Tuesday, 20 August
14:00 – 15:00
Aula Magna Left
Challenges for Baltic marine science
Ulrich Bathmann, IOW, ulrich.bathmann@io-warnemende.de
Based on marine science history in the Baltic Sea, we propose action to contribute to the UN Decade of Ocean Science for Sustainable Development 2021-2030. Several larger scientific missions are discussed that might help to create larger international programs.
Marine research in the Baltic has a long tradition. The International Synoptic Survey of the Baltic Sea (1964) started a series of many international scientific experiments. HELCOM emerged on the basis of two Helsinki Conventions. The Baltic Sea was the blueprint for European marine science interacting with politics.
The future marine science in the Baltic region might build upon this tradition, the IPCC report and the UN-Sustainable Development Goals (SDG´s). 3 important aspects for mankind are related to the oceans: their interaction with climate change (e.g. changes in sea level, pH, biodiversity), their value for providing resources (e.g. food, minerals, energy) and the threat of direct anthropogenic disturbance (e.g. pollution with plastic and anthropogenic chemicals, overfishing, land loss).
Baltic Marine Scientists are in a perfect starting position to lead future interdisciplinary programs. We propose some topics for the next decade: Carbon sink in the ocean–scientific basis for political action; ocean health; future of marine biodiversity-options for action; and protection and use of marine systems. Also, BANOS CSA may support international coordinated activities.
The synergies of human pressures driving coastal acidification
Jacob Carstensen, Aarhus University, jac@bios.au.dk
Carlos Duarte, King Abdullah University of Science and Technology
Coastal ecosystems show much more variable and intense rates of pH variability over time than the open ocean. This variability is largely due to inputs of freshwater, nutrients and organic matter from land, typically resulting from human activities in the watershed. The role of human activities in driving changes in pH implies that human intervention to prevent adverse effects is possible.
Increasing CO2 in the atmosphere has led to a gradual and predictable decrease in pH in the open ocean, but coastal acidification is more variable, exhibiting rates more than one order of magnitude higher than ocean acidification. Spatial and temporal decoupling of production and respiration in coastal ecosystems can lead to seasonal and long-term changes in pH exceeding 1 unit. Largest excursions in pH are observed in stratified and high-latitude systems, where the metabolic imbalance is most pronounced. Enhanced nutrient input from land, stimulating ecosystem productivity and thus raising pH levels, can counteract ocean acidification in shallow and well-mixed coastal systems, whereas eutrophication and ocean acidification are synergistic pressures in stratified systems where bottom waters may display low pH and high pCO2. Coastal oligotrophication resulting from nutrient management can amplify the effect of rising CO2 in the atmosphere on pH in the euphotic zone, but may also alleviate acidification in bottom waters of stratified systems. Ecosystem management needs to consider the balance between the negative consequences of eutrophication and acidification.
The stickleback wave: a spatially propagating regime shift in the Baltic Sea
Johan Eklöf, Stockholm University, johan.eklof@su.se
Göran Sundblad, Swedish University of Agricultural Sciences; Mårten Erlandsson, Swedish University of Agricultural Sciences; Serena Donadi, Swedish University of Agricultural Sciences; Joakim Hansen, Baltic Sea Center, Stockholm University; Britas Klemens Eriksson, GELIFES, Groningen University; Ulf Bergström, Swedish University of Agricultural Sciences
We used >13,000 fish surveys over four decades along the 1200 km western Baltic Sea coastline, to demonstrate a regime shift from dominance of large to small predatory fish, that propagates through space like falling dominos. The shift was accelerated by predator-prey reversal and emphasizes the need to account for spatial heterogeneity to predict and manage regime shifts in large ecosystems.
Gradual environmental changes can sometimes trigger major shifts in the structure and function of ecosystems. Studies of such ‘regime shifts’ typically focus on temporal dynamics using time-series, but ignore the role of spatial variability within ecosystem. Here, we use data from >13,000 fish surveys conducted over four decades (1979-2017) along the 1200 km western Baltic Sea coastline, to demonstrate a shift from dominance of large predatory fish (perch Perca fluviatilis and pike Esox lucius) to a small prey fish, three-spined stickleback (Gasterosteus aculeatus), that gradually propagates through space like falling dominos. The shift started in offshore areas and the outer archipelago in the early 2000s, but has then gradually propagated towards the mainland coast as a ‘stickleback wave’. Moreover, causal modeling based on data from an ecosystem field survey in 32 shallow bays in 2014 shows that stickleback predation on juveniles of the large predatory fish (predator-prey reversal) accelerates the regime shift. Consequently, we need to increasingly account for spatial heterogeneity and animal migration to predict and manage regime shifts in large ecosystems.
