Development of fouling communities on vertical structures in the Baltic Sea

The pillars of the bridge connecting the Island of Öland with the Swedish mainland were rebuilt between 1990 and 2000. The renovation produced pristine vertical concrete substrates, which became submerged in known years and seasons. The fouling communities on the pillars were examined in 2001 to determine whether the community structure could be explained in terms of either orderly successional development or of seasonal variation in the settlement of benthic organisms. As well, the communities on the pillars were compared to communities on the vertical surfaces of boulders in the area. The results indicated that an annual species composition is the final stage in the succession on the observed, vertical constructions. The few perennial species add to the variation between pillars as they increase in biomass (Polysiphonia fucoides) or become out-competed (Balanus improvisus). Also, observed seasonal differences in the biomass of these perennial species indicated that the time of year free space becomes available might be an important determinant of the future structure of the community. Comparison between the pillar and boulder communities showed that the artificial structures were not surrogates for the natural hard substrate: pillar communities differed in that they lacked most perennial algal species and had a high biomass of B. improvisus.     

Biomass Size Spectra of Near-Shore Shallow-Water Benthic Communities in the Gulf of Gdańsk Southern Baltic Sea

The concept of size spectra, developed by S heldon & P arsons 1967 and S heldon et al. 1972, seeks to describe community structure by evoking the distribution of biomass over a sequence of equal intervals of the logarithm of body size. In this study, biomass size spectra were prepared for benthic macro- and meiobenthos communities at 5 stations, differing in their sediment characteristics, located in the shallow, coastal area of the Gulf of Gdańsk Southern Baltic Sea. The purpose of this study was to determine whether the community spectra would allow distinct separation of ecological categories of the benthos and whether habitat differences between stations would significantly affect benthic size spectra.
Benthic biomass at the stations sampled depended mainly on nematodes and oligochaetes among the meiobenthos and on hydrobiid snails and M. edulis among the macrobenthos. Regardless of habitat, size spectra peaked initially at the meiofaunal range weight class 25 1. 19–501.19 ng C, identical to that reported in other studies. The separation between meio- and macrobenthic peaks, however, was not as pronounced as that found in other studies. Normalized size spectra demonstrated that most of the variations in the spectra between stations was introduced by macrobenthos, which differed between the coarse- and fine-grained sediments. Nonetheless, those differences were not strong enough to significantly affect the spectra. In consequence, the benthic biomass spectra of all the stations were found to conform to a common pattern and could be represented by a single, average spectrum.     

Effects of water exchange and vegetation on the macroinvertebrate fauna composition of shallow land-uplift bays in the Baltic Sea

Shallow bays with soft sediment bottoms are common habitats along the Swedish and Finnish Baltic Sea coastline. These bays undergo a process of geomorphometric evolution with the natural isostatic land-uplift process, whereby open bays and sounds decrease in depth and are gradually isolated from the sea, forming bays with narrow openings. This study tested the relationship between the morphometric isolation of the bays from the sea and the macroinvertebrate fauna community of these bays. Additionally, we tested the specific role of the submerged vegetation as an indicator of the macroinvertebrate fauna community. We chose two environmental factors for the analyses, water exchange of the bays and the taxon richness of the macroflora in the bays. We found a hierarchical relationship between water exchange, flora taxon richness, and fauna biomass and taxon richness using structural equation modelling: decreased biomass and taxon richness of fauna were related to decreased flora taxon richness, which in turn was related to decreased water exchange. Using multivariate redundancy analysis, the two environmental factors included in the model were found to explain 47.7% of the variation in the fauna taxon composition and 57.5% of the variation in the functional feeding groups of the fauna. Along the morphometric isolation gradient of the bays, the fauna assemblages changed from a community dominated by gastropods, bivalves, and crustaceans, to a community mainly consisting of a few insect taxa. Moreover, the proportion of predators, gathering collectors, and shredders increased while that of filtering collectors and scrapers decreased. Our results indicate that the density and taxon richness of macroinvertebrate fauna are higher in less morphometrically isolated bays than in more isolated bays in the Baltic Sea. Furthermore, we suggest that the taxon richness of macroflora can serve as an indicator of the fauna community.     

