Project: Collaborative Research: BoCP-Implementation: The influence of different nutrient delivery modes on functional biodiversity of marine plankton in a changing ocean

PI Provided Abstract

This is a combined field and laboratory program with a modeling effort to evaluate if different physical modes of nutrient delivery, in close proximity to each other, exert sufficient controls on nutrient availability and influence phytoplankton functional biodiversity and that of their zooplankton grazers. Distinct mechanisms have been identified that enhance nutrient concentrations to the upper ocean, but which are expected to support different rates and time histories of nutrient delivery. We hypothesize that varying physiological traits of phytoplankton nutrient acquisition and storage will conform to these inputs. The proposed study site is the Galápagos Archipelago in the eastern equatorial Pacific Ocean.

Measurements collected there by members of our team since 2014 suggest three modes of nutrient delivery are operative (topographic upwelling, island wakes and internal tides), and that phytoplankton communities differentially respond to these modes. For this project, intensive shipboard sampling will be augmented by 12-month deployments of a vertical profiler mooring to observe i) an isolated island wake and ii) interaction of the archipelago with the Equatorial Undercurrent (EUC) and upwelling on the western side of the archipelago. Internal tides are believed to have a significant influence on the system and also will be observed. The longer-term observational efforts will generate time series of currents, hydrographic properties including nitrate and chlorophyll a fluorescence and include biweekly water sampling of the region for molecular characterization of the phyto- and zoo-plankton communities. Intensive shipboard surveys will additionally measure a suite of hydrographic and plankton properties, including community composition, primary productivity, nutrient uptake rates and changes in gene expression driven either directly or indirectly by the physical forcing. Laboratory culture studies using phytoplankton isolates obtained from the region will be used to characterize nutrient uptake and storage characteristics to complement the field studies. The result will also inform parameterization of a simple plankton model forced by time series of nutrient delivery representative of the three physical modes at play, used to test if bottom-up control can explain observed distributions and temporal variability. A suite of phytoplankton parameterizations will be investigated, informed by observed species-specific characteristics, to determine which phytoplankton functional traits are favored by which physical mode. The overarching goal of the project is to examine how these specific physical mechanisms influence the functional biodiversity of plankton communities through increasing nutrient inputs into the mixed layer, leading to strong, yet perhaps predictable biological variability in a changing ocean environment.

NSF Abstract

All living organisms must acquire nutrients from their environment to survive and grow. Phytoplankton and their zooplankton grazers in the ocean, which constitute the base levels of the planet’s largest food webs and play an essential role in global carbon cycling, are no exception. However, the rules governing how different physical mechanisms of nutrient delivery to marine ecosystems structure plankton biodiversity and interaction networks along with their trophic dependencies are poorly understood. This project examines how these specific physical mechanisms influence the functional biodiversity of plankton communities through increasing nutrient inputs into the mixed layer, leading to strong, yet perhaps predictable biological variability in a changing ocean environment. This research reveals details on how environmental disturbances of varying spatial and temporal scales affect ecosystem function and elucidates the dynamics between taxonomic biodiversity and functional diversity with respect to ecosystem stability. Insights gained from this program about controls on productivity and biodiversity are applicable to many island and upwelling systems globally. Engagement of local partners to collect additional observations and dissemination of research findings to the Galápagos community enable a two-way dialog about system function and the issues faced by the indigenous community due to climate change. The project also provides training for graduate students and undergraduates from underrepresented groups and a K-12 teacher.

This project combines field and laboratory studies with a modeling effort to evaluate if different physical modes of nutrient delivery, in close proximity to each other, exert sufficient controls on nutrient availability that influences plankton functional diversity and associated dynamics. The study site is the Galápagos archipelago in the eastern equatorial Pacific Ocean where intensive shipboard sampling is augmented by 12-month deployments of a vertical profiler mooring to observe i) an isolated island wake and ii) interaction of the archipelago with the Equatorial Undercurrent (EUC) and upwelling on the western side of the archipelago. Internal tides, believed to have a significant influence on the system, are also being observed. Varying functional traits of plankton such as nutrient acquisition strategies and storage are being measured to investigate whether they are selected upon by these inputs. The cruise and longer-term observational efforts generate a spatial survey and time series of physical, chemical and biological properties. Laboratory culture studies using phytoplankton isolates obtained from the region are used to quantify phytoplankton functional traits in relation to nutrient acquisition and storage. The results inform parameterization of a plankton NPZ model forced by time series of nutrient delivery representative of the three physical modes at play, used to test if bottom-up control can explain observed distributions and temporal variability. This research advances ecological theory on biodiversity dynamics and functional biodiversity by testing the hypothesis that functional redundancy drives ecosystem stability, achieved through resistance to change or resiliency.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.