Dynamic Imaging Particle Analysis Blog

Studying copepods and phaeocystis to understand climate and food webs

Dr Hans JakobsenHans H. Jakobsen, Ph.D is a senior researcher in the Department of Bioscience, Marine Diversity and Experimental Ecology at Aarhus University in Denmark. His list of published papers and articles is extensive and impressive. 

Studying Copepods

Much of Dr. Jakobsen’s work involves the study of grazer interaction among plankton organisms. He’s about to start a small project with his colleagues at neighboring Roskilde University where they will follow the dynamics in copepod rearing tanks. 

For the study, Dr. Jakobsen will assist the group at Roskilde University to establish a commercial system that can rear copepods to be used as first-feeding prey in aquaculture. One of the main problems in aquaculture, especially if you want to domesticate new species and produce high volumes of fish for consumption, is to supply a steady amount of food. Many of these fish will not eat, or grow poorly on a diet of rotifers; they only eat copepods. The fish larvae also grow much bigger in a shorter time with copepods as prey, so the idea is to develop a system that they can deploy to provide a continuous food supply of live copepods. “One of the things we hope to better understand is the microbial communities that always develop in these systems,” says Dr. Jakobsen. “We’ve done some preliminary tests where you can see the different kind of groups with the FlowCam, and we hope to learn how these groups may influence the dynamic interactions within the microbial communities.”

The copepod rearing tanks are very dirty. Dr. Jakobsen and his colleagues use the high magnification power in the FlowCam to get images of the waste in the tanks. “With these images we can estimate the biomass of the ciliate community and much of the stuff that develops together with the copepods in the tanks,” explains Dr. Jakobsen. “The copepods do not really seem to be affected by all the “junk” in the tanks, but it's the kind of information you need to know when you want to set up a system.”

Dr. Jakobsen first saw the FlowCam many years ago when he was doing his post-doctorate work in the United States. It’s the first instrument of its kind to combine flow cytometry and digital imaging to measure size and shape of microscopic particles and live cells in vivo in a fluid medium. He became interested in the instrument when he realized it can replace a lot of the tedious work and hours spent using a traditional microscope. In particular, the FlowCam has the ability to quantify and size colonial phytoplankton structures which have shown to be very useful in Dr. Jakobsen's research.

Mesocosm studies and phaeocystis

And at some point in his career, Dr. Jakobsen became interested in mesocosm work. Mesocosms are experimental water enclosures. They are designed to mimic natural water conditions more closley than laboratory experiments with a limited amount of water. Mesocosm studies are a very powerful tool when trying to define food web interactions, since they allow researchers to study processes that otherwise are difficult to study in the lab. These types of studies can be used for particle characterization in ecosystem models making it really good platform for using a FlowCam.

Colony_of_Phaeocystis_pouchetiiPhaeocystis is a key species globally and play an important seasonal role in many ecosystems. A unique attribute of phaeocystis is its ability to form a floating colony with hundreds of cells embedded in a gooey mucilaginous matrix that can multiply massively during blooms. These colonies can be up to a millimeter and larger. It's very time consuming to quantify the number of cells embedded in the matrix on a microscope when they're affixed to slides as they tend to break apart. The images collected by the FlowCam are transformed into cell biomass which has proved very useful when you want to estimate the amount of carbon associated with colonial phaeocystis. “With the FlowCam you can estimate the number of cells in a colony, from the unfixed material," notes Dr. Jakobsen.

Dr. Jakobsen worked with chemists and taxonomists from all over the world in these studies. He contributed by characterizing phaeocystis and their formations. This work also contributed to his pursuit of plankton characterization with the FlowCam.

Bringing the FlowCam to sea

Dr. Jakobsen also brings his FlowCam to sea. Recently he participated with an international group led by a researcher form UNIB in Bergen, Norway. They cruised the North Atlantic aiming to understanding the planktonic food web across a north-south gradient. By traveling northwards the research group was able to study food web structures from post-spring phytoplankton bloom at the southern cuise stations, and across spring bloom to almost winter like conditions close to the northern sea ice boundary all within a 10 day cruise.



Climate studies such as ocean acidification and temperature increases, and how these variables act in a synergistic fashion in the ocean food web dynamic are urgent questions to answer. Some of the main concerns that drive this research are how fishing grounds, which ultimately sustain many human communities globally, will be affected by elevated temperatures and CO2 in our oceans. Also the role of changing food web structures is an important focal point for biologists because the oceans also are functioning as carbon “sinks”, removing carbon out of the atmosphere. This process is often referred to as “the biological pump”; yet the understanding of how the pump will be affected by the climate changes remains poor.

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Topics: Marine Research, User Spotlight, Aquatic Research