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Biological Oceanography of the Baltic Sea

herausgegeben von: Pauline Snoeijs-Leijonmalm, Hendrik Schubert, Teresa Radziejewska

Verlag: Springer Netherlands

Enthalten in: Springer Professional "Wirtschaft+Technik" , Springer Professional "Technik"

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Über dieses Buch

This is the first comprehensive science-based textbook on the biology and ecology of the Baltic Sea, one of the world’s largest brackish water bodies. The aim of this book is to provide students and other readers with knowledge about the conditions for life in brackish water, the functioning of the Baltic Sea ecosystem and its environmental problems and management. It highlights biological variation along the unique environmental gradients of the brackish Baltic Sea Area (the Baltic Sea, Belt Sea and Kattegat), especially those in salinity and climate.

pt;font-family:"Arial","sans-serif"; color:#262626">The first part of the book presents the challenges for life processes and ecosystem dynamics that result from the Baltic Sea’s highly variable recent geological history and geographical isolation. The second part explains interactions between organisms and their environment, including biogeochemical cycles, patterns of biodiversity, genetic diversity and evolution, biological invasions and physiological adaptations. In the third part, the subsystems of the Baltic Sea ecosystem – the pelagic zone, the sea ice, the deep soft sea beds, the phytobenthic zone, the sandy coasts, and estuaries and coastal lagoons – are treated in detail with respect to the structure and function of communities and habitats and consequences of natural and anthropogenic constraints, such as climate change, discharges of nutrients and hazardous substances. Finally, the fourth part of the book discusses monitoring and ecosystem-based management to deal with contemporary and emerging threats to the ecosystem’s health.

Inhaltsverzeichnis

Frontmatter

The Baltic Sea environment

Frontmatter

Chapter 1. Brackish water as an environment

Abstract

Water is the most abundant compound on the surface of the Earth and the chemical basis for life on Earth.

The strong polarity of the water molecule assigns special physical and chemical properties to water as the direct environment in which aquatic organisms live, propagate and interact.

The surface tension of water creates the pleuston habitat and the viscosity of water requires adaptations, but it is also utilised by organisms for their life functions.

Water remains liquid over a broad range of temperatures, and the density anomaly of water makes ice float, which allows life to exist below the ice even when the water surface freezes.

In the brackish water of the Baltic Sea the ionic composition and the marine carbonate system deviate from marine water, which requires physiological adaptations of the organisms living in the Baltic Sea.

Natural brackish waters are classified according to ecologically relevant salinity ranges.

Hendrik Schubert, Dirk Schories, Bernd Schneider, Uwe Selig

Chapter 2. Why is the Baltic Sea so special to live in?

Abstract

Geographical position, geological development, hydrographical features, climate and physical drivers together create the Baltic Sea environment.

Baltic Sea water is brackish and characterised by pronounced salinity gradients, both in horizontal and vertical directions, because of the large volume of freshwater runoff from over 100 rivers, which mixes with the saline water from the Kattegat that enters the Baltic Sea via narrow shallow straits.

Being a semi-enclosed continental sea with a large drainage area compared to its water volume, the Baltic Sea ecosystem is heavily impacted by the surrounding landmasses.

The water residence time in the Baltic Sea is long (30–40 years), and therefore discharged nutrients and toxic compounds circulate within the sea for a long time, which contributes to its vulnerability to eutrophication and chemical contamination by hazardous substances.

The Baltic Sea Area is geologically young and the Baltic Sea ecosystem is extremely young in an evolutionary perspective. Only few macroscopic species are fully adapted to its low-salinity environment.

Chief factors that affect species distributions in the Baltic Sea along local, regional and ecosystem-wide gradients are salinity, climate, ice cover, currents, permanent salinity stratification, hypoxia, and benthic substrate types (rock, sand, mud).

Environmental drivers vary either in time or space or both and contribute to the north-south “large-scale Baltic Sea gradient”, along which many species experience physiological stress, lose the ability to reproduce sexually and reach the ecological limit of their occurrence.