Long-term changes in summer phytoplankton communities of the open northern Baltic Sea

Changes in the biomass and species composition of phytoplankton may reflect major shifts in environmental conditions. We investigated relationships between the late summer biomass of different phytoplankton taxa and environmental factors, and their long-term (1979–2003) trends in two areas of the Baltic Sea, the northern Baltic proper (NBP) and the Gulf of Finland (GF), with statistical analyses. An increasing trend was found in late summer temperature and chlorophyll a of the surface water layer (0–10 m) in both areas. There was also a significant decrease in summer salinity and an increase in winter dissolved inorganic nitrogen to phosphorus (DIN:DIP) ratio in the NBP, as well as increases in winter DIN concentrations and DIN:SiO₄ ratio in the GF. Simultaneously, the biomass of chrysophytes and chlorophytes increased in both areas. In the NBP, also the biomass of dinophytes increased and that of euglenophytes decreased, whereas in the GF, cyanobacteria increased and cryptophytes decreased. Redundancy analysis (RDA) indicated that summer temperature and winter DIN concentration were the most important factors with respect to changes in the phytoplankton community structure. Thus, the phytoplankton communities seem to reflect both hydrographic changes and the ongoing eutrophication process in the northern Baltic Sea.     

Trophic Status of the South-Eastern Baltic Sea: A Comparison of Coastal and Open Areas

Primary production, nutrient concentrations, phytoplankton biomass (incl. chlorophyll a) and water transparency (Secchi depth), are important indicators of eutrophication. Earlier basin-wide primary production estimates for the Baltic Sea, a shallow shelf sea, were based mainly on open-sea data, neglecting the fundamentally different conditions in the large river plumes, which might have substantially higher production. Mean values of the period 1993–1997 of nutrient concentrations (phosphate, nitrate, ammonium and silicate), phytoplankton biomass, chlorophyll a (chl a) concentration, turbidity and primary production were calculated in the plumes of the rivers Oder, Vistula and Daugava and Klaipeda Strait as well as the open waters of the Arkona Sea, Bornholm Sea, eastern Gotland Sea and the Gulf of Riga. In the plumes, these values, except for primary production, were significantly higher than in the open waters. N:P ratios in the plumes were >16 (with some exceptions in summer and autumn), indicating potential P-limitation of phytoplankton growth, whereas they were <16 in the open Baltic Proper, indicating potential N-limitation. On the basis of in situ phytoplankton primary production, phytoplankton biomass and nutrient concentrations, the large river plumes and the Gulf of Riga could be characterized as eutrophic and the outer parts of the coastal waters and the open sea as mesotrophic. Using salinity to define the border of the plumes, their mean extension was calculated by means of a circulation model. Taking into account the contribution of coastal waters, the primary production in the Baltic Proper and the Gulf of Riga was 42·6 and 4·3×10⁶ t C yr⁻¹, respectively. Hence, an annual phytoplankton primary production in the whole Baltic Sea was estimated at 62×10⁶ t C yr⁻¹. The separate consideration of the plumes had only a minor effect on the estimation of total primary production in comparison with an estimate based on open sea data only. There is evidence for a doubling of primary production in the last two decades. Moreover, a replacement of diatoms by dinoflagellates during the spring bloom was noticed in the open sea but not in the coastal waters. A scheme for trophic classification of the Baltic Sea, based on phytoplankton primary production and biomass, chl a and nutrient concentrations, is proposed.     

