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.     

Vertical and spatial distribution of biogenic silica in the sediment of the gulf of Riga,Baltic Sea

The vertical and spatial concentration trends of biogenic silica (BSi) were investigated in a variety of sediment types from the Gulf of Riga. These trends were compared with the concentration of organic carbon to examine how variations in the mass sedimentation and the dissolution rate of BSi versus bacterially mediated oxidation of organic matter affect the distribution of BSi in different environments. The effects of important physical and biogeochemical factors on the distribution of BSi have also been examined.

The concentration of BSi in the surface sediment at accumulation bottoms ranges between 0.8–1.5 mmol/g with an average concentration of 1.1 mmol/g. This is about two times the concentration that has been reported in similar sediments in the open Baltic proper. Much lower concentrations were measured in erosion and transitional areas; on average around 0.2 and 0.6 mmol/g, respectively.

A comparison between recent sedimentation rate measurements (²¹⁰Pb) and concentrations of BSi within different accumulation bottoms suggests an approximate inverse relationship with each other. The importance of variation in the sedimentation rate on the surface BSi concentration is supported by the fact that higher C_org/BSi ratios are found in periphery accumulation zones close to transition areas (larger supply of carbon rich allochthonous material that dilutes settled amounts of BSi) than at accumulation bottoms in the central part of the Gulf. The C_org/BSi ratio in the sediment is always lower than in living siliceous algae which shows that the microbial degradation of organic carbon is always greater than the inorganic dissolution of BSi, irrespective of the assemblage of silica and non‐silica species.

The general vertical concentration pattern at accumulation sites showed a decreased concentration with increased depth down to 2–6 cm below seafloor where the concentration gradually equalizes. The concentration in the equalizing zone is on average about 20% lower than in the uppermost centimeter. This implies that the main part of the BSi entering the accumulation bottoms is permanently buried and that a great amount of silica already has been released during halmyrolysis. The spatial and vertical BSi trends at sites in transitional and erosional areas reflects prevailing sedimentation conditions with a low concentration in sections with a dominance of sand and gravel (no deposition of fine material) and a higher concentration in the sections containing stiff glacial clay (former accumulation area).

The average annual burial amount of BSi in the Gulf has been estimated to be around 50 000 tons of which most is buried in accumulation bottoms outside the central muddy part of the Gulf. The buried amount is about 60% of the annual river load of silica.     

Interactions between cod, herring and sprat in the changing environment of the Baltic Sea: A dynamic model analysis

The interactions between cod (Gadus morhua), herring (Clupea harengus) and sprat (Sprattus sprattus) in the Central Baltic Sea were examined with a simple dynamic model, an alternative to more complicated and data-demanding multispecies and ecosystem models. The main aims of the study were to compare the effect of alternative structures on the model output and examine the control relationships in the fish assemblage under different environmental conditions. The effect of environmental conditions was modelled using a stock-recruitment equation for cod incorporating an environmental index. The model output was especially sensitive to the functional response in predation by cod on herring and sprat. The type II functional response led to a collapse of the clupeid stocks when cod was abundant, while the type III response produced more realistic stock dynamics. According to the simulations, an abundant cod stock was able to keep the sprat stock at a low level, while the herring stock was less affected and benefited from the decreased density of sprat. Simulation of different fishing scenarios indicated that reducing fishing mortality to the level currently advised by ICES would allow the recovery of the cod stock even in unfavourable environmental conditions.     

Self-purification capacity and management of Baltic coastal ecosystems

It is expected that the Baltic region becomes a major centre of economic growth and prosperity in Europe already during this decade (Anon. 2000). Therefore, an Agenda 21 for the Baltic region (Baltic 21) was developed to ensure a sustainable development. Especially the coastal ecosystems are subject to increasing anthropogenic pressure e.g. eutrophication, traffic, harbours, tourism or offshore wind parks. Eutrophication remains the main ecological problem in the Baltic Sea and has serious negative social and economical consequences. Inner and outer coastal waters play an important role as buffers and filters for the Baltic proper. Consequently, the utilization and preservation of their self-purification capacity is of great importance. Combined results of our own coastal research and of the international workshop ‘Baltic coastal ecosystems: structure, function and coastal zone management’ (Rostock University, November 2001) are presented here. Conclusions for an improved integrated coastal zone management of Baltic coastal ecosystems will be presented.     

