Search

Benthic-pelagic coupling is manifested as the exchange of energy, mass, or nutrients between benthic and pelagic habitats. It plays a prominent role in aquatic ecosystems, and it is crucial to functions from nutrient cycling to energy transfer in food webs. Coastal and estuarine ecosystem structure and function are strongly affected by anthropogenic pressures; however, there are large gaps in our understanding of the responses of inorganic nutrient and organic matter fluxes between benthic habitats and the water column. We illustrate the varied nature of physical and biological benthic-pelagic coupling processes and their potential sensitivity to three anthropogenic pressures - climate change, nutrient loading, and fishing - using the Baltic Sea as a case study and summarize current knowledge on the exchange of inorganic nutrients and organic material between habitats. Traditionally measured benthic-pelagic coupling processes (e.g., nutrient exchange and sedimentation of organic material) are to some extent quantifiable, but the magnitude and variability of biological processes are rarely assessed, preventing quantitative comparisons. Changing oxygen conditions will continue to have widespread effects on the processes that govern inorganic and organic matter exchange among habitats while climate change and nutrient load reductions may have large effects on organic matter sedimentation. Many biological processes (predation, bioturbation) are expected to be sensitive to anthropogenic drivers, but the outcomes for ecosystem function are largely unknown. We emphasize how improved empirical and experimental understanding of benthic-pelagic coupling processes and their variability are necessary to inform models that can quantify the feedbacks among processes and ecosystem responses to a changing world., (© 2017 The Authors. Global Change Biology Published by John Wiley & Sons Ltd.)

Climate change has multiple effects on Baltic Sea species, communities and ecosystem functioning through changes in physical and biogeochemical environmental characteristics of the sea. Associated indirect and secondary effects on species interactions, trophic dynamics and ecosystem function are expected to be significant. We review studies investigating species-, population- and ecosystem-level effects of abiotic factors that may change due to global climate change, such as temperature, salinity, oxygen, pH, nutrient levels, and the more indirect biogeochemical and food web processes, primarily based on peer-reviewed literature published since 2010. For phytoplankton, clear symptoms of climate change, such as prolongation of the growing season, are evident and can be explained by the warming, but otherwise climate effects vary from species to species and area to area. Several modelling studies project a decrease of phytoplankton bloom in spring and an increase in cyanobacteria blooms in summer. The associated increase in N:P ratio may contribute to maintaining the "vicious circle of eutrophication". However, uncertainties remain because some field studies claim that cyanobacteria have not increased and some experimental studies show that responses of cyanobacteria to temperature, salinity and pH vary from species to species. An increase of riverine dissolved organic matter (DOM) may also decrease primary production, but the relative importance of this process in different sea areas is not well known. Bacteria growth is favoured by increasing temperature and DOM, but complex effects in the microbial food web are probable. Warming of seawater in spring also speeds up zooplankton growth and shortens the time lag between phytoplankton and zooplankton peaks, which may lead to decreasing of phytoplankton in spring. In summer, a shift towards smaller-sized zooplankton and a decline of marine copepod species has been projected. In deep benthic communities, continued eutrophication promotes high sedimentation and maintains good food conditions for zoobenthos. If nutrient abatement proceeds, improving oxygen conditions will first increase zoobenthos biomass, but the subsequent decrease of sedimenting matter will disrupt the pelagic–benthic coupling and lead to a decreased zoobenthos biomass. In the shallower photic systems, heatwaves may produce eutrophication-like effects, e.g. overgrowth of bladderwrack by epiphytes, due to a trophic cascade. If salinity also declines, marine species such as bladderwrack, eelgrass and blue mussel may decline. Freshwater vascular plants will be favoured but they cannot replace macroalgae on rocky substrates. Consequently invertebrates and fish benefiting from macroalgal belts may also suffer. Climate-induced changes in the environment also favour establishment of non-indigenous species, potentially affecting food web dynamics in the Baltic Sea. As for fish, salinity decline and continuing of hypoxia is projected to keep cod stocks low, whereas the increasing temperature has been projected to favour sprat and certain coastal fish. Regime shifts and cascading effects have been observed in both pelagic and benthic systems as a result of several climatic and environmental effects acting synergistically. Knowledge gaps include uncertainties in projecting the future salinity level, as well as stratification and potential rate of internal loading, under different climate forcings. This weakens our ability to project how pelagic productivity, fish populations and macroalgal communities may change in the future. The 3D ecosystem models, food web models and 2D species distribution models would benefit from integration, but progress is slowed down by scale problems and inability of models to consider the complex interactions between species. Experimental work should be better integrated into empirical and modelling studies of food web dynamics to get a more comprehensive view of the responses of the pelagic and benthic systems to climate change, from bacteria to fish. In addition, to better understand the effects of climate change on the biodiversity of the Baltic Sea, more emphasis should be placed on studies of shallow photic environments. The fate of the Baltic Sea ecosystem will depend on various intertwined environmental factors and on development of the society. Climate change will probably delay the effects of nutrient abatement and tend to keep the ecosystem in its "novel" state. However, several modelling studies conclude that nutrient reductions will be a stronger driver for ecosystem functioning of the Baltic Sea than climate change. Such studies highlight the importance of studying the Baltic Sea as an interlinked socio-ecological system. [ABSTRACT FROM AUTHOR]

