Bacterial diversity and function in the Baltic Sea with an emphasis on cyanobacteria

In this article we summarize the current knowledge of Baltic Sea cyanobacteria, focusing on diversity, toxicity, and nitrogen fixation in the filamentous heterocystous taxa. We also review the recent results of our microbial diversity studies in planktonic and benthic habitats in the Baltic Sea. Based on molecular analyses, we have improved the understanding of cyanobacterial population structure by assessing genetic diversity within species that are morphologically inseparable. Moreover, we have studied microbial functions such as toxin production and nitrogen fixation in situ under different environmental conditions. Phosphorus limitation of bloom-forming, nitrogen-fixing cyanobacteria was clearly verified, emphasizing the importance of continuous efforts to reduce this element in the Baltic Sea. We have designed a rapid and reliable detection method for the toxic cyanobacterium Nodularia spumigena, which can be used to study bloom formation of this important toxin producer.     

Zoobenthos as indicators of ecological status in coastal brackish waters: a comparative study from the Baltic Sea

A new method for classifying soft-bottom zoobenthic assemblages along the Finnish coasts (northern Baltic Sea) is presented and tested against traditional physicochemical monitoring data in the complex Archipelago Sea. Although multivariate methods for assessing the state of the marine environment have become widely used, few numerical indices can operate over a wide salinity range. We compare indices currently in use and propose a new index, BBI (brackish water benthic index), for the low-saline and species-poor Baltic coastal waters. BBI offers a salinity-corrected tool for classification of the soft-bottom zoobenthos under the demands of the European Union Water Framework Directive.     

Climate change effects on the Baltic Sea borderland between land and sea

Coastal habitats are situated on the border between land and sea, and ecosystem structure and functioning is influenced by both marine and terrestrial processes. Despite this, most scientific studies and monitoring are conducted either with a terrestrial or an aquatic focus. To address issues concerning climate change impacts in coastal areas, a cross-ecosystem approach is necessary. Since habitats along the Baltic coastlines vary in hydrology, natural geography, and ecology, climate change projections for Baltic shore ecosystems are bound to be highly speculative. Societal responses to climate change in the Baltic coastal ecosystems should have an ecosystem approach and match the biophysical realities of the Baltic Sea area. Knowledge about ecosystem processes and their responses to a changing climate should be integrated within the decision process, both locally and nationally, in order to increase the awareness of, and to prepare for climate change impacts in coastal areas of the Baltic Sea.     

Echoes from the Past: A Healthy Baltic Sea Requires More Effort

Integrated sediment multiproxy studies and modeling were used to reconstruct past changes in the Baltic Sea ecosystem. Results of natural changes over the past 6000 years in the Baltic Sea ecosystem suggest that forecasted climate warming might enhance environmental problems of the Baltic Sea. Integrated modeling and sediment proxy studies reveal increased sea surface temperatures and expanded seafloor anoxia (in deep basins) during earlier natural warm climate phases, such as the Medieval Climate Anomaly. Under future IPCC scenarios of global warming, there is likely no improvement of bottom water conditions in the Baltic Sea. Thus, the measures already designed to produce a healthier Baltic Sea are insufficient in the long term. The interactions between climate change and anthropogenic impacts on the Baltic Sea should be considered in management, implementation of policy strategies in the Baltic Sea environmental issues, and adaptation to future climate change.     

Framework for the environmental impact assessment of operational shipping

Shipping is an important source of pollution affecting both atmospheric and aquatic environments. To allow for efficient mitigation of environmental degradation, it is essential to know the extent of the impacts of shipping in relation to other sources of pollution. Here, we give a perspective on a holistic approach to studies of the environmental impacts of operational shipping through presentation of an assessment framework developed and applied on a case of shipping in the Baltic Sea. Through transfer of knowledge and concepts, previously used in assessments of air pollution, now applied to assessments of marine pollution and underwater noise, the horizon of understanding of shipping-related impacts is significantly improved. It identifies the main areas of environmental degradation caused by shipping and potential improvements through legislation and technological development. However, as the vast majority of contaminants discharged into the sea are not routinely monitored and assessed, the links between pressure of contaminants from shipping and environmental state and impacts will not be caught in the current environmental regulatory frameworks.     

