Radioactivity in the Baltic Sea

The Baltic Sea is, like the Mediterranean, a marginal sea, which with the Black Sea, were marine environments contaminated from the Chernobyl accident.

Radiocaesium and plutonium isotopes were studied in water, sediment and macroalgae in the Baltic Sea since 1982. the inventory of ¹³⁷Cs in the Baltic increased from 0.65 PBq to 5.85 PBq following the Chernobyl accident. the corresponding increase for ^{239 + 240}Pu was less significant and yielded 1.5 TBq to a total value of 16.5 TBq.

For plutonium, 98% is trapped in the sediment and the net-exchange of this element through the Baltic straits is very small (1 GBq/year), while for radiocaesium, 45% is in the water phase and there is a net-loss of 60 000 GBq annually into the adjacent water (Kattegatt).     

Inorganic skeleton of the demosponge Halichondria panicea. Seasonality in spicule production in the Baltic Sea

Seasonality in spicule production of the demosponge Halichondria panicea (Pallas, 1766) was studied in the Western Baltic from July 1992 to July 1993. Spicule production increased in parallel with increasing temperatures in spring, being most pronounced during summer after release of larvae. Large proportions of up to 30% immature spicules occurred in the population during skeleton production peaks, and this resulted in reduction of mean spicule dimensions by ≃20%. Effects on spicule width were more obvious than on spicule length. In winter, when wave forces were largest, higher percentages of mineral skeleton were observed: 50% of dry weight compared to 40% in summer. Enhanced spicule densities in the tissues were not attained by marked spicule production but through a reduction in organic content by shrinking. In spring, growth of body tissue was faster than the build-up of skeleton, so that the relative amount of the latter was reduced. The indirect, growth-related developments of the skeleton were inversely proportional to temperature and directly to salinity, silicate concentrations and wave energy. Spicule size and the number of immature spicules were correlated with temperature and only slightly with salinity. No correlation with oxygen concentration or pH could be detected. Received: 3 April 1997 / Accepted: 8 August 1997     

Primary production and environmental factors in an oligotrophic biome in the Aegean Sea

The rate of the primary production of the phytoplankton community in the Petalion Gulf, Aegean Sea, was studied from January 1970 to May 1971, at a station situated at approximately Latitude 37°54N; Longitude 24°11E. A variety of physical and chemical parameters such as chlorophyll, primary nutrients (N,P,Si), temperature, salinity, oxygen and light penetration were also studied simultaneously. The rate of the gross primary production varied from 40 to 200 mg C m^-2 day^-1, with a mean value of 90 mg C m^-2 day^-1. The annual gross primary production was calculated to be 33 g C m^-2, which is the minimum known value in the Aegean and Mediterranean Seas. Maximum production was found at the depth of 20 m on the average, mainly due to high light intensities. Petalion Gulf supports a small photosynthetic biomass, as indicated by the low seasonal values of chlorophyll a (0.01 to 0.18 mg m^-2), the highest values being found in the summer. The low production rate noted may have been due to the low nutrient concentrations found: N, 0.04 to 0.32 g-at/1; P, 0.00 to 0.15 g-at/1; Si, 0.45 to 2.25 g-at/1. It is suggested that inorganic phosphorus and nitrogen may alternate in limiting primary production rates in these oligotrophic waters. The temperate waters of the Petalion Gulf are stratified in summer (15.5° to 24.7°C) and well-mixed in winter (12.9° to 15.0°C); they are oxygen-saturated throughout the year, and of high transparency, with 86 m depth for the euphotic zone on the average yearly. The Petalion Gulf is therefore characterized as a typical oligotrophic biome in the Aegean and Eastern Mediterranean Seas.     

