Photosynthetic carbon acquisition in the red algaGracilaria conferta

Photosynthetic properties of the common red algaGracilaria conferta, collected from the eastern Mediterranean Sea were investigated in 1989, in order to begin evaluating its adaptative strategies with regard to the inorganic carbon composition of seawater, and to test whether the alleged C₄ photosynthesis of anotherGracilaria species is common within the genus. Net photosynthetic rates ofG. conferta were, under ambient conditions of inorganic carbon (ca. 10µM, CO₂ and 2.2 mM HCO ₃ ^- ), not sensitive to O₂ over the range 10 to 300µM, and the CO₂ compensation point was low (ca. 0.005µM). Ribulose-1,5-bisphosphate carboxylase/oxygenase was the major carboxylating enzyme, with a crude extract activity of 175µmol CO₂ g^–1 fresh wt h^–1 while phosphoenolpyruvate carboxylase and phosphoenolpyruvate carboxykinase were present at 70 and 20%, respectively, of that activity. No activities of the decarboxylases NAD-and NADP-malic enzyme could be detected. The¹⁴C pulse-chase incorporation pattern showed thatG. conferta fixes inorganic carbon via the photosynthetic carbon reduction cycle only, with no evidence for photosynthetic C₄ acid metabolism. Photosynthesis at the natural seawater pH of 8.2 was, at 25°C and saturating light, saturated at the ambient inorganic carbon concentration of 2.5 mM. It is proposed that, under ambient inorganic carbon conditions, a CO₂ concentrating system other than C₄ metabolism provides an internal CO₂ concentration sufficient to suppress the O₂ effect on ribulose-1,5-bisphosphate carboxylase/oxygenase and, thus, on photorespiration, in a medium where the external free CO₂ concentration is lower than theK _m(CO₂) of the carboxylating enzyme. Since inorganic carbon, under natural saturating light conditions, seems not to be a limiting factor for photosynthesis ofG. conferta, it likely follows that other nutrients limit the growth of this alga in nature.     

Photosynthetic carbon acquisition in the red alga Gracilaria conferta

In this continuing study on photosynthesis of the marine red alga Gracilaria conferta, it was found that ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) in crude extracts had a K _m (CO₂) of 85 M. Since seawater contains only ca. 10 M CO₂, it appears that this alga must possess a CO₂ concetrating system in order to supply sufficient CO₂ to the vicinity of the enzyme. Because this species is a C₃ plant (and thus lacks the C₄ system for concentrating CO₂), but can utilize HCO₃ ^- as an exogenous carbon source, we examined whether HCO₃ ^- uptake could be the initial step of such a CO₂ concetrating system. The surface pH of G. conferta thalli was 9.4 during photosynthesis. At this pH, estimated maximal uncatalyzed HCO₃ ^- dehydration (CO₂ formation) within the unstirred layer was too slow to account for measured phostosynthetic rates, even in the presence of an external carbonic anhydrase inhibitor. This observation, and the marked pH increase in the unstirred layer following the onset of light, suggests that a HCO₃ ^- transport system (probably coupled to transmembrane H⁺/OH^- fluxes) operates at the plasmalemma level. The involvement of surface-bound carbonic anhydrase in such a system remains, however, obscure. The apparent need of marine macroalgae such as G. conferta for CO₂ concentrating mechanisms is discussed with regard to their low affinity of Rubisco to CO₂ and the low rate of CO₂ supply in water. The close similarity between rates of Rubisco carboxylation and measured photosynthesis further suggests that the carboxylase activity, rather than inorganic carbon transport and intercoversion events, could be an internal limiting factor for photosynthetic rates of G. conferta.     