Nitrogen fixation by cyanobacteria stimulates production in Baltic food webs

Filamentous, nitrogen-fixing cyanobacteria form extensive summer blooms in the Baltic Sea. Their ability to fix dissolved N₂ allows cyanobacteria to circumvent the general summer nitrogen limitation, while also generating a supply of novel bioavailable nitrogen for the food web. However, the fate of the nitrogen fixed by cyanobacteria remains unresolved, as does its importance for secondary production in the Baltic Sea. Here, we synthesize recent experimental and field studies providing strong empirical evidence that cyanobacterial nitrogen is efficiently assimilated and transferred in Baltic food webs via two major pathways: directly by grazing on fresh or decaying cyanobacteria and indirectly through the uptake by other phytoplankton and microbes of bioavailable nitrogen exuded from cyanobacterial cells. This information is an essential step toward guiding nutrient management to minimize noxious blooms without overly reducing secondary production, and ultimately most probably fish production in the Baltic Sea.     

Baltic Sea management: Successes and failures

Severe environmental problems documented in the Baltic Sea in the 1960s led to the 1974 creation of the Helsinki Convention for the Protection of the Marine Environment of the Baltic Sea Area. We introduce this special issue by briefly summarizing successes and failures of Baltic environmental management in the following 40 years. The loads of many polluting substances have been greatly reduced, but legacy pollution slows recovery. Top predator populations have recovered, and human exposure to potential toxins has been reduced. The cod stock has partially recovered. Nutrient loads are decreasing, but deep-water anoxia and cyanobacterial blooms remain extensive, and climate change threatens the advances made. Ecosystem-based management is the agreed principle, but in practice the various environmental problems are still handled separately, since we still lack both basic ecological knowledge and appropriate governance structures for managing them together, in a true ecosystem approach.     

How will Ocean Acidification Affect Baltic Sea Ecosystems? An Assessment of Plausible Impacts on Key Functional Groups

Increasing partial pressure of atmospheric CO₂ is causing ocean pH to fall—a process known as ‘ocean acidification’. Scenario modeling suggests that ocean acidification in the Baltic Sea may cause a ≤3 times increase in acidity (reduction of 0.2–0.4 pH units) by the year 2100. The responses of most Baltic Sea organisms to ocean acidification are poorly understood. Available data suggest that most species and ecologically important groups in the Baltic Sea food web (phytoplankton, zooplankton, macrozoobenthos, cod and sprat) will be robust to the expected changes in pH. These conclusions come from (mostly) single-species and single-factor studies. Determining the emergent effects of ocean acidification on the ecosystem from such studies is problematic, yet very few studies have used multiple stressors and/or multiple trophic levels. There is an urgent need for more data from Baltic Sea populations, particularly from environmentally diverse regions and from controlled mesocosm experiments. In the absence of such information it is difficult to envision the likely effects of future ocean acidification on Baltic Sea species and ecosystems.     

PAH Metabolites in Bile Fluids of Dab (Limanda limanda) and Flounder (Platichthys flesus): Spatial Distribution and Seasonal Changes (7 pp)

Background, Aim and Scope Polycyclic aromatic hydrocarbons (PAH) are important environmental contaminants which may lead to increased levels of neoplastic aberrations or tumours in fish liver. Therefore, monitoring of PAH and their effects are part of several international environmental programmes. The aim of the present field study was to investigate the concentrations of the PAH metabolites in fish bile, to elucidate spatial, seasonal and species differences as well as to discuss different strategies of normalisation with regard to environmental monitoring. Materials and Methods: PAH metabolites were determined in the bile fluid of dab (Limanda limanda) and flounder (Platichthys flesus) caught in the North Sea and Baltic Sea between 1997 and 2004. After enzymatic deconjugation, two metabolites were determined by means of HPLC. The limit of detection and the limit of quantification were calculated. The accuracy of the method was tested with a standard reference material. Results were referred to bile volume as well as to biliverdin. Results: The main metabolite, 1-hydroxypyrene, was determined in concentrations from <0.7 to 838 ng/ml in bile of dab (Limanda limanda) and flounder (Platichthys flesus) caught between 1997 and 2004. The values for 1-hydroxyphenanthrene in fish bile were considerably lower (<0.4 – 87 ng/ml). Significant differences in the 1-hydroxypyrene levels were found between summer and winter surveys as well as between the sampling sites in the data set from 2004 (383 dabs and 62 flounders): Highest levels of PAH contamination were found in dab from the German Bight and in flounder from the Baltic Sea. Discussion: Spatial differences in 1-hydroxypyrene concentrations between North Sea and Baltic Sea were discussed, as well as differences in relation to season, sex and species. Three parameters of normalisation (biliary protein, biliverdin and bile pigments) were discussed. Biliverdin was identified as a suitable parameter for the normalisation of PAH metabolites in field samples. Conclusions: Spatial differences in 1-hydroxypyrene concentrations of dab demonstrate the usefulness of PAH metabolites in fish bile as a monitoring parameter in marine regions. Significant differences in 1-hydroxypyrene concentrations were found between summer and winter sampling campaigns. This may be linked to an annual cycle of 1-hydroxyprene in dab. It is also possible that bile synthesis/release in dab differs between the seasons. There is no indication for a time trend from 1997 to 2004. Recommendations and Perspectives: It is recommended to relate PAH metabolites in fish bile to biliverdin concentrations. Although the concentrations are low in offshore regions and bile volumes are small, the method presented here allows one to measure PAH metabolites on an individual level which is a crucial prerequisite for meaningful monitoring studies.     