In an ecosystem-wide perspective, the large-scale Baltic Sea gradient is the principal ecological characteristic of the Baltic Sea.

Pauline Snoeijs-Leijonmalm, Elinor Andrén

Ecological processes in the Baltic Sea

Frontmatter

Chapter 3. Biogeochemical cycles

Abstract

The internal cycles of carbon, nitrogen and phosphorus in the Baltic Sea are, like in other seas, mainly controlled by biological production and degradation of organic matter (OM).

Biological activity also modulates the acid/base balance (pH), which is mainly a function of alkalinity and the total CO₂ concentration.

Particulate organic matter (POM) produced in the photic zone sinks into deeper water layers and is deposited on the sediment surface, where it is mineralised. Mineralisation is a form of microbial oxidation and thus leads to oxygen depletion. Due to its semi-enclosed position and its bottom topography, large-scale oxygen depletion of deep bottoms is common in the Baltic Sea.

Under anoxic conditions, the burial of phosphorus bound to ferric oxide is inhibited and the availability of phosphate for incorporation in new OM production increases.

In stagnant waters, the oxic/anoxic interface may migrate from the sediment into the water column, forming a pelagic redoxcline. Such a redoxcline occurs in large areas of the Baltic Sea.

At oxygen concentrations close to zero, nitrate acts as an oxidant and is reduced to elemental nitrogen (denitrification). After the exhaustion of both oxygen and nitrate, OM is oxidised by sulphate, which is reduced to toxic hydrogen sulphide.

The final step in the mineralisation process is the microbial formation of methane in deeper sediment layers, which reflects the internal oxidation/reduction of OM.

A significant fraction of the organic carbon, nitrogen and phosphorus escapes mineralisation and is permanently buried in the sediment. On a long-term basis, this loss, together with export to the North Sea and internal sinks, is mainly balanced by riverine inputs and atmospheric deposition to the Baltic Sea.

Bernd Schneider, Olaf Dellwig, Karol Kuliński, Anders Omstedt, Falk Pollehne, Gregor Rehder, Oleg Savchuk

Chapter 4. Patterns of biodiversity

Abstract

More than 4,400 known species live in the brackish Baltic Sea. Of these, 4 % are cyanobacteria, 51 % unicellular eukaryotes (protists), 8 % macrophytes, 32 % invertebrates and 5 % vertebrates.

In the Baltic Sea Area (Baltic Sea and the transition zone), the species richness of these five groups is >6,600, 50 % higher than in the Baltic Sea alone, while the water volume increases by only 4 %.

The higher richness in the transition zone is caused by North Sea species that still occur in the Kattegat and Belt Sea but cannot survive in the low salinity of the Baltic Sea. Unicellular organisms may be especially diverse in the transition zone as they move with the water masses of different salinities from the Skagerrak and the Baltic Sea that mix here.

The true number of species is much higher than the diversity reported from both the Baltic Sea and the transition zone since most archaean and bacterial species, as well as many protists, fungi and small invertebrates, are still unknown.

The dominant species in the Baltic Sea proper are mainly hardy, estuarine species, accompanied by a number of glacial relicts, freshwater species and ~130 (non-indigenous) brackish-water species. In the three large gulfs of the Baltic Sea (the Gulfs of Bothnia, Finland and Riga), and near large freshwater discharges along the entire coasts, freshwater species dominate below a salinity of ~4.

The species richness of cyanobacteria, heterotrophic bacteria and benthic diatoms is not impeded in the Baltic Sea. These groups are highly diverse in both marine and freshwater and enter the Baltic Sea from both habitats.

Macroscopic organisms show a species minimum at salinity 5–7. There are very few “true” brackish-water species in the Baltic Sea, and the loss of marine species, e.g. macroalgae, polychaetes, crustaceans and molluscs, along the large-scale Baltic Sea gradient is poorly compensated for by species entering the Baltic Sea from freshwater such as charophytes, vascular plants, oligochaetes and insect larvae.

Despite a pool of >1,500 macroscopic species, the evenness of the communities in the Baltic Sea proper is low, as they are typically dominated by mass occurrences of a few macroscopic species that build simple food webs in a highly productive system.

