exponential functions to detrend all measurement time series before averaging them into a final master chronology that spanned 1901-2003. The resulting geoduck chronology showed strong interannual and interdecadal variability and closely tracked the Pacific Decadal Oscillation, including the regime shifts of 1945 and 1976. Geoduck growth is most strongly limited by cold winters, as indicated by strongly positive (r > 0.6) correlations with Jan-March sea surface temperatures. Ultimately, geoduck growth chronologies could be used for i) crossdating as a means of age validation, ii) establishing climate-growth relationships, and iii) climate reconstructions for periods prior to instrumental records.