GLOBEC 2000 -- A long-Term Observation Program Using Natural Stable Isotope Abundance for Detecting Coastal Gulf of Alaska Zooplankton Source Fluctuations in Fishes

Prince William Sound Science Center, Cordova AK

Investigators

Abstract

Decadal-scale changes in the production cycles of the sub-Arctic Pacific Ocean have been conjectured to effect population changes in fishes via their zooplankton forage base. Zooplankton populations occurring near the Gulf of Alaska continental shelf break appear to undergo dramatic oscillations in abundance over decadal time scales. These consist principally of inter-zonal (because life-history stages span shallow- and deep-water zones) zooplankton (primarily Neocalanus spp. copepods) stocks that are driven onto the shelf providing the ecosystem with an important forage base. The data arising from this project will enable the assessment of seasonal (during 2001 and 2003) and inter-annual 15N/14N and 13C/12C variability of large-bodied zooplankton (primarily Neocalanus) across the Gulf of Alaska continental shelf during their peak occurrence in spring and summer each year, that will be matched to analogous measurements for juvenile pink salmon and other fishes. These data will be used to isotopically characterize coastal and oceanic (offshore) organic carbon sources and their utilization by fishes. Isotopic shifts in fishes and diapausing copepods are expected to shift in synchrony varying proportionately with the intensity of cross-shelf transport. This project will augment and complement existing and continuing core LTOP observations being made along the Seward Line transect (GAK1 to GAK13) and select stations near and in Prince William Sound. Samples that were acquired by the P.I. from fall 1997 through summer 2000 on pilot LTOP project (Weingartner, P.I.) cruises will be analyzed for 13C/12C and 15N/14N content as part of this project during FY2001 and FY2002. Additional samples will be collected and analyzed as part of this project from 2001 through 2005. The data will also be used to validate the tacit assumption in NEP GLOBEC retrospective studies that 15N/14N values of lower food chain biota are constant so that so that changing values can be interpreted to reflect varying food chain length or salmon run size.