Inorganic carbon uptake by photosynthetically active protoplasts of the red macroalga Chondrus crispus

Photosynthetically active protoplasts were isolated from Chondrus crispus Stackh. by treating thalli with -carrageenase produced from batch culture of Pseudomonas carrageenovora. Using the silicone oil centrifugation technique, it was found that the protoplasts: (1) did not generally accumulate inorganic carbon (C_i) above the concentration in their incubation medium; (2) were saturated at C_i concentrations of 3 to 4 mM; (3) had an intracellular pH of 7.50 when incubated at pH 7.5; and (4) their initial carbon fixation rate was reduced by carbonic anhydrase inhibitors. Although the carbon fixation rate of the protoplasts was about 30% that of thallus fragments, presumably due to the relatively harsh protoplast isolation treatment, the behavior of the protoplasts was similar to that of fragments. This similarity indicates that the protoplasts are photosynthetically active and behave as thallus fragments. Further, the data are consistent with the hypothesis that C. crispus acquires C_i for photosynthesis by the diffusion of CO₂ across the plasma membrane.     

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.     

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).     

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.     

Release of dissolved organic carbon from the estuarine intertidal macroalga Enteromorpha prolifera

The estuarine macroalga Enteromorpha prolifera was collected from Coos Bay, Oregon, USA during 1981, and its release of photosynthate as dissolved organic carbon (DOC) was studied using ¹⁴C as a tracer. During photosynthesis in 30 S sea water, with a fixation rate averaging 7.37 mg C g^-1 dry wt h^-1, release ranged from 0.13 to 0.57 mg C g^-1 dry wt h^-1 and from 1.65 to 6.23% of total fixed carbon. Release of DOC appears to be linear with time over 3 h. As exposed algae become increasingly desiccated, their photosynthetic rates decline dramatically, but upon reimmersion the highly desiccated algae lose a larger fraction of their fixed carbon than the slightly desiccated algae. This loss comes in a pulse release of DOC over the initial 15 min, followed by declining release rates. The pulse loss due to rainfall is 5 times greater than that due to tidal resubmergence, and may briefly exceed the prior photosynthetic rate. Although lowering the salinity from 30 to 5 does not substantially alter photosynthetic rates, it does increase the DOC release range up to 1.02 mg C g^-1 dry wt h^-1 and 16.10% of fixed carbon. Heterotrophic microbes from the algal habitat readily use the available DOC at about 15% h^-1.     

Total labile carbon in the euphotic zone of the Baltic Sea as measured by BOD

Total labile organic carbon was estimated in the euphotic zone of the Baltic Sea by a method based on the determination of the biological oxygen demand (BOD); the method is extremely simple, requires little sample water, and is quite precise (±4.5 μmol O₂/l or ±40.4 μgC_lab/l). The amount found was 1,150 μgC_lab/l, or about 29% of the total organic carbon. At 1 m, a relationship between biological activity, as measured by chlorophyll content, and the amount of labile carbon was found: ln C_lab (μg/l)=ln 6.87 (μg/l) +0.272 ln chlorophyll (μg/l), with a correlation coefficient of 0.86, which is significantly greater than zero at the 0.001 level.     

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.     

Carbon acquisition strategies for marine macroalgae

A model system was developed to analyse differences in carbon acquisition strategies among macroalgae. During photosynthesis in a limited volume of seawater the capability of the algae to assimilate inorganic carbon as well as to change the alkalinity of the seawater was analysed. These properties were then related to the status of the carbonate equilibrium system of the seawater. The experimental system was assumed to simulate the conditions in the boundary layer during periods of low water exchange or high intensity irradiations. Fundamental differences were found between different algal classes, suggesting that capabilities to adapt to specific environmental conditions may be connected with dissimilarities in carbon acquisition strategies. In general, green algae were able to reach the highest pH (10.8 at 5°C), and thus to achieve the highest reduction in the level of inorganic carbon via a simple HCO₃ ^–/OH^– ion exchange process. For brown algae, pH increases due to carbon uptake never exceeded pH 9.7 (9.5 in a saltwater scale). In spite of this, members of the Fucaceae (littoral brown algae) were able to extract almost all of the dissolved inorganic carbon (DIC). This was achieved through a gradual decrease in the alkalinity of the enclosed water, so that the carbon assimilation could continue without any concomitant increase in pH. For red algae, the specific response was an increase in the level of inorganic carbon. Thus, for this algal class, no specific strategy for handling a shortage of inorganic carbon was documented. Within each algal class, differences in pH and DIC compensation points could be related to differences in the depths at which the algal species occurred. This paper also introduces a low cost and convenient method of analysing DIC in seawater.     