Coastal erosion of the Eastern Gulf of Finland and influence of natural factors
Olga Kovaleva, A.P. Karpinsky Russian Geological Research Institute, olya_pavlikova@mail.ru
Alexander Sergeev, A.P. Karpinsky Russian Geological Research Institute; Daria Ryabchuk, A.P. Karpinsky Russian Geological Research Institute
Analysis of coastal processes in the Eastern Gulf of Finland and coastal dynamics shows enhancing of the coastal recession rate under conditions of storm occurrence increasing and global sea level rise
Evolution of the coastal zone of the Eastern Gulf of Finland (EGoF) is ongoing under different conditions of global, regional and subregional scales (climate, tectonic, geological structure, hydrometeorological, anthropogenic activity, etc.). According to recent field investigations maximal migration rates of different coastal segments of the EGoF are varied from 3.3 m/year (Sergeev et al., 2018) to 5 m/year (Ryabchuk et al., 2011) in Kurortny district, up to 2 m/year in the Kotlin Island (Dvornikov et al., 2018) etc. The most extreme erosion events occur under combination of three parameters: long-lasting western and south-western winds, storm surge (up to 2 m) and absent of ice cover. Climate change will lead to the sea level rise in EGoF region up to 0.84 m till the end of the century according to the negative scenario (Gordeeva, Malinin, 2014). More than 25% of the EGoF coastal zone could be potentially suffer from flooding; almost 90% of the coasts will be exposed to erosion. The work is supported by the RSF project № 17-77-20041.
Wednesday, 21 August
9:45 – 10:45
Aula Magna Left
CO2 and inorganic nitrogen fluxes associated to diatoms and cyanobacteria in the Baltic Sea
Helle Ploug, University of Gothenburg, Helle.Ploug@marine.gu.se
Using stable isotopic tracers and advanced mass spectrometry (inc. SIMS), we describe C and N fluxes associated to chain forming diatoms and N2 fixing, filamentous Cyanobacteria at a single cell level as well as their contributions to total C and N fluxes in the plankton community during spring and summer in the Baltic Sea.
Using stable isotopic tracers and advanced mass spectrometry, we analysed CO2 fixation and transformations of dissolved inorganic nitrogen (DIN) from a single cell level to a community level within the euphotic zone in the Baltic Sea. CO2-assimilation in Skeletonema marinoi and Chaetoceros sp. comprised < 19% of total CO2 fixation and <46% of total nitrate assimilation in the plankton community during the spring bloom. Turbulence stimulated both CO2 fixation and formation of fast-sinking aggregates with concentrations of ammonium leaking to the ambient water. N2 fixing cyanobacteria contributed 21% to total CO2 fixation, and Aphanizomenon spp. contributed by 70-80% to total N2 fixation from June to August. Approximately 80% of primary production was fueled by ammonium regeneration. Large cyanobacteria release ca. 30% of their recently fixed N2 as ammonium which is rapidly assimilated into other organisms, including diatoms. The assimilation of C and N into diatoms can support surprisingly high growth rates during summer when DIN concentrations are low. Low biomass suggests that diatoms may be preferentially grazed by zooplankton and sink out as fecal pellets and/or aggregates.
Characterizing the urban chemical mixture: an inventory of micropollutants in wastewater released in the Baltic Sea catchment
Emma Undeman, Stockholm university, emma.undeman@su.se
Matti Leppänen, Finnish Environment Institute; Ksenia Pazdro, Institute of Oceanology of the Polish Academy of Sciences
The importance of municipal WWTPs as entry routes for hazardous substances is in many cases neither well studied nor acknowledged in current European wastewater policy. Here we present an assessment of what kind of chemicals that have been analyzed in the ca 25 000 wastewater samples included in this study, their typical levels and detection frequencies.
