Development and fate of Eutreptiella gymnastica bloom in nutrient-enriched enclosures in the coastal Baltic Sea

Response of the phytoplankton community to bottom-up (nutrients,organic carbon source) and top-down (fish) manipulations, bothsingly and together, were studied daily during a 3 week periodin July 1993 by using eight 50 m³ mesocosms in the coastal northernBaltic Sea. Nutrient additions (once per week) invoked a seriesof blooms of Eutreptiella gymnastica Throndsen (Euglenophyceae)(up to 13 x 10³ cells ml^–1) which formed the major part(60–90%) of the total autotrophic biomass. After rapiddepletion of nutrients (2–3 days) from the surface layer(0–6 m) downwards migration and a subsequent peak of E.gymnasticain the lower part of the water columns (6–12 m) followed.Settled material collected from the bottom of the enclosurescontained a considerable amount of E.gymnastica cells and restingcysts. Nevertheless, sinking loss rates of E.gymnastica wereestimated to be less than 1% day^–1 of the suspended cellnumbers. The fate of E.gymnastica blooms was estimated to begrazing through mesozooplankton. However, provided the nutrientsare plentiful in the water column, the growth potential of E.gymnasticaappears to exceed the ambient grazing pressure. If the nutrientsbecome depleted, it seems to be effectively controlled by mesozooplanktongrazing, which is probably limiting the likelihood of massiveE.gymnastica blooms in the coastal Baltic Sea. Our study suggeststhat E.gymnastica appears to be a fast-growing fugitive (bloom)species with flexible behavioural (vertical migration) and lifehistory (cyst formation) adaptations which is able to exertdominant role and direct trophic relations similar to otherbloom species adapted for decaying turbulence and high nutrientenvironments.     

Succession and soil development in man-made coastal ecosystems at the Baltic Sea

By the creation of Køge Bay Seaside Park in 1978 the opportunity was given to study the establishment of vegetation and primary succession in a man-made coastal area. As the soil consists of marine material from the Baltic Sea, no organic matter or seedbank was present. The first steps of primary succession were followed in 1980, when the initial inventories of flora immigration and soil development were carried out in coastal grasslands and plantings. The surveys were repeated in 1992 and 1993. Except for the planted woody species and a few sown grasses, all other species of plants have reached the area through natural dispersal of diaspores. The total number of species in the permanent plots has increased from 26 in 1980 to 91 in 1993. The results indicate that this number will continue to increase in the coming years until a certain level. Then it will probably decrease as a result of competition from woody species, unless the vegetation is kept in a steady state by disturbances or management. Today the area is very far from the initial situation, and the off-shore barrier has changed towards a landscape dominated by small groves and grasslands of an urban common type.     

Soil microbial biomass and the fate of phosphorus during long-term ecosystem development

Background

Soil phosphorus availability declines during long-term ecosystem development on stable land surfaces due to a gradual loss of phosphorus in runoff and transformation of primary mineral phosphate into secondary minerals and organic compounds. These changes have been linked to a reduction in plant biomass as ecosystems age, but the implications for belowground organisms remain unknown.

Methods

We constructed a phosphorus budget for the well-studied 120,000 year temperate rainforest chronosequence at Franz Josef, New Zealand. The budget included the amounts of phosphorus in plant biomass, soil microbial biomass, and other soil pools.

Results

Soil microbes contained 68–78 % of the total biomass phosphorus (i.e. plant plus microbial) for the majority of the 120,000 year chronosequence. In contrast, plant phosphorus was a relatively small pool that occurred predominantly in wood. This points to the central role of the microbial biomass in determining phosphorus availability as ecosystems mature, yet also indicates the likelihood of strong competition between plants and saprotrophic microbes for soil phosphorus.

Conclusions

This novel perspective on terrestrial biogeochemistry challenges our understanding of phosphorus cycling by identifying soil microbes as the major biological phosphorus pool during long-term ecosystem development.     