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.     

Bacteriolytic Bacillus species isolated from brackish waters of the Southern Baltic Sea

The present study examines antagonistic relationships between different microorganisms inhabiting brackish water and includes a systematic screening for bacteriolytic prokaryotes in the brackish waters of the Southern Baltic Sea (Nordruegenscher Bodden) sampled in July/August 2009. Ten of the 35 marine bacteriolytic isolates belong to the genus Bacillus. Five isolates (B. pumilus, B. subtilis, B. megaterium, B. licheniformis) lysed living microbial cells such as the bacteria Arthrobacter citreus, Arthrobacter protophormiae, Micrococcus luteus, Pseudomonas putida and the yeast Trichosporon mucoides. These and other bacteria (Aeromonas sp., Bacillus subtilis, Chromobacterium violaceum, Citrobacter freundii, Enterobacter aerogenes, Proteus mirabilis, Pseudomonas aeruginosa and Serratia marcescens) were also lysed as autoclaved and pasteurized cells on agar plates. One isolate of Bacillus pumilus showed a distinct bacteriolysis activity against pasteurized cells of A. citreus in liquid culture. Our results suggest that Bacillus species may play a role as opportunistic predators in the marine microbial food web.     

Antimicrobial activities of marine sponges from the Mediterranean Sea

Extracts from marine sponges collected along the French coast of Mediterranean in 1983 have been tested for antibacterial and antifungal activities. The distribution of antimicrobial activities against five classes of microorganisms (5 Gram-positive and 5 Gram-negative terrestrial bacteria, 10 marine bacteria, 15 human pathogenic fungi and 5 phytopathogenic fungi) among 28 species of marine demosponges is reported. Antibacterial activity against Gram-positive bacteria (77%) is much more frequent than against Gram-negative bacteria (53%). Activity against marine bacteria and yeast is less frequent (32%). Those sponges which contain a large quantily of symbiotic bacteria display a weak antifungal activity.     

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     

Ostracod species-specific utilisation of sediment detritus and newly settled cyanobacteria, Aphanizomenon sp., in the Baltic Sea: evidence from stable carbon isotopes

The three meiobenthic ostracod species Candona neglecta, Paracyprideis fennica and Heterocyprideis sorbyana are commonly encountered in the deep (20-40 m) soft bottoms of the Baltic proper, and may contribute more to the total meiobenthic biomass than any other group. Experimental data indicate substantial differences in their utilisation of settling phytodetritus, with C. neglecta able to exploit newly settled organic material to a larger extent than P. fennica and H. sorbyana. Ostracod species composition, as well as ostracod and sediment carbon isotope contents, were studied in the field from an area with local differences in potential food resources. The study was performed during the late period of summer blooms of the cyanobacteria Aphanizomenon sp. Results showed that when all samples were taken together, adult C. neglecta (-22.4‰) was significantly more depleted in '¹³C than adult P. fennica (-21.0‰) and H. sorbyana (-20.3‰), indicating differences in food selection among the species. The flocculent sediment layer had, in all instances, lighter carbon ratios than did the lower layers. This trend was mirrored in most cases in the slight enrichment in C. neglecta compared to generally greater enrichment in the other two species. Carbon signatures of C. neglecta also varied significantly between stations, indicating that this species fed on different resources depending on location. Juvenile C. neglecta were far more depleted in '¹³C than adults and reflected the carbon signature of the cyanobacteria Aphanizomenon sp. The latter is known to be the most '¹³C-depleted phytoplankton member in the area.     

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.     

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