Bornholm Sea Research Articles

Complete Genome Sequences of Chesapeake Bay Synechococcus Strains CBW1002 and CBW1006 Isolated in Winter.

Synechococcus are picocyanobacteria with a cosmopolitan distribution. They are capable of surviving in a wide variety of environmental conditions. Synechococcus have been isolated from the Chesapeake Bay during winter months, and they show an impressive tolerance to cold temperatures. Cold-adapted Synechococcus are unique and diverse, as they have complex phylogenetic lineages closely related to subalpine cluster II, Bornholm Sea cluster, CB7 cluster, and some novel lineages which are independent from summer estuarine strains in subcluster 5.2. CBW1002 and CBW1006 are the first complete genomes to represent Bornholm Sea cluster Synechococcus strains. They have some of the largest genomes among the Synechococcus (3.8 Mb) and share many unique and cryptic homologs which could give insight into their ability to tolerate such cold and dynamic conditions in the Chesapeake Bay estuary.

First evidence of spawning of eastern Baltic cod (Gadus morhua callarias) in the Belt Sea, the main spawning area of western Baltic cod (Gadus morhuaL.)

Two cod stocks (western Baltic cod, WBC, and eastern Baltic cod, EBC) are managed in the Baltic Sea which is characterized by different main spawning areas and different main spawning periods. In this study we analyse the spatial and temporal occurrence of spawning individuals of both cod stocks in the main spawning grounds of the Baltic Sea based on eight microsatellite loci. Our results suggest that EBC (Gadus morhua callarias) has formed currently temporally stable, substantially homogeneous population not only in the Bornholm Sea (ICES SD: 25) but also in the Arkona Sea (ICES SD: 24). The presented analyses proved that EBC (G. m. callarias) can temporarily also spawn in the Belt Sea.

Improving Oxygen Conditions in the Deeper Parts of Bornholm Sea by Pumped Injection of Winter Water

Vertical diffusivity and oxygen consumption in the basin water, the water below the sill level at about 59 m depth, have been estimated by applying budget methods to monitoring data from hydrographical stations BY4 and BY5 for periods without water renewal. From the vertical diffusivity, the mean rate of work against the buoyancy forces below 65 m depth is estimated to about 0.10 mW m−2. This is slightly higher than published values for East Gotland Sea. The horizontally averaged vertical diffusivity κ can be approximated by the expression κ = a 0 N −1 where N is the buoyancy frequency and a 0 ≈ 1.25 × 10−7 m2 s−2, which is similar to values for a 0 used for depths below the halocline in Baltic proper circulation models for long-term simulations. The contemporary mean rate of oxygen consumption in the basin water is about 75 g O2 m−2 year−1, which corresponds to an oxidation of 28 g C m−2 year−1. The oxygen consumption in the Bornholm Basin doubled from the 1970s to the 2000s, which qualitatively explains the observed increasing frequency and vertical extent of anoxia and hypoxia in the basin water in records from the end of the 1950s to present time. A horizontally averaged vertical advection–diffusion model of the basin water is used to calculate the effects on stratification and oxygen concentration by a forced pump-driven vertical convection. It is shown that the residence time of the basin water may be reduced by pumping down and mixing the so-called winter water into the deepwater. With the present rate of oxygen consumption, a pumped flux of about 25 km3 year−1 would be sufficient to keep the oxygen concentration in the deepwater above 2 mL O2 L−1.

Inter-annual and seasonal variations in the air–sea CO 2 balance in the central Baltic Sea and the Kattegat

We estimated the net annual air–sea exchange of carbon dioxide (CO 2) using monitoring data from the East Gotland Sea, Bornholm Sea, and Kattegat for the 1993–2009 period. Wind speed and the sea surface partial pressure of CO 2 ( pCO 2 w), calculated from pH, total alkalinity, temperature, and salinity, were used for the flux calculations. We demonstrate that regions in the central Baltic Sea and the Kattegat alternate between being sinks (−) and sources (+) of CO 2 within the −4.2 to +5.2 mol m −2 yr −1 range. On average, for the 1994–2008 period, the East Gotland Sea was a source of CO 2 (1.64 mol m −2 yr −1), the Bornholm Sea was a source (2.34 mol m −2 yr −1), and the Kattegat was a sink (−1.16 mol m −2 yr −1). Large inter-annual and regional variations in the air–sea balance were observed. We used two parameterizations for the gas transfer velocity ( k) and the choice varied the air–sea exchange by a factor of two. Inter-annual variations in pCO 2 w between summers were controlled by the maximum concentration of phosphate in winter. Inter-annual variations in the CO 2 flux and gas transfer velocity were larger between winters than between summers. This indicates that the inter-annual variability in the total flux was controlled by winter conditions. The large differences between the central Baltic Sea and Kattegat were considered to depend partly on the differences in the mixed layer depth.