向日葵光合特性及其对不同生态条件的响应

对向日葵光合特性及其对不同生态条件响应的研究结果表明 :向日葵光饱和点为 1 70 0 μE·m-2 ·s-1 ,光补偿点为 95～ 1 2 0 μE·m-2 ·s-1 ;向日葵在光饱和点范围内 ,净光合速率随着光强的增加而增加 ,但随着相对湿度的增加而减小 ;向日葵光合适温为 2 3～ 33℃ ;气孔导度不是导致向日葵光合“午休”的主要影响因素 ,而光合有机物质可溶性糖的积累所产生的抑制作用才是光合“午休”的主要原因。     

Distribution of labile and residual particulate carbon in the Baltic Sea

During the September 1971 cruise of F. K. Alkor in the central Baltic Sea, the surface or summer water layer down to a depth of about 30 m was found to contain 187.4 g/l of particulate organic carbon, with a C:N (atoms) ratio of 8.97. This carbon was 44% (89.9 g/l) labile to bacterial decomposition, as determined by burning an aliquot of each sample in a CHN-analyser before and after maintenance in nutrientenriched sea water at 20°C for 3 months. The particulate material from the intermediate or winter water layer, with a depth ranging from 30 to 70 m, contained only 48% (43.1 g/l) of the labile carbon found in the summer surface layer, and had a significantly higher C:N ratio (11.25). These two facts indicate that a considerable breakdown of the organic material had taken place. The material, removed from the particulate state during this process, was 48% (89.7 g/l) of the original total particulate carbon, and was relatively nitrogen-rich, with a C:N ratio of 6.49. In this material, 52% (46.8 g/l) of the organic carbon was labile. The particulate material in the rest of the water column showed no significant changes until it reached the sediment. The slurry immediately above the sediment had a C:N ratio of 9.15, indicating the introduction of nitrogen from either dissolved or colloidal material. Labile carbon (44% of the total) was also present in sufficient quantities to support life and to make this an important diagenetic site.     

Predator-inducible changes in blue mussels from the predator-free Baltic Sea

Blue mussels, Mytilus spp., have inhabited the brackish Baltic Sea, an environment lacking predatory crabs and starfish, for several thousand years. In this paper we examined whether Baltic Mytilus that were transplanted to the North Sea showed predator-inducible plasticity like their "marine" conspecifics. Our experiments showed that native North Sea Mytilus changed their morphology when exposed to waterborne scents from shore-crabs and starfish. These predators induced different kinds of changes, with emphasis on shell thickness and adductor muscle size, respectively. Baltic Mytilus responded in a similar way to crab scents, whereas starfish scents had a relatively weak effect on the morphology. Crab and starfish scent induced strengthening of the byssal attachment in North Sea Mytilus, with crabs providing more stimulation than starfish. Baltic mussels also improved the byssal attachment when exposed to either of the predators, but the attachment strength, as well as the response to crabs, were relatively weaker than that of North Sea mussels. We conclude that inducible plasticity still is present in Baltic Mytilus, despite their recent evolution in a predator-free environment. There is probably no strong selective pressure against inducible plasticity, but it could also be maintained in the population by gene flow from Mytilus in the adjoining North Sea. The question whether Baltic Mytilus are M. edulis or M. trossulus may also be relevant for the present results.     

Comparison of sterol composition of some Baltic Sea and Black Sea mussels

Sterol composition of three Baltic Sea mussels (Mytilus edulis, Cardium glaucum, Mya arenaria) was compared with the sterol composition of three biologically closely related mussels from the Black Sea (Mytilus galloprovincialis, Cardium edule, Mya arenaria). The qualitative sterol composition of the mussels studied was similar, but some quantitative differences were found.     

Stoichiometry of mesozooplankton in N- and P-limited areas of the Baltic Sea

The Baltic Sea is a very suitable site for stoichiometric studies, since its subbasins differ in their concentration of elemental components, and primary production can therefore be either nitrogen or phosphorus limited. To reveal if the nutrient limitation of mesozooplankton mirrors that of the primary producers, carbon, nitrogen and phosphorus content of both seston and grazers (Acartia sp., Centropages hamatus, Daphnia cristata, Eurytemora affinis, Limnocalanus macrurus, Temora longicornis) were measured in midsummer in the Baltic proper, the Gulf of Finland and the Gulf of Bothnia. The mineral ratios of the different taxa were equal, apart from L. macrurus with notably higher C:P and N:P ratios. Molar C:N ratios were relatively stable (5.1-6.3), whereas C:P and N:P ratios fluctuated more (41-144 and 6.6-24). However, zooplankton elemental composition and limitation did not depend on the limiting nutrient of the phytoplankton, the seston mineral ratio or the sea area. Both the seston-zooplankton elemental imbalance and the food threshold ratio indicated phosphorus limitation of most of the grazers. While L. macrurus may be C or N limited, the possible P deficiency of the other studied taxa suggests that the Baltic Sea zooplankton may act as a potential phosphorus sink, as the freshwater secondary producers do.     