Resuspension patterns in the Baltic proper

Waves induce resuspension of surface sediments and contribute to the long-term mobilisation of particulate matter from erosion to accumulation bottoms. This has a major impact on the nutrient cycle in shallow seas by enhancing degradation, microbial production and recycling. The Baltic Sea represents such an area. The aim of this work is to analyse the spatial and temporal resuspension patterns in the Baltic Sea. To estimate the bottom friction velocity, modelled wave data are used in combination with data on grain size. This new data set is compared to a resuspension threshold of friction velocity to estimate the events of resuspension.The variation in bottom friction velocity, resuspension frequency and duration are related to wind climate, fetch, water depth and sediment type. Substantial resuspension can be found down to 40–60 m, with durations from one day to as much as two weeks. The highest winds in the area are highly anisotropic with a dominance of S-SW-W winds and the highest resuspension frequencies are found along the shallow eastern coasts. A seasonal pattern is observed with relatively high friction velocities and high resuspension frequencies during winter. There is also a variation depending on grain size, where sediments with fine and medium sand have a considerably higher percentage of resuspension events than bottoms with other dominant grain sizes. Five sub-areas are identified, characterised by different sediment types, resuspension and wind characteristics. If, in the future, wind speed increases as predicted, resuspension of sediments will also increase with effects on the nutrient cycle.     

Effects of eelgrass (Zostera marina) canopy removal and sediment addition on sediment characteristics and benthic communities in the Northern Baltic Sea

The eelgrass Zostera marina is a key structural and functional species across the European coastline. The separate and interactive effects of eelgrass canopy removal and sediment addition on the sediment characteristics and the structure of benthic communities were studied in a factorial field experiment in the Northern Baltic Sea in July–August 2006. The removal of eelgrass canopy temporarily increased the sediment oxygen consumption, reduced the content of fine particles (<100 μm) and organic matter in the sediment, and increased the share of sand fraction (250–500 μm). Sediment addition increased the content of fine particles (<100 μm) and reduced the share of sand fraction (250–1000 μm). The effects were strongest in the presence of eelgrass canopy. Benthic invertebrates and macroalgae were affected by eelgrass canopy removal but not by sediment addition. The removal of eelgrass canopy significantly decreased benthic species richness and invertebrate and macroalgal densities. To conclude, our experiment demonstrates that Z. marina defines the patterns of benthic macroalgae and invertebrates but has moderate effects on sediment structure and metabolism in the Northern Baltic Sea.     

Using Mean Sea Surface Topography for Determination of Height System Differences across the Baltic Sea

The mean sea surface topography in the Baltic Sea and adjacent waters is reliably known in the Nordic height system NH 60. Using this knowledge we estimate differences between NH 60, based on the Amsterdam zero point, and Russian, Polish, and German height systems along the southeastern coast of the Baltic Sea, based on the Kronstadt zero point. The differences agree within a few centimeters. We also make a simple study of the mean sea level difference between Kronstadt and Amsterdam (which is found to have been approximately 25 cm when sea level was still to be seen there).     

A note on the economics of Swedish Baltic Sea fisheries

The cod stocks in the Baltic Sea are important not only for fisheries but for the entire ecosystem utilized by numerous stakeholders around the coast. All such activities have economic values. In this note the economics of the Swedish Baltic Sea cod fishery is estimated in relation to the sector's interaction with other users of the Baltic Sea ecosystem. The results show a negative resource rent for the fishery, € −5 million without public expenses (subsidies and administrative costs), and € −13 million including public expenses. The interactions between the fisheries and tourism, seal population, carbon dioxide emissions, recreational fishing, and discards are discussed, and when monetary estimates are available these are related to the estimated resource rent.     

Variations in the Baltic Sea wave fields

The surface waves in the Baltic Sea are hindcast with the spectral wave model HYPAS during a 12-month period. The model results show a strong temporal and spatial variation in the wave field due to the physical dimensions of the different basins and the predominant wind field. The highest waves in the area are found in the outer part of Skagerrak, as well as in the central and southern parts of the Baltic Proper. To get significant waves above 6 m high, strong winds (15–20 m/s) must have been blowing for 6 to 24 h from a favourable direction over a deep area.     

