Research group MPEA

Marine Phytoplankton Ecology and Applications

Meet the Researcher: Carolin Peter


Meet the Researcher: Introducing Carolin Peter

This April, Carolin Peter joins us from her home in Germany to begin her PhD research in MPEA. A self-described lover of cold weather, “the colder and darker it is, the better I feel!” Carolin looks forward to her research on the effects of climate change on various phytoplankton species and the community composition here at Lnu. With three published papers already under her belt, Carolin will head to Kalmar next month. Below, an interview with Carolin Peter.


What is your background as a marine biologist and researcher?

I did my bachelor’s thesis working with algae – harmful dinoflagellates off the coast of Sweden, actually! And with my Master’s agree I specialized in Marine Biology, and again my focus was plankton. I am really, really interested in plankton. Any chance I got, I chose plankton over something like fish, for example.

I did my master’s thesis on the interactions between Caribbean sponges and their microalgal symbionts. My supervisor was a chemist, and he had found out that the substance which is presumably produced by the sponge converts light from the UV range to the range that is usable for microalgae. We wondered about the purpose of this, because it’s a rather energy-consuming process, and we thought, “Well! They have so little light down there, it might be to help the symbiotic algae produce more oxygen or more sugars.”

So that’s what I focused on. I had 9 different kinds of microalgae, which I exposed to a chemically synthesized version of that sponge-derived substance and checked the oxygen evolution using optodes to see whether the oxygen evolution would increase, and whether that depends on the light conditions. We assumed that the more light you offer, the less important the additional photons provided by the sponge molecule become, so we assumed that the effect would be greatest at lowest light conditions and then decrease with light intensity.


Fascinating! And what will be your research focus when you come to Lnu?

I will be looking at the impact of climate change on phytoplankton communities. Specifically, higher light conditions and higher temperatures. What we know so far is that these changes should favor smaller plankton, but the larger plankton species sometimes are better at taking up nutrients and due to lower nutrient availability caused by a decrease in mixing as a result of climate change, it might also be that the larger ones are favored. So that will be my focus. I will analyze the LMO data series to check how the composition of the phytoplankton changed seasonally and over time, and I will also do mesocosms and laboratory experiments to determine, for example, the nutrient uptake in typical small-scale and large-scale phytoplankton species for comparison.


What do you most look forward to about living and working in Sweden?

Regarding working in Sweden, specifically, the colder climate. I had my childhood in southern parts of Germany, then went north to Bremen for university, and now I am slowly moving farther up north!


At this rate, you may end up in the Arctic!

I was in the Arctic, actually! I was taking a course on phytoplankton in the arctic, analysing  phytoplankton and zooplankton samples and compared the composition between areas that had been free of ice for some time and others that had been underneath the ice.


It seems your areas of interest really involve communities and interactions among the species.

Absolutely. I love the interactions between the species. While I feel it’s important to perform laboratory experiments where you focus only on one species to be able to really understand what they are capable of, I feel like the more realistic approach is to focus on the whole community and see how things are actually out in the world. That has at least been my perspective thus far.


Carolin, we are really excited for you to join our research group, and the LNU community. Welcome!


-Caroline Littlefield & Carolin Peter

Wrapping up the summer field work season with BUG2020


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