Figure 1. Thin sections of otoliths from yellowfin sole (A) and Pacific ocean perch (B) and shells of Arctic surf clam (C) showing annually resolved growth increments. These increment widths are being measured and used to develop chronologies of growth (sclerochronologies) as a measure of ecosystem productivity.
Time series datasets of growth derived from otoliths and other hard parts have become an increasingly important tool to describe impacts of climate on marine ecosystems. Borrowing methods from the tree-ring science of dendrochronology, these marine sclerochronologies can provide insight into the effects of climate change on interannual variation in growth as well as act as proxies for environmental variables such as temperature, for which long-term instrumental records are often unavailable. The AFSC’s Age and Growth Program in collaboration with researchers at the University of Texas are developing a new multi-species sclerochronology based on growth-increment measurements of Bering Sea species at different functional levels in the ecosystem. Our goal is to develop climate indicators based on otoliths from yellowfin sole (Fig. 1a) and Pacific ocean perch (Fig. 1b), as well as shells from Arctic surf clams (Fig. 1c), and “measure” the sensitivity of these sentinels to climate variability and ecosystem forcing. Each species’ chronology (time series) is annually resolved and provides a “down looking” integration of ecosystem productivity as it cascades up through multiple trophic levels.
Figure 2. Standardized time series of annually resolved yellowfin sole (yellow line) and Pacific ocean perch (red line) growth increments in the Bering Sea along with the Pacific decadal oscillation (PDO, blue line). Deviations above unity indicate growth is better than average suggesting that growth of these species is generally coherent with the PDO.
Published results of the Bering Sea yellowfin sole (YFS) chronology, which span half a century (Fig. 2), reveal accelerate growth of this species during years of significant ice retreat and warmer bottom temperatures. Building upon these findings, we have developed a biochronology for Pacific ocean perch (POP) which currently spans the years 1946 to 2006 (Fig. 2) and is by far the oldest sclerochronology developed to date in Alaskan waters. Significant positive correlations were detected between the POP chronology and the Multivariate ENSO Index (MEI), the Pacific Decadal Oscillation (PDO), and sea surface temperature, and negative correlations were detected between the chronology and spring sea ice cover, all indicating that warm conditions are important for growth. Climate regime shifts, such as the well documented events in 1976-77 and 1988-89 were strongly evident in the growth increment widths of both YFS and POP. Our next steps are to extend the YFS and POP chronologies back to the turn of the century using archived otolith specimens, develop a chronology for Arctic surf clams (which appear to live 50-60 years), and integrate these with other indicators such as seabird productivity in the Bering Sea.
