Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

We sampled the density of all euphausiid life stages during dusk (within 1 hour of sunset) with a 60-cm diameter, 200-μm mesh ring net lifted vertically from 10 m off the bottom to the surface. We also characterized the nighttime density and vertical distribution of adult Euphausia pacifica using a 0.25 m2 Hydrobios MultiNet (five-net capacity) towed obliquely to collect depth-stratified samples. Flowmeters were used to monitor the volume of water filtered for all collections and samples were preserved in a 5% buffered formalin and seawater solution.

In the laboratory, samples from the vertical tows were quantitatively diluted to 4–10 times their settled volume and 2–3 subsamples were taken with a 1-mL Stempel pipette to quantify early life stages. In addition, one 10 mL Stempel pipette subsample was evaluated for any stages not found in the smaller subsamples. Euphausiid life stages were identified and classified as nauplius, calyptopis, furcilia, or juvenile/adult. All euphausiids from vertical tows were classified regardless of species, and a small portion may have been the sub-dominant species Thysannoessa raschii. Euphausiids from the oblique tows that were larger than 10 mm total length were identified as E. pacifica, sexed, and measured. Samples that contained > 30 large euphausiids were split prior to analysis.

Densities (#/m3) were calculated by life stage from each net.

BCO-DMO processing notes:

• Adjusted parameter names to comply with database requirements.
• Converted date to ISO format.

Description from NSF award abstract:
Low dissolved oxygen (hypoxia) is one of the most pronounced, pervasive, and significant disturbances in marine ecosystems. Yet, our understanding of the ecological impacts of hypoxia on pelagic food webs is incomplete because of our limited knowledge of how organism responses to hypoxia affect critical ecosystem processes. In pelagic food webs, distribution shifts of mesozooplankton and their predators may affect predator-prey overlap and dictate energy flow up food webs. Similarly, hypoxia may induce shifts in zooplankton community composition towards species that impede energy flow to planktivorous fish. However, compensatory responses by species and communities might negate these effects, maintaining trophic coupling and sustaining productivity of upper trophic level species. The PIs propose to answer the question "Does hypoxia affect energy flow from mesozooplankton to pelagic fish?" They approach this question with a nested framework of hypotheses that considers two sets of processes alternatively responsible for either changes or maintenance of pelagic ecosystem energy flows. They will conduct their study in the Hood Canal, WA. Unlike most hypoxia-impacted estuaries, hypoxic regions of Hood Canal are in close proximity to sites that are not affected. This makes it logistically easier to conduct a comparative study and reduces the number of potential confounding factors when comparing areas that are far apart.

Improved understanding of how hypoxia impacts marine ecosystems will benefit the practical application of ecosystem-based management (EBM) in coastal and estuarine ecosystems. Effective application of EBM requires that the impacts of human activities are well understood and that ecological effects can be tracked using indicators. This project will contribute to both of these needs. The PIs will share their findings on local and national levels with Federal, State, Tribal, and County biologists. To increase exposure of science to underrepresented groups, the PIs also will provide Native American youth with opportunities to participate in field collections and laboratory processing through summer internships. The PIs will collaborate with the NSF-funded Pacific Northwest Louis Stokes Alliance for Minority Participation and tribes from the Hood Canal region to recruit and mentor students for potential careers in marine science. This project will support several undergraduate researchers, two Ph.D. students, a post-doc, and two early-career scientists.