Long-term trends in abundance of cladocerans in the Central Baltic Sea

Long-term dynamics (1960-1997) of the cladoceran species Bosmina coregoni maritima, Evadne nordmanni and Podon spp. are described for the Gdansk Deep and the Gotland Basin (Central Baltic Sea). By using correlation analyses on seasonal time-series, the influence of temperature and salinity on the abundance of cladoceran species was investigated. A clear affinity to higher temperature was found for B. coregoni maritima in summer as well as for E. nordmanni and Podon spp. in spring. In addition to temperature, association tests with salinity revealed besides species-specific preferences, regional and temporal differences. Contrary to B. coregoni maritima, both other species were positively associated to salinity in summer and autumn in the Gdansk Deep. In the Gotland Basin only E. nordmanni was positively correlated to salinity in autumn. Differences in the response to hydrographic variables are possibly stage specific, i.e. between resting eggs and adults, or due to a different adaptation to the abiotic environment.     

Genetic differentiation in Hediste diversicolor (Polychaeta: Nereididae) for the North Sea and the Baltic Sea

Genetic differentiation between North Sea and Baltic Sea Hediste diversicolor (O.F. Müller, 1776) (Polychaeta: Nereididae) populations was studied by allozyme electrophoresis on starch gel. Thirteen loci were analyzed in eight populations. The level of genetic variation was very low (mean H _o = 0.000 to 0.015). Differentiation between H. diversicolor populations is quite high (F _ST = 0.892) and reflected by three enzyme loci (MDH-I*, MDH-II*, IDH-I*). The reduced gene flow (N _m<1) may be explained by the limited dispersal capacity of the species. Regardless of whether found in the North Sea or Baltic Sea, there appear to be two different genetic types which are parapatric or sympatric in some places. The two types hybridize at three localities, but no signs of hybridization have been found at one (Tallinn). Received: 26 June 1997 / Accepted: 10 September 1997     

Metals in Zooplankton from the Baltic Sea, 1980-84

Between 1980 and 1984, plankton was collected for metal analysis during four expeditions in the Baltic Sea. for comparison, samples from adjacent areas of the northeastern Atlantic Ocean were also taken. the mixed net-plankton samples were analyzed by AAS for metals (Al, Cd, Co, Cr, Cu. Fe, Mn, Ni, Pb, and Zn). the results are discussed with regard to spatial and temporal trends and for comparison with data from other authors. Correlations among the contents of the different metals and between the metal contents and 'external factors' including salinity, season, percentage of co-collected phytoplankton, and concentration of dissolved and particulate metals in the water are considered.

There is a tendency for higher metal contents in plankton from the brackish Baltic Sea (Al, Mn and Hg), while other metals (e.g. Cd) show higher levels in samples taken from the marine environment. Except for mercury, no clear correlations could be found between the metal content in plankton and the dissolved concentration of the same metal in the ambient water. Otherwise, the contents of aluminium, iron, manganese and zinc in the suspended particulate matter and in the plankton seem to be partly related to each other.     

