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Coastal marine ecosystems and areas of the open ocean are experiencing low oxygen - or hypoxic - events. In a human, acute hypoxia can lead to respiratory distress and organ failure. This fate already happening to aquatic life across the globe. Fish can swim away from hypoxic waters, but their growth and health may be impacted by the exposure to low oxygen conditions. As the climate changes, hypoxic events occur for longer periods of time and at greater intensities. The full impacts on fish and aquatic ecosystems have been difficult to quantify, though models have painted a bleak picture.
The mission of Project Breathless is to explore the ecosystem consequences of hypoxia. This includes studying biomarkers in fishes that help assess hypoxia exposure over time and across trophic levels, and integrating the results with food web models.
The mission of Project Breathless is to explore the ecosystem consequences of hypoxia. This includes studying biomarkers in fishes that help assess hypoxia exposure over time and across trophic levels, and integrating the results with food web models.
Project Breathless researchers conduct chemical examinations of fishes' eyes, ears and muscle tissue to search for biomarkers that indicate exposure to hypoxia. A biomarker is a substance found in an organism that indicates the environmental conditions it encountered during its lifetime. For example, the presence of the element manganese in a fish's otolith may indicate that it was exposed to hypoxic conditions.
A reference diagram showing ways that hypoxia exposure impacts organisms and aquatic systems. Credit: K. Limburg
Using biomarkers as proxies for hypoxia, Project Breathless researchers investigate:
How does hypoxia alter habitat use for fishes?
How does hypoxia alter habitat productivity and food webs?
How does hypoxia affect/enhance trophic transfer of methylmercury?
How do hypoxia-induced changes in food webs affect aquatic ecosystem services?
PhD student Hadis Miraly examines fish eye lenses. Photo credit: Hadis Miraly
A Baltic cod otolith. Photo credit: Jess Lueders-Dumont
Project Breathless studies hypoxia impacts on:
Function and structure of food webs
Release and bioaccumulation of contaminants
Corresponding losses of ecosystem services
The study of food webs is useful in that it focuses on interactions between organisms through their interconnected food chains. Because oxygen impacts an organism's growth, we can track the impact of hypoxia as it moves up the web. Loss of dissolved oxygen can also alter living conditions of organisms. Deoxygenation can cause chemical reactions and changes to biogeochemical cycling, setting the stage for microbial processes that negatively impact conditions. These can include increases in mercury availability and microbial communities that convert it into methylmercury, which in this organic form is a neurotoxin. This neurotoxin can then accumulate in food webs.
Negative impacts to food webs extend beyond marine systems. Because people consume fish from oceans, we can also be considered part of the food web. Using this line of thinking, we can view marine systems as providing goods and services, in this case food for human consumption, but also maintenance of complex food webs that maintain energy and nutrient flows. A well-functioning ecosystem can provide a lot of food, but as the system deteriorates due to issues such as deoxygenation, acidification, and warming, we run into further risk of imperiling the resources on which we depend. We are developing criteria to assess impacts on ecosystem services that can affect human well-being. This will provide scientists and policy-makers alike with important insights into the impacts of climate change on marine systems.
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