Fast Ferry Traffic as a Qualitatively New Forcing Factor of Environmental Processes in Non-Tidal Sea Areas: A Case Study in Tallinn Bay,Baltic Sea

The impact of wake wash from high-speed ferries on the coastal environment in non-tidal seas is analysed in terms of wave energy and power, and properties of the largest waves. Shown is that hydrodynamic loads caused by heavy high-speed traffic may play a decisive role not only in low-energy coasts but also in certain areas with high wind wave activity. For example, ship-generated waves form, at least, about 5–8% from the total wave energy and about 18–35% from the wave power in the coastal areas of Tallinn Bay exposed to dominating winds. The periods of wake waves from high-speed ships frequently are much larger than dominating periods of wind waves. The leading waves typically have a height of about 1 m and a period of 10–15 s. Such waves extremely seldom occur in natural conditions in many regions of semi-enclosed seas. They cause unusually high hydrodynamic loads in the deeper part of the nearshore. The fast ferry traffic thus is a qualitatively new forcing component of vital impact on the local ecosystem. It is demonstrated that wakes from high-speed ferries may trigger considerable changes of the existing balance of coastal processes. Owing to their low decay rates combined with their exceptional compactness after crossing many kilometres of the sea surface, such wakes may cause considerable remote impact of the ship traffic. This feature has to be addressed in the analysis of the impact of harbours and associated ship traffic in the neighbourhood of vulnerable areas.     

Levels and congener profiles of PCDD/Fs and dioxin-like PCBs in Baltic wild salmon (Salmo salar)

Baltic salmons were caught from two Latvian rivers during the spawning seasons of 2010 and 2011 for the determination of seventeen 2,3,7,8-chlorine-substituted dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and 12 dioxin-like polychlorinated biphenyls (PCBs). A partially automated clean-up procedure was used for sample preparation, followed by capillary gas chromatography hyphenated to high-resolution mass spectrometry. The concentrations of PCDD/F&;PCB-TEQ ranged from 6.6 to 18.2?ng?kg^?1 fresh weight and this confirms the previous reports of relatively high concentrations of PCDD/Fs, and especially of dioxin-like PCBs in Baltic wild salmon, in most samples exceeding maximum recommended levels (MRLs) in toxicity equivalency quotients (PCDD/F-PCB-TEQ) of the World Health Organization (WHO 1998) according to EC COMMISSION REGULATION No 1881/2006. The results suggest that high consumption of Baltic wild salmon could entail the risk of exceeding the TDI for adults and teenagers. Extra care must be taken when Baltic wild salmon is included in childrens's diet to avoid exceedance of the recommended TDI of 4?pg?kg^?1 body weight for this group.     

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.     