Effects of subsidized spiders on coastal food webs in the Baltic Sea area

The aim of this study was to examine top-down effects of cursorial spiders in subsidized coastal food webs. Top-down effects were examined by selectively removing cursorial spiders, mainly wolf spiders, from small islands (26–1834 m²) during 2004–2007. The removal success varied among islands and years, and spider densities were reduced by 30–65%. To examine treatment effects, arthropods were sampled using a vacuum sampling device at three occasions each summer. The densities of other arthropod predators, especially web spiders and carabids, were higher on islands where cursorial spiders had been removed compared to control islands. This treatment effect probably occurred through a combination of competitive release and reduced intraguild predation from cursorial spiders. No treatment effects were found on herbivore or detritivore densities and plant biomass. This lack of effect may either be because spiders indeed have fairly weak effects on herbivore and detritivore densities on Baltic shorelines or that the removal success of spiders was insufficient for observing such effects. Treatment effects may also be weak because negative effects exerted by spiders on herbivore and detritivore populations were balanced by increased predation by insect predators.     

Temporal and spatial variation of coastal zooplankton in the Baltic Sea

When analysing temporal variation monthly mean abundances of zooplankton sampled at a eoastal station in the northern Baltic Sea between 1976 and 1988 showed the lowest between-year variation in the summers The coefficients of variation were estimated at 50% for rotifers in June. 70% for cladocerans in August and between 30 and 50% for different copepodite stages in August Moreover in the summers, all dominating zooplankton groups were abundant Estimates of yearly biomass or production of zooplankton must, however, be based on frequent sampling during the whole year because of large differences between months in zooplankton composition and abundance
In 1989. spatial variation was analyzed by sampling zooplankton on three occasions along a 9 8 km transect with 15 stations, 700 m apart All taxonomic/life-stage groupings of zooplankton were heterogeneously distributed Geostatistical analysis did not give a definite answer to what the minimum distance between stations should be to obtain independent samples but indicated that 700 to 1400 m would be sufficient in most cases For most of the zooplankton groupings the coefficients of variation in the sampled area were estimated at 20-40% on all sampling occasions     

Community development and modes of phosphorus utilization in a late summer ecosystem in the central Gulf of Finland, the Baltic Sea

The development of a filamentous, nitrogen-fixing cyanobacterial bloom was followed during July–August 1990 in a stratified basin in the central Gulf of Finland, Baltic Sea. Hydrography, dissolved inorganic, particulate and total nutrients, chlorophyll a, alkaline phosphatase activity, ³²PO₄-uptake and phytoplankton species were measured. The study period was characterized by wind-induced mixing events, followed by marked nutrient pulses and plankton community responses. Phosphate uptake was highest throughout the study period in the size fraction dominated by bacteria and picocyanobacteria (< 2 µm) and the proportion of uptake in the size fraction 2–10 µm remained low (2–6%). Higher phosphate turnover times were observed in a community showing signs of enhanced heterotrophic activity. The bloom of filamentous, nitrogen-fixing cyanobacteria Aphanizomenon flos-aquae was promoted by a nutrient pulse with an inorganic nutrient ratio (DIN:DIP) of 15. The results show that the quality, frequency and magnitude of the physically forced nutrient pulses have an important role in determining the relative share of the different modes of phosphorus utilization and hence in determining the cyanobacterial bloom intensity and species composition in the Baltic Sea.     

Zoobenthic diversity-gradients in the Baltic Sea: Continuous post-glacial succession in a stressed ecosystem

