Phosphatase activities in relation to phosphorus nutrition in Nodularia spumigena (Cyanobacteriaceae)

Alkaline phosphatase activities were examined in blooms of Nodularia spumigena Mertens in the Peel-Harvey estuarine system, Western Australia. Variations in phosphatase activity occurred geographically and diurnally, as well as over the duration of a bloom. These variations were well correlated with differences in the phosphorus nutritional status of the Nodularia. In the laboratory, Nodularia phosphatase production was inversely proportional to cellular phosphorus, but not to external soluble reactive phosphorus.     

Nutrient levels and the development of diatom and blue-green algal blooms in a shallow Australian estuary

In the Peel-Harvey estuary system, Western Australia, some 90%of riverflow and nutrient loading occurs in three winter months.Diatom blooms follow riverflow, but are replaced by blooms ofthe blue-green Nodularia spumigena Mert., especially in HarveyEstuary. By analysis of time series data from 1977–1983,it is shown that the magnitude of the Nodularia bloom in summeris related to the minimum salinity of the estuary (and hencetotal river flow), maximum phosphate concentration and totalriverine phosphorus loading, in the previous winter. The relationshipshave a predictive capacity. It is argued that diatom bloomstrap phosphorus, which is sedimented largely as faecal pellets;the phosphorus is recycled and supports Nodularia growth underwarmer conditions, and the amount available determines Nodulariabiomass. Nodularia blooms collapse when summer salinities reach30     

Relationship of cellular phosphorus in the cyanobacterium Nodularia to phosphorus availability in the Peel-Harvey Estuarine System

A laboratory-determined critical concentration of phosphorus in the cyanobacterium Nodularia spumigena was used to assess the phosphorus sufficiency of field populations in the Peel-Harvey Estuarine System, Western Australia. Nutrient addition bioassays indicated that phosphorus was the limiting nutrient. Since river flow, and thus phosphorus input, to the estuary ceases 1–2 months before the onset of Nodularia blooms, the phosphorus contained in these blooms was derived from sediment release and nutrient recycling. A progressive increase in the mean cellular phosphorus concentration of Nodularia from 1981 to 1983 indicated that sediments were releasing a greater amount of phophorus each year. Although evidence suggests that the biomass of recent Nodularia blooms is now limited by physical factors, the additional phosphorus contained in each bloom will increase the supply of phosphorus to other organisms. Cellular phosphorus concentrations in Nodularia appeared to be correlated with river phosphorus loadings in the Peel Inlet but not in the Harvey Estuary.     

Potential triggers of akinete differentiation in Nodularia spumigena (Cyanobacteriaceae) isolated from Australia

Nodularia spumigena, like many cyanobacteria, produces specialised reproductive structures, known as akinetes, which are believed to allow survival under unfavourable conditions. This study investigated the effects of salinity, nitrogen and phosphorus concentration at two irradiances on akinete differentiation in a N. spumigena isolate from the Gippsland Lakes, Victoria, Australia. A computer image analysis program was used to photograph filaments and assess production of akinetes over time in separate experiments for each environmental parameter. Heterocyst production and cell morphology were also examined. The results suggest that akinete production increases over time. Production of akinetes is further increased at low and high salinities and with the addition of nitrate. Higher irradiance increases akinete differentiation, although in combination with different phosphorus concentrations causes varied effects. The development and sedimentation of akinetes may provide an inoculum for reoccurring blooms. Heterocysts were only observed during experiments with varying salinity and nitrogen exposures. Light quantity appeared to play a large role in heterocyst production. The ability of N. spumigena to produce akinetes and heterocysts is likely to be part of the reason for its success and continual occurrence in estuarine environments low in nitrogen, such as the Gippsland Lakes, Victoria, Australia. Factors known to reduce heterocyst and akinete production will provide new insight to possible management controls for this species.     