Based on the Baltic Earth Assessment Reports of this thematic issue in Earth System Dynamics and recent peer-reviewed literature, current knowledge of the effects of global warming on past and future changes in climate of the Baltic Sea region is summarised and assessed. The study is an update of the Second Assessment of Climate Change (BACC II) published in 2015 and focuses on the atmosphere, land, cryosphere, ocean, sediments, and the terrestrial and marine biosphere. Based on the summaries of the recent knowledge gained in palaeo-, historical, and future regional climate research, we find that the main conclusions from earlier assessments still remain valid. However, new long-term, homogenous observational records, for example, for Scandinavian glacier inventories, sea-level-driven saltwater inflows, so-called Major Baltic Inflows, and phytoplankton species distribution, and new scenario simulations with improved models, for example, for glaciers, lake ice, and marine food web, have become available. In many cases, uncertainties can now be better estimated than before because more models were included in the ensembles, especially for the Baltic Sea. With the help of coupled models, feedbacks between several components of the Earth system have been studied, and multiple driver studies were performed, e.g. projections of the food web that include fisheries, eutrophication, and climate change. New datasets and projections have led to a revised understanding of changes in some variables such as salinity. Furthermore, it has become evident that natural variability, in particular for the ocean on multidecadal timescales, is greater than previously estimated, challenging our ability to detect observed and projected changes in climate. In this context, the first palaeoclimate simulations regionalised for the Baltic Sea region are instructive. Hence, estimated uncertainties for the projections of many variables increased. In addition to the well-known influence of the North Atlantic Oscillation, it was found that also other low-frequency modes of internal variability, such as the Atlantic Multidecadal Variability, have profound effects on the climate of the Baltic Sea region. Challenges were also identified, such as the systematic discrepancy between future cloudiness trends in global and regional models and the difficulty of confidently attributing large observed changes in marine ecosystems to climate change. Finally, we compare our results with other coastal sea assessments, such as the North Sea Region Climate Change Assessment (NOSCCA), and find that the effects of climate change on the Baltic Sea differ from those on the North Sea, since Baltic Sea oceanography and ecosystems are very different from other coastal seas such as the North Sea. While the North Sea dynamics are dominated by tides, the Baltic Sea is characterised by brackish water, a perennial vertical stratification in the southern subbasins, and a seasonal sea ice cover in the northern subbasins. [ABSTRACT FROM AUTHOR]