The Baltic Sea, formed after the latest glaciation, is an enclosed, low-saline, non-tidal ecosystem and has steep latitudinal and vertical gradients from sub-arctic conditions in the north to temperate in the south. The sea has undergone rapid changes since the glaciation, and the “ecological age” of the present ecosystem is only about 8000 years. Primary successional processes are still ongoing, and numerous ecological niches (e.g. large-bodied sediment bioturbators) remain available for immigration. The system is species-poor and vulnerable to the threat of exotic invasive species, and to date about 50 zoobenthic species have established populations in the Baltic Sea. The present biota is a mixture of species of different ecological and zoogeographical origin (marine to limnic; northern Arctic marine and limnic, to North Sea and Atlantic marine). The current distribution patterns of zoobenthos are illustrated, using marine, limnic and non-indigenous examples of structure and ecosystem functions. The species richness decreases from over 1600 marine benthic species in the open Skagerrak to about 500 in the western parts of the Baltic Sea, approximately 80 in the southern regions, to less than 20 in the northern regions. On the other hand, limnic species increase diversity in the inner reaches of the Gulf of Finland and the Gulf of Bothnia. Polychaetes, molluscs and echinoderms are dramatically reduced in numbers from the south to the north.     

Life on the margin: genetic isolation and diversity loss in a peripheral marine ecosystem, the Baltic Sea

Marginal populations are often isolated and under extreme selection pressures resulting in anomalous genetics. Consequently, ecosystems that are geographically and ecologically marginal might have a large share of genetically atypical populations, in need of particular concern in management of these ecosystems. To test this prediction, we analysed genetic data from 29 species inhabiting the low saline Baltic Sea, a geographically and ecologically marginal ecosystem. On average Baltic populations had lost genetic diversity compared to Atlantic populations: a pattern unrelated to dispersal capacity, generation time of species and taxonomic group of organism, but strongly related to type of genetic marker (mitochondrial DNA loci had lost c. 50% diversity, and nuclear loci 10%). Analyses of genetic isolation by geographic distance revealed clinal patterns of differentiation between Baltic and Atlantic regions. For a majority of species, clines were sigmoid with a sharp slope around the Baltic Sea entrance, indicating impeded gene flows between Baltic and Atlantic populations. Some species showed signs of allele frequencies being perturbed at the edge of their distribution inside the Baltic Sea. Despite the short geological history of the Baltic Sea (8000 years), populations inhabiting the Baltic have evolved substantially different from Atlantic populations, probably as a consequence of isolation and bottlenecks, as well as selection on adaptive traits. In addition, the Baltic Sea also acts a refuge for unique evolutionary lineages. This marginal ecosystem is thus vulnerable but also exceedingly valuable, housing unique genes, genotypes and populations that constitute an important genetic resource for management and conservation.     

Origin and fate of dissolved organic matter in four shallow Baltic Sea estuaries

Coastal waters have strong gradients in dissolved organic matter (DOM) quantity and characteristics, originating from terrestrial inputs and autochthonous production. Enclosed seas with high freshwater input therefore experience high DOM concentrations and gradients from freshwater sources to more saline waters. The brackish Baltic Sea experiences such salinity gradients from east to west and from river mouths to the open sea. Furthermore, the catchment areas of the Baltic Sea are very diverse and vary from sparsely populated northern areas to densely populated southern zones. Coastal systems vary from enclosed or open bays, estuaries, fjords, archipelagos and lagoons where the residence time of DOM at these sites varies and may control the extent to which organic matter is biologically, chemically or physically modified or simply diluted with transport off-shore. Data of DOM with simultaneous measurements of dissolved organic (DO) nitrogen (N), carbon (C) and phosphorus (P) across a range of contrasting coastal systems are scarce. Here we present data from the Roskilde Fjord, Vistula and Öre estuaries and Curonian Lagoon; four coastal systems with large differences in salinity, nutrient concentrations, freshwater inflow and catchment characteristics. The C:N:P ratios of DOM of our data, despite high variability, show site specific significant differences resulting largely from differences residence time. Microbial processes seemed to have minor effects, and only in spring did uptake of DON in the Vistula and Öre estuaries take place and not at the other sites or seasons. Resuspension from sediments impacts bottom waters and the entire shallow water column in the Curonian Lagoon. Finally, our data combined with published data show that land use in the catchments seems to impact the DOC:DON and DOC:DOP ratios of the tributaries most.

