Hypoxia occurs when dissolved oxygen concentrations in aquatic habitats drop below levels required by living organisms. The increased frequency, duration and intensity of hypoxia events worldwide have led to impaired health and functioning of marine and freshwater ecosystems. Although the potential impacts of hypoxic exposure are severe, there is little known about the consequences of systemic, sub-lethal exposure to hypoxic events for populations and communities of fishes. The objective of this project is to determine whether sub-lethal exposure to hypoxia during early life stages leads to poor growth and hence increased mortality. This project will use "environmental fingerprint" methods in fish ear stones (otoliths) retrospectively to identify periods of hypoxia exposure. The project will compare consequences of hypoxia exposure in different fish species from the Gulf of Mexico, the Baltic Sea, and Lake Erie, thus examining the largest anthropogenic hypoxic regions in the world spanning freshwater, estuarine, and marine ecosystems. In addition, the research will increase awareness of hypoxia-related issues by disseminating curriculum materials to high schools in southern Texas that are dominated by Hispanic and Latino American students. As a part of this program, two high school teachers will be sponsored to participate in the National Oceanic and Atmospheric Administration "Teacher At Sea" program, where they will gain first-hand experience in biological sampling in the northern Gulf of Mexico "Dead Zone" and help lead teacher training workshops for additional high school teachers to implement hypoxia-related curriculum in their classrooms. In addition, this project will contribute significantly to basic information for critical stakeholder groups in Baltic Sea and Great Lakes fisheries via the International Council for the Exploration of the Sea and the Great Lakes Fisheries Commission. Two graduate students and one post-doc will also be supported in part by this project.
This project will employ long-term, permanent markers incorporated into fish otoliths to identify life-long patterns of sub-lethal hypoxia exposure far beyond time spans currently achievable using molecular markers. This work will capitalize on patterns of geochemical proxies such as Mn/Ca and I/Ca incorporated into otoliths and analyzed using laser ablation inductively coupled plasma mass spectrometry to identify patterns of sub-lethal hypoxia exposure. The investigators will then determine whether exposure results in differential growth and survival patterns compared to non-exposed fish by tracking cohorts over time and identifying characteristics of survivors. Because this work involves multiple species in multiple hypoxic regions, it will allow cross-system comparisons among unique ecosystems. The results from this project will thus provide unprecedented insight into effects of hypoxia exposure in three major basins using novel biogeochemical proxies, thereby paving the way for a fuller understanding of the impacts of "dead zones" on coastal resources.
