213 Cushman Symposium: Microfossils of Extremophiles: Living in the Danger Zone

This session will assemble studies documenting microfossil presence and/or microfossil-generating taxa in extreme environments, widely defined present and past, and those elucidating adaptations employed by extremophiles, to inform interpretations of the geologic record.

Tuesday, 21 October 2025
1:30 PM - 5:30 PM
HBGCC, 303C

Deformed Tests of Foraminifera from a Polluted Deep Ocean Dumpsite

Paper number: 213-8
Program: Technical Sessions
Time: 3:30 PM – 3:45 PM

Authors

Abstract

Between the 1940s and 1970s, chemical companies disposed of DDT‑containing waste barrels in designated deep‑ocean dump sites between Catalina Island and Los Angeles, California. These activities impacted marine wildlife and raised ongoing concerns about human carcinogens. In contaminated marine environments, benthic foraminifera often respond to both chemical pollutants and broader environmental conditions, making them valuable for disentangling multiple stressor effects. In 2021, the R/V Falkor visited one such site in the San Pedro Basin and collected sediment push cores near barrels using a remotely operated vehicle. Surface intervals (0–1 cm) were processed for live benthic foraminifera using Rose Bengal staining and compared to sedimentary geochemistry.

Test deformities occurred only in live individuals from near this region, primarily in Eubuliminella exilis, Uvigerina peregrina, and Bolivina spissa. These deformities included double apertures, twisted or rotated tests, abnormal or extra chambers, inflated/deflated chambers, and uncoiling. Eubuliminella exilis showed the most consistent deformities, especially near certain barrel transects.

The deformity rates showed the strongest positive correlation with PCBs (R² = 0.92), followed by the DDT breakdown product DDMU (R² = 0.89) and PAHs (R² = 0.82), suggesting a multi‑pollutant stress regime. Potential mechanisms include structural weakening of tests leading to breakage and repair, or sub‑lethal stress responses altering chamber formation. Deformity rates also correlated positively with temperature (R² = 0.91) and negatively with salinity (R² = -0.87), patterns possibly linked to basin flushing cycles. While populations appeared tolerant of legacy DDT, abundance dropped sharply at the highest DDT concentrations, suggesting a threshold beyond which communities cannot persist. Population size and diversity correlated most strongly with environmental factors, particularly total organic carbon, underscoring the role of food availability.

These results highlight the ecological plasticity of benthic foraminifera in a contaminated deep‑sea environment and point to specific pollutants, such as DDMU, as potential contributors to morphological abnormalities. Expanded sampling and finer‑resolution core analysis are needed to clarify the timing, causes, and broader ecological consequences of deformities in foraminifera from the San Pedro Basin.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-413914

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