Abiotic factors influencing cyanobacterial bloom development in the Gulf of Finland (Baltic Sea)

Blooms of cyanobacteria are a recurrent phenomenon in the Baltic Sea, including the Gulf of Finland. The spatial extension, duration, intensity and species composition of these blooms varies widely between years. Alg@line data collected regularly from ferries as well as weather service and marine monitoring data from 1997 to 2005 are analysed to determine the main abiotic factors influencing the intensity and species composition of cyanobacterial blooms in the Gulf of Finland. It is demonstrated that the development of the Nodularia spumigena Mertens bloom is highly dependent on weather conditions such as photosynthetically active radiation and water temperature. Nutrient conditions, especially the surplus of phosphorus (according to Redfield ratio) related to the pre-bloom upwelling events in the Gulf, affect the intensity of Aphanizomenon sp. (L.) Ralfs blooms. Differences in bloom timing and duration indicate that, if the preconditions (like nutrient ratio/concentration and weather conditions) for bloom formation are favourable, then the Aphanizomenon bloom starts earlier, the overall bloom period is longer and the Nodularia peak might appear in a wider time window. Handling editor: K. Martens     

Proteomic profiling of the Baltic Sea cyanobacterium Nodularia spumigena strain AV1 during ammonium supplementation

The cyanobacterium Nodularia spumigena dominates the annual, toxic summer blooms in the Baltic Sea. Although Nodularia has been receiving attention due to its production of the hepatotoxin nodularin, molecular data regarding the regulation of nitrogen fixation is lacking. We have previously reported that N. spumigena strain AV1, unlike model filamentous cyanobacteria, differentiates heterocysts in the absence of detectable nitrogen fixation activity. To further analyze the uncoupling between these two linked processes, we assessed the impact of ammonium ions on the N. spumigena metabolism using a proteomic approach. Proteomic profiling was performed at three different times during ammonium supplementation using quantitative 2-dimensional gel electrophoresis followed by MS/MS analysis. Using this approach, we identified 34 proteins, 28 of which were unique proteins that changed successively in abundance during growth on ammonium. Our results indicate that N. spumigena generally exhibits lower energy production and carbon fixation in the presence of ammonium and seems to be inefficient in utilizing ammonium as an external nitrogen source. The possibility of ammonium toxicity due to PSII damage was investigated and the results are discussed. Our findings have implications in regard to the strategies considered to manage the cyanobacterial blooms in the Baltic Sea.     

Nutrient and phytoplankton responses to a flood event in a series of interconnected coastal lakes: Myall Lakes Australia

Myall Lakes is a large brackish coastal lake on the east coast of Australia that was considered pristine until the occurrence of blue-green algal blooms in 1999. The temporal and spatial extent of chemical and biological changes to the water column of Myall Lakes was studied intensively after a rain event in 2002. Water quality profiles (T, EC, pH, DO), turbidity (secchi), nutrients (TN, NO _x , NH₄ ⁺, DON, TP, FRP, DOP, Si), and phytoplankton (chl a and cell counts) were measured at nine sites on eight occasions immediately after the rain event. Freshwater inflows affected a large area of the lake. Greatest changes were seen in areas close to the mouth of the upper Myall River which is the largest freshwater input to the lakes. Here, greatly elevated concentrations of NO _x , TP, and FRP (up to two orders of magnitude higher than background) were recorded immediately after the rain event but persisted for only 2 to 8 days. Slightly elevated concentrations of TP and NO _x were seen in inflows from the smaller Boolambayte Creek. Stratification was associated with bottom water anoxia and release of ammonia from the sediments. Identification of the sources of nutrient species delivered from different parts of the catchment, combined with studies of nutrient loads can assist managers to develop effective nutrient reduction strategies to reduce the incidence of blue-green algal blooms in Myall Lakes.     

Benthic fauna affects recruitment from sediments of the harmful cyanobacterium Nodularia spumigena

Physical disturbance and feeding by macrofauna in the sediment can potentially affect bloom initiation of phytoplankton species that have benthic stages in their life cycle. In this experimental study, we investigated how different species of macrozoobenthos can affect the recruitment of Nodularia spumigena from the sediment to the water column. N. spumigena is a toxic, nitrogen-fixing filamentous cyanobacterium, which forms large summer blooms in the Baltic Sea. Benthic recruitment from resting stages (akinetes) and vegetative cells deposited on the seafloor have long been suspected to initiate the blooms. We found that, depending on species-specific traits, deposit-feeding macrofauna (an amphipod, Monoporeia affinis, a bivalve, Macoma balthica and an invasive polychaete, Marenzelleria cf. arctia) has the potential to either reduce or facilitate recruitment of this cyanobacterium. Shorter filament length in treatments with fauna than in the treatment without indicates feeding on or mechanical destruction of N. spumigena by the animals. Our results show the importance of an often overlooked aspect of phytoplankton bloom initiation, the role of macrozoobenthos.     

