Ecophenotypic responses of benthic foraminifera to oxygen availability along an oxygen gradient in the California Borderland

Abstract

Spatial variation in environmental conditions can elicit predictable size and morphological responses in marine organisms through influences on physiology. Thus, spatial and temporal variation in marine organism size and shape are often used to infer paleoenvironmental conditions, such as dissolved oxygen concentrations. Benthic foraminifera commonly serve as a tool for reconstructing past ocean oxygen levels. For example, benthic foraminiferal species assemblages, within‐ and among‐species patterns of test morphology, and geochemical analyses of carbonate tests are often employed to reconstruct past marine conditions. In this study, we measured the sizes and shapes of modern foraminifera representing four species that inhabit a steep oxygen gradient in the Santa Monica Basin on the Southern California Borderland with the aim of quantifying the influence of oxygen availability on foraminiferal morphology, both within and among species. Most foraminifera rely on aerobic respiration, but the four benthic foraminifera from the Santa Monica Basin do not show the predicted size and morphological responses to variations in dissolved oxygen concentrations based on first principles of cell physiology: Bolivina spissa shows no volume or volume‐to‐surface area response, Uvigerina peregrina increases in both test volume and volume‐to‐surface area ratio with decreasing dissolved oxygen concentrations, and both Bolivina argentea and Loxostomum pseudobeyrichi decrease in test volume, but only L. pseudobeyrichi shows a decrease in test volume‐to‐surface area ratio with decreasing oxygen concentrations as expected from physiological predictions. These findings imply that the morphological responses of individual foraminiferal species are not necessarily representative of the responses of other foraminiferal species within the community. Our findings further suggest that these species use physiological strategies such as depressed metabolic rates and alternative energy metabolisms to persist in low oxygen environments and, therefore, cannot be used in any simple way as paleo‐oxygen indicators. Should Proterozoic (1,000–542 million years ago) protists have possessed metabolic strategies similar to foraminifera, the sizes and shapes of protists in the fossil record may not usefully constrain ambient oxygen conditions during the appearance and initial taxonomic radiation of heterotrophic eukaryotes.

Enhanced Carbonate Dissolution Associated With Deglacial Dysoxic Events in the Subpolar North Pacific

“…This indicates that, for U. peregrina , there is an association between morphological differences and ρ V . Size and growth rate in marine benthic organisms can vary along oxygen gradients and will increase or decrease with oxygenation depending on the physiological preferences of the species (Belanger et al., 2020; Glock et al., 2019; Keating‐Bitonti & Payne, 2017). In U. peregrina from GoA, shell volumes are greatest where Mo/Al and the relative abundance of dysoxia‐tolerant foraminifera are highest (Figure 3), similar to results from SBB (Davis et al., 2016), which indicates an association between larger U. peregrina shells and lower oxygen environments.…”

Environmental influence on growth history in marine benthic foraminifera

“…Adult foraminifera living in OMZs are often larger than predicted based on first principles of cell physiology (Keating-Bitonti and Payne 2017). Several benthic foraminiferal species recovered from oxygen-limited waters were documented with bacterial endosymbionts or with large vacuoles with NO 3 concentrations greater than levels found in the ambient environment (refer to Supplementary Table S1; Risgaard-Petersen et al 2006; Piña-Ochoa et al 2010; Koho et al 2011; Bernhard et al 2012a, b).…”

Southern California margin benthic foraminiferal assemblages record recent centennial-scale changes in oxygen minimum zone

“…Identification of benthic foraminiferal taxa was based on previously published descriptions and images of benthic foraminifera (see the Supplement, Fig. S4, for images of dominant taxa and taxonomic reference list) (Balestra et al, 2018;Erdem and Schönfeld, 2017;Keating-Bitonti and Payne, 2017;Moffitt et al, 2014;Setoyama and Kaminski, 2015). Assemblages in the 63-150 µm fraction were quantified from the same sediment fraction as the >150 µm to allow for comparison of abundance between the two groups.…”