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Tracking Baltic hypoxia and cod migration over millennia with natural tags
Karin E Limburg1, Carina Olson, Yvonne Walther
1Department of Environmental and Forest Biology, College of Environmental Science and Forestry, State University of New York, Syracuse, NY 13210, USA. klimburg@esf.edu
Summary
Baltic Sea hypoxia impacts cod growth, evidenced by manganese/calcium ratios in otoliths. This elemental tagging reveals historical hypoxia exposure and fish habitat shifts over millennia.
Area of Science:
- Marine biology
- Paleoceanography
- Fish ecology
Background:
- Coastal hypoxia is increasing, threatening fish habitats.
- Understanding hypoxia's impact on fish is crucial but limited.
- Otolith elemental analysis offers a method to study past environmental conditions.
Purpose of the Study:
- To investigate the relationship between Baltic Sea hypoxia and cod otolith chemistry.
- To reconstruct historical hypoxia exposure in cod populations.
- To assess long-term changes in cod migration and habitat use.
Main Methods:
- Analysis of manganese/calcium (Mn/Ca) ratios in modern and ancient cod otoliths.
- Correlation of otolith Mn/Ca with Baltic Sea hypoxia extent.
- Examination of strontium/calcium (Sr/Ca) and barium/strontium (Ba/Sr) ratios for salinity, temperature, and habitat use.
Main Results:
- Significant correlation found between Baltic Sea hypoxia and otolith Mn/Ca ratios in young cod.
- Elevated Mn/Ca ratios indicate exposure to manganese from hypoxia-induced redox dynamics.
- Ancient otoliths show low Mn/Ca, except for one Iron Age sample, suggesting varying historical hypoxia.
- Sr/Ca patterns indicate consistent migration habits across time.
- Ba/Sr ratios suggest modern cod increasingly use more saline habitats with age.
Conclusions:
- Otolith elemental ratios serve as a reliable proxy for reconstructing past hypoxia exposure in fish.
- This method can reveal historical fish movement patterns near hypoxic zones.
- Archival otolith collections offer a valuable resource for understanding long-term ecological changes in marine environments.