Screening of hydrophobic DNA adducts in flounder (Platichthys flesus) from the Baltic Sea

Neoplasia and other histopathological lesions in flounder (Platichthys flesus) liver have been investigated in several European sea areas, including the Baltic Sea. Several studies have been able to link neoplasm epizootics in fish with the exposure to genotoxins such as polycyclic aromatic hydrocarbons (PAHs). The level of hydrophobic DNA adducts in tissue DNA reflects the exposure of the organism to PAHs.Using hydrophobic DNA adduct levels as biomarkers, possible PAH exposure was assessed in flounder from 10 different sites in the Baltic Sea, collected during the years 1995–1997. The results show that the overall levels of hepatic DNA adducts were low and, in general, the chromatograms appeared clean. The highest levels of DNA adducts were found at two sites in the southern Baltic Sea. There were no statistically significant differences in adduct levels between the sites. Our results indicate that flounder from studied off shore sites of the Baltic Sea had not been exposed to a greater extent to large polycyclic hydrophobic hydrocarbons in their environment.     

Atmospheric Nutrient Input to the Baltic Sea from 1850 to 2006: A Reconstruction from Modeling Results and Historical Data

In this study, a consistent basin-wise monthly time series of the atmospheric nutrient load to the Baltic Sea during 1850-2006 was compiled. Due to the lack of a long time series (1850-1960) of nutrient deposition to the Baltic Sea, the data set was compiled by combining a time series of deposition data at the Baltic Nest Institute from 1970 to 2006, published historical monitoring data and deposition estimates, as well as recent modeled Representative Concentration Pathways (RCP) emission estimates. The procedure for nitrogen compounds included estimation of the deposition in a few intermediate reference years, linear interpolation between them, and the decomposition of annual deposition into a seasonal deposition pattern. As no reliable monitoring results were found for the atmospheric deposition of phosphorus during the early period of our study, we used published estimates for the temporal and spatial pattern of the phosphorus load.     

Development of Tools for Integrated Monitoring and Assessment of Hazardous Substances and Their Biological Effects in the Baltic Sea

The need to develop biological effects monitoring to facilitate a reliable assessment of hazardous substances has been emphasized in the Baltic Sea Action Plan of the Helsinki Commission. An integrated chemical–biological approach is vitally important for the understanding and proper assessment of anthropogenic pressures and their effects on the Baltic Sea. Such an approach is also necessary for prudent management aiming at safeguarding the sustainable use of ecosystem goods and Services. The BEAST project (Biological Effects of Anthropogenic Chemical Stress: Tools for the Assessment of Ecosystem Health) set out to address this topic within the BONUS Programme. BEAST generated a large amount of quality-assured data on several biological effects parameters (biomarkers) in various marine species in different sub-regions of the Baltic Sea. New indicators (biological response measurement methods) and management tools (integrated indices) with regard to the integrated monitoring approach were suggested.     

The Challenge of Bridging Science and Policy in the Baltic Sea Eutrophication Governance in Finland: The perspective of Science

This article examines the views of scientists on intricacies of scientific knowledge that affect science–policy interface in the Baltic Sea eutrophication governance in Finland. The analysis demonstrates that these intricacies can be divided into five categories: (1) uncertainty of knowledge concerning ecological processes, (2) heterogeneity of knowledge, (3) societal and political call for (certain) knowledge, (4) contingency of the knowledge that ends up taken as a baseline for decision making and further research, and (5) linkages of knowledge production, processing, and communication to particular characteristics of individual researchers and research societies. By explicating these aspects, this article illustrates the ways in which scientific knowledge concerning eutrophication is human-bound and susceptible to interpretation, thus adding on to the uncertainty of the Baltic Sea environmental governance. The aim is, then, to open up perspectives on how ambiguities related to science–policy interface could be coped with.     

