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Week in pictures: Brackish-water ecology course 2018

Did you know that field courses have been organized in Seili since the 1960s? This week undergraduate biology and geography students from the University of Turku arrived to Seili to learn about the special characteristics and ecology of the Baltic Sea and Archipelago Sea. During the course week, students participated in sampling cruises on board of the Institute’s vessels r/v Aurelia and Seili 5 and conducted several laboratory exercises. The course has been organized in its current state since 2003 and is teached by the staff of the Archipelago Research Institute. Here’s a photo roundup of the course week.

STL UTU murtovesikurssi 2018

After the introductory lecture at Turku University campus, it was time to start the  first sampling cruise from the Aurajoki River. At 10:00 sharp, we embarked on our research vessel r/v Aurelia and headed toward the first sampling point just outside the Aurajoki river. At Linnanaukko (named after its proximity to the Turku castle), the students got to observe the river’s effect on Secchi-depth, salinity, water temperature and bottom macrofauna.

STL UTU murtovesikurssi 2018

The sampling cruise continued along the Airisto inlet towards Seili island.  The water quality (temperature, salinity and oxygen content) was monitored with water samples, collected with a Limnos-water sampler as well as with a profiling CTD-sonde.

STL UTU murtovesikurssi 2018

On Monday, our journey was favored by the weather gods and the students were able to practice their sampling skills in calm and idyllic weather.

STL UTU murtovesikurssi 2018

Thanks to the good weather, we arrived to Seili on record time! Nevertheless, this meant no extra free time for the students as the day continued with an introduction to common Baltic Sea zooplankton species. The Institute’s new seawater laboratory was put to the test and found perfect for these types of exercises.

STL UTU murtovesikurssi 2018

On Tuesday, we embarked r/v Aurelia again at 08:00 and headed towards the outer archipelago . Weather forecasts showed heavy winds for the day so an emergency training exercise was in order.

STL UTU murtovesikurssi 2018

Marine research can sometimes be very laborous. Lifting the CTD-sonde, tied to a metal frame, from the 100 meter depth of Ådofjärden equates to a workout!

STL UTU murtovesikurssi 2018

During the first two days several bottom sediment samples were taken with Ekman and Van Veen sediment grabs. Preparing the samples for sieving is also known as “mud-therapy”.

STL UTU murtovesikurssi 2018

Sometimes there is no choice but to change the course program due to apparent weather conditions. The heavy wind speed (11-12 m/s) forced us to skip beach seining at Boskär-island and we headed toward Seili a bit earlier than anticipated.

STL UTU murtovesikurssi 2018

But no worry! Soon after returning to Seili, the students started identifying macrofauna from the sediment samples. And how many interesting species there were! Especially polychaetes became familiar – Marenzelleria spp. abundances were at best up to 200 individuals/per sample.

STL UTU murtovesikurssi 2018

On Wednesday morning, on board of our Seili 5 vessel, we headed towards Iso-Kuusinen island in the middle archipelago.  On our way to Iso-Kuusinen, we stopped to take samples at Päiväluoto, the Institute’s at-sea monitoring station where water and plankton samples have been collected since 1966.

STL UTU murtovesikurssi 2018

At Iso-Kuusinen, the students were introduced to a beach seine, a qualitative sampling method used to study especially fish, but also invertebrate and algal species in the littoral zone.

STL UTU murtovesikurssi 2018

What would a brackish-water course be without getting our feet wet (well, sort of). At the sandy beach, the students were sent hunting for burrowing clams.

STL UTU murtovesikurssi 2018

The final sampling exercise of the week was fishing. Nordic multimesh gillnets were set at three depths (surface, middle and bottom) outside Saunasaari island, in order to study the variability in fish species, their size, weight and location in the water column. The handling of nets went perfectly and we were not left empty handed! After measurements were taken, the fish were put to a freezer and are later send to the University’s Biology department  for other students to study on.

