Funded NEP Project

GLOBEC 2000 -- A long-term observation program using natural stable isotope abundance for detecting coastal Gulf of Alaska zooplankton source fluctuations in fishes
T. Kline [Prince William Sound Science Center]

Decadal-scale changes in the production cycles of the subarctic Pacific Ocean have been conjectured to effect population changes in fishes via their zooplankton forage base. Zooplankton occurring near the Gulf of Alaska continental shelf break appear to undergo dramatic oscillations in abundance over decadal time scales. Interzonal zooplankton stocks are driven onto the shelf providing the ecosystem with an important forage base. Natural stable isotope data suggested that the transport of zooplankton from th e Gulf of Alaska into Prince William Sound may provide significant quantities of forage for food webs and may be a good method for detecting changes in biophysical coupling in the greater Coastal Gulf of Alaska region. This project will augment and complement existing and continuing core LTOP observations being made along the Seward Line transect (GAK1 to GAK13). 3080 samples that were acquired by the P.I. from fall 1997 through summer 2000 on pilot LTOP project (Weingartner, P.I.) cruises will be isotopically analyzed as part of this project during FY2001 and FY2002. From fall 2000 to summer 2005, 2450 samples per year will be collected and isotopically analyzed as part of this project. The data arising from these samples will enable the assessment of seasonal and inter-annual 15N/14N and 13C/12C variability of large-bodied zooplankton 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 characterize isotopically coastal oceanic organic carbon sources and their utilization by fishes, which is expected to vary proportionately with the intensity of cross-shelf transport, thus effecting a relationship between intensity of cross-shelf transport and success of coastal fish populations. These 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.

DATA COLLECTION DETAILS

Natural abundance of N-15/N-14 and C-13/C-12 measured by mass spectrometer on freeze-dried samples reflecting organismal composition (whole macrozooplanters or sub-samples of fishes); additionally a no-cost by-product datum for each sample will be C/N ratio (since %C and %N data are generated during mass spectrometry). Zooplankton will be collected by MOCNESS sampler on oceanographic vessel and fishes by appropriate net on fishing vessel (for salmon it would be best to have samples for which otoliths were analyzed). The contents of MOCNESS codend number one (used as a drougue during deployment) will be used since it is deployed throughout the upper 100m, produces a generous sample (particularly useful when zooplankton are less abundant), and since this non-quantitative sample is not otherwise useful. The spatial and temporal extent of sampling is:

Coastal Gulf of Alaska adjacent to Seward, AK eastward to and including Prince William Sound.
Spring through fall productivity period, more intensive sampling for Neocalanus earlier and for euphausiids later while fish will be sampled (salmon as principal focus) when they occur in the study area. Isotopic analysis will also be done on salmon sampling project samples (re. RFP).

This page was last updated on September 22, 2000.

Maintained by:
Hal Batchelder [hbatchelder@coas.oregonstate.edu
College of Oceanic & Atmospheric Sciences
Oregon State University
Corvallis, OR 97331-5503
phone: 541-737-4500; FAX 541-737-2064