Interannual variability of phyto-bacterioplankton biomass and production in coastal and offshore waters of the Baltic Sea

The microbial part of the pelagic food web is seldom characterized in models despite its major contribution to biogeochemical cycles. In the Baltic Sea, spatial and temporal high frequency sampling over three years revealed changes in heterotrophic bacteria and phytoplankton coupling (biomass and production) related to hydrographic properties of the ecosystem. Phyto- and bacterioplankton were bottom-up driven in both coastal and offshore areas. Cold winter temperature was essential for phytoplankton to conform to the successional sequence in temperate waters. In terms of annual carbon production, the loss of the spring bloom (diatoms and dinoflagellates) after mild winters tended not to be compensated for by other taxa, not even summer cyanobacteria. These results improve our ability to project Baltic Sea ecosystem response to short- and long-term environmental changes.     

A Multivariate Baltic Sea Environmental Index

Since 2001/2002, the correlation between North Atlantic Oscillation index and biological variables in the North Sea and Baltic Sea fails, which might be addressed to a global climate regime shift. To understand inter-annual and inter-decadal variability in environmental variables, a new multivariate index for the Baltic Sea is developed and presented here. The multivariate Baltic Sea Environmental (BSE) index is defined as the 1st principal component score of four z-transformed time series: the Arctic Oscillation index, the salinity between 120 and 200 m in the Gotland Sea, the integrated river runoff of all rivers draining into the Baltic Sea, and the relative vorticity of geostrophic wind over the Baltic Sea area. A statistical downscaling technique has been applied to project different climate indices to the sea surface temperature in the Gotland, to the Landsort gauge, and the sea ice extent. The new BSE index shows a better performance than all other climate indices and is equivalent to the Chen index for physical properties. An application of the new index to zooplankton time series from the central Baltic Sea (Latvian EEZ) shows an excellent skill in potential predictability of environmental time series.     

Past,current and future Swedish freshwater monitoring from an authority perspective

The synthesis of the BONUS+ research is introduced. The HELCOM Baltic Sea Action Plan is examined as a case to illustrate the potentials and challenges in building the science–policymaking interface on a macroregional level. The projects address environmental challenges in the Baltic Sea as defined by the Baltic Sea Action Plan, or consider the environmental governance and decision making within the Baltic Sea context in general. Eutrophication, biodiversity, hazardous substances, maritime activities, and the environment governance are addressed, as are crosscutting issues, such as the impact of climate change, maritime spatial planning and impacts of future development on ecosystem services. The projects contributed to relevant policy developments: 37 consultations carried out at EU level, 49 modifications to policy documents and action plans, 153 suggestions for the efficacy of pertinent public policies and governance, and in 570 occasions, scientists working in BONUS+ projects served as members or observers in scientific and stakeholder committees.     

Formation of PFOA from 8:2 FTOH in closed-bottle experiments with brackish water

The formation of perfluorooctanoate (PFOA) from 1H,1H,2H,2H-perfluorodecanol (8:2 FTOH) was studied for the first time in laboratory experiments with brackish water. The water samples were collected from the Baltic Sea, which is one of the largest brackish water areas in the world and is polluted with PFOA and other perfluorinated compounds. The formation of PFOA was studied in closed-bottle experiments at different water temperatures. As a reference experiment, a modified OECD 310 test was conducted with sludge from a wastewater treatment plant and with brackish water. The PFOA and 8:2 FTOH were concentrated from water samples by solid-phase extraction (SPE) and were analysed using liquid chromatography–mass spectrometry. The effect of oxygen concentration on the formation of PFOA was studied using surface water samples with high and low oxygen contents. Other experiments were performed with oxygen-rich surface water and oxygen-deficient bottom water. The formation of PFOA was observed in all experiments; it was higher in the trial performed with brackish water than in the reference test carried out with sludge. Clear temperature dependence was observed in the formation of PFOA in brackish water tests; after a 30-day test period, a sixfold increase was observed in the amount of PFOA in surface water between the temperatures of 15 and 20 °C. Microbes were suggested as the major cause of the formation of PFOA, but other environmental characteristics, such as oxygen, could also affect the formation potential of PFOA.     