Similar posts:

Field courses introduces to the surrounding nature (English summary at the end of the post)

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


New research project investigates parasites found in the Baltic herring

In the Archipelago Research Institute, the reproductive biology of the Baltic herring (Clupea harengus membras) has been studied for over 30 years, since 1984. During the last few years we have discovered large amounts of parasitic worms in the body cavity of herring, collected from the Airisto Inlet. The phenomenon is new as no worms have been previously discovered in our samples. Dna-analyses conducted by the University of Eastern Finland showed that the parasitic worms are in fact two species (Corynosoma strumosum ja C. semerme), belonging to the phylum Acanthocephala. A new research project, studying the distribution and occurrence of these worms in the local herring, seal and great cormorant populations will begin next summer. 

Acanthocephala, also called thorny- or spiny headed worms, are commonly found in fish and seals. In Finland, 11 species are known to occur. The parasitic worms don’t infect humans. The Baltic herring is a safe and nutritious food fish and no cold treatment is required when preparing the fish.


According to our preliminary studies, in 2014-2015, approximately 15% of herring in the Airisto Inlet were infected by the parasitic worms.

Corynosoma-worms use herring as an intermediate host. The grey seal (Halichoerus grypus) and/or ringed seal  (Pusa hispida) are definitive hosts for the Corynosomaspecies. Of the two seal species, the grey seal is common in the Bothnian Sea and nowadays also in the Archipelago Sea. The steady increase of the grey seal population and its spread to the middle- and inner archipelago might have caused the parasitic infection in herring. The species C. strumosum has also been discovered in  Great Cormorants (Phalacrocorax carbo). Therefore, it is possible that the bird species is also a definitive host as the increase of the cormorant population coincides with the timing of our findings.


Parasitic worms may cause negative effects for commercial herring fishery. Therefore, it is important to understand the extent of the phenomenon and the causes behind it.

The two-year study is funded by the Archipelago Sea Fisheries Action Group (officially Saaristomeren kalatalouden toimintaryhmä in Finnish). The research is carried out together with the Joensuu Molecular Ecology Group of the University of Eastern Finland. The project’s field work begins next summer. The aim is to chart the distribution and occurrence of the parasitic worm species in the local herring population. We will also investigate whether the Great Cormorant is a definitive host in addition to the grey seal.

Stay tuned for updates from the field!

Watching nature’s family drama unfold on live webcam

In the eastern side of the Seili island, on top of a leading mark, is a nesting  Osprey (Pandion haliaetus) couple totally unaware of its fame. The breeding of this second largest predatory bird species in Finland has been monitored through a web camera since 2006. The Osprey web camera was installed in Seili by the Turku University of Applied Sciences as part of NatureIT-projects and later, continued as part of and BalticSeaNow projects. The last project, EU-funded BalticSeaNow ended in February 2013. Since 2015, the Archipelago Research Institute has participated in the maintenance and funding of the web camera and connections. The latest addition to the camera was a microphone, added to the camera assembly in 2016, so that sound can be transmitted. The Osprey cam can be found in the website, updated and administered by the Archipelago Institute.

Like several other web cameras in Finland and worldwide, the Osprey cam of Seili has been very popular since its beginning. At its best, the ospreys have reached one million views per year! The camera is operated year round. During winter, viewers can admire the changing archipelago scenery and white-tailed eagles, crows, and ravens, occasionally visiting the nest.

At the moment, it is quiet, only the whistling sound of wind is heard through the speakers. The male osprey, called Vasuri (loose translation “lefty” or “left hand”), and the oldest two chicks, unofficially called Pomo (“the boss”) and Kakkonen (loose translation “the second” or “number two”), started the migration to Africa in August. The year has been a dramatic one for the osprey couple. The female osprey, called Tilda, disappeared from the nest in June. The couple had been nesting in Seili since 2011; before that, e.g. an osprey couple, called Tapani and Liisa, occupied the nest.

This spring, Tilda and Vasuri laid 3 eggs. The chicks were ringed in June. After the disappearance of Tilda, another dramatic event occurred in July, when the youngest sibling fell from the nest to its death as a result of food competition with the older siblings. This sort of behaviour, called siblicide, is rather common among birds and has been found to e.g. improve the survival of the remaining young (for more information on avian siblicide see e.g Mock et al. 1990).

Next spring, in March-April, when the ospreys return from their wintering grounds, nature’s drama continues and it remains to be seen whether Vasuri will return to the nest or will the nest be occupied by a totally new osprey couple..

References and more information:

Edit: corrected date.

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