Field station full of stories

Category: zooplankton

New paper! Influence of environmental conditions, population density, and prey type on the lipid content in the northern Baltic Herring

Our new paper, where we investigated the effects of different environmental stressors on the lipid content of the northern Baltic Herring (Clupea harengus membras) was recently accepted for publication in the Canadian Journal of Fisheries and Aquatic Sciences.

In this study we collected herring samples from local trap net fishermen during 1987-2006 and 2013-2014 and analysed their lipid content and fatty acid composition. We discovered that the average lipid content of herring muscle has decreased on average from 5-6% wet weight (w.wt) to 1.5% w.wt. The decrease in sea water salinity and increased size of the herring stock explained best the declining lipid content. Also,  sea water temperature during January-April also had a significant effect in our modelling. We estimated that the amount of the lipid storage incorporated in the spawning stock decreased by approximately 45% during the study, with respective energy content decreases. Fatty acid composition analysis revealed that herring lipids contained a high proportion of essential fatty acids EPA (20:5n-3) and DHA (22:6n-3), which likely originated from its main summertime prey, the freshwater calanoid copepod Limnocalanus macrurus – a zooplankton species that has become highly abundant in the Bothnian Sea.

Global climate change can affect the energy content of fish by altering their lipid physiology and consumption.The results of this study illustrate that various climate change induced processes are leading to changes in the lipid content of the Baltic Herring and, consequently, to changes in the energy flows of the northern Baltic ecosystem.


Herring from the Archipelago Sea. Photo: Johannes Sahlsten

Rajasilta, M., Hänninen, J., Laaksonen, L., Laine, P., Suomela, J.-P., Vuorinen, I. & Mäkinen, K. 2018. Influence of environmental conditions, population density, and prey type on the lipid content in Baltic Herring (Clupea harengus membras) from the northern Baltic Sea. Canadian Journal of Fisheries and Aquatic Sciences (accepted for publication)

Read more about the project:

The Baltic herring project


Ways FINMARI infrastructure has improved our research

High-quality research and teaching requires investment in good research infrastructures. The FINMARI consortium was founded in 2013 and since then, with its support, we have been able to modernize and improve our research infrastructure.  Good research equipment help researchers and students across disciplines to study various interesting and important questions, related for example to the climate change. Here we introduce some of the equipment we have recently acquired.

Last week, we visited Tvärminne, the Zoological Station of the University of Helsinki and attended in the FINMARI Researcher Days. During the two-day meeting, we presented our latest work as well as heard many interesting presentations from other FINMARI partner organizations. In the photo, our master’s student Markus Weckström is giving a presentation on his master’s thesis. Photo: Jari Hänninen.

What is FINMARI?

Finnish Marine Research Infrastructure (FINMARI) is a cross-institutional consortium founded in 2013 and coordinated by the Marine Research Centre of SYKE. The consortium assembles research institutes, universities and a state-owned company, all with a strong interest in marine research. The distributed infrastructure network includes field stations, research vessels an multi-purpose icebreakers, laboratory facilities, ferryboxes, fixed measurement platforms and buoys.

Our research vessel r/v Aurelia is a part of the FINMARI infrastructure network.The 18,1 m long vessel hosts small wet and dry labs and is equipped with standard hydrographic and marine biological research and sampling equipment (incl. CTD, sediment corers and grabs, An acoustic Doppler current profiler (ADCP), on-line chlorophyll fluorometer, Meridata digital sonar system and other sonars), weather station, differential GPS, Navi Fisher navigating system. R/v Aurelia operates in the Archipelago Sea.

The latest major additions to our research infrastructure have been a Hydro-Bios Multinet Mini and a Manta trawl. The Multinet allows the collection of 5 parallel horizontal or vertical zooplankton samples (mesh size 100 um) and thereby essentially increases sampling efficiency by allowing the collection of more samples in less time. The Manta-trawl is a horizontal net system (mesh size 335 um), which allows researchers to collect microplastics and plankton from the surface waters.