Climate change has multiple direct and indirect potentially synergistic effects on Baltic Sea species, organism communities, and on ecosystem functioning, through physical and biogeochemical environmental characteristics of the sea. Associated indirect and secondary effects on species interactions, trophic dynamics and ecosystem function are expected to be significant. Evidence on effects of climate are compiled from and reviewed for field studies, experimental work, as well as modelling studies primarily from published literature after 2010. The responses vary within and between species groups, even between sibling species. Such subtle differences, as well as secondary feedbacks and altered trophic pathways, make projections difficult. Some common patterns arise from the wealth of recent studies, however. It is likely that the combined effects of increased external nutrient loads, stratification and internal loading will improve the conditions for cyanobacterial blooms in large parts of the Baltic. In the northernmost areas the increasing allochtonous DOM may further complicate the picture by increasing heterotrophy and by decreasing food web efficiency. This effect may, however, be counteracted by the intensification of the bacteria-flagellate-microzooplankton-mesozooplankton link, which may change the system from a bottom-up controlled one to a top-down controlled one. In deep benthic communities, continued eutrophication may promote higher sedimentation of organic matter and increase zoobenthic biomasses, but eventually increasing stratification and hypoxia/anoxia will disrupt benthic-pelagic coupling, leading to reduced benthic biomass. In the photic benthic systems warmer winters with less ice and nutrient increase enhances eutrophication. The projected salinity decline suppresses marine species, and temperature increase overgrowth of perennial macroalgae by annual filamentous alga throughout the growing-season, and major changes in the marine entire ecosystem are expected. The changes in environmental conditions probably also lead to increased establishment of non-indigenous species, potentially affecting food web dynamics in large areas of the Baltic Sea. However, several modelling studies have concluded that nutrient reductions according to the Baltic Sea Action Plan of Helsinki Commission may be a stronger driver for ecosystem functions in the Baltic Sea than climate change. Such studies highlight the importance of studying the Baltic Sea as an interlinked socio-ecological system. Knowledge gaps include uncertainties in projecting the future salinity level as well as stratification under different climate forcings. This weakens our ability to project how overall biodiversity, pelagic productivity, fish populations, and macroalgal communities may change in the future. Experimental work must be better integrated into studies of food web dynamics, to get a more comprehensive view of the responses of the pelagic and benthic systems to climate change, from bacteria to fish. Few studies have holistically investigated the shallow water ecosystems holistically. There are complex climate-induced interactions and multiple feedbacks between algae, grazers and their predators, that are poorly known, as are the effects of non-native invasive species. Finally, both 2D species distribution models and 3D ecosystem models could benefit from better integration of approaches including physical, chemical and biological parameters. [ABSTRACT FROM AUTHOR]

Based on the Baltic Earth Assessment Reports of this thematic issue in Earth System Dynamics and recent peer-reviewed literature, current knowledge about the effects of global warming on past and future changes in climate of the Baltic Sea region is summarized and assessed. The study is an update of the Second Assessment of Climate Change (BACC II) published in 2015 and focusses on the atmosphere, land, cryosphere, ocean, sediments and the terrestrial and marine biosphere. Based on the summaries of the recent knowledge gained in paleo-, historical and future regional climate research, we find that the main conclusions from earlier assessments remain still valid. However, new long-term, homogenous observational records, e.g. for Scandinavian glacier inventories, sea-level driven saltwater inflows, so-called Major Baltic Inflows, and phytoplankton species distribution and new scenario simulations with improved models, e.g. for glaciers, lake ice and marine food web, have become available. In many cases, uncertainties can now be better estimated than before, because more models can be included in the ensembles, especially for the Baltic Sea. With the help of coupled models, feedbacks between several components of the Earth System have been studied and multiple driver studies were performed, e.g. projections of the food web that include fisheries, eutrophication and climate change. New data sets and projections have led to a revised understanding of changes in some variables such as salinity. Furthermore, it has become evident that natural variability, in particular for the ocean on multidecadal time scales, is greater than previously estimated, challenging our ability to detect observed and projected changes in climate. In this context, the first paleoclimate simulations regionalized for the Baltic Sea region are instructive. Hence, estimated uncertainties for the projections of many variables increased. In addition to the well-known influence of the North Atlantic Oscillation, it was found that also other low-frequency modes of internal variability, such as the Atlantic Multidecadal Variability, have profound effects on the climate of the Baltic Sea region. Challenges were also identified, such as the systematic discrepancy between future cloudiness trends in global and regional models and the difficulty of confidently attributing large observed changes in marine ecosystems to climate change. Finally, we compare our results with other coastal sea assessments, such as the North Sea Region Climate Change Assessment (NOSCCA) and find that the effects of climate change on the Baltic Sea differ from those on the North Sea, since Baltic Sea oceanography and ecosystems are very different from other coastal seas such as the North Sea. While the North Sea dynamics is dominated by tides, the Baltic Sea is characterized by brackish water, a perennial vertical stratification in the southern sub-basins and a seasonal sea ice cover in the northern sub-basins. [ABSTRACT FROM AUTHOR]

Eutrophication, i.e. nutrient over-enrichment, has been a topic for academic and societal debate for the past five decades both on land and in aquatic systems fed by nutrients as diffuse loading from agricultural lands and as wastewater from industrial and municipal point-sources. The use of nutrients (primarily nitrogen and phosphorus) in excess became a problem with the onset of large-scale production and use of artificial fertilizers after World War II, and the effects on the aquatic environment became obvious some two to three decades later. In this Perspective, four seminal papers on eutrophication are discussed in light of the current knowledge of the problem, including future perspectives and outlooks in the light of global climate change and the demand for science-based holistic ecosystem-level policies and management options. [ABSTRACT FROM AUTHOR]