Anisotropy of wind and wave regimes in the Baltic proper

The directional distribution of moderate and strong winds in the Baltic Sea region is shown to be strongly anisotropic. The dominating wind direction is south-west and a secondary peak corresponds to north winds. North-west storms are relatively infrequent and north-east storms are extremely rare. Angular distribution of extreme wind speed also has a two-peaked shape with maxima corresponding to south-west and north winds, and a deep minimum for easterly winds. The primary properties of the anisotropy such as prevailing winds, frequency of their occurrence, directional distribution of mean and maximum wind speeds coincide on both sides of the Baltic proper. The specific wind regime penetrates neither into the mainland nor into the Gulf of Finland or the Gulf of Riga.Properties of the saturated wave field in the neighbourhood of proposed sites of the Saaremaa (Ösel) deep harbour are analysed on the basis of the wave model WAM forced by steady winds. The directional distribution of wave heights in typical and extreme storms is highly anisotropic. Remarkable wave height anomalies may occur in the neighbourhood of the harbour sites.     

Ecological consequence of the introduction of the polychaete Marenzelleria cf. viridis into a shallow-water biotope of the northern Baltic Sea

Effects of the North American polychaete Marenzelleria cf. viridis on a simple shallow-water benthic community of the northern Baltic Sea were studied in a field experiment combining natural densities of dominating macrofaunal species. The presence of M. cf. viridis increased benthic production (chlorophyll a) and reduced the survival of the native polychaete Nereis diversicolor. Adult Macoma balthica caused a significant mortality on M. cf. viridis whereas adult Cerastoderma glaucum had no effect on M. cf. viridis. We suggest that the competitive interactions between M. cf. viridis and M. balthica are a possible key factor determining the distribution pattern of M. cf. viridis in the Baltic Sea.     

The Baltic Sea environment and the European Union: Analysis of governance barriers

The EU enlargement brought the Baltic Sea into the sphere of EU environmental policymaking, making the sea, with the exception of Russia, an EU inland sea. Yet, the state of the Baltic Sea environment is deteriorating at an alarming pace. This paper describes the evolution of the EU governance of the Baltic Sea environment, focussing on governance barriers. The findings demonstrate how the choice of analytical lens influences the construction of governance barriers and the respective intervention strategies. Such understanding can help policy practitioners in their search for successful measures to improve the governance situation in the Baltic Sea region.     

Activity Concentrations and Fluxes of Radiocesium in the Southern Baltic Sea

The activity concentrations of dissolved¹³⁷Cs have been determined in the water column and¹³⁷Cs and¹³⁴Cs in the sediments and the sediment porewaters of the southern Baltic Sea. The mean activity concentration of dissolved¹³⁷Cs in the Gdansk Deep declined from 109 Bq m⁻³in June 1986 to 61 Bq m⁻³in 1999. In sediments, the activity concentrations of¹³⁷Cs (33-231 Bq kg⁻¹) were highest in muds and the activity concentrations of¹³⁴Cs were about 6% of the total Cs activity. The Chernobyl contribution to¹³⁷Cs activity was between 43% and 77%. The porewater activity concentrations of¹³⁷Cs in muddy sediments were in the range 71 to 3900 Bq m⁻³and were higher than those in the overlying seawater. The diffusive flux of dissolved¹³⁷Cs from the muddy sediments was estimated in the range 5 to 480 Bq m⁻²year⁻¹. The flux of¹³⁷Cs from sediment porewaters of the southern Baltic Sea was about 45% of the total, including fluxes of¹³⁷Cs from wet and dry atmospheric deposition and the fluvial inputs. The results were used to elucidate the rate of recovery of the sediments and the waters of the southern Baltic from Chernobyl-derived¹³⁷Cs.     