With few species in each functional group (e.g. habitat-forming macrophytes, filter-feeding animals, pelagic fish), there is a high risk that the loss or drastic reduction of a single key species may alter functions that are important for the maintenance of the ecosystem, such as provision of habitats, balanced food webs and resilience.

Pauline Snoeijs-Leijonmalm

Chapter 5. Biological invasions

Abstract

The term “non-indigenous species” (NIS) represents a biogeographical category, which indicates human involvement in the introduction of a certain species to a particular ecosystem and has nothing to do with putting “good” or “bad” tags on these species.

A biological invasion is the spread of a NIS or a cryptogenic species (of uncertain or unknown origin) to an area where it did not previously occur.

About 130 NIS and cryptogenic species have been introduced to the Baltic Sea Area by anthropogenic activities.

Most NIS have arrived to the Baltic Sea during recent decades due to intensification of global trade, human mobility and removal of custom barriers, although the first introductions are thought to have taken place already centuries ago.

The NIS in the Baltic Sea mainly originate from the coastal waters of three source areas (the North American east coast, the Ponto-Caspian region and East Asia), which are connected to the Baltic Sea by a number of introduction pathways, such as shipping and human-made canals.

In the Baltic Sea, NIS are represented by many taxonomic groups, from unicellular plankton organisms to crustaceans, molluscs, fish, waterbirds and mammals.

Many of the NIS in the Baltic Sea have increased functional diversity, bringing new and unusual functions to the species-poor Baltic Sea ecosystem.

Some NIS may spread, highly increase in abundance and cause an adverse impact on biological diversity, ecosystem functioning, socio-economic values and/or human health. These NIS are called “invasive alien species”.

As it cannot be predicted which NIS will become invasive and cause harm in a particular ecosystem, a precautionary approach, preventing the arrival of new NIS in general, is advisable.

Sergej Olenin, Stephan Gollasch, Maiju Lehtiniemi, Mariusz Sapota, Anastasija Zaiko

Chapter 6. Genetic diversity and evolution

Abstract

Genetic variability among individuals, populations and species represents the basic level of biodiversity, and is a prerequisite of adaptive evolution.

Adaptive evolution is driven by natural selection that acts at the level of individual phenotypes.

Genetic variation can also be used as a tool to study the history of species and populations, and to explore their current structure and reproductive strategies.

Genetic markers that are presumably neutral to selection are used in measuring connectivity among Baltic populations and their uniqueness compared to those in the neighbouring marine or freshwater habitats. Genetic markers have often revealed the presence of previously unknown cryptic species that are much older than the Baltic Sea.

In most taxa studied, some genetic differentiation has arisen post-glacially between the Baltic Sea and North Sea populations, e.g. in the Atlantic herring Clupea harengus and the Atlantic cod Gadus morhua.

Despite such differentiation, few of the Baltic organisms are considered as locally evolved endemic taxa. An exception is the partly asexually reproducing brown algal species Fucus radicans, which has evolved locally and now coexists with its ancestor Fucus vesiculosus in the northern Baltic Sea.

The unique blue mussel and Baltic clam populations in the Baltic Sea are closely related to Pacific lineages (Mytilus trossulus and Macoma balthica balthica) but are distinct from the neighbouring North Sea populations (Mytilus edulis and Macoma balthica rubra). They have been modified by interbreeding in the transition zone between the Baltic Sea and the North Sea, and now constitute hybrid swarms.

A current methodological shift from single-gene approaches to genome-wide studies will help in distinguishing genes and patterns of variation that are affected by selection from those that merely reflect population structure, and in identifying characters that account for the adaptations to the unique Baltic Sea environment.

Risto Väinölä, Kerstin Johannesson

Chapter 7. Physiological adaptations

Abstract

Strategies of aquatic organisms to cope with ambient environmental conditions involve avoidance reactions or more profound behavioural and physiological adjustments, collectively called “adaptations”.

Modulative (irreversible) and modificative (reversible) adaptations are short-term compensatory changes (acclimations) in an individual in response to environmental change, which are made possible through phenotypic plasticity.