Ecological connectivity of the marine protected area network in the Baltic Sea,Kattegat and Skagerrak: Current knowledge and management needs

Marine protected areas (MPAs) have become a key component of conservation and fisheries management to alleviate anthropogenic pressures. For MPA networks to efficiently promote persistence and recovery of populations, ecological connectivity, i.e. dispersal and movement of organisms and material across ecosystems, needs to be taken into account. To improve the ecological coherence of MPA networks, there is hence a need to evaluate the connectivity of species spreading through active migration and passive dispersal. We reviewed knowledge on ecological connectivity in the Baltic Sea, Kattegat and Skagerrak in the northeast Atlantic and present available information on species-specific dispersal and migration distances. Studies on genetic connectivity are summarised and discussed in relation to dispersal-based analyses. Threats to ecological connectivity, limiting dispersal of populations and lowering the resilience to environmental change, were examined. Additionally, a review of studies evaluating the ecological coherence of MPA networks in the Baltic Sea, Kattegat and Skagerrak was performed, and suggestions for future evaluations to meet management needs are presented.Supplementary InformationThe online version contains supplementary material available at 10.1007/s13280-021-01684-x.     

DOC removal paradigms in highly humic aquatic ecosystems

Background, aim, and scope  Dissolved humic substances (HS) usually comprise 50–80% of the dissolved organic carbon (DOC) in aquatic ecosystems. From a trophic and biogeochemical perspective, HS has been considered to be highly refractory and is supposed to accumulate in the water. The upsurge of the microbial loop paradigm and the studies on HS photo-degradation into labile DOC gave rise to the belief that microbial processing of DOC should sustain aquatic food webs in humic waters. However, this has not been extensively supported by the literature, since most HS and their photo-products are often oxidized by microbes through respiration in most nutrient-poor humic waters. Here, we review basic concepts, classical studies, and recent data on bacterial and photo-degradation of DOC, comparing the rates of these processes in highly humic ecosystems and other aquatic ecosystems. Materials and methods  We based our review on classical and recent findings from the fields of biogeochemistry and microbial ecology, highlighting some odd results from highly humic Brazilian tropical lagoons, which can reach up to 160 mg C L⁻¹. Results and discussion  Highly humic tropical lagoons showed proportionally lower bacterial production rates and higher bacterial respiration rates (i.e., lower bacterial growth efficiency) than other lakes. Zooplankton showed similar δ¹³C to microalgae but not to humic DOC in these highly humic lagoons. Thus, the data reviewed here do not support the microbial loop as an efficient matter transfer pathway in highly humic ecosystems, where it is supposed to play its major role. In addition, we found that some tropical humic ecosystems presented the highest potential DOC photo-chemical mineralization (PM) rates reported in the literature, exceeding up to threefold the rates reported for temperate humic ecosystems. We propose that these atypically high PM rates are the result of a joint effect of the seasonal dynamics of allochthonous humic DOC input to these ecosystems and the high sunlight incidence throughout the year. The sunlight action on DOC is positive to microbial consumption in these highly humic lagoons, but little support is given to the enhancement of bacterial growth efficiency, since the labile photo-chemical products are mostly respired by microbes in the nutrient-poor humic waters. Conclusions  HS may be an important source of energy for aquatic bacteria in humic waters, but it is probably not as important as a substrate to bacterial growth and to aquatic food webs, since HS consumption is mostly channeled through microbial respiration. This especially seems to be the case of humic-rich, nutrient-poor ecosystems, where the microbial loop was supposed to play its major role. Highly humic ecosystems also present the highest PM rates reported in the literature. Finally, light and bacteria can cooperate in order to enhance total carbon degradation in highly humic aquatic ecosystems but with limited effects on aquatic food webs. Recommendations and perspectives  More detailed studies using C- and N-stable isotope techniques and modeling approaches are needed to better understand the actual importance of HS to carbon cycling in highly humic waters.     

The Governance of the Mitigation of the Baltic Sea Eutrophication: Exploring the Challenges of the Formal Governing System

This article focuses on the governing system of the mitigation of eutrophication in the Baltic Sea. Policies and measures of the Baltic Sea coastal countries, the macro--regional (HELCOM) level, and the level of the European Union are described and governance challenges explicated. We found that the main challenges at different governance levels include: differences between coastal countries in terms of environmental conditions including environmental awareness, overlaps of policies between different levels, the lack of adequate spatial and temporal specification of policies, and the lack of policy integration. To help to meet these challenges, we suggest closer involvement of stakeholders and the public, the improvement of the interplay of institutions, and the introduction of a “primus motor” for the governance of the mitigation of eutrophication in the Baltic Sea.