Seasonal maturity development of Baltic cod in different spawning areas: importance of the Arkona Sea for the summer spawning stock

We investigated the seasonal maturity development of cod in four areas of the Baltic Sea. Two different spawning peaks were identified and found to be consistent over the period 1992–2005. In the Kiel Bight and Mecklenburg Bight (ICES SD 22) a spawning peak was observed from March to April (spring spawning). In the areas of the Arkona Sea (ICES SD 24) and Bornholm Sea (ICES SD 25) the spawning peak occurred during summer. In the Bornholm Sea, the main spawning activities began in June and ended in September, with a spawning peak in June–August (summer spawning). In the Arkona Sea, which is a transition area between the Mecklenburg Bight and the central Baltic Sea, spawning began in March and lasted until July, with a spawning peak in June–July (summer spawning). Seasonal maturity development and proportions of spawning cod in June in the Arkona Sea were similar to that of the Bornholm Sea. In addition, the proportion of spawning cod in the Arkona Sea was positively correlated with the size of the spawning stock in the Bornholm Sea. Our results provide evidence of a spatial expansion of spawning activities of the summer spawning stock from the eastern Baltic Sea into the Arkona Sea. Therefore, the Arkona Sea should be considered as one of the spawning habitats of the summer spawning stock of Baltic cod.

Differentiation of western and eastern Baltic Sea cod stocks (Gadus morhua) by means of stable isotope ratios in muscles and otoliths

Summary Stable isotope analysis of Baltic Sea cod from the Bornholm Sea (ICES-SD 25) and western Baltic (Belt Sea, ICES-SD 22) revealed significant differences in the δ15N and δ13C values of the dorsal muscle, as well as in the δ18O values of otoliths. The method pledges to become especially appropriate to the Baltic due to the high variability in oxygen isotope ratios associated with its estuarine nature.

The potential fecundity of cod in the Baltic Sea from 1993 to 1999

Summary Investigations on the reproduction biology of cod in the Baltic Sea (Gadus morhua L. and G. morhua callarias L.) were carried out beginning in 1993, with yearly sampling of gonads to estimate the potential absolute and relative individual fecundity in the Belt Sea (subdivision, SD: 22) and in the Arkona Sea (SD: 24). Additional samples were taken in the Bornholm Sea (SD: 25). The potential absolute fecundity of the total area of investigation is described by the regression models: Fa = 6.89 × TL3.09 and Fa = −40 586 + 977.7 × W. As a further result the mean relative fecundity was 978 oocytes per gram body weight. Furthermore, it was shown that there was a difference in development of the potential individual fecundity between the Belt Sea cod and the original eastern Baltic cod stock. In contrast to the stable fecundity of cod in the Belt Sea, the fecundity of the large females in the Bornholm Sea significantly increased from 1993 to 1999. This change is related to a decrease in the dry weight of oocytes in the ovaries. In the same period this cod stock dramatically decreased.

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

Primary production, nutrient concentrations, phytoplankton biomass (incl. chlorophylla) 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, chlorophylla (chla) 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 4·3×106tCyr−1, respectively. Hence, an annual phytoplankton primary production in the whole Baltic Sea was estimated at 62×106tCyr−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, chla and nutrient concentrations, is proposed.

Morphological Aberrations in Females of the Genus Acartia (Copepoda, Calanoida) in the Baltic Sea

Morphological aberrations of the 5th pair of legs (P5) of females of the calanoid copepod genus Acartia from the Baltic Sea were observed. The aberrant shape of P5 ranged from thickening to doubling or tripling of the apical spines on one or both legs or even introduction of additional segments. From 7 to 16% of A. bifilosa females showed a deformation of P5 in the samples taken recently from German coastal waters, the Bornholm Sea, and the Lithuanian coast, but lower frequencies were observed in the specimens from the Polish coast (no abnormalities) as well as from the Gotland Sea (2%). In A. tonsa, A. longiremis, and A. discaudata, less than 4% of the females were abnormal. Coastal-open-sea or pollution gradients did not explain this. In A. bifilosa from the Kiel Bight, females from a sample collected in 1924 showed a similar frequency (14%) and the same structure of P5 aberrations in comparison with recent ones. It is suggested, that the described abnormalities are most likely a natural phenomenon for this genus.