Toxicity and isolation of the cyanobacterium Nodularia spumigena from the southern Baltic Sea in 1986

Three water bloom samples were collected in August 1986 from the southern Baltic Sea. Acute toxicity of the samples was determined by mouse bioassay and the toxins were further studied by HPLC. The bloom samples contained equal amounts of cyanobacteria Nodularia spumigena and Aphanizomenon flos-aquae and were hepatotoxic. Two hepatotoxic Nodularia spumigena strains were isolated from the samples. The isolates produce a toxic peak indistinguishable from the bloom material in the HPLC analysis. The toxicity of the fractions was verified by mouse bioassay. Thus the toxicity of the bloom samples was in all likelihood caused by Nodularia spumigena.     

Large-scale patterns of Nodularia spumigena blooms in Pyramid Lake,Nevada, determined from Landsat imagery: 1972–1986

Magnitude and long-term periodicity of summer-autumn blooms of the nitrogen-fixing cyanobacterium, Nodularia spumigena, were characterized for hyposaline Pyramid Lake, Nevada, from Landsat MSS band 3 film negatives. Predicted lakewide mean chlorophyll a concentrations for Landsat overpasses during the July–October Nodularia bloom season ranged from 27 to 72 mg m^–3 with an overall average concentration of 32 ± 7 mg m^–3 between 1972 and 1986. Nodularia blooms were usually annual events. Blooms were not observed on Landsat images in only three of 15 years (1973, 1980, 1982) and midsummer calcium carbonate whitings occurred in two of these years (1973, 1980). Magnitude of Nodularia blooms was highly variable among years and very large blooms, where maximum mean chlorophyll a concentration exceeded one standard deviation of the 15 year overall mean (> 39 mg m^–3) appeared in 1974, 1975, 1977, 1979, 1984, 1985 and 1986. Very large early-July blooms always occurred during or following years of above average fluvial discharge to Pyramid Lake (1984–1986) and were associated with meromixis produced by the large influx of freshwater.Several problems arise using Landsat remote sensing to estimate magnitude and periodicity of scum-forming blue-green algal blooms. These complications may reduce accuracy and precision of phytoplankton biomass estimates made from Landsat images. Nevertheless, Landsat remote sensing enabled us to quantify relative bloom magnitude with limited collection of ground-based data and at a large-scale temporal and spatial resolution not possible using alternative methodologies.     

GENETIC, MORPHOLOGICAL, AND TOXICOLOGICAL VARIATION AMONG GLOBALLY DISTRIBUTED STRAINS OF NODULARIA (CYANOBACTERIA)

Morphological, toxicological, and genetic variation was examined among 19 strains of Nodularia. The strains examined could be morphologically discriminated into four groups corresponding to N. spumigena Mertens, N. sphaerocarpa Bornet et Flahault, and two strains that did not clearly correspond to currently accepted Nodularia species. Genetic variation was examined using nucleotide sequencing of the phycocyanin intergenic spacer region (cpcBA-IGS) and RAPD-PCR. The PCR-RFLP of the cpcBA-IGS differentiated four genotypes corresponding to the four morphological groups. However, nucleotide sequencing of 598 bp of the 690-bp fragment showed that one of the three strains corresponding to N. sphaerocarpa (PCC 7804) was genetically divergent from the other two, suggesting that it constitutes a distinct species. Nucleotide variation within the morphospecies groups was limited (<1%), and all 14 Australian strains of N. spumigena possessed identical cpcBA-IGS sequences. The RAPD-PCR differentiated the same groups as the cpcBA sequencing and discriminated each of the seven different Australian populations of N. spumigena. Strains from within a bloom appeared genetically identical; however, strains isolated from different blooms could be separated into either a western or a southeastern Australian cluster, with one strain from western Australia showing considerable genetic divergence. The pattern of variation suggests that individual blooms of N. spumigena are clonal but also that Australian N. spumigena populations are genetically distinct from each other. Examination of genetic distance within and between blooms and within and between morphological groups showed clear genetic dicontinuities that, in combination with the cpcBA-IGS data, suggest that Nodularia contains genetically distinct morphospecies rather than a continuous cline of genetic variation. Furthermore, these morphospecies are genetically variable, exhibiting hierarchical patterns of genetic variation on regional and global scales. Production of the hepatotoxin nodularin was not restricted to one genetic lineage but was distributed across three of the five genotypic groups. A strain of N. spumigena from a nontoxic Australian population was found to fall within the range of genetic variation for other toxic Australian strains and appears to be a unique nontoxic strain that might have arisen by loss of toxin production capacity.     

