Table of Contents

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

Krill were collected from surface waters (upper 50 m) at each sampling station during the nighttime using a 60-cm diameter Bongo frame equipped with black 335-μm mesh nets and non-filtering cod ends towed for <10 min at 2-3 kts. Healthy female E. pacifica (obvious ovary) were identified under a microscope, kept chilled (10-14 °C) at all times, and were gently transferred using broad spoons to prevent damage.

Krill were measured for total length (from behind the eye to the end of the telson) at 6X using a calibrated eyepiece reticle then flash frozen individually in liquid nitrogen. Total length was converted to dry weight (DW) using a published length-weight regression (Feinberg et al. 2007).

Protein content was determined according to the bicinchoninic acid (BCA) method (Smith et al. 1985) using a Pierce BCA Protein Assay Kit (Thermo Scientific).

ETS activity was assayed using the method of Owens and King (1975), as modified by Gómez et al. (1996), and adapted for a 96-well plate. Assays and blanks were measured in triplicate at 25 °C, calculated according to Packard and Christensen (2004), and corrected to in situ temperatures (depth integrated) using the Arrhenius equation with an activation energy of 15 kcal mol-1 (Packard et al. 1975) and standardized to protein specific activity, spETS.

AARS was measured following the method of Yebra and Hernadez-León (2004), modified by Yebra et al. (2011), and adapted for a 96-well plate (Yebra et al. 2017). All activities were corrected to in situ temperatures with the Arrhenius equation using an activation energy of 8.57 kcal mol-1 (Yebra et al. 2005) and standardized to protein specific activity, spAARS. spAARS_1 was measured with the NADH Blank and calculated as described by Mclaskey et al. (2020). For each sample, assays and NADH Blanks were measured in triplicate.

Oxygen consumption of individual krill was measured at 12 °C by closed-cell respirometry in 22-mL vials containing optical oxygen sensors (PSt7 PreSens) and a 12-mm magnetic stir bar separated from the animal by 200-μm mesh. Measurements were taken every 15 minutes for 2 hours. Krill were kept in filtered seawater to clear their guts for ~1 hr prior to respirometry.

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.