Wrapping up the summer field work season with BUG2020
2020-08-17
August and September in the Baltic Sea is full of life fueled by the summer sun. Phytoplankton at the base of the marine food web are rapidly photosynthesizing, and cyanobacteria in particular are producing their annual summer blooms at the surface of the warm and stratified waters. We took the opportunity to conduct experiments at the LNU marine field station in Kårehamn, Öland, in beautiful summer weather investigating the growth and mortality of Baltic picocyanobacteria.
Pictured: PhD student Javier Alegria-Zufia and Dr. Hanna Farnelid recovering an array containing bottles of experimental seawater for the grazing study. After initially collecting seawater, the different experimental groups are contained in bottles and placed in these arrays, which are kept as close to ambient conditions as possible. The incubated experimental seawater experiences the same light and temperature conditions as a natural population would for the duration of the incubation, before being retrieved for sampling.
Tiny picocyanobacteria are prominent members of this community of phytoplankton. They can divide and become more abundant or they may become food for others in the food chain. Picocyanobacteria sustain their growth by consuming the available nutrients in the surrounding waters. Like many of us here on planet Earth, these microbes have preferences for their nutritional intake. Where a person might choose a banana over an apple for their daily fruit consumption, picocyanobacteria can have preferences for nitrate or ammonium as a source for critically needed nitrogen to grow. These nutrient preferences impact both the respective nutrient concentrations remaining in the water as well as the growth strategy of the cells that consume them. It is, however, still a mystery what the preferences are for picocyanobacteria that live and grow in the Baltic Sea.
The study, titled BUG2020 for Baltic Uptake and Grazing investigates the preferences for nutrient sources and the mortality rates of picocyanobacteria growing at the Linnaeus Marine Observatory (LMO), located 10 km offshore the east coast of Öland. To determine nutrient preferences, seawater was incubated with stable isotope labeled nutrients. In addition, dilution experiments were performed focusing on the grazing and mortality of Baltic picocyanobacteria. Measuring growth rates at several dilutions of relaxed grazing and virus pressure allows for the calculation of grazing rates on the algae, which is important in understanding the cycling of nutrients throughout the Baltic Sea.
-Christien Laber, Laboratory Engineer
The BUG2020 experiment is a collective effort within the Marine Phytoplankton Ecology and Applications research group. The members working on BUG2020 are:
Hanna Farnelid, Associate Professor
Elin Lindehoff, Associate Professor
Christien Laber, Laboratory Engineer
Javier Alegria-Zufia, PhD student
Catherine Legrand, Professor