Factors Affecting the Germination of Akinetes of Nodularia spumigena (Cyanobacteriaceae)

Nutritional and physical factors which influence the germination of akinetes of Nodularia spumigena (Cyanobacteriaceae) were examined. Low concentrations of phosphorus (<0.9 μM) were required for germination. Nitrate had no effect, but ammonia, at concentrations of >45 μM, inhibited germination. Salinities of >20‰ were inhibitory to germination. Optimum temperatures were 22°C or greater. Germination did not take place in the dark, but only very low light intensities (0.5 microeinstein m⁻² s⁻¹) were necessary to initiate germination. Red light (620 to 665 nm) was required. More than 24 h of continuous exposure to light was necessary for any significant germination to occur. The conditions for germination corresponded with conditions in the Peel-Harvey Estuary, Western Australia, 2 to 3 weeks before large summer Nodularia blooms.     

Assimilation of Diazotrophic Nitrogen into Pelagic Food Webs

The fate of diazotrophic nitrogen (N_D) fixed by planktonic cyanobacteria in pelagic food webs remains unresolved, particularly for toxic cyanophytes that are selectively avoided by most herbivorous zooplankton. Current theory suggests that N_D fixed during cyanobacterial blooms can enter planktonic food webs contemporaneously with peak bloom biomass via direct grazing of zooplankton on cyanobacteria or via the uptake of bioavailable N_D (exuded from viable cyanobacterial cells) by palatable phytoplankton or microbial consortia. Alternatively, N_D can enter planktonic food webs post-bloom following the remineralization of bloom detritus. Although the relative contribution of these processes to planktonic nutrient cycles is unknown, we hypothesized that assimilation of bioavailable N_D (e.g., nitrate, ammonium) by palatable phytoplankton and subsequent grazing by zooplankton (either during or after the cyanobacterial bloom) would be the primary pathway by which N_D was incorporated into the planktonic food web. Instead, in situ stable isotope measurements and grazing experiments clearly documented that the assimilation of N_D by zooplankton outpaced assimilation by palatable phytoplankton during a bloom of toxic Nodularia spumigena Mertens. We identified two distinct temporal phases in the trophic transfer of N_D from N. spumigena to the plankton community. The first phase was a highly dynamic transfer of N_D to zooplankton with rates that covaried with bloom biomass while bypassing other phytoplankton taxa; a trophic transfer that we infer was routed through bloom-associated bacteria. The second phase was a slowly accelerating assimilation of the dissolved-N_D pool by phytoplankton that was decoupled from contemporaneous variability in N. spumigena concentrations. These findings provide empirical evidence that N_D can be assimilated and transferred rapidly throughout natural plankton communities and yield insights into the specific processes underlying the propagation of N_D through pelagic food webs.     

