UC Berkeley

Past ecological information is critical for contextualizing the rapid, decadal to centennial-scale climate changes characteristic of novel human regimes—such as colonialism, industrialization, and urbanization. Yet these changes occur over 1-100 year “invisible timescales,” making them difficult to resolve with traditional biological and paleontological methods. In this dissertation, I use a highly temporally-resolved fossil record from an extraordinary system, benthic foraminifer fossils preserved in the marine varves of the Santa Barbara Basin (SBB), to examine the short-term impacts of environmental shifts on individuals and communities over the Common Era, an interval that includes both environmental stasis and rapid change.

Here I use the largest dataset of benthic foraminifera images and morphometric measurements generated to date to assess trends in life history reproduction, intra- and interspecific body size, and community-level diversity and abundance. In Chapter 1, I introduce benthic foraminifera from the SBB as an extraordinary system for high-resolution paleoecology. In Chapter 2, I detail the high-throughput imaging method I employ to produce a dataset of over 20,000 foraminifer images and measurements. In Chapter 3, I use these data to document the reproductive life history of biserial Bolivina foraminifera from ~50 CE to 2008 CE to examine the range of natural variation in reproductive mode and how reproduction is correlated with environmental variables. In Chapter 4, I apply a ~760-year-long dataset of individual measurements to characterize connections between intraspecific and community body size and whether size is modulated by life history and environmental variation. In Chapter 5, I undertake a multivariate analysis of diversity, biomass, and environmental data to assess how benthic foraminifer communities are structured from ~1834-2008 CE. Finally, I synthesize my findings in Chapter 6 and outline a vision for how paleoecology and the historical sciences more broadly can be in conversation with other disciplines to better understand the impacts of social and ecological change on the ocean.

I find that all aspects of ecology examined—life history, body size, abundance, and community structure—undergo state changes in the 19th and 20th centuries. The timing of change corresponds to major shifts in human-environment interactions that accompanied the colonization and industrialization of California. Taken together, these findings suggest that not only do SBB benthic foraminifera communities change towards the present day, but that modern communities are more changeable than those of the past, demonstrating heightened variability in individual characteristics that have species- and community-scale ecological consequences.