The multiple plankton sampler on board of r/v Aurelia.

Sampling microplastics in the Arctic with the manta trawl. Did you know that the net was named after the Manta ray due to their similar shape?

In 2015, we acquired 10 aquaria racks. Each rack includes 12 aquaria with a closed water circulation to a flow-through system. Recently the aquaria have been used to study how the projected future salinity conditions of the Baltic Sea will affect the genetics of bladderwrack (Fucus vesiculosus).

University and school courses visiting Seili have been able to use new  improved stereo microscopes since 2016.

In spring 2018, we will also receive a side scan sonar system for shallow water, with which we’ll be able to study for example the bottom morphology of fish spawning grounds. The equipment can also open new research possibilities for example in marine archaeology.

Researchers interested in working  abroad may apply for funding at Assemble plus provides transnational access to marine biological research facilities and resources. At Seili, we offer a wide variety of services, including access to a brackish-water coastal ecosystem, state-of-the-art experimental facilities, historical observation data, and various research support services. Contact us for more information or stay tuned for new funding calls!

Training course on Baltic Sea zooplankton identification

A rhythmic clicking sound of counters echoes in the seminar building when we count the Bosmina longispina maritima water fleas from the samples. The glass slide I’m viewing under the microscope is full of life as rotifers and cladocerans battle for space. Every now and then, a large shadow covers my field of view – under themicroscope, even a small copepod looks like a giant. ”Must be either Acartia or Eurytemora” I think in my mind and a more careful examination of the species head, antenna and other anatomical structures prove it as the latter.

Zooplankton is a central part of marine and freshwater ecosystems, a link between different trophic levels of the food chain. For research and monitoring purposes it is crucial that the samples are analyzedaccurately and correctly. However, zooplankton species identification is not easy and mastering the skill takes many years of practice. Nevertheless, few advanced courses exist.

This week, a training course on Baltic Sea zooplankton identification, an advanced transnational course, was organized in Seili by the Institute. During the course, participants from various countries got to deepen their identification skills under person to person guiding.

After arriving in Seili on Monday morning, we started with the basics, the morphology and identification of copepods, and moved on to smaller organisms, cladocerans, rotifers, protozoans and nauplii, as the week progressed. The words P5 (the fifth leg), segment, hair, and furca were repeated often. The teachers, the recently retired research director of the Institute Ilppo Vuorinen and the Institute’s trusted plankton analyst, Satu Zwerver from Plankton Zwerver, patiently explained and showed the differences between the species with the help of the Institute’s own zooplankton guide(in Finnish) and Telesh et al. (2009)  Zooplankton of the Open Baltic Sea Atlas. A sampling cruise with r/v Aurelia to the Archipelago Sea gave the participants a  deserved break from microscopes.

Due to the brackish-water of the Baltic Sea, we observed and identified both marine and freshwater species. The theory was put into practice when we started to analyze the samples. We quickly discovered that the species identification is not as easy as it might seem. We learned the tricks of the trade but an experienced analyst can quickly identify a species from its appearance. Experience and knowledge were transferred with lively conversation when we compared cuvettes, and subsampling and counting methods.

On our final day, we discussed the many pros and cons of zooplankton imaging techniques, the future of zooplankton identification. There was also a rare treat when we got to analyze an Eastern Mediterranean sample that one of the participants had brought from Israel. For us more familiar with the Baltic Sea zooplankton it was fun to notice that even though the species are different, it was relatively easy to do a rough classification of the animals. We were also lucky to observe some Arrow worms (Chaetognatha), which are absent from the Northern Baltic Sea. Alas, nothing lasts forever and after presenting the group assignments it was time to sum up the week, pack our bags and move away from the microscope, but just for now..

The course was supported by The Finnish Foundation for Nature Conservation, Rafael Kuusankoski memorial fund.