Photosynthetic production and its regulating factors in the Baltic Sea

Measurements of primary production in the Baltic Sea over a period of 2 years (1969/1971) by the ¹⁴C method are reported. The rate of total annual production for the Baltic Sea proper and the Gulf of Finland including coastal areas appears to lie between 35 and 40 gC·m², a rate which can be assumed as characteristic for oligotrophic waters with a low production rate. An apparent increase in productivity between the 2 years could be noted. Calculations for the water mass below the halocline show that between 0.7 and 0.8 ml/l oxygen is used up during a period of 3 months required for the development of anoxic conditions. The major portion of the organic matter in the Baltic Sea undergoes decomposition in the sub-photic zone above the halocline. The ratio of organic material in deep water to the total available oxidizable matter appears to remain constant with time; therefore, the apparent increase in productivity in the photic layer does not affect apprecibly the development of anoxic conditions in deep water. Of the different areas investigated, the Gulf of Finland seems to be the most productive. In the southern Baltic Sea, the rate of production over 5 years between 1966 and 1971 has not changed appreciably. In fact, it shows a trend toward a slight decrease, whereas, in other areas of the Baltic Sea, the rate of production indicates an apparent increase. Comparison with oceanic coastal areas of the west coast of Sweden shows that the rate of production there is higher than in the Baltic Sea. Of the micronutrients controlling productivity in the photic layer of the Baltic Sea, nitrate has a stronger limiting effect on plant growth than phosphate, a fact which is in agreement with existing conceptions on the subject. Dissolved iron does not seem to exert any appreciable influence on the productivity.     

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.     

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.     

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.     

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     

Recent Changes in the Hydrobiology of the Aral Sea

Since 1992 attempts have been made to isolate and conserve the northern part of the Aral Sea of means of a dam. Changes in the main aquatic communities between 1985 and 1994 based on field work, laboratory investigations and literature surveys are described and the future prospects for the region are discussed.     

Bioactivity as an Options Value of Sea Cucumbers in the Egyptian Red Sea

Abstract:  The utility of a species can be divided into its direct, indirect, and options values. In the marine environment, direct consumptive values predominate and often lead to overexploitation at the expense of significant options values derived through bioprospecting for natural products. We surveyed the waters of the Egyptian Red Sea coast (Gulf of Aqaba [north] and the Red Sea [south]) for species of sea cucumbers and analyzed extracts from species for a range of bioactivities with potential biomedical applications. All habitat types were surveyed within these regions. We found 22 species of sea cucumber of which two, Holothuria fuscogilva and Holothuria flavomaculata , were recorded in Egypt for the first time. Although none of the species identified were unique to the Gulf of Aqaba, 10 species were only found in the Red Sea sector. Bioassay results showed that although no species had antibacterial activity, most extracts exhibited activity against Candida and Leishmania but were most active against a LoVo mammalian carcinoma cell line. Our most significant finding was the intraspecific variation in bioactivity in individuals collected from different habitat types and sectors of the coast. This variation may reflect the effect of environment on secondary metabolite production or may indicate significant genetic diversity between populations within a species. Our results indicate a potentially significant options value to sea cucumbers through bioprospecting. Given the importance of economic development in countries such as Egypt and the perceived low conservation value of invertebrates such as sea cucumbers, the linking of these factors to conservation is vital for the maintenance and sustainable exploitation of these animals .     

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.     

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     

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.     

Toxicity of four oil dispersants to some animals from the Baltic Sea

Four oil dispersants of interest for practical use in the Baltic Sea were tested as regards toxicity to animals from the littoral zone of the same area. The dispersants tested were Corexit 7664, Berol TL-188, Berol TL-198, all water-base dispersants, and BP 1100-X, an oil-base dispersant. Two species of fish, two species of bivalves and two species of crustaceans were tested. Significant differences in toxicity were found between the water-base dispersants at concentrations above 1700 ppm. Below this concentration there were no significant differences. The dispersants contain similar surfactants in similar concentrations, but differ with respect to types and amount of solvent. The observed differences at high concentrations are, therefore, argued to be connected chiefly to differences between these solvents. Differences in toxicity to different animal types were found between the water-base dispersants and the oil-base dispersants. The toxicity of Corexit 7664 was (96h LC₅₀ approximate values): fish, 1000 ppm; bivalves, 2000 ppm; crustaceans, 10,000 ppm. The toxicity order was strikingly reversed for BP 1100-X: crustanceans, 150 ppm; bivalves, 2000 ppm; fish, 10,000 ppm. This difference in toxicity for different animal types is suggested to be connected mainly to differences in the chemical character of the outer layer of the body surface of the animals.