Strong triggers for physiological adaptations that are more specific for the Baltic Sea than for most other water bodies are low salinity and low oxygen levels.

Mechanisms for adaptation to the salinity of the Baltic Sea, as well as to salinity fluctuations in Baltic coastal regions due to freshwater discharge, involve ion regulation (through ion channels, ion exchange proteins or primary ion pumps) and osmotic adaptation (e.g. through intracellular concentrations of osmotically active substances, such as low-molecular carbohydrates, amino acids and nucleic acids).

Low oxygen levels are dealt with by avoidance or a more effective energy metabolism.

Stress proteins provide cellular and whole-body responses of organisms to a vast range of changes in environmental conditions, e.g. water temperature, salinity, acidification, light availability, chemical pollution and hypoxia.

The photosynthetic apparatus of autotrophs is designed to cope with variability in irradiance; it becomes more efficient at low irradiance and more protective against excess energy at high irradiance.

Hendrik Schubert, Irena Telesh, Mikko Nikinmaa, Sergei Skarlato

Subsystems of the Baltic Sea ecosystem

Frontmatter

Chapter 8. The pelagic food web

Abstract

Environmental drivers and food web structure in the pelagic zone vary from south to north in the Baltic Sea.

While nitrogen is generally the limiting nutrient for primary production in the Baltic Sea, phosphorus is the limiting nutrient in the Bothnian Bay.

In the Gulf of Bothnia the food web is to a large extent driven by terrestrial allochthonous material, while autochthonous production dominates in the other parts of the Baltic Sea.

Changes in bacterioplankton, protist and zooplankton community composition from south to north are mainly driven by salinity.

Bacteria are crucial constituents of the pelagic food web (microbial loop) and in oxygen-poor and anoxic bottom waters where they mediate element transformations.

Diatoms and dinoflagellates are the major primary producers in the pelagic zone. Summer blooms of diazotrophic (nitrogen-fixing) filamentous cyanobacteria are typical of the Baltic Sea, especially in the Baltic Sea proper and the Gulf of Finland.

The mesozooplankton (mainly copepods and cladocerans) channel energy from primary producers and the microbial food web to fish and finally to the top predators in the pelagic system (waterbirds and mammals).

Herring and sprat populations are affected by the foraging intensity of their main predator (cod), and therefore the environmental conditions that affect cod may also influence mesozooplankton due to food web effects “cascading down the food web”.

Anthropogenic pressures, such as overexploitation of fish stocks, eutrophication, climate change, introduction of non-indigenous species and contamination of top predators by hazardous substances, cause changes in the pelagic food web that may have consequences for the balance and stability of the whole ecosystem.

Agneta Andersson, Timo Tamminen, Sirpa Lehtinen, Klaus Jürgens, Matthias Labrenz, Markku Viitasalo

Chapter 9. Life associated with Baltic Sea ice

Abstract

The formation of sea ice impacts directly on the physical dynamics of water masses (e.g. wind stress at the sea surface) and air-sea exchange processes (e.g. vertical heat fluxes).

The annual cycle of formation, consolidation and melting of sea ice has a major influence on the ecology of both the benthic and pelagic components of the Baltic Sea ecosystem.

There is considerable inter-annual variation in the extent of sea ice in the Baltic Sea and thus in the size of the habitat for sympagic (ice-associated) microbial and metazoan communities as well as for larger organisms living on the ice, notably the ringed seal.

There is a pronounced gradient in ice characteristics, from more saline ice in the south of the Baltic Sea to freshwater ice in the north. The former is more porous and supports more ice-associated biology than the latter.

The Baltic sympagic communities consist mainly of prokaryotic and eukaryotic microbes (bacteria, diatoms, dinoflagellates, flagellates), ciliates and rotifers. These communities are recruited from the plankton when the ice forms, followed by an ice-adapted successional pattern with an expansion of substrate-bound pennate diatoms, which does not occur in the seawater beneath the ice.

The sea-ice food webs inside the ice are truncated compared to the open-water food webs because organisms larger than the upper size limit of the brine channels are lacking in the internal sympagic communities.

