Award: OCE-1219948

Goals: Sea-surface temperature has increased over the last century, rising atmospheric partial pressure of carbon dioxide (pCO2) is lowering oceanic pH and the extent and intensity of low-oxygen bottom waters is growing. Biological and ecological impacts of these ongoing changes– warming, acidification and hypoxia– have been studied independently, but few studies have explored interactions among these stressors. Foraminiferan protists have two valuable attributes to multiple-stressor-impact studies: 1) They have species with tests (shells) composed of either calcium carbonate or non-carbonate materials. Those with carbonate tests may be more challenged by lower pH. 2) Many foraminifera perform complete denitrification when oxygen is insufficient for aerobic respiration. Few taxa have such mineralogical and physiological variability. Our overall goal was to determine the response of benthic foraminifera, in terms of community composition, survival and growth, to co-varying parameters of pH and dissolved oxygen, and to assess the influence of warming on these responses. We hypothesized that a combination of higher pCO2 (i.e., lower pH), lower [O2], and higher temperature compared to current-day conditions significantly affects calcareous foraminifera. Conversely, we hypothesized that agglutinated and thecate foraminifera were less affected by such conditions. Hypotheses were addressed using material collected from a continental-shelf site, with the following specific aims: (1) Using procedures experimentally controlling pCO2, [O2] and temperature, we documented calcareous and non-calcareous (agglutinated+ tectinous) foraminiferal assemblage responses to a regime matrix. Treatments were: Control (present-day; 400ppm CO2; aerated); Hypoxia present-day; Acidified (2000ppm; aerated); Hypoxia+Acidified; Preindustrial (275ppm; aerated). All were subject to 2 temperatures. (2) Use micropaleontological approaches to determine the preindustrial benthic foraminiferal assemblage at our site and compare that assemblage to that produced in our preindustrial treatment and to modern-day assemblages. Outcomes: Thirty-seven taxa were identified in samples from our 10.5-month-long experiment. Multivariate statistics revealed that all but one sample from both hypoxic treatments clustered together at 5% significance while 21 of the 24 samples from the 3 aerated treatments grouped together, with remainders branching closely. Thus, Preindustrial, Control and Acidified treatments generally cluster together, suggesting that pCO2 is less important than oxygen in driving this community?s species composition. Species responses varied. For example, Stainforthia fusiformis (calcareous) was more abundant in hypoxia and also survived acidification and warming; it rarely occurred in Aerated treatments. Elphidium cf. E. excavatum (calcareous) was inhibited by hypoxia and was absent in all triple-stress samples; Preindustrial and Acidified treatments promoted their highest abundances. Warming did not severely impact their abundance. Cornuspira (calcareous) was inhibited by hypoxia and acidification; it was more abundant in Control and Preindustrial samples than in Acidified samples and was slightly more abundant in warmer samples. An unidentified tectinous species, tentatively identified as Micrometula on the basis of a partial 18 rDNA gene sequence, occurred in each sample. It was most abundant in cooler hypoxic+acidified samples; warming negatively impacted their abundance. Our hypothesis that calcareous foraminifera are more negatively impacted by these stressors than agglutinated or tectinous foraminifera was not fully demonstrated. A differential vulnerability in foraminifera existed, but not on a test-composition basis. Our aim to compare the in situ preindustrial community to our experimentally produced preindustrial community was partly successful. Because the <53-micron fraction served as experiment inoculum, the locally important Globobulimina turgida was excluded because its initial chamber is too large. E. excavatum was also abundant downcore, consistent with its high abundance in Preindustrial samples. In a 2.5-month experiment, we used the same treatments (without warming), but used "adult" agglutinated specimens as inoculum. For substrate, we used glass spheres instead of natural sediment. We determined growth by identifying chambers composed of spheres. Agglutinated foraminiferal growth rate is not well established. Species-specific reactions existed. Results of this and the long-term experiment are generally similar. Differential responses of these species indicate that not all agglutinating foraminifera are adapted to predicted environments. Overall, these 3 stressors significantly impacted the foraminiferal community, with species-specific differences. Shifts will occur in foraminiferal species? compositions but extinction of the phylum, as asserted by some, is not supported by our data. Broader impact activities and products included education and training for students and early-career researchers. One postdoctoral researcher was supported for ~1.5 years, receiving extensive training and experience. An undergraduate conducted 3 months of research, gaining cruise experience. Seven more under/graduate students joined the oceanographic cruise to obtain first-hand experience. Three under/graduate students and a high school student were trained in pertinent laboratory techniques, data analysis, manuscript preparation and submission. Results were presented in 7 invited seminars at universities/research institutions, 2 invited presentations and 6 contributed presentations at conferences, and 3 lectures as part of short courses/workshops. Two journal articles were published, 1 more is submitted and at least 2 more will be submitted shortly. One of the published papers is directed to the general public. Partial gene-sequence data for the most common species was deposited in a public database. Last Modified: 11/18/2016 Submitted by: Joan M Bernhard