Doctoral Dissertation Research: Dissolved organic nitrogen uptake by harmful algal blooms in the Chukchi Sea

Harmful algal blooms (HABs) happen when the growth of colonies of algae threaten human and/or ecosystem health. Some HABs involve algae that produce potent neurotoxins that can harm shellfish, marine mammals, seabirds, and other critical resources. In the past 15-years, toxic HABs have been observed in the Pacific Arctic Ocean and pose a potential threat to Indigenous and other local communities that depend on hunting and fishing for food.

This project supplements data collected during a research cruise led by scientists from the Woods Hole Oceanographic Institution (WHOI) to better understand the factors promoting these blooms. The team is determining whether algae that form HABs are better than other algae at using dissolved organic nitrogen (DON) for growth by characterizing different nitrogen compounds in the Chukchi Sea and how quickly various algae species take up these compounds.

The investigators are collaborating with the broader WHOI team to communicate the research results and their implications for Alaskan communities and coastal management via brochures, public lectures, radio interviews, and discussions with Indigenous communities, local scientists, and local officials. The project is also training one undergraduate student through the Stanford Undergraduate Research in Geoscience and Engineering program and two graduate students at Stanford University.

This project complements other measurements collected during a research cruise led by scientists from the Woods Hole Oceanographic Institution (WHOI). The principal cruise goal is to better understand the factors promoting these blooms. This project is examining the hypothesis that the preference for DON over dissolved inorganic nitrogen by dinoflagellate HAB species contributes to their success in July and August in the Chukchi Sea, an area that is known to be nitrogen-limited in the summer.

The investigators will sample DON concentrations across the Chukchi Sea and relate them to HAB distributions. A series of 15N-labelled tracer incubations will be conducted onboard the research vessel to measure bulk uptake rates of nitrate, ammonium, urea, and dissolved free amino acids by the entire phytoplankton community. Nanoscale secondary ion mass spectrometry, which measures individual cell isotopic composition, will be used to determine single-cell nitrogen uptake rates from the same incubations.

Nitrogen uptake by HAB species and HAB-dominated communities will be compared to that of diatom species and diatom-dominated communities, as diatoms are traditionally considered the dominant bloom-forming phytoplankton in the Chukchi Sea.

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.