Hazardous substances are recognized as a threat to the Baltic Sea in the EU’s water legislation. However, the importance of municipal WWTPs as entry routes for these substances is in many cases neither well studied nor acknowledged in current wastewater policy. There is a lack of knowledge regarding which chemicals are present in wastewater and their observed negative effects. The lack of knowledge leads to a lack of policy action as currently available data do not suffice to establish requirements for acceptable loads or removal efficiencies of micropollutants entering MWWTPs. In this study, we aim to map micropollutants measured in wastewater emitted in the Baltic Sea catchment. Data were compiled from national monitoring databases, project reports and scientific literature. We found data for ca 830 unique substances measured in ca 25 000 samples of effluents emitted in the Baltic Sea catchment. In ca half of the ca samples, the concentration of the analyzed substance was above the analytical limit of the method. The type of compounds with highest detection frequency were organophosphates, sweeteners, fluorescent whitening agents and components in household products.
High-frequency automated observing systems to meet the monitoring and assessment needs in the Baltic Baltic Sea
Urmas Lips, Tallinn University of Technology, urmas.lips@taltech.ee
Inga Lips, Tallinn University of Technology; Stella-Theresa Stoicescu, Tallinn University of Technology; Jenni Attila, Finnish Environment Institute; Gregor Rehder, Leibniz Institute of Baltic Sea Research Warnemünde
We present a BONUS SEAM project review of the present status and future outlook of the application of automated observations in the Baltic Sea. We assess the potential of combining traditional monitoring with ships-of-opportunity (SOOP) and other autonomous approaches (profilers, gliders) to improve the confidence of status assessments.
High-frequency observations applying autonomous platforms and novel sensors have become an essential component of ocean observing systems to meet the needs of marine research, operational oceanography, and environmental monitoring and assessment. We present a BONUS SEAM project review of the present status and future outlook of the application of automated observations in the Baltic Sea. We assess the potential of combining traditional monitoring with ships-of-opportunity (SOOP) and other autonomous approaches (profilers, gliders) to improve the confidence of status assessments based on chlorophyll a, oxygen debt and consumption, cyanobacterial bloom, and acidification indicators. Examples of application of earth observation data in combination with traditional and SOOP monitoring data for environmental assessments will be shown. We analyze the methodological and technological challenges of the routine use of automated platforms for monitoring and assessment needs, also regarding the quality assurance and data handling. The gaps in the present observational networks and ways to jointly improve the high-frequency automated observation system of the Baltic Sea are presented.
Plant traits and ecosystem processes in the northern Baltic Sea
Charlotte Angove, University of Helsinki, charlotte.angove@helsinki.fi
Alf Norkko, University of Helsinki and Stockholm University; Camilla Gustafsson, University of Helsinki
We compared the importance of different plant traits for ecosystem processes such as primary production and nutrient uptake. By doing so, we could infer what is likely to be limiting plant growth. For example, whether capturing light (height, leaf area) was more important for primary production than sourcing nutrients (root length, root properties).
Aquatic plant meadows are valuable as part of the coastal filter and for nurturing food webs which support commercially important fish species. Therefore, it is important to understand how plants maintain their productivity. In the northern Baltic Sea, the brackish water conditions allow plants with a variety of different traits to co-colonise the same meadow. We compared the importance of different plant traits for ecosystem processes such as primary production and nutrient uptake. By doing so, we could infer what is likely to be limiting plant growth. For example, whether capturing light (height, leaf area) was more important for primary production than sourcing nutrients (root length, root properties). In this presentation I will be summarising the findings of three field experiments to communicate their overall message about how plants maintain their productivity in the northern Baltic Sea. Our results suggest that the demands of the plants are the main drivers of nitrogen concentrations in their surrounding sediments, and that the plant demand drives short term nitrogen uptake rates by plants. However, such demands are likely to be driven by plant community responses to light.
Thursday, 22 August
9:45 – 10:45
Aula Magna Left
Developments in the policy and management landscape supporting the recovery of the Baltic Sea
Maria Laamanen, Ministry of the Environment, Åbo Akademi University, maria.laamanen@ym.fi
The talk will cover current developments in the policy and management landscape at global, EU and Baltic Sea regional levels contributing to the recovery of the Baltic Sea, and the role of science in supporting these developments and especially the formulation of the HELCOM Baltic Sea Action Plan.
Pollution loads into the Baltic Sea have decreased significantly and recovery of the ecosystem from eutrophication has started. However, other, newer pressures, such as global change, pharmaceuticals and microplastics act on the ecosystem and risk to counteract the positive development. How can policy and management be adapted to ensure that a healthy Baltic Sea can be achieved? The talk will cover the evolving policy and governance landscape at the UN and EU levels, as well as the Baltic Sea regional work for a healthier Baltic Sea. The work on updating of the HELCOM Baltic Sea Action Plan in 2018-2021 based on relevant science will be covered. HELCOM has agreed to focus the updating of the BSAP inter alia on protection of biodiversity and reduction of eutrophication, marine litter and microplastics, underwater noise as well as pressures on benthic habitats. In that work, the Finnish HELCOM chairmanship 2018-2020 prioritizes the need to further reduce nutrient loads, to shift to nutrient cycling and better understand interaction between global change and the Baltic Sea. The work in the Baltic Sea region is to be fully aligned with Agenda2030 for sustainable development.
