Maximum rates of N2 fixation and primary production are out of phase in a developing cyanobacterial bloom in the Baltic Sea

Although N2-fixing cyanobacteria contribute significantly to oceanic sequestration of atmospheric CO2, little is known about how N2 fixation and carbon fixation (primary production) interact in natural populations of marine cyanobacteria. In a developing cyanobacterial bloom in the Baltic Sea, rates of N2 fixation (acetylene reduction) showed both diurnal and longer-term fluctuations. The latter reflected fluctuations in the nitrogen status of the cyanobacterial population and could be correlated with variations in the ratio of acetylene reduced to 15N2 assimilated. The value of this ratio may provide useful information about the release of newly fixed nitrogen by a cyanobacterial population. However, although the diurnal fluctuations in N2 fixation broadly paralleled diurnal fluctuations in carbon fixation, the longer-term fluctuations in these two processes were out of phase

Some environmental factors influencing phytoplankton in the Southern Ocean around South Georgia

Data on phytoplankton and zooplankton biomass, and physical and chemical variables, are combined with a published multivariate description of diatom species composition to interpret variation within an area around South Georgia surveyed during an austral summer. Large-scale species distributions could be equated to the different water masses which reflected the interaction of the Antarctic Circumpolar Current with the island and the Scotia Ridge. Small-scale factors were found to act at an interstation scale and imposed local variation on the biogeographic pattern. Nutrient depletion could be related to phytoplankton biomass but no single inorganic nutrient of those measured (NO 3 −N, PO 4 −P and silica) could be identified as important. The ratio Si:P appeared to be more important as an ecological factor. The impact of grazing by krill and other zooplankton could only be resolved as differences in phytoplankton biomass and phaeopigment content. Diatom species composition showed a relation to local krill abundance very different from that suggested by published studies, but could be explained as the effect of earlier grazing outside the study area. The effects of vertical mixing could not account for interstation differences as pycnocline depth was uniformly greater than euphotic depth, and vertical stability very low. Some comparison was made with data collected in 1926–31 by the Discovery Investigations. Significant differences in the distribution of certain taxa such as Chaetoceros criophilum and C. socialis were traced to major differences in hydrology.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46983/1/300_2004_Article_BF00443379.pd

Meso- and macrozooplankton communities in the Weddell Sea, Antarctica

The present paper describes composition and abundance of meso- and macrozooplankton in the epipelagic zone of the Weddell Sea and gives a systematic review of encountered species regarding results of earlier expeditions. Material was sampled from 6 February to 10 March 1983 from RV Polarstern with a RMT 1+8 m (320 and 4500 μm mesh size). In agreement with topography and water mass distribution three distinct communities were defined, clearly separated by cluster analysis: The Southern Shelf Community has lowest abundances (approx. 9000 ind./1000 m3). Euphausia crystallorophias and Metridia gerlachei are predominating. Compared with the low overall abundance the number of regularly occurring species is high (55) due to many neritic forms. Herbivores and omnivores are dominating (58% and 35%). The North-eastern Shelf Community has highest abundances (about 31 000 ind./1000 m3). It is predominated by copepodites I–III of Calanus propinquus and Calanoides acutus (61%). The faunal composition is characterized by both oceanic and neritic species (64). Fine-filter feeders are prevailing (65%). The Oceanic Community has a mean abundance of approximately 23 000 ind./1000 m3, consisting of 61 species. Dominances are not as pronounced as in the shelf communities. Apart from abundant species like Calanus propinquus, Calanoides acutus, Metridia gerlachei, Oithona spp. and Oncaea spp. many typical inhabitants of the Eastwind Drift are encountered. All feeding types have about the same importance in the Oceanic Community

Associations of cyanobacterial toxin, nodularin, with environmental factors and zooplankton in the Baltic Sea

Concentrations of a cyanobacterial toxin, nodularin, were measured in the Baltic Sea in 1998 and 1999. Statistical associations of nodularin concentrations with environmental factors were tested by multiple regression analysis. To reveal the toxin-producing organism, colonies of Aphanizomenon and filaments of Nodularia