Global climate change decreases the extension and thickness of the sea ice as well as the length of the ice season, and therefore the seasonal effects that sea ice has on the Baltic Sea winter-spring ecosystem dynamics.

David N. Thomas, Hermanni Kaartokallio, Letizia Tedesco, Markus Majaneva, Jonna Piiparinen, Eeva Eronen-Rasimus, Janne-Markus Rintala, Harri Kuosa, Jaanika Blomster, Jouni Vainio, Mats A. Granskog

Chapter 10. Deep soft seabeds

Abstract

The deep soft seabeds of the Baltic Sea Area offer a wide range of ecological niches for invertebrates (zoobenthos), from the high-diversity marine regions characterised by large and long-lived organisms in the Skagerrak to the species-poor, almost limnic, systems in the inner reaches of the Bothnian Bay and the Gulf of Finland.

The zoobenthos processes nutrients and organic matter in the sediments, oxygenates the sediments through bioturbation and bioventilation, affects nutrient fluxes at the sediment/water interface, and acts as a link in both bottom-up and top-down control of the entire Baltic Sea ecosystem.

The steep spatial and seasonal gradients of the Baltic Sea structure the zoobenthic communities and shape their functional roles in the food webs as well as in benthic-pelagic coupling.

Eutrophication and widespread hypoxia and anoxia are major factors that shape the taxonomic composition, functionality and successional patterns of the zoobenthic communities.

As the zoobenthos still recovers from the last glaciation through an on-going succession, there are plenty of vacant niches available in the Baltic Sea for the introduction and establishment of non-indigenous species, and these species may have profound impacts on the whole ecosystem.

Due to the sensitivity of the zoobenthos to environmental change and its relative longevity, zoobenthos abundance, biomass and community composition are used as indicators of ecosystem health.

Modern science combines field surveys with experiments and advanced mathematical modelling, linking physical and chemical drivers with food web processes. Flux measurements and broad functional analyses, in combination with molecular studies, provide information on processes that reshape our understanding of ecosystem functioning.

Urszula Janas, Erik Bonsdorff, Jan Warzocha, Teresa Radziejewska

Chapter 11. The phytobenthic zone

Abstract

Phytobenthic communities consist of macrophytes (macroalgae, vascular plants and mosses) with their accompanying fauna and microorganisms.

The phytobenthic communities occur in the photic zone, which in the Baltic Sea extends from the water surface down to a ~20 m water depth, but in turbid coastal waters only down to ~5 m.

The type of vegetation is determined by the available substrate, which is a result of geography and geology in combination with currents. Most macroalgae grow attached to hard substrates whereas vascular plants and charophytes grow on sandy or soft (silt and mud) substrates.

Generally, the coastal areas of the Baltic Sea consist of mixed substrates with an intermingled vegetation of vascular plants and algae. In the northern Baltic Sea hard substrates dominate in the outer archipelagos, and in the southeastern Baltic Sea sandy and muddy substrates dominate.

Luxuriant stands of macrophytes provide food, shelter and spawning habitats for the associated sessile and mobile micro-, meio- and macrofauna, including fish.

On an ecosystem-wide scale, the phytobenthic communities vary along the large-scale Baltic Sea gradient. Biomass decreases with lower salinity and colder climate, while the proportion of freshwater species increases.

On a local scale, the phytobenthic communities are mainly, directly or indirectly, shaped by water movement (e.g. by the occurrence of sandy beaches and rocky shores) and winter ice cover. Light and substrate availability give rise to typical depth zonation patterns, ending with soft-substrate communities deepest down.

On a small scale (patches), phytobenthic community structure and composition is influenced by microhabitat structure and biotic interactions.

The phytobenthic communities in the brackish Baltic Sea are more sensitive to disturbance than their marine counterparts due to low diversity, physiological stress and the loss of sexual reproduction when species approach their salinity limit.

