“Moin” everyone from the base of GAME, the GEOMAR Helmholtz Centre for Ocean Research Kiel! We are Alisa Berning and Christin Baensch and together we form Team Kiel. As you might expect, GAME in 2020 is totally different from previous projects. The worldwide COVID-19 pandemic forced us to stay in Germany and conduct our experiment at GEOMAR. Initially, Alisa was supposed to work at the Universidad Católica del Norte in Coquimbo, Chile, while Christin should have worked at the Institute for Marine and Antarctic Studies in Hobart, Tasmania. Despite the difficult circumstances, we felt lucky to have formed a new team and to start our experiments, which were only slightly delayed, in June. Alisa was already living in Kiel, because she is studying Biological Oceanography at the University of Kiel, whereas Christin moved here from Oldenburg in Lower Saxony where she is studying Marine Environmental Sciences. We complement each other very well and working together has always been a lot of fun (as you can see in the first picture). Apart from that, it is of course a great pity that our actual team partners in Hobart and Coquimbo have to work alone, but we are still in contact with them and exchange our experiences within the project frequently.
The GAME project in 2020 is dealing with ocean plastic pollution again. But different from previous GAME projects that focused on the biological effects of microplastics, we are working on a plastic fraction that we can see with the naked eye. It is the type of plastic waste that gives us horrible pictures of animals dying due to the ingestion of plastic debris or entanglement. Now we are investigating the impact of macroplastic on Mytilus edulis/Mytilus trossulus communities and organismsthat are associated with them. The two very similar species Mytilus edulis and Mytilus trossulus are both common benthic filter feeders in the Kiel Fjord and they can only be distinguished reliably by molecular biological genetic identification.
After having conducted a short pilot study that focused on establishing the methods for measuring mussel aggregate performance, such as filtration capacity and oxygen consumption, and having prepared everything for the main experiment, we could not wait to start collecting all the mussels for our experiment – 2100 in total. Our sampling site is located directly in front of GEOMAR, where a lot of mussels grow on the jetties in the Kiel Fjord. We collected mussels in the size range of 4.5 cm to 5.5 cm. All fauna and flora that already lived attached to the mussels needed to be removed as we wanted to assess the abundance and variety of species that will establish on our mussels during the seven weeklong exposure phase in the fjord. Luckily, we had a lot of friends, who were armed with kitchen sponges and who helped us with the cleaning. Also, all the seagulls of the Baltic Sea accompanied us during the collection hoping to get a good lunch from picking the mussels that were out of the targeted size range.
Directly after having collected the mussels, we arranged batches of 30 mussels on quadratic carrier plates by placing the animals around pieces of different types of macroplastic debris. Furthermore, we fixed a plastic mesh material along the edges to keep the mussels on the plate during bad weather conditions. Then, we let them form aggregates that represent mini-versions of mussel beds. For this, we transferred the animals to an indoor flow-through system that is located in one of the climate chambers of GEOMAR. As you can see in the picture below, we were eager to determine the effect of straws, plastic bottles, plastic bags and fishing line on the mussel aggregates. In addition to the plastic type, we were also interested in the potential effect of different amounts of plastic on the mussel bed communities. For this, we established treatment levels with aggregates that contained low and high amounts of plastic. Finally, we had control groups consisting of aggregates without plastic. During the aggregation phase that lasted for one week, we took good care of our new pets. As it turned out, mussels need a lot of attention like daily cleaning and feeding for their well-being. For our next pet, we would rather go for a more independent animal.
During the one week in the climate chamber, the mussels aggregated really nicely and we felt like they were ready to be released into their home, the Kiel Fjord, again. So, we attached a perforated brick as a weight and ropes to each carrier plate to keep it in a horizontal position even during the storms to come and deployed the constructions from the jetty in front of GEOMAR. Even after deployment, we still needed to look after our mussels, but from the daily care that was need during the aggregation phase in the lab, the workload decreased to cleaning the mesh material around the carrier plate from filamentous algae once every two weeks. Of course, we did not want to disturb our little divas, so we went snorkelling instead of pulling the aggregates out of the water while standing on the jetty.
Seven weeks later things got serious for us and our mussel aggregates. It was time to get them out of the water and start with the measurements that were supposed to reveal the possible influence the plastic debris potentially had on the aggregates during the deployment in the fjord. To prevent the mobile fauna, such as Palaemon species, Gammarus species and Idotea balthica, that lives inside the aggregates from escaping, we went snorkelling in the freezing cold water (it was the end of October) and tied a net around the aggregates before pulling them out of the water. They certainly would have preferred to stay in the fjord, but it was time for our mussels to return to the climate chamber and go through a marathon of measurements.
In the comfortable climate chamber, which is humid and has a temperature of 16°C, we collected the mobile fauna and the total particulate matter (TPM) from the interstices between the mussels. Then, we measured the filtration and respiration rates of the entire aggregates and assessed their complexity as well as stability. This was done during two very work-intensive weeks and at some point we felt like living in the climate chamber. In those weeks, we had to overcome major and minor difficulties, like fixing disconnected tubes in our flow-through system and mopping up the resulting floods in the climate chamber. But we got used to wiping the floor and sometimes even the ceiling and as clubs are closed right now, we used the breaks between the measurements to turn the climate chamber into a secret concert hall that you couldn’t even find in the Lonely Planet.
We are very happy that we managed this huge workload! But now our 2100 mussels are waiting for us in the freezer. In the last work step, we want to identify all the epiflora and -fauna that established on the mussels during the seven weeks in the fjord as well as the mobile fauna. Furthermore, we want to standardize all the respiration, filtration and aggregate complexity measurements we took to the dry weight of our aggregates. For this, we are currently drying and weighing the soft tissue of each mussel. This is, of course, to the joy of the people working in the same building as they can experience the breath-taking smell from the drying oven in almost the whole floor. Alisa’s idea to use gloves when scraping the softbody out of the shells was golden, because without them our hands would smell like rotten mussels for several years (approximately 😉 ).
Congratulations if you made it so far and thank you for your interest in our story of the last months. As previously mentioned, GAME is very different this year and we will probably not come together again with the other teams for a common analysis of the data that we collected. But we already learned a lot so far and we are glad we had the chance to take part in this project. Right now, we are looking forward to starting with our statistical analyses and to apply the theoretical knowledge we gained during the preparation course in March. But we are also very sad that the project is almost finished and we are sure that we will even miss the smell of the mussels one day.
Many love greetings from the beautiful city at the Baltic Sea,
Alisa & Christin