Table of Contents

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

This dataset is part of Project Breathless, which brings together an interdisciplinary team of ecologists, economists and communication scholars to increase understanding of the impact of low oxygen dead zones in lakes and oceans.  The project team focuses on how low oxygen conditions influence fish, their habitats and the food webs that support them, as well as ecosystem services, including fisheries production.

This dataset is one of three examining Baltic fishes using data collected during routine surveys for monitoring the status of fish stocks:

• Dataset 967907 (this dataset of stables isotopes and mercury) summarizes capture data as well as basic biological information; it also includes all stable isotopic ratio and total mercury data collected from muscle tissue (though not from every fish). 
• Dataset 967925 (Baltic fishes otolith chemistry) contains all of the Baltic Sea fish otolith chemistry data; it also includes data from 14 Icelandic cod otoliths that were used as an out-group for part of the study
• Dataset 967934 (Baltic fishes eye lens chemistry) contains all of the eye lens chemistry data.

(See Related Datasets section below for links)

Fish were collected during routine surveys performed for monitoring the status of fish stocks, either by national fishery management agencies (Department of Aquatic Resources, Swedish University of Agricultural Sciences, Icelandic Marine and Freshwater Research Institute) or international collaborative effort (Baltic International Trawl Survey). Fish were caught by trawl or by gillnet sets, then frozen for later processing.

In the lab, fish were measured for length and weighed. Sex and spawning stage were determined where possible. Otoliths and eye lenses were removed, cleaned, and stored until workup (see Related Datasets section below). Samples of dorsal muscle tissue were collected for mercury and stable isotope analysis and were dried to constant weight.

Total mercury analyses were conducted using atomic absorption spectrophotometry on a Milestone DMA-80 tri-cell unit (Milestone Srl, Italy). Briefly, the method involves thermal decomposition of a sample, amalgamation of mercury, and absorbance of mercury using a spectrophotometer. Quality assurance and quality control was following EPA Method 7473, including daily calibration checks, the use of blanks, certified reference materials, and matrix spike/matrix spike duplicates. Sample duplicates were analyzed on a minimum of 20% of samples.

Stable isotopic ratio analyses for carbon (C), nitrogen (N), and sometimes sulfur (S) were conducted by either the Stable Isotope Facility at the University of California at Davis or at the Cornell University Isotope Laboratory. Both facilities routinely analyze solid samples, such as ours, using elemental analyzers on the front end of isotope ratio mass spectrometers (EA-IRMS). Delta values are expressed relative to Vienna Pee Dee Belemnite (for carbon), air (for nitrogen), and Vienna Canyon Diablo Troilite (for sulfur) standards. Light stable isotopes of C and N were analyzed at UC Davis with PDZ Europa ANCA-GSL elemental analyzer interfaced to a PDZ Europa 20-20 isotope ratio mass spectrometer (Sercon Ltd., Cheshire, UK). At Cornell, a Thermo Delta V isotope ratio mass spectrometer (IRMS) is interfaced to a NC2500 elemental analyzer (EA). Sulfur isotopes were analyzed separately on the same mass spectrometer at Cornell.

(For otolith chemistry and fish eye lens chemistry results, see Related Datasets section below.)

Results data on total mercury and C, N, and S stable isotopes were received as-is from outside labs, with no further processing.

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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.