Hans Kautsky, Georg Martin, Pauline Snoeijs-Leijonmalm

Chapter 12. Sandy coasts

Abstract

Sandy coasts, including the epilittoral part of sandy beaches and the shallow sandy sublittoral, are particularly extensive in the southern and southeastern part of the Baltic Sea.

In the Baltic Sea ecosystem, sandy coasts function as biocatalytic filters by decomposing organic matter (including detritus) most of which originates directly or indirectly (e.g. via waterbirds) from the sea.

Sandy coasts are unstable, erodable environments which change in time and space due to e.g. erosion in winter and deposition of sand on the beaches in summer, and to the constant shifting of the substrate by winds and currents.

The sandy epilittoral and shallow sublittoral habitats support a variety of life forms, from microbes to birds, and are the space in which diverse processes involved in energy flow and matter cycling operate at different temporal and spatial scales.

The sandy coast food webs are partly based on the direct input of solar energy and nutrients used by primary producers (phytoplankton, microphytobenthos, macrophytes) whose production is subsequently utilised by invertebrates (meiobenthos, macrozoobenthos), fish and birds.

Another part of the sandy coast food webs is based on the input of organic material in the form of detritus, a source of energy for microbial communities consisting of bacteria, fungi, yeasts and actinomycetes as well as of heterotrophic protists living attached to sand grains and in the interstices.

Birds collect invertebrate prey from the sand on the beach or from the shallow sublittoral and contribute to the organic matter pool of the sandy habitat.

The sandy coasts of the Baltic Sea experience heavy anthropogenic pressure which primarily involves tourism and recreation, but also effects of eutrophication, establishment of non-indigenous species, sand extraction and dredging, fishing, infrastructure and shore defence constructions.

Teresa Radziejewska, Jonne Kotta, Lech Kotwicki

Chapter 13. Estuaries and coastal lagoons

Abstract

Estuaries and coastal lagoons, semi-enclosed inland water bodies, are highly productive systems and function as a transitional zone between land and sea.

In the Baltic Sea Area, it may be difficult to discriminate between lagoon-type estuaries and lagoons with some freshwater influence because there is a continuum between pure estuaries and pure lagoons with respect to flow dynamics.

The estuaries and lagoons in the Baltic Sea Area are highly dynamic environments as they experience pronounced erratic changes in water level and salinity and their shallowness induces high variability of light and water temperature.

The variability of the environment and high organic enrichment enhances the diversity of planktonic and benthic protists (unicellular autotrophic, mixotrophic and heterotrophic eukaryotes); in contrast, the diversity of the macrozoobenthos is low.

In the shallow areas of coastal lagoons with the bottom covered by organic matter-rich fine-grained sediment (mud, silt), the sediment stability is often very low.

Wherever organic mud dominates, a large part of the consumer spectrum is absent. Consequently, food webs may have “open ends” and organic matter is channelled to decomposers or to the sediment for burial rather than to consumers.

Estuaries and lagoons are sensitive to eutrophication, which may result in shifts from a macrophytobenthos-dominated system to a phytoplankon-dominated one, or from a grazing food web to a microbial food web.

Estuaries and lagoons are also sensitive to introductions of non-indigenous species, which may have the potential of increasing eutrophication by eliminating planktonic filter feeders (e.g. the carnivorous cladoceran Cercopagis pengoi) or decreasing eutrophication symptoms by a large filtration capacity that clears the water and allows a macrophytobenthic vegetation to reoccur (e.g. the bivalve Dreissena polymorpha).

Hendrik Schubert, Irena Telesh

Monitoring and ecosystem-based management of the Baltic Sea

Frontmatter

Chapter 14. Biological indicators

Abstract

Changes in living conditions caused by natural variability or anthropogenic activities elicit distinct responses of species, populations and communities. Bioindication is the recording of such responses and the entity measured is called a “bioindicator”.

A bioindicator can be any relevant component or measure that can be used to estimate the environmental status based on the performance of all types of organisms (prokaryotes, protists, macroalgae, vascular plants, invertebrates, fish, mammals), including bulk measurements such as the chlorophyll a concentration in the seawater or the lower depth limit of macrophytes.