Occurrence of the semi-catadromous European eel Anguilla anguilla in the Baltic Sea

Strontium (Sr) and calcium (Ca) contents in the otoliths of yellow and silver European eels [Anguilla anguilla (L.)] collected from coastal waters of the Baltic Sea and a freshwater lake in Sweden were examined by wavelength dispersive X-ray spectrometry with an electron microprobe. The mean Sr/Ca ratios from elver check to otolith edge were significantly higher for the eels from coastal waters (5.39 ± 1.09‰) than for those from the lake (0.71 ± 0.89‰). The evidence indicates that European eels in the Baltic Sea do not necessarily migrate into freshwater streams during the growth phase. Received: 30 September 1999 / Accepted: 6 April 2000     

Contrasting population structures in two sympatric fishes in the Baltic Sea basin

Detailed multispecies studies on the patterns of genetic variability and differentiation in marine environments are still rare. Using mitochondrial and nuclear genetic markers, we compared genetic variability and population structuring of threespine (Gasterosteus aculeatus) and ninespine (Pungitius pungitius) sticklebacks from the same eleven marine and six freshwater locations within the Baltic Sea basin. Analyses of both marker types revealed a significantly lower degree of genetic structuring in both marine and freshwater populations of threespine than those ninespine sticklebacks. Isolation-by-distance (IBD) was detected across the marine populations in both species, suggesting spatially limited gene flow. However, the levels of genetic diversity and differentiation across the localities were uncorrelated between the two species in both marine and freshwater environments. Accordingly, estimates of effective population sizes were larger and migration rates were higher for three- than for ninespine sticklebacks. Hence, ninespine stickleback populations from the Baltic Sea basin appear to be subject to stronger genetic drift than sympatric threespine sticklebacks, and the proximate reason for this difference is likely to be found from autecological differences between the two species. In accordance with the earlier studies, genetic variability was higher and the degree of genetic differentiation was lower in marine than in freshwater populations in both species.     

On the distribution of particulate metals,chlorophyll and seston in the Baltic Sea

During the end of the phytoplankton spring bloom, about 100 water samples were taken at 23 stations in the Baltic Sea. The samples were analyzed for particulate Cu, Fe, Zn, Cd, and Pb by atomic absorption as well as for chlorophyll and seston. Further subsamples were counted with an inverted microscope, and phytoplankton carbon content was calculated. The hydrographical-biological state of the Baltic Sea during spring is described. Two different water masses could be differentiated and these were separated by the halocline. The concentrations of particulate metals are in accordance with those published by other authors. No significant differences could be calculated between mean values of particulate metal concentrations in the two water bodies. Correlations between particulate metal concentrations and chlorophyll, seston, phytoplankton carbon and cell-count were calculated for both photic layer and deeper waters. Significant correlations were found only in the photic layer. The importance of standing crop for metal accumulation in seston is discussed.     

Nodularin concentrations in Baltic Sea zooplankton and fish during a cyanobacterial bloom

Toxic cyanobacterial blooms, dominated by Nodularia spumigena, are a recurrent phenomenon in the Baltic Sea during late summer. Nodularin, a potent hepatotoxin, has been previously observed to accumulate on different trophic levels, in zooplankton, mysid shrimps, fish as well as benthic organisms, even in waterfowl. While the largest concentrations of nodularin have been measured from the benthic organisms and the food web originating from them, the concentrations in the pelagic organisms are not negligible. The observations on concentrations in zooplankton and planktivorous fish are sporadic, however. A field study in the Gulf of Finland, northern Baltic Sea, was conducted during cyanobacterial bloom season where zooplankton (copepod Eurytemora affinis, cladoceran Pleopsis polyphemoides) and fish (herring, sprat, three-spined stickleback) samples for toxin analyses were collected from the same sampling areas, concurrently with phytoplankton community samples. N. spumigena was most abundant in the eastern Gulf of Finland. In this same sampling area, cladoceran P. polyphemoides contained more nodularin than in the other areas, suggesting that this species has a low capacity to avoid cyanobacterial exposure when the abundance of cyanobacterial filaments is high. In copepod E. affinis nodularin concentrations were high in all of the sampling areas, irrespective of the N. spumigena cell numbers. Furthermore, nodularin concentrations in herring samples were highest in the eastern Gulf of Finland. Three-spined stickleback contained the highest concentrations of nodularin of all the three fish species included in this study, probably because it prefers upper water layers where also the risk of nodularin accumulation in zooplankton is the highest. No linear relationship was found between N. spumigena abundance and nodularin concentration in zooplankton and fish, but in the eastern area where the most dense surface-floating bloom was observed, the nodularin concentrations in zooplankton were high. The maximum concentrations in zooplankton and fish samples in this study were higher than measured before, suggesting that the temporal variation of nodularin concentrations in pelagic communities can be large, and vary from negligible to potentially harmful.     

