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Ostracodes are small (0.5 – 1.5 mm), seafloor-dwelling crustaceans who are sensitive to different environmental conditions. Changes in the environment affect their growth so, scientists can study their shells to learn about past ocean and environmental conditions. Since 1991, USGS researchers have been compiling a database of ostracode samples that’s making it easier to learn about the past.

Scientists use ostracodes as indicators of ocean conditions and change. These organisms secrete bivalved shells made of calcite, which are commonly preserved in Arctic Ocean sediments. Because of their small size, ostracodes have a rich fossil history. Plus, because they are sensitive to environmental factors such as temperature, salinity, oxygen levels, sea ice, and food availability, ostracode species serve as valuable ecological indicators. 

The USGS Land-Sea Linkages in the Arctic Project aims to make ostracodes a more useful tool for understanding Arctic benthic (seafloor) ecosystems and ocean changes over the past 50 years and longer. Since 1991, researchers have been building the Arctic Ostracode Database (AOD), an ostracode census dataset from more than 1600 surface sediment samples collected from across the Arctic Ocean and subarctic seas. This comprehensive database includes the year each sample was collected and information about the site, such as latitude, longitude, water depth, bottom water temperature and salinity.

ten examples of different Arctic ostracode species
ten examples of Arctic ostracode species

The two images above are examples of the diversity of shells from Arctic ostracode species. There are approximately 100 different species living in the Arctic Ocean. (Images taken by Laura Gemery, USGS and appear in Gemery et al., 2015, An Arctic and Subarctic ostracode database: biogeographic and paleoceanographic applications. Hydrobiologia. DOI 10.1007/s10750-015-2587-4)


Why is the Arctic Ostracode Database important?

The Arctic Ostracode Database (AOD) serves as an important tool for assessing the impact of recent large-scale environmental changes on Arctic and subarctic benthic ecosystems. The AOD currently has samples providing baseline ecosystem data back to collections made in the 1933, with especially high-resolution data around Alaska since 2009. New faunal data is added every year. Specifically, this database offers:

map showing distribution of ostracode species in Arctic Ostracode Database across Arctic Ocean
The Arctic Ostracode Database (AOD) provides modern census data of benthic marine ostracodes in surface sediment samples collected from shallow to deep areas of the Arctic Ocean. The dots designate the sample locations, with specific taxa groups color-coded by deep-sea (blue) and coastal (yellow) areas. Map courtesy of Huai-Hsuan M. Huang.
  • Baseline species abundance and distribution data - useful for conducting comparative faunal surveys in the future and examining past paleoecological studies of fossil assemblages from sediment cores;
  • Opportunities to test hypotheses - especially about how ongoing ecosystem changes in the Arctic and subarctic regions can be attributed to anthropogenic climate change;
  • Insights into how ostracodes, at the base of the food web, respond to climate-related changes - including variations in surface productivity, sea-ice extent, temperature, salinity, and other environmental factors;
  • A way to test evolutionary questions using ostracode comparative anatomy - such as the phenomenon of eye loss in deep-sea species.

How is the Arctic Ostracode Database being used?

A recent study titled “Sight and Blindness: The Relationship Between Ostracode Eyes, Water Depth, and Light Availability in the Arctic Ocean” (Zhang et al., 2024) uses the AOD to investigate the distribution of eyes in marine organisms relative to water depth and light availability, which sheds light on a poorly understood aspect of marine biology. 

USGS scientists collaborated with colleagues from London, England, Hong Kong, China, Jena, Germany, and Taipei, Taiwan to test whether marine species living in deep and dark waters lose their eyes through evolutionary processes. Because eyes require significant energy to develop and maintain, if they’re not necessary, they are genetically selected out after many generations. 

ostracode species with eye tubercles identified
Two species of eyed ostracodes that exhibit eye tubercles and inhabit continental shelf environments. Eye tubercles are externally visible semi-globular structures of the calcareous shell, one in each of the two valves. The presence of eye tubercles is a good indication that the ostracode possessing them is (or was) sighted (Zhang et al., 2024).

The team tested this hypothesis by looking at different ostracode species in the AOD. By examining the depth distribution of blind vs. eyed ostracodes, they found that the number of species with the ability to see declines with depth. 

Why is this important? The presence or absence of eyes is a good first approximation (proxy) for light penetration into ocean waters, and therefore, the depth of the seafloor when the species lived in the past. This information can then be used when reconstructing past environments and sea levels. 

The AOD was also applied to examine how species living in and around the Arctic Ocean have prehistorically changed their distributions in response to climate change, including migrating southward in response to colder (stadial and glacial) periods (Zhang et al., 2022). The AOD has also been used to analyze and understand Arctic ostracodes beyond the scale of a local project to across the Arctic Ocean and subarctic seas.

The AOD is accessible as an open-source file through NOAA’s National Centers for Environmental Information (NCEI) World Data Service for Paleoclimatology (



Cronin T.M., L. Gemery, W.M. Briggs, Jr., E.M. Brouwers, E.I. Schornikov, A. Stepanova, A. Wood, M. Yasuhara, S. Siu. 2021. Arctic Ostracode Database 2020. NOAA's National Centers for Environmental Information (NCEI).

Gemery, L., T.M. Cronin, W.M. Briggs, E.M. Brouwers, E. Schornikov, A. Stepanova, A.M. Wood, M. Yasuhara. 2015. An Arctic and Subarctic Ostracode Database: Biogeographic and Paleoceanographic Applications. Hydrobiologia, 786:(1), 59-95. doi: 10.1007/s10750-015-2587-4.

Huang, H-H. M., M. Yasuhara, D. J. Horne, V.Perrier, A.J. Smith, S.N. Brandão. 2022. Ostracods in databases: State of the art, mobilization and future applications, Marine Micropaleontology, 174. 

Zhang, J., M. Yasuhara, C.-L.Wei, S.Y. Tian, K.T. Aye, L. Gemery, T.M. Cronin, P. Frenzel, D. J. Horne. 2024. Sight and blindness: The relationship between ostracod eyes, water depth, and light availability in the Arctic Ocean. Limnology and Oceanography.

Zhang, P., H-H. M. Huang, Y. Hong, S. Y. Tian, J. Liu, Y. Lee, J. Chen, J. Liang, H. Wang, M. Yasuhara. 2022. Southward migration of Arctic Ocean species during the last glacial period. Geophys. Res. Lett. 49: e2022GL100818. DOI:10.1029/2022GL100818

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