To be able to conclude if environmental change has taken place based on bioindication, it is essential to have knowledge of the specific ecological requirements of the organisms with respect to their habitats.

Bioindication using individuals or species includes e.g. behavioural adaptations, modifications of organ and cell structures and changes in population dynamics.

Bioindication by recording dramatic increases or decreases in the proportion and/or density of species in a community provides a conspicuous sign of environmental change, especially when this includes the extinction of species.

Strong decreases and extinctions of species in a community coupled to immigration of non-indigenous species may signify a shift in community composition that has a bearing on the functioning of the entire ecosystem.

Bioindication is a major tool used in the implementations of the EU environmental legislation: the Habitats Directive (HD), the Water Framework Directive (WFD) and the Marine Strategy Framework Directive (MSFD).

Michael L. Zettler, Alexander Darr, Matthias Labrenz, Sigrid Sagert, Uwe Selig, Ursula Siebert, Nardine Stybel

Chapter 15. Bio-optical water quality assessment

Abstract

The colour of the sea, i.e. its spectral reflectance, depends on the absorbing and scattering properties of substances in the water.

The main optical in-water constituents are chlorophyll a (Chl a), coloured dissolved organic matter (CDOM) and suspended particulate matter (SPM).

Optical data can be obtained from sensors deployed into the water or by remote sensing imagers on aircrafts or satellites.

With remote sensing, the optical properties of large geographical areas can be surveyed with high temporal and spatial resolution.

Chl a can be used as a proxy of phytoplankton biomass, CDOM as a marker of terrestrial freshwater and decay processes of marine primary producers and SPM as an indicator of land runoff and wind-driven resuspension of sediments.

Remote sensing of Chl a, CDOM and SPM can assist in the evaluation of water quality, e.g. the state of eutrophication, the extent of freshwater runoff, the depth of the photic zone and the breadth of the coastal zone.

The bio-optical characteristics of the brackish Baltic Sea differ from those of other seas. Due to the large overall freshwater influence, CDOM is usually the dominant optical in-water constituent not only near river discharges, but also in the open waters of the Baltic Sea.

The CDOM concentrations in the open waters of the Baltic Sea are inversely related to the large-scale Baltic Sea salinity gradient, with CDOM absorption highest in the northern Baltic Sea and lowest in the southwestern Baltic Sea.

Due to the high CDOM absorption regional Baltic Sea algorithms are required to derive water quality parameters that can be used as indicators of ecosystem health.

Susanne Kratzer, Piotr Kowalczuk, Sławomir Sagan

Chapter 16. Chemical pollution and ecotoxicology

Abstract

Baltic Sea organisms appear to be particularly sensitive to persistent hazardous substances because many of them are physiologically stressed in their brackish-water environment.

The profile of chemical pollution of the Baltic Sea has changed during the past decades with reductions in the concentrations of many “legacy contaminants” such as DDTs, PCBs, dioxins and trace metals. However, many of these compounds degrade very slowly and their concentrations are still unacceptably high.

Radionuclides from the Chernobyl nuclear power plant accident still contaminate the Baltic Sea but are slowly returning to pre-Chernobyl levels.

The growing oil tankers traffic is increasing the risk of major oil spills in the Baltic Sea. In addition, dumped chemical weapons on the seafloor are likely to leak due to corrosion.

An increasing amount of “contaminants of emerging concern”, e.g. industrial chemicals, pharmaceuticals and ingredients of personal care products, most of them with unknown toxicity and environmental behaviour, ends up in the Baltic Sea.

Standardised biotests are widely used to examine the quality of water and sediments, but despite their usefulness in this context they often lack ecological relevance.

The term “biomarker” is used for a distinctive biological or biologically derived indicator (e.g. gene expression, enzyme activity, imposex, behaviour, growth, reproduction) of exposure to or effects of hazardous substances in the environment.

Biomarkers can be used to assess the effects of hazardous substances in organisms from different trophic levels. They allow rapid detection of potential toxic exposure and damage by providing information on the actual health status of organisms, including the effects of non-bioaccumulative substances and mixture toxicity. A major challenge remains in linking biomarker responses observed in field-collected organisms to effects at the population and community levels.