     

Seasonal and short-term variation in denitrification and anammox at a coastal station on the Gulf of Finland,Baltic Sea

Benthic processes were measured at a coastal deposition area in the northern Baltic Sea, covering all seasons. The N₂ production rates, 90–400 μmol N m⁻² d⁻¹, were highest in autumn-early winter and lowest in spring. Heterotrophic bacterial production peaked unexpectedly late in the year, indicating that in addition to the temperature, the availability of carbon compounds suitable for the heterotrophic bacteria also plays a major role in regulating the denitrification rate. Anaerobic ammonium oxidation (anammox) was measured in spring and autumn and contributed 10% and 15%, respectively, to the total N₂ production. The low percentage did, however, result in a significant error in the total N₂ production rate estimate, calculated using the isotope pairing technique. Anammox must be taken into account in the Gulf of Finland in future sediment nitrogen cycling research. Handling editor: J. Cole     

Methodological challenges in assessing the environmental status of a marine ecosystem: case study of the Baltic Sea

Assessments of the environmental status of marine ecosystems are increasingly needed to inform management decisions and regulate human pressures to meet the objectives of environmental policies. This paper addresses some generic methodological challenges and related uncertainties involved in marine ecosystem assessment, using the central Baltic Sea as a case study. The objectives of good environmental status of the Baltic Sea are largely focusing on biodiversity, eutrophication and hazardous substances. In this paper, we conduct comparative evaluations of the status of these three segments, by applying different methodological approaches. Our analyses indicate that the assessment results are sensitive to a selection of indicators for ecological quality objectives that are affected by a broad spectrum of human activities and natural processes (biodiversity), less so for objectives that are influenced by a relatively narrow array of drivers (eutrophications, hazardous substances). The choice of indicator aggregation rule appeared to be of essential importance for assessment results for all three segments, whereas the hierarchical structure of indicators had only a minor influence. Trend-based assessment was shown to be a useful supplement to reference-based evaluation, being independent of the problems related to defining reference values and indicator aggregation methodologies. Results of this study will help in setting priorities for future efforts to improve environmental assessments in the Baltic Sea and elsewhere, and to ensure the transparency of the assessment procedure.     

Development of a phytoplankton indicator system for the ecological assessment of brackish coastal waters (German Baltic Sea coast)

The implementation of the European Water Framework Directive (WFD) requires the development of ecologically-based classification systems for anthropogenically-induced eutrophication in all types of water bodies. Due to the inherent high temporal and spatial variability of hydrological and geochemical parameters of the coastal waters of the southern Baltic Sea, discrimination between anthropogenic impact and natural variability is necessary. The development of statistical methods for this discrimination was the main aim of this study. These methods were used to derive indicative phytoplankton parameters for different stages of eutrophication for the investigation area. For this purpose, a long-term phytoplankton data series was analysed, which covered a broad salinity and eutrophication gradient. In order to detect eutrophication effects, the analysis was restricted to phytoplankton spring bloom events and to the salinity range between 5 and 10 psu, i.e. superimposing seasonal and hydrodynamic effects were eliminated. An artificial abiotic degradation vector was developed based on four typical water quality parameters. A total of 11 potentially indicative phytoplankton parameters on different taxonomical levels arose from a correlation analysis with this degradation vector. These indicators were then tested for their ability to discriminate between three eutrophication levels. Finally, seven phytoplankton indices could be proposed: total phytoplankton biovolume, the percentage of diatoms and the biovolume of different size ranges of diatoms and one indicative species (Woronichinia compacta). Guest editors: A. Razinkovas, Z. R. Gasiūnaitė, J. M. Zaldivar & P. Viaroli European Lagoons and their Watersheds: Function and Biodiversity     

Provision of aquatic ecosystem services as a consequence of societal changes: The case of the Baltic Sea