Seasonal and long-term variations in the body size of planktonic copepods in the northern Baltic Sea

Seasonal and long-term variations in the body size of planktonic copepods were studied in the northern Baltic Sea. The influence of temperature, salinity and phytoplankton concentration to the body size of Eurytemora affinis, Acartia bifilosa and Limnocalanus macrurus (Calanoida) was examined at three sea areas, differing in their hydrographical and trophic conditions (an archipelago area and an enclosed bay on the SW coast of Finland in 1992 and at an open sea station in the Gulf of Bothnia in 1991). There was an inverse relationship between copepod body length and temperature, while there was a direct effect of phytoplankton concentration. According to multiple regression analysis, the relative importance of these factors varied according to species, developmental stage and study area. In the archipelago area, copepod body size was mainly determined by temperature, while in the open Gulf of Bothnia, phytoplankton concentration was usually more important. Interannual variation in the summer body length of E. affinis and A. bifilosa was examined using samples collected over 18 years (1967 to 1984) in the archipelago area. In this analysis, the inverse relationship between water temperature and copepod body size disappeared; in E. affinis the average female length correlated positively with summer temperature. We suggest that the length and timing of the study period greatly influence the investigator's view of the factors regulating copepod body size.     

Polymorphism of mannose phosphate isomerase in North Sea and Baltic Sea populations of the amphipods Gammarus zaddachi and G. salinus

Genetic variation at the mannosephosphate isomerase (MPI) locus was examined in the euryhaline sibling species Gammarus zaddachi Sexton and G. salinus Spooner. Both crustacean amphipods share identical enzyme mobilities, following electrophoresis on vertical starch gels. The MPI locus turned out to be highly polymorphic; it is encoded by 6 alleles in G. zaddachi and 7 alleles in G. salinus. Geographic variation of allelic diversity was studied in samples from 9 G. zaddachi and 10 G. salinus populations, primarily obtained from Baltic Sea and North Sea sites. Patterns of inter- and intraspecific heterogeneity are described. Differences in allelic composition exist between Baltic and North Sea samples of G. salinus. In G. zaddachi, levels of polymorphism are higher in North Sea populations than in those from Baltic Sea areas. The significance of these findings is discussed in the light of previous biochemical genetic investigations on the population structure of the two amphipods considered.     

Succession and growth limitation of phytoplankton in the Gulf of Bothnia (Baltic Sea)

A one year field study of four stations in the Gulf of Bothnia during 1991 showed that the biomass was ca. two times, and primary productivity ca. four times, lower in the north (Bothnian Bay) than in the south (Bothnian Sea) during the summer. Nutrient addition experiments indicated phosphorus limitation of phytoplankton in the Bothanian Bay and the coastal areas in the northern Bothnian Sea, but nitrogen limitation in the open Bothanian Sea. A positive correlation between the phosphate concentration and the production/biomass ratio of phytoplankton was demonstrated, which partly explained the differences in the specific growth rate of the phytoplankton during the summer. Differences in photosynthetic active radiation between the stations also showed a covariation with the primary productivity. The relative importance of nutrient or light limitation for photosynthetic carbon fixation could not, however, the conclusively determined from this study. Marked differences in phytoplankton species composition from north to south were also observed. The number of dominating species was higher in the Bothnian Sea than in the Bothnian Bay. The distribution of some species could be explained as due to nutrient availability (e.g. Nodularia spumigena, Aphanizomenon sp.), while salinity probably limits the distribution of some limnic as well as marine species. The potentially toxic phytoplankton N. spumigena, Dinophysis acuminata and Chrysochromulina spp. were common in the Bothnian Sea but not in the Bothnian Bay. The pico- and nanoplankton biomass during late summer was higher than previously reported due to a revised carbon/volume ratio.