The accelerating climate change is expected to cause alterations in the bioavailability and toxicity of chemicals and their spread in the ecosystem due to changing environmental conditions.

Kari K. Lehtonen, Anders Bignert, Clare Bradshaw, Katja Broeg, Doris Schiedek

Chapter 17. Ecosystem health

Abstract

Humans have inhabited the Baltic Sea drainage area for thousands of years, but only in recent decades have the impacts from anthropogenic activities surpassed what could be considered sustainable levels from a Baltic Sea ecosystem perspective.

Human-induced degradation of the health of the Baltic Sea ecosystem accelerated in the 1950s.

Assessments of the ecosystem state in the 2000s have shown that anthropogenic pressures, which impair the overall ecosystem health are currently present in all parts of the Baltic Sea.

The major anthropogenic pressures that have contributed to impoverished biodiversity in the Baltic Sea comprise eutrophication, chemical contamination by hazardous substances and overfishing.

Ecosystem regime shifts took place in the Baltic Sea in the late 20th century, primarily due to hunting, fishing and eutrophication, in combination with changes in climatic conditions.

Some of the anthropogenic impacts, such as local sewage pollution, contamination by organochlorines and some mammal and bird population declines due to toxins and hunting, have largely been alleviated.

However, widespread eutrophication that is evident through bottom hypoxia and shifts in biodiversity is still likely to pose great challenges for the management of the Baltic Sea in the near future.

After many decades of scientific research, environmental assessments and political negotiations, international legislation and regional cooperation are currently in force to bring the Baltic Sea ecosystem into a healthier state than it is today.

Maria Laamanen, Samuli Korpinen, Ulla Li Zweifel, Jesper H. Andersen

Chapter 18. Ecosystem goods, services and management

Abstract

Humans are an imperative component of the Earth’s ecosystems as we transform them to meet our economic and cultural needs.

Seas and oceans contribute to the local, regional and global development of human society. The downside of this development is environmental deterioration resulting from increasing competition for sea space and coastal areas between different and conflicting interests.

Natural environmental stressors are exacerbated by anthropogenic pressures in the drainage areas of all aquatic systems. The interplay of such pressures is particularly pronounced in semi-enclosed seas such as the Baltic Sea, which are often multi-use and multi-stakeholder areas.

The ecosystem goods and services offered by the Baltic Sea can be classified as provisioning (resources obtained by exploitation for e.g. human food), regulating (direct natural regulation processes, e.g. gas and climate regulation), cultural (non-material benefits, e.g. recreation) and supporting (processes necessary to sustain the other goods and services, e.g. primary production).

The management of the Baltic Sea ecosystem has its success stories, such as regulations for the exploitation of living resources and discharges of hazardous substances. It also has its failures, eutrophication management being perhaps the most evident one.

Trans-national networking and cross-border cooperation are crucial for improving the health of the Baltic Sea ecosystem. This is not always easy because the different countries around the Baltic Sea experience different social constraints.

The large-scale anthropogenic pressures on the Baltic Sea can only be dealt with by ecosystem-based management (EBM). EBM is an integrated approach to management that considers the entire ecosystem, including humans, and aims to maintain the sustainable supply of ecosystem goods and services by keeping the ecosystem in a healthy, productive and resilient condition.

Marine spatial planning (MSP) may be the vehicle for scientific knowledge to inform and influence decision-making.

Jan Marcin Węsławski, Eugeniusz Andrulewicz, Christoffer Boström, Jan Horbowy, Tomasz Linkowski, Johanna Mattila, Sergej Olenin, Joanna Piwowarczyk, Krzysztof Skóra

Backmatter

Titel: Biological Oceanography of the Baltic Sea
herausgegeben von: Pauline Snoeijs-Leijonmalm
Hendrik Schubert
Teresa Radziejewska
Verlag: Springer Netherlands
Electronic ISBN: 978-94-007-0668-2
Print ISBN: 978-94-007-0667-5
DOI: https://doi.org/10.1007/978-94-007-0668-2