Aquatic ecosystem services are important for human wellbeing, but they are much less studied than terrestrial ecosystem services. The objectives of this study are to broaden, itemize and exemplify the human-nature interactions in modeling the future provision of aquatic ecosystem services. We include shared socioeconomic and representative concentration pathways, used extensively in climate research, as drivers of change for the future development of the Baltic Sea. Then we use biogeochemical and ecosystem models to demonstrate the future development of exemplary supporting, provisioning and cultural ecosystem services for two distinct combinations of regionally downscaled global climate and socioeconomic futures. According to the model simulations, the two global futures (“Sustainable well-being” vs. “Fossil-fuelled development”) studied lead to clearly deviating trajectories in the provision of marine ecosystem services. Under the “Sustainable well-being”-scenario primary production decreases by 20%, catches of demersal fish increases and the recreation opportunities increase significantly by the end of the ongoing century. Under the “fossil-fuelled development”-scenario primary production doubles, fisheries focus on less valued pelagic fish and the recreation possibilities will decrease. Long-term projections of aquatic ecosystem services prepared for alternative global socioeconomic futures can be used by policy makers and managers to adaptively and iteratively adjust mitigation and adaptation effort with plausible future changes in the drivers of water pollution.     

Selective predation by herring and mysids, and zooplankton community structure in a Baltic Sea coastal area

In lakes, fish and invertebrate predation are recognized asstrong structuring forces on zooplankton communities. The objectof this investigation was to study whether predation has a similarpotential in a coastal area of the brackish Baltic Sea and ifit could explain observed differences in zooplankton communitystructure between a reference area and an eutrophied area. Speciescomposition and daily vertical migration of zooplankton andzooplanktivores, and the diets of the latter, were studied inJuly and August at two 30 m deep stations differing in primaryproductivity. The biomass of zooplankton >35 µm wasdominated by copepods, but cladocerans and rotifers also occurredin significant numbers. The dominating zooplanktivores wereherring (Clupea harengus) and the mysid shrimp Mysis mixta.They fed almost exclusively on zooplankton, mainly copepods,and their estimated food consumption equalled or exceeded thesummer copepodite production. The structure of the zooplanktoncommunity cannot be explained by effects of predation or byfeeding conditions alone. Increases in rotifer and cladoceranabundances with increased primary production suggests effectsof food supply. However, a generally rapid decline in the annualsummer peak of cladocerans may be caused by predation. The totalabundance of copepods did not increase with improved feedingconditions, but there was a shift in species dominance. Thecopepod Ewytemora affinis hirundoides, which was intensivelypreyed upon, increased with increased phytoplankton production,while Acartia bifilosa and/or A.longiremis, which was less eaten,decreased. Predation may explain a pronounced daily verticalmigration of the most predated copepods. They occurred in deeperwater during the day, when the visually feeding herring wereactive, and moved closer to the surface at night when M.mixtaleft the bottom, to forage in the water column.     

Ecological classification of macroalgae and angiosperm communities of inner coastal waters in the southern Baltic Sea

A classification system of macroalgae and angiosperms for the inner coastal waters of the Baltic coast of Mecklenburg-Vorpommern (Germany) was developed according to the guidelines of the European Water Framework Directive. These guidelines ask for a five-step classification scheme (high, good, moderate, poor, bad) of the ecological state based on submerged macrophytes.The approach is based on the comparison of the occurrence and distribution of plant communities in 1999–2003 with historical data of submerged macrophytes and their community structure. Due to the lack of appropriate data, historical depth distribution limits of plant communities were calculated based on modelled historical underwater light climate.Despite the fact of very heterogeneous salinities (0.5–20.0 practical salinity units, psu) and substrate types (silty–sandy) in the study area, two general main criteria were identified as appropriate indicators of eutrophic degradation of the inner coastal waters: (1) the lower distribution depth of plant communities and (2) the loss of charophyte-dominated plant communities. Based on these two criteria, a five-step classification scheme is proposed for the characterisation of the ecological state. The depth limit boundaries between the ecological classes were calculated by 5, 25, 50 and 75% reduction of the water transparency. Based on this calculation, the ecological status is described by the gradual upward shift of the vegetation depth limit. Complementary to the decrease of depth limits the loss of charophyte-dominated plant communities characterises the border between moderate and poor ecological conditions.