The effect of salinity on the growth,toxin production,and morphology of <Emphasis Type="BoldItalic">Nodularia spumigena</Emphasis> isolated from the Gulf of Gdańsk,southern Baltic Sea

Culture experiments on the toxic Nodularia spumigena strain NSGG-1 isolated from the Gulf of Gdańsk showed a significant effect of salinity on growth and nodularin production. Growth of the NSGG-1 strain, was optimal between 7 and 18 psu, lower at 3 and 24 psu and was significantly inhibited at the extreme salinities of 0 and 35 psu. Nodularin (NOD) content of N. spumigena, estimated by the NOD/Chla ratios, correlated positively with salinity and increased from 0 to 35 psu. The NOD/Chla ratio on day 10 of growth was high, and, reached the maximum at day 30. A sudden increase in salinity from 7 to 18 and 35 psu resulted in plasmolysis of Nodularia cells. Salinity was also observed to have other effects on NSGG-1; the filaments were longest at 7 psu, while an increased number of akinetes were formed at 35 psu. The number of heterocytes was markedly reduced at the extreme salinities. This latter finding might explain why Nodularia blooms do not occur outside a certain salinity range in nitrogen-deficient waters.     

Sedimentation of Nodularia spumigena and distribution of nodularin in the food web during transport of a cyanobacterial bloom from the Baltic Sea to the Kattegat

Nodularia spumigena is a toxic cyanobacteria that blooms in the Baltic Sea every year. In the brackish water of the Baltic Sea, its toxin, nodularin, mainly affects the biota in the surface water due to the natural buoyancy of this species. However, the fate of the toxin is unknown, once the cyanobacteria bloom enters the more saline waters of the Kattegat. In order to investigate this knowledge gap, a bloom of N. spumigena was followed during its passage, carried by surface currents, from the Baltic Sea into the Kattegat area, through the Öresund strait. N. spumigena cells showed an increased cell concentration through the water column during the passage of the bloom (up to 130 10³ cells ml⁻¹), and cells (4.2 10³ cells ml⁻¹) could be found down to 20 m depth, below a pycnocline. Sedimentation trap samples from below the pycnocline (10–12 m depth) also showed an increased sedimentation of N. spumigena filaments during the passage of the bloom. The toxin nodularin was detected both in water samples (0.3–6.0 μg l⁻¹), samples of sedimenting material (a toxin accumulation rate of 20 μg m^-2 day⁻¹), zooplankton (up to 0.1 ng ind.⁻¹ in copepods), blue mussels (70–230 μg kg⁻¹ DW), pelagic and benthic fish (herring (1.0–3.4 μg kg⁻¹ DW in herring muscle or liver) and flounder (1.3-6.2 μg kg⁻¹ DW in muscle, and 11.7-26.3 μg kg⁻¹ DW in liver). A laboratory experiment showed that N. spumigena filaments developed a decreased buoyancy at increased salinities and that they were even sinking with a rate of up to 1,7 m day⁻¹ at the highest salinity (32 PSU). This has implications for the fate of brackish water cyanobacterial blooms, when these reach more saline waters. It can be speculated that a significant part of the blooms content of nodularin will reach benthic organisms in this situation, compared to blooms decaying in brackish water, where most of the bloom is considered to be decomposed in the surface waters.     

Deposit-feeders accumulate the cyanobacterial toxin nodularin

Blooms of toxic cyanobacteria may potentially affect food web productivity and even be a human health hazard. In the Baltic Sea, regularly occurring summer blooms of nitrogen-fixing cyanobacteria are often dominated by Nodularia spumigena, which produces the potent hepatotoxin nodularin. Evidence of sedimentation of these blooms indicates that benthic fauna can be exposed to nodularin. In a one month experiment, we simulated the settling of a summer bloom dominated by N. spumigena in sediment microcosms with three species of sediment-dwelling, deposit-feeding macrofauna, the amphipods Monoporeia affinis and Pontoporeia femorata and the bivalve Macoma balthica, and analyzed nodularin in the animals by HPLC–ESI–MS (high-performance liquid chromatography–electrospray ionization–mass spectrometry). We found nodularin in quantities of 50–120 ng g⁻¹ DW. The results show that deposit-feeding macrofauna in the Baltic Sea may contribute to trophic transfer of nodularin.     