The ocean is a lifeline for human existence, but current practices risk severely undermining ocean sustainability. Present and future social−ecological challenges necessitate the maintenance and development of knowledge and action by stimulating collaboration among scientists and between science, policy, and practice. Here we explore not only how such collaborations have developed in the Nordic countries and adjacent seas but also how knowledge from these regions contributes to an understanding of how to obtain a sustainable ocean. Our collective experience may be summarized in three points: 1) In the absence of long-term observations, decision-making is subject to high risk arising from natural variability; 2) in the absence of established scientific organizations, advice to stakeholders often relies on a few advisors, making them prone to biased perceptions; and 3) in the absence of trust between policy makers and the science community, attuning to a changing ocean will be subject to arbitrary decision-making with unforeseen and negative ramifications. Underpinning these observations, we show that collaboration across scientific disciplines and stakeholders and between nations is a necessary condition for appropriate actions. [ABSTRACT FROM AUTHOR]

The article reflects on anthropogenically induced climate change has created intriguing scientific problems pertaining to the seas and the oceans on earth that can be monitored, analysed, modelled and understood. The land-based perspective is rewarding and is also limiting in its lack of three-dimensionality as the vastness of the seas and the oceans is so much more than the surface they observe from a distance.

Coastal waters are important in linking zoobenthos and fish, as many coastal fishes feed on benthic prey in these habitats. Major drivers, such as eutrophication and climate change, may alter this link, whereas shifts in the importance of these drivers may induce different responses in zoobenthos and fish, respectively, potentially changing productivity of coastal ecosystems. The aim of this study was to assess in which way abundance and distribution of benthic-feeding fish and biomass of zoobenthos have changed over time in response to eutrophication (Secchi depth) and climate change (temperature and salinity), respectively. This was done by analyzing gross changes in the responses over three decades (1983-2012) and across depth zones. Eutrophication and climate change caused different though specific impacts on fish and zoobenthos, respectively. Throughout the 1980s, increasing benthic-feeding fish abundance in shallow waters (<6 m) was primarily attributed to eutrophication (decreasing Secchi depth), implying increased system productivity. During the 2000s, the effect of eutrophication levelled out, whereas temperature caused contrasting development of fish abundance at different depth zones. Shallow waters had lower fish abundances during warm years compared with colder ones, while the abundance increased in deeper, aphotic waters (6-20 m). In the deep waters, zoobenthos showed a contrasting, declining trend in biomass, coinciding with the decrease in salinity during the 2000s. This suggests altered ecosystem productivity and potential food shortage for benthic-feeding fish exploring the deep waters. An intensification of these trends is likely in the future, as climate change scenarios suggest further temperature increase and salinity decrease. [ABSTRACT FROM AUTHOR]

Climate change is challenging species' abilities to respond and function. In the Arctic, shifts in temperature and ice cover are disrupting established biological interactions and thereby ecosystem structure and function. By examining epibenthic communities in coastal and continental shelf habitats of Northeast Greenland that have been ice-locked for centuries, we provide a contemporary baseline of benthic functional diversity through a trait-based approach. We show clear trends in biodiversity and traits from a priori defined groups of fjord, shelf, shelf break, and slope habitats. With biodiversity and functional indices, we identified how fjord and shelf communities could be vulnerable to current and future changes in climate conditions. Using a hierarchical model of species communities (HMSC) we found taxa occurrences, regardless of taxonomic relatedness, were mainly driven by changes in depth, salinity, and oxygen and less so by temperature. Though rising global temperatures are undoubtedly altering the physiochemical structure of the shelf area, our study underscores the significance of often-overlooked environmental factors in Arctic climate change studies. Moreover, we highlight how species traits have a significant role in forming and maintaining community composition by explaining a high amount of among-taxa variation in taxa occurrences and taxa responses to the environment. While the significance of this is not known in relation to community resilience, as Arctic shelf processes intensify (e.g., Atlantification), changes in benthic communities and their ecological roles will ultimately affect ecosystem functioning and the broader dynamics of complex seascapes. • Complex seascapes across continental shelves drive diverging traits of benthos. • Arctic benthos responds to depth, oxygen, and salinity more than temperature. • Benthic community traits are central in explaining taxa occurrences. [ABSTRACT FROM AUTHOR]

The article focuses on a study on the Baltic Sea as a time machine to observe consequences and mitigation of future coastal perturbations, due to its unique combination of ecosystem deterioration and an early history of multistressor disturbance. It refers to rapid progression of global pressures demonstrated by the Baltic Sea.