Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
  • BCO-DMO Processing Description
• Related Publications
• Related Datasets
• Parameters
• Instruments
• Project Information
• Funding

Fish collection locations and associated information are found in an accompanying dataset for this project: https://www.bco-dmo.org/dataset/916418.

Fish eye lenses were dried and then processed for stable isotope analyses. When sufficient eye lens mass was available, lenses were peeled from the outer layer towards the eye lens core, and each layer or core material was analyzed separately. When insufficient material was available for peeling, eye lenses were analyzed whole to obtain a single isotope ratio measurement for that individual fish. Eye lens processing methods were similar to those reported by Bell-Tilcock et al. 2021.

Samples were packed into individual tin capsules for stable isotope analyses. All isotope analyses were conducted at the University of California, Davis Stable Isotope Facility. Text describing their methods below are from https://stableisotopefacility.ucdavis.edu/

Samples were analyzed for 13C and 15N isotopes using a PDZ Europa ANCA-GSL elemental analyzer interfaced to a PDZ Europa 20-20 isotope ratio mass spectrometer (Sercon Ltd., Cheshire, UK). Samples are combusted at 1000 degrees Celsius (°C) in a reactor packed with chromium oxide and silvered copper oxide. Following combustion, oxides are removed in a reduction reactor (reduced copper at 650°C). The helium carrier then flows through a water trap (magnesium perchlorate and phosphorous pentoxide). N2 and CO2 are separated on a Carbosieve GC column (65°C, 65 milliliters per minute (mL/min)) before entering the IRMS. During analysis, samples are interspersed with several replicates of at least four different laboratory reference materials. The long term standard deviation is 0.2 ‰ for 13C and 0.3 ‰ for 15N. The final delta values, delivered to the customer, are expressed relative to international standards VPDB (Vienna Pee Dee Belemnite) and Air for carbon and nitrogen, respectively.

Stable isotope ratios of 34S in solid samples are measured using an Elementar vario ISOTOPE cube interfaced to an Isoprime PrecisION IRMS (Cheadle Hume, Stockport, UK). Samples are combusted at 1000°C in a reactor packed with tungsten oxide and elemental copper. Immediately following combustion, sample gases are reduced with elemental copper at 900°C and subsequently pass through a buffering reactor filled with quartz chips held at 900°C. SO2 and CO2 are then separated by purge and trap, allowing for full separation and peak focusing. Following separation, the SO2 adsorption trap is heated and the sample SO2 passes directly to the IRMS for measurement.

During analysis, samples are interspersed with replicates of several laboratory reference materials to monitor and allow for correction of any potential variation in drift and linearity. Final 34S delta values are obtained after adjusting the provisional measurements such that correct 34S delta values for laboratory quality assurance materials are obtained. The long-term reproducibility of this method is ± 0.4 ‰.

Data are provided as reported by the analytical facility without additional processing.  Duplicate samples from some eye lens layers from some fish were analyzed separately to assess within-layer variation. Those results are provided separately and indicated as duplicates within the datasheet.

- Imported fish collection location data (file "916418_v2_fish_collection_locations.csv").
- Imported original file "Eye Lens SIA UPLOAD.xlsx" into the BCO-DMO system.
- Flagged "NA" as a missing data value (missing data are empty/blank in the final CSV file).
- Added the following columns from the fish collection location data file to this dataset by joining on Fish_ID: Station_Latitude, Station_Longitude, Date_Collected, Species.
- Saved the final file as "961971_v1_fish_eye_lens_stable_isotopes.csv".

NSF Award Abstract:
Ocean oxygen loss (deoxygenation) is increasing due to climate warming. This warming, together with nutrient loading, is causing many marine and freshwater systems to experience increasing episodes of hypoxia (low oxygen) of greater duration and intensity. Impacts on fish and fisheries have been difficult to quantify; direct observation has been challenged by a lack of long-term exposure indicators. This team has successfully refined the use of fish chemical biomarkers in fish otoliths (earstones) to directly assess lifetime hypoxia exposure in fishes. This project will those findings to look for additional biomarkers and models, to expand our understanding of how hypoxia affects fish and their food webs, contaminant transfers, and ecosystem services including economic impacts. The project includes a unique way of training students in science communication, posing the question: What forms of media and "messaging strategies" about deoxygenation are most effective at raising public awareness and understanding? Students are developing entries for PlanetForward's Storyfest, which is a contest to tell compelling stories to foster environmental understanding and solutions. Students from historically underrepresented, economically disadvantaged backgrounds are particularly sought out to participate. The investigators will engage with regional, national, and international management agencies and other relevant stakeholder groups to share information.

This project encompasses a novel, linked set of interdisciplinary studies of food webs, and ecosystem services assessment. The thematic questions explored in this project are: 1. How does hypoxia alter habitat use for fishes? 2. How does hypoxia-altered habitat use and habitat productivity change food webs? 3. How does hypoxia affect/enhance trophic transfer of methylmercury? 4. How do hypoxia-induced changes in food webs affect aquatic ecosystem services? The set of linked studies will employ chemical analyses of otoliths and eye lenses, combined with chemical analyses of muscle tissues (Questions 1 and 3), physiologically-structured food web modeling informed by monitoring time-series (Questions 2 and 4), and a scoping workshop to address ecosystem services (Question 4). The investigators are using a "trans-basin" comparative approach to system-specific responses, studying fishes in Lake Erie, the Baltic Sea, and a Gulf of Mexico estuary. They study three species from each system that represent different degrees of benthic reliance, to discern differential responses to the increasingly hypoxic environment. This research provides novel insight about variable biotic responses to oxygen loss and the impacts on ecosystem functioning.