Vibrio abundances in early bacterial assemblages on microplastics along a 2000 km Baltic Sea coastline
Katharina Kesy, Leibniz-Institute for Baltic Sea Research, katharina.kesy@io-warnemuende.de
Sonja Oberbeckmann, Leibniz-Institute for Baltic Sea Research; Bernd Kreikemeyer, Institute of Medical Microbiology, Virology and Hygiene, University Medical Center Rostock; Matthias Labrenz, Leibniz-Institute for Baltic Sea Research
Factors influencing the microplastic-associated bacterial assemblages were investigated to understand the impact of this novel habitat on the Baltic Sea ecosystem, including the potential of microplastics to act as dispersal vector for potentially pathogenic Vibrio. Incubation experiments with polystyrene, polyethylene, and wood were conducted, covering a distance of 2000 km Baltic Sea coastline.
Microplastics (MP) in aquatic environments are novel habitats for surface colonizing microorganisms, among them potentially pathogenic Vibrio. Due to their persistence and their great dispersal potential, MP could act as a vector for these. We tested whether the substrate or the spatial factor is more influential on the developing bacterial assemblages and Vibrio. Incubation experiments using polystyrene (PS), polyethylene (PE), and wood were conducted during a Baltic Sea summer cruise, covering a salinity gradient of 4.5– 9 PSU. Bacterial assemblages were analysed using 16S rRNA-gene amplicon sequencing and distance based Redundancy Analysis. The sample type was the most important factor in structuring bacterial assemblages overall, but environmental factors, mainly salinity became the dominating factor in differentiating attached biofilms on the PE, the PS and the wood. Vibrio was more abundant on the PE and the PS than on the seston, but highest on the wood and positively correlated with salinity. This study demonstrates that temporal- as well as spatial dynamics should be considered when assessing the potential of MP as vectors for bacterial assemblages and putative pathogens.
Centurial life-history changes in the eastern Baltic cod (Gadus morhua) stock in relation to hydrography, benthos and stock size
Henrik Svedäng, Stockholm University, henrik.svedang@su.se
Oleg Savchuk, Stockholm University; Ale Pålsson, Stockholm University; Viktor Thunell, SLU; Alf Norkko, University of Helsinki; Anna Villnäs, University of Helsinki; Bo Gustafsson, Stockholm University; Christoph Humborg, Stockholm University
Presently, the productivity of eastern Baltic cod is severely reduced. Spawning locations have ceased functioning, and individual cod growth, condition, and health status have deteriorated. Here we describe the spatiotemporal development of reproductive volumes in spawning areas in relation to hypoxia and benthic feeding opportunities together with cod life-history variation.
Today, the productivity of the eastern Baltic cod is severely reduced. In spite of progressively smaller fishing quotas over the last decade, fishers have difficulties in finding cod enough to fill up their shares. Since the late 1980s, two out of three spawning locations have ceased functioning, which implies less larval dispersal and hence a smaller distribution area. More recently individual cod growth, body condition, and health status have deteriorated. We explore unique data describing the spatiotemporal development of reproductive volumes in spawning areas in relation to hypoxia and benthic feeding opportunities together with cod life-history variation. Variations in reproductive opportunities in different basins over time, as well as dynamics of hypoxic/anoxic areas are reconstructed from hydrographic data since 1906. Trends in benthos composition and biomasses were extracted from surveys in the Baltic Sea. Finally, century-long time series on cod population, growth and maturation indices were obtained from historical Swedish trawl surveys. These results give an opportunity to describe the development of the eastern Baltic cod stock in relation to key environmental factors.
