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Project Breathless undertakes sampling and analysis of fish from each study area - the Baltic Sea, Lavaca Bay and Lake Erie. Research partners:
Sample up to 100 fish of each study species from normal oxygen to hypoxic conditions.
Study species include Baltic cod and flounder; Gulf red drum, southern flounder and Atlantic croaker; and Lake Erie yellow perch and walleye, as well as the invasive round goby.
One otolith and one eye lens from each fish are analyzed for trace elements using laser ablation inductively coupled mass spectrometry.
Muscle tissue of each fish is analyzed for total mercury.
Portions of eye lenses from the inner and outer thirds (relative to the core) are examined using stable isotope analyses to observe dietary changes.
identifying earstone geochemical biomarkers
identifying earstone geochemical biomarkers
Otoliths, also known as ear stones, are calcium carbonate structures located in the inner ear of fishes. They play an important role in both hearing and balance. Like rings in a tree, a cross section of an otolith shows periods of growth across the lifetime of a fish. Project Breathless researchers use otolith-based age and growth chronologies to examine each individual fish’s life history. Concurrently, we use chemical analysis to monitor the conditions that the fish encountered in the water, including hypoxia exposure. This combination of techniques provides a more holistic view of an individual fish’s life history outcomes, and associates them with growth, movement, reproductive fitness, and trophic interactions.
Otoliths are sectioned and analyzed with laser ablation inductively coupled mass spectrometry to look for a suite of trace elements (Ba, Cu, Mg, Mn, P, Sr, Zn) and the major element calcium. A trace element of special interest is manganese, which is found in dissolved form only under low oxygen conditions. The project also explores the use of the ratio of the elements magnesium to calcium (Mg/Ca) as a lifetime metric of fish metabolism and condition. Otoiths are pulverized and examined using another technique, stable isotope analysis, to inform food web modeling.
Enhanced image of a Baltic cod otolith. Note the concentric growth rings. Photo credit: Yvette Heimbrand & Karin Limburg. Baltic Sea fishing vessel photo credit: Yvette Heimbrand
exploring ecotoxicology with eye lenses
exploring ecotoxicology with eye lenses
Fish eye. Photo credit: Yvette HeimbrandBaltic Sea photo credit: Yvette Heimbrand
Hypoxia can cause chemical reactions and changes to biogeochemical cycling, setting the stage for microbial processes that negatively affect aquatic conditions. These processes can include increases in mercury availability and microbial communities that convert it into methylmercury, which is the organic form of a neurotoxin. This neurotoxin can then accumulate in food webs.
Our aim is to test whether mercury chronologies (or total mercury accumulation) in fishes' eye lenses correlate with otolith lifetime hypoxia exposure chronologies. Like otoliths, eye lenses add annual growth rings and have great potential as recorders of chemical indicators of aquatic conditions. Eye lenses are composed of proteins, which have different chemical affinities than the calcium carbonate structure of otoliths, so they take up different trace elements, including mercury. Eye lenses are analyzed for a suite of trace elements (Ca, Cu, Hg, P, Pb, Rb, S, and Zn). The presence of mercury is also analyzed in muscle tissue and compared with eye lens findings.
food web & Habitat Impacts
food web & Habitat Impacts
Low oxygen conditions on the ocean floor forces some fish that feed near the sea bottom, like Baltic cod, to modify their eating habits and habitat preferences. Project Breathless combines otolith research with mathematical analysis to expand on the development of a dynamical model of the Baltic Sea food web.
Otoliths of Baltic cod have been analyzed to track long-term changes in trophic status as a function of hypoxia. Stable isotope analysis is used to measure the nitrogen found in proteins inside of otoliths, which can indicate a fish’s trophic level. This technique is used to compare the diets of Baltic cod that lived during the decades of 1980, 1990, 2000 and 2010. Hypoxic conditions and fish growth rates have varied across the decades, with consistent increases in hypoxia and declines in growth rates since 2000. Currently we are extending our historical analysis back into the 1930s, and are chronicling the changes in Baltic ecosystem status "seen through the heads of fishes," by means of otolith chemistry.
Baltic cod diet data inform the refinement of a dynamical model, which is used to identify and assess the relative importance of three different mechanisms by which hypoxia affects the food web:
reductions in habitat and species-specific changes in habitat use.
reduced food availability in hypoxic ocean floor habitats, with fewer prey species leading to food-shortages.
reduced access to enough oxygen for some species to maintain basic physiological processes.
All of these impacts can cause changes in the interactions among species in the food web, affecting its structure and functioning, as well as the ecosystem services it provides. This food web model has been developed to study the Baltic Sea, but it will result in a broadly applicable understanding of hypoxia induced food web alterations and should become useful in other hypoxic ecosystems. In addition to analyzing the effects of hypoxia on the native Baltic Sea food web, we will later develop the model to include the invasive round goby, which is now expanding its range in the Baltic Sea.
ecosystem services assessment
ecosystem services assessment
Project Breathless seeks to quantify the loss of ecosystem services for humans that are caused by hypoxic events. A major concern is the loss of fisheries production. Exposure to hypoxia has been shown to impact growth rates and body condition of some species of fish that humans depend on for food. Quantifying size and condition changes of fish in response to hypoxia exposure will enable calculations that project future fisheries stocks. Other ecosystem services that may be examined include the recreational and cultural benefits of abundant coastal resources, and the economic benefits of tourism.
Baltic cod and flounder caught while sampling. The cod is undersized and in poor condition. Photo credit: Yvette Heimbrand.
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