Water exchange in the Pomeranian Bight investigated by satellite data and shipborne measurements

The Pomeranian Bight is characterized by the main freshwater input into the western Baltic Sea coming from the Oder and Peene rivers. The rate of river discharge is driven by varying sea level in the southern Baltic, and the distribution patterns of the river plume are dominated by the local wind. This study uses daily available sea surface temperature (SST) maps (4–6 times a day), derived from Advanced Very High Resolution Radiometer (AVHRR) data of the NOAA satellites, to investigate these patterns in relation to the meteorological conditions. Comparisons of SST maps with shipborne measurements for different wind situations confirm the usability of satellite data for investigation of the river discharge. On the basis of about 125 available NOAA scenes scattered over all seasons in the period of 1991–1994, typical horizontal distribution patterns were derived for wind directions of the eight octants. Chlorophyll concentration maps derived from Coastal Zone Colour Scanner (CZCS) data of the NIMBUS-7 satellite are, in special cases, more detailed than corresponding SST patterns (channel 6). They confirm the patterns and the transport of suspended material. Long-term wind records from the Arkona weather station indicate the dominant wind directions and the seasonal variations in wind forcing leading to seasonal preferred patterns and transport directions of the river plume into and out of the bight. Dominant westerly winds in summer, autumn and winter produce an eastward transport along the Polish coast into the Bornholm Sea and further into the Gdansk Bay over more than 300 km. In the period of the main freshwater inflow in spring, easterly winds are dominant and transport the river water along the German coast into the Arkona Sea. This is confirmed by high accumulation rates at the bottom of the Arkona Basin. The results of these investigations allow a prediction of distribution patterns and main transport directions in relation to the prevailing wind situation.

The gas vesicles, buoyancy and vertical distribution of cyanobacteria in the Baltic Sea

The mean pressures required to collapse gas vesicles in turgid cells of cyanobacteria from the Baltic Sea were 0·91 MPa (9·1 bar) in Aphanizomenon flos-aquae, 0·83 MPa in Nodularia sp. collected from the main deep basins and 0·34 MPa in Nodularia from shallower coastal regions. The gas vesicles were strong enough to withstand the depth of winter mixing, down to the permanent halocline (60 m in the Bornholm Sea, 90 m in the Eastern Gotland Sea) or to the sea bottom (30 m or less in the shallow Arkona Sea and Mecklenburg Bight). The cyanobacteria had low cell turgor pressures, within the range 0·08–0·18 MPa. The colonies were highly buoyant: the Aphanizomenon colonies floated up at a mean velocity of 22 m per day and the Nodularia colonies at 36 m per day. The colonies remained floating when up to half of the gas vesicles had been collapsed. In summer the cyanobacteria were mostly restricted to the water above the thermocline and in calm conditions their concentration increased towards the top of the water ...

The gulf of Bothnia: The northernmost part of the Baltic Sea

The Baltic Sea, one of the largest brackish water areas in the world, can be characterized as a young, cold sea containing an impoverished ecosystem due to salinity stress. The present Baltic Sea was formed as late as 2000 to 2500 years ago when the Danish sounds became more narrow and shallow. The inflow of freshwater from the surrounding land areas caused the Baltic to gradually attain its brackish character. Today the Baltic covers an area of some 366,000 km2 as a series of basins separated by shallower areas and filled with about 22,000 km3 of brackish water. These basins are, from north to south, the Gulf of Bothnia, the Gulf of Finland, the Gotland Sea and the Bornholm Sea. The climate gradient ranges from almost arctic conditions in the extreme north to a more maritime climate in the southern parts. The North Sea salt water is connected to the Baltic through the shallow Kattegat and the sills in the Danish sounds. The inflow of salt water occurs in two different ways,viz. as a continuous flow along the bottom due to the salinity gradient and as pulses of salt water generated by the distribution of air pressure and the direction of the wind. The freshwater input (500 km3) from mainly the large rivers equals roughly the net outflow and stresses the south-bound current along the Swedish coast that also compensates for the salt water inflow. Tidal movements can be seen in the southern Baltic, but are of minor importance for the system. The residence time of the total water mass is 25 years and the hydrographical conditions within the different basins are stable and dominated by a permanent halocline, and a thermocline developing every spring. The salinity ranges from about 1–2 per mille in the innermost part of the Gulf of Bothnia to 10–15 per mille in the Bornholm Sea. Total vertical mixing takes place during winter in at least the northern parts of the sea. Due to the climate-gradient, the ice condition differs from about four months of total ice-cover in the inner parts of the Gulf of Bothnia to one month or less of coastal ice in the southern part of the Baltic. Thus, the seasonal effect is more pronounced in the northern parts.