Unusual observations of productivity patterns during the spring bloom 2018 in the Central Baltic Sea suggest vertical nutrient shuttling and the potential for climate-induced changes
Gregor Rehder, Leibniz Institute for Baltic Sea Research (IOW), gregor.rehder@io-warnemuende.de
Jens D. Müller, Leibniz Institute for Baltic Sea Research (IOW); Henry Bittig, Leibniz Institute for Baltic Sea Research (IOW); Seppo Kaitala, Finnish Environment Institute (SYKE); Bernd Schneider, Leibniz Institute for Baltic Sea Research (IOW); Simo-Matti Siiriä, Finnish Meteorological Institute (FMI); Laura Tuomi, Finnish Meteorological Institute (FMI); Norbert Wasmund, Leibniz Institute for Baltic Sea Research (IOW)
The unusual meteorological setting of spring 2018 lead to hitherto unobserved processes during the spring bloom in the central Baltic Sea. We report the highest phytoplankton abundance and carbon uptake in the upper layer ever observed. Vertical shuttling of nitrate by phytoplankton appears the best explanation, which demonstrate the potential of climate-driven ecosystem changes in the Baltic Sea.
The unusual meteorological conditions in spring 2018 had dramatic consequences on the development of the spring bloom in the central Baltic Sea. Based on recent and long-term data from the ICOS voluntary observing ship Finnmaid, Finnish BGC-Argo floats, HELCOM monitoring, and remote sensing, we deduce the following sequence of events and mechanisms: (1) rapid surface warming led to the development of a shallow thermocline, complete depletion of inorganic nutrients in the upper 15 m, but still considerable loads of nitrate and phosphate below the mixed layer, by mid-April; (2) until mid-May, nitrate got completely depleted down to 60m depth, despite the persistent strong and stable thermocline; (3) carbon system observations and vertical Chl a data show that the productivity was focused in the mixed layer, where pCO2 dropped down to 40 µatm, indicating unpreceded high carbon fixation in the upper layer; (4) dominance of the dinoflagellate Peridiniella catenata supports that the bloom was sustained by vertical shuttling of nitrate towards the mixed layer. The findings demonstrate the potential of climate-driven changes in the major biogeochemical functioning of the Baltic Sea.
Friday, 23 August
9:45 – 10:45
Aula Magna Left
The Baltic Sea – fixing eutrophication and hypoxia
Daniel Conley, Lund University, daniel.conley@geol.lu.se
Alf Norkko, University of Helsinki; Jacob Carstensen, Aarhus University; Bo Gustafsson, Stockholm University; Michelle McCrakin, Stockholm University; Caroline Slomp, Utrecht University
Eutrophication and the lack of bottom water oxygen are well documented in the Baltic Sea caused by the over-enrichment from nutrients. Although significant progress has been made, the time scales of nutrient reductions and improvement is slow. We will discuss the efforts that have taken place in the last decade to speed up recovery and address the challenges of reducing hypoxia and eutrophication.
Eutrophication and the lack of oxygen in bottom waters are well documented in the Baltic Sea and are caused from the over-enrichment from nutrients. Although significant progress has been made, the time scales of nutrient reductions and improvement of eutrophication is slow. In addition, the time scales of progress and anticipated change by society within current management regimes is taking too long. A number of efforts have taken place with the goal of speeding up the recovery by mitigating hypoxia and reducing nutrients in the water column. Many of the geoengineering efforts are aimed at reducing the impact of the legacy of nutrient inputs in sediments. The methods range from enhancing vertical mixing to phosphorus sequestration. In addition, biological methods including aquaculture and changing food web structures have been implemented. Here we evaluate different restoration methods used in the last decade in an attempt to reverse the trends and speed up recovery. In addition, we will address potential problems including lag effects, legislation and the precautionary principle. Finally, we will address the challenges of reducing hypoxia and eutrophication in the Baltic Sea.
Invertebrate-bacteria associations as hotspots for benthic nitrogen cycling processes in estuarine ecosystems
Mindaugas Zilius, Klaipeda University/University of Ferrara, mindaugas.zilius@jmtac.ku.lt
Ulisse Cardini, Stazione Zoologica Anton Dohrn/Klaipeda University; Stefano Bonaglia, Stockholm University/Klaipeda University; Aurelija Samuiloviene, Klaipeda University; Anastasija Zaiko, Klaipeda University/Cawthron Institute/University of Auckland; Jolita Petkuviene, Klaipeda University; Irma Vybernaite-Lubiene, Klaipeda University; Tobia Politi, Klaipeda University; Ugo Marzocchi, Klaipeda University/Stazione Zoologica Anton Dohrn; Marco Bartoli, Klaipeda University/Parma University
Interactions between benthic invertebrates and bacteria are important in regulating nitrogen cycling in estuarine sediments. We are studying targeted microbial N transformations and identifying genetic potential in benthic invertebrate hosts within INBALANCE project. Measured rates and quantified functional genes reveal that invertebrate hosts are hidden hotspots of nitrogen cycling in estuaries.