Changes in the Composition of the Diatom Flora During the Last Century Indicate Increased Eutrophication of the Oder Estuary, South-western Baltic Sea

Four short sediment cores from the Oder estuary, south-western Baltic Sea, were studied with respect to their siliceous microfossil and organic carbon content. The sediments were dated by²¹⁰Pb. The objective was to detect and date changes in the composition of the diatom flora and link these changes to increased human impact in the drainage area during recent centuries. Two of the cores showed an unperturbed sedimentary sequence representing a complete historical record. A change in the composition of the diatom assemblages attributable to anthropogenic factors was recorded. This was dated to about 1900 in the Oderhaff. The change consisted of an increase in species that thrive in eutrophic waters and those indicating increased salinity or the availability of inorganic nutrients.     

Photochemical production of ammonium and transformation of dissolved organic matter in the Baltic Sea

The release of ammonium from the photochemical degradation of dissolved organic matter (DOM) has been proposed by earlier studies as a potentially important remineralisation pathway for refractory organic nitrogen. In this study the photochemical production of ammonium from Baltic Sea DOM was assessed in the laboratory. Filtered samples from the Bothnian Bay, the Gulf of Finland and the Arkona Sea were exposed to UVA light at environmentally relevant levels, and the developments in ammonium concentrations, light absorption, fluorescence and molecular size distribution were followed. The exposures resulted in a decrease in DOM absorption and loss of the larger sized fraction of DOM. Analysis of the fluorescence properties of DOM using parallel factor analysis (PARAFAC) identified 6 independent components. Five components decreased in intensity as a result of the UVA exposures. One component was produced as a result of the exposures and represents labile photoproducts derived from terrestrial DOM. The characteristics of DOM in samples from the Bothnian Bay and Gulf of Finland were similar and dominated by terrestrially derived material. The DOM from the Arkona Sea was more autochthonous in character. Photoammonification differed depending on the composition of DOM. Calculated photoammonification rates in surface waters varied between 121 and 382 μmol NH₄⁺ L^− 1 d^− 1. Estimated areal daily production rates ranged between 37 and 237 μmol NH₄⁺ m^− 2 d^− 1, which are comparable to atmospheric deposition rates and suggest that photochemical remineralisation of organic nitrogen may be a significant source of bioavailable nitrogen to surface waters during summer months with high irradiance and low inorganic nitrogen concentrations.     

One hundred years of hydrographic measurements in the Baltic Sea

The first measurements of salinity of the deep water in the open Baltic Sea were made in the last decades of the 1800s. At a Scandinavian science meeting in Copenhagen in 1892, Professor Otto Pettersson from Sweden suggested that regular measurements of hydrographic parameters should be carried out at some important deep stations in the Baltic Sea. His suggestion was adopted and since that time we have rather complete hydrographical data from the Bornholm Deep, the Gotland Deep, and the Landsort Deep and from some stations in the Gulf of Bothnia. The measurements were interrupted in the Baltic Proper during the two World Wars. At the beginning only salinity, temperature and dissolved oxygen were measured and one or two expeditions were carried out annually, mostly in summer. In the 1920s also alkalinity and pH were occasionally measured and total carbonate was calculated. A few nutrient measurements were also carried out. After World War II we find results from four or more expeditions every year and intercalibration of methods was arranged. Results of temperature, salinity and dissolved oxygen measurements from the Bornholm Deep, the Gotland Deep, the Landsort Deep and salinity measurements from three stations in the Gulf of Bothnia, covering the whole 20th century are presented and discussed. The salinity distribution and the variations between oxygen and hydrogen sulphide periods in the deep water of the Gotland Deep and the Landsort Deep are demonstrated. Series of phosphate and nitrate distribution in the Gotland Deep are shown from the 1950s to the present and the effects of the stagnant conditions are briefly discussed. Two large inflows of highly saline water, the first during the First World War and the second in 1951, are demonstrated. The 20th century minimum salinity of the bottom water in the Baltic Proper in 1992 is discussed.