Settling cyanobacterial blooms do not improve growth conditions for soft bottom meiofauna

Summer blooms of the toxin-producing cyanobacteria Nodularia spumigena are frequent in the Baltic Sea and recent findings suggest that they may be an important food source for the benthos below the euphotic zone. To investigate the effects of settling spring and summer phytoplankton blooms on meiofaunal growth, we assayed concentrations of nucleic acids in three ostracod species (Candona neglecta; Heterocyprideis sorbyana and Paracyprideis fennica) and one genus of nematodes (Paracanthonchus spp.) after incubation in sediments with the one of the following food additions: (1) diatoms, (2) the cyanobacterium Nodularia spumigena, (3) Tetraphyll® as a known high-quality food source, (4) lignin as a refractory artificial food, and (5) control (no added organic matter). The ribosomal ribonucleic acid (RNA) content and RNA:DNA ratios of the tested organisms were lower in the cyanobacteria treatment than in the diatom treatment, with the difference in RNA:DNA ratios being statistically significant for all species except C. neglecta. Moreover, individuals incubated with N. spumigena showed RNA:DNA levels similar to those found in the lignin and control treatments. Furthermore, N. spumigena had lower concentrations of both enzymatically hydrolysable amino acids (EHAA) and eicosapentaenoic acid (EPA) than diatoms suggesting lower nutritional quality for consumers. These results indicate that recently settled summer blooms of N. spumigena are nutritionally poor and do not improve conditions for meiofaunal growth in Baltic sediments. In contrast, input of diatoms to the sediments during spring is crucial for meiofaunal growth.     

A Fuzzy Logic Model to Describe the Cyanobacteria Nodularia spumigena Blooms in the Gulf of Finland, Baltic Sea

A fuzzy logic model to describe the seasonal evolution of Nodularia spumigena blooms in the Gulf of Finland was built and calibrated on the basis of monitoring data. The model includes three phosphate sources: excess phosphate after the annual spring bloom and parameterised phosphate transport to the upper mixed layer by turbulent mixing and upwelling events. Surface layer temperature and wind mixing form the physical conditions controlling the growth of N. spumigena. Model simulations revealed that phosphate input caused by turbulent mixing and upwelling have to be taken into account to achieve the best fit with observed data. Testing the fuzzy model for early prediction of maximum N. spumigena biomass about a month before the usual occurrence of blooms, gave good results. The potential use of the model for prediction of bloom risk at a certain location along the Estonian or Finnish coast was tested. The bloom transport velocities used in the fuzzy model were pre-calculated by a 3D numerical circulation model for different wind regimes.     

Nitrogen fixation by Nodularia spumigena Mertens (Cyanobacteriaceae). 2: Laboratory studies

The effects of changes in diurnal light patterns, salinity, and phosphorus on nitrogen fixation (as measured by acetylene reduction) by Nodularia spumigena Mertens were examined. As well, the effects of added inorganic nitrogen on growth, nitrogen fixation and heterocyt frequencies, and changes in nitrogen fixation and heterocyst frequencies during the growth cycle of Nodularia in cultures were determined.The diurnal pattern of nitrogenase activity in Nodularia was primarily light-induced, though dark activity did occur. Nitrogenase activity following a period of darkness exceeded the normal light rate (> 90 compared to 50 nmol · C₂H₂ reduced · ml^–1 · h^–1). Nitrogen fixation was reduced by high and very low salinities (5 to 10 was the optimum range), and added phosphorus stimulated nitrogenase in P-starved cells. Added nitrogen (ammonium or nitrate) had no effect on the growth of Nodularia, but in short term studies, ammonium completely inhibited nitrogenase activity. Heterocyst frequencies were greatest in the log phase of growth (to 40 per mm). During stationary phase, nitrogenase activity was negligable.     

Occurrence of cyanobacterial blooms in the baltic sea in relation to environmental conditions

Cyanobacterial blooms occur regularly in summer in central parts of the Baltic Sea. They are mainly composed of Aphanizomenon sp. and Nodularia spumigena. Both species have almost similar ecological requirements and can roughly be considered a uniform functional group. In order to identify factors that might favour bloom development, water quality data from monitoring programmes were compared with bloom distribution. A salinity from 3.8 to 11.5 PSU proved important for the spatial distribution of the bloom development. The bloom's onset was triggered by temperatures approximating 16°C provided that global radiation was > 120 W/m² (daily mean) and wind speed was < 6 m/s. Nutrient concentrations decreased immediately before the bloom. The bloom's development ceased with poor weather conditions characterized by low irradiation or high wind speed.