Collaborative Research: BoCP-Implementation: The Impact of Climate Change on Functional Biodiversity Across Spatiotemporal Scales at Lake Tanganyika, Africa: Participant Support

Overview Africa’s Great Rift Valley is home to some of the most ancient and spectacularly diverse lake ecosystems found anywhere on Earth. Lake Tanganyika, the largest of these lakes and an important fishery, provides an unparalleled opportunity to investigate the response of functional diversity to rapid climate change in a tropical inland aquatic setting. At Lake Tanganyika, the future of biodiversity and ecosystem services are uncertain. Pelagic fish are crucial nutrition for the region, but knowledge of food web structure and function is restricted spatially and limited chiefly to contemporary time scales. Our project seeks to test hypotheses about the organization of the pelagic ecosystem and feedbacks between pelagic and benthic communities across space and time using an integrative geological-paleobiological approach. We propose to collect new sediment cores from analogous depositional settings along a north-to-south transect from the lake, and to rigorously date these deposits at annual-centennial resolution using radiocarbon. We will generate detailed microfossil, geochemical, and environmental DNA datasets to evaluate the composition of pelagic and benthic communities across four intervals of profound climate change: the cool-dry Last Glacial Maximum (~22-20 ka), the warm-wet African Humid Period (~12-10 ka), the warm-dry Middle Holocene (~6-4 ka), and the high-frequency hydroclimate oscillations of the Common Era (~2 ka – present). These lake-wide datasets will transform our understanding of the rules of assembly and key traits for the pelagic ecosystem of a large tropical lake, and allow us to forecast the response of Lake Tanganyika’s provisioning ecosystem services and biodiversity to warmer climates and an amplified hydrological cycle. Intellectual Merit Lacustrine food webs have been studied routinely using direct measurements of biotic and abiotic variables, but the hydroclimate dynamics of a changing planet are largely absent in contemporary datasets. Fisheries managers therefore face a grand challenge in forecasting food web behavior, which is particularly problematic in low-latitude regions where food insecurity is growing amidst severe climatic uncertainty. Lake Tanganyika is renowned for its high-resolution sedimentary and paleoecological record. Our project is the first to use these ancient sediments to set up a series of historical experiments to track functional biodiversity lake-wide. This framework integrates geochemical and fossil tools to assess pelagic and benthic community structure and function under different scenarios of climate change and the adaptive responses of key organisms to these changes. Because the hydroclimate conditions of the Late Quaternary are underrepresented in historical data, this approach enables us to evaluate the consequences of environmental change for Lake Tanganyika’s food web in a way that was previously impossible. In addition, we aim to identify shared and divergent responses to climatic fluctuations across the lake’s diverse fauna, and to link these responses to trait-based understanding of community assembly and functioning. This work holds potential for predicting changes in biodiversity through global change in large tropical lakes more generally. Broader Impacts A key aspect of increasing our impact is to reach out to Lake Tanganyika’s stakeholders (governmental ecosystem managers, fisheries scientists, and non-governmental conservation planners), and to transfer knowledge that can benefit sustainability planning and policy development. This will be accomplished through direct engagement (on-site meetings and training workshops in Africa), a Wikipedia page, a YouTube channel, and broad dissemination of a white paper in English, Swahili, and French that synthesizes project results for decision makers. The project emphasizes mentoring and training of students at several universities, including two from EPSCoR states. The project will pursue STEM outreach to students from under-represented groups, particularly those from minority, first generation college, and depressed socioeconomic backgrounds, to provide new opportunities for exposure to the geosciences. The project will also pave the way for reconstructing Lake Tanganyika’s ecological and evolutionary history in deep time via scientific drilling.