Thursday, April 13, 2006
Pacific rockfish, tree rings, and climate-driven linkages between marine and terrestrial ecosystems
Dendrochronology (tree-ring analysis) techniques are applied to otolith growth increments of the long-lived splitnose rockfish (Sebastes diploproa) to i) generate a high resolution, multidecadal growth chronology and ii) relate those growth patterns to ocean variability and tree ring chronologies. First, common growth patterns were visually cross-matched among otolith thin sections to ensure that all growth increments were identified. Growth increments were then measured from the dorsal distal margin to the focus along a continuous transect. Next, each set of otolith measurements was detrended using a cubic spline, which removed age-related effects on growth and standardized each time series to a mean of one. These detrended time series were then averaged into a single master chronology, which we correlated with monthly averages of the Northern Oscillation Index, sea surface temperature, the Pacific Decadal Oscillation, and upwelling. Growth was positively and significantly (p < 0.01) correlated with indicators of cool, productive ocean conditions, especially during the winter and spring months. February sea surface temperatures accounted for half of the variance in splitnose rockfish growth. The splitnose chronology also showed significant negative correlations with high elevation tree-ring chronologies throughout the Pacific Northwest. Tree ring data accounted for over 40% of variance in the rockfish chronology, allowing a reconstruction rockfish growth to the year 1600AD. These techniques of establishing long-term chronologies and climate-growth relationships could be applied to a variety of long-lived fish species.
Bryan Black is an Assistant Professor/Senior Research Scientist at the Oregon State University Hatfield Marine Science Center and Adjunct Assistant Professor at the Oregon State University Department of Forest Science. Trained as a forest ecologist, Bryan uses tree-ring data to reconstruct forest dynamics and quantify the effects of climate on forest growth. More recently, Bryan has applied these same tree-ring techniques to growth increments in long-lived aquatic organisms. Resulting chronologies can be used to establish climate-growth relationships and compare growth patterns across terrestrial, freshwater, and marine ecosystems.