Ecological interactions between benthic invertebrates and bacteria are important in regulating nitrogen (N) cycling in estuarine sediments. However, the magnitude of N-cycling attributed to invertebrate-bacteria associations remains poorly characterized in many estuaries. An investigation of N-cycling in invertebrate-bacteria systems may reveal hidden paths of energy and matter transfer. In this study, we present the results of the first approach quantifying targeted microbial N transformations and characterize the microbiome of benthic invertebrate hosts in estuarine systems spanning from boreal to temperate regions. Combining multiple N isotopes tracers with more recent methods such as functional genomics we can disentangle benthic N-cycling attributed to the invertebrate-bacteria associations, and elucidate how these vary along multiple gradients. Obtained results show that activity of gene markers, representing different N-cycling processes, is higher in invertebrate hosts relatively to ambient sediments or burrows. In addition, 16S rRNA analysis shows that studied invertebrates host distinctive microbiome suggesting intimate cooperation rather than causal relationship.
Allochthonous Organic Matter Supports Benthic but Not Pelagic Food Webs in Shallow Coastal Ecosystems
Pia Bartels
Jenny Ask, Umeå University; Agneta Andersson, Umeå University; Jan Karlsson, Umeå University; Reiner Giesler, Umeå University
We estimated allochthony in the biomass of benthic and pelagic consumers in a shallow coastal ecosystem in the northern Baltic Sea. We used deuterium as a tracer of allochthony and found variability in both space and time. There was also variation in allochthony between consumer groups, with higher values for zoobenthos (26.2 ± 20.9%) than for zooplankton (0.8 ± 0.3%).
Rivers transport large amounts of allochthonous organic matter (OM) to the ocean every year, but there are still large gaps in how allochthonous OM is processed in the marine environment. We estimated the relative contribution of allochthonous OM (allochthony) to the biomass of benthic and pelagic consumers in a shallow coastal ecosystem in the northern Baltic Sea. We used deuterium as a tracer of allochthony and assessed both temporal (monthly from May to August) and spatial variation (within and outside river plume). We found variability in allochthony in space and time and across species, with overall higher values for zoobenthos (26.2 ± 20.9%) than for zooplankton (0.8 ± 0.3%). Allochthony of zoobenthos was generally higher close to the river mouth than outside of the river plume, whereas it did not vary spatially for zooplankton. Also, zoobenthos allochthony was higher in deeper than in shallower areas, indicating that allochthonous OM might be more important when autochthonous resources are limited. Our results suggest that climate change predictions of increasing inputs of allochthonous OM to coastal ecosystems may affect basal energy sources supporting coastal food webs.
Evaluation of the efficiency of DNA metabarcoding to complement microscopic analysis of phytoplankton: case study in the coastal Bothnian Sea
Agneta Andersson, Umeå University, agneta.andersson@umu.se
Daniela Figueroa, Umeå University; Sonia Brugel, Umeå University; Eric Capo, Umeå University; Li Zhao, Umeå University; Siv Huseby, Umeå University
Phytoplankton is used as a quality factor for assessment of ecological state in marine systems. In this project we evaluate the accuracy of DNA metabarcoding to produce comparable result with microscopic analysis of phytoplankton classes. We found that estimates of carbon biomass derived from microscopy showed the most similar results to DNA metabarcoding of different phytoplankton classes.
Phytoplankton is used as a quality factor for assessment of ecological state in marine systems. In monitoring programs the phytoplankton species composition, abundance, biovolume and carbon biomass are analyzed using microscopy. In this project we evaluate the accuracy of DNA metabarcoding to produce comparable result with microscopic analysis when analyzed at the phytoplankton class level. Water samples were collected in a coastal area in the northern Bothnian Sea in October 2016. The samples were analyzed using microscopy and high-throughput sequencing of the 16S and 18S rRNA genes from 25-1000 mL filtered seawater. Estimates of carbon biomass and DNA sequencing from 500 mL filtered seawater showed the most similar results of different phytoplankton classes. The abundance and biovolume estimates showed larger differences to DNA sequencing. Further, we found that the traditional phytoplankton taxonomy and the DNA data-bases do not use the same nomenclature, which obstruct comparison of the two methods. Our study show that DNA methods have to be further developed and databases harmonized before DNA analysis can be implemented in marine phytoplankton monitoring.
