148-12 Life Above the Mud: Epibenthic Foraminifera Living on Elevated Substrates from Hypoxic Margins to Arctic Seafloors

Session: Insights from Microfossils and Their Modern Analogs: From Traditional to Emerging Approaches (Posters)

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Abstract:

Epibenthic foraminifera, those living at/above the sediment water interface, are valuable in reconstructing ocean conditions because their shell geochemistry reflects bottom waters rather than pore waters. Lobatula wuellerstorfi, one of the most recognizable epibenthic foraminifera, has traditionally been considered restricted to well‑oxygenated settings. However, recent in situ experiments and specimen recoveries from coarse‑grained seafloor sediments challenge these assumptions, revealing greater ecological flexibility. Seafloor Epibenthic Attachment Cubes (SEA³s) deployed off Oregon (~600m water depth over 6 months) and at Station M (~4000 m) in the Pacific show that foraminifera readily colonize elevated artificial substrates, including plastic mesh, even under low-oxygen conditions. Morphometric analyses revealed strong internal scaling among test features in both populations, though Station M specimens differed notably in form. These individuals, dominated by sexually produced megalospheric forms, showed reduced proloculus size and a skewed overall size distribution. At the Oregon margin, two distinct size groups of Lobatula wuellerstorfi were present, as is typical for this species based on alternating generations. In contrast, the Station M population was made up mostly of larger individuals thought to result from sexual reproduction, and they had unusual shapes—especially smaller initial chambers (proloculi) and uneven size distributions. At Station M, a new arborescent monothalamid (Adhaerentella dendrocoronam) was also discovered. 

In contrast, summer 2025 collections from the well-oxygenated Arctic waters of the Labrador Sea (off Canada and Greenland) documented foraminiferal colonization of natural elevated substrates such as rocks, worm tubes, and agglutinated structures. Abundant taxa included L. wuellerstorfi, Lobatula lobatula, Rupertia stabilis, Cibicides, and Cibicidoides. These findings emphasize the importance of substrate stability and texture—not just oxygen concentration—as drivers of epifaunal habitat preference.

Together, these observations reveal the broad ecological range of modern epifaunal foraminifera and raise important questions for paleoceanographic interpretations. If these taxa are more adaptable in depth, oxygen tolerance, and substrate preference than previously assumed, their fossil occurrences require more nuanced interpretation. This poster highlights the role of elevated substrates in structuring benthic communities and the ecological plasticity of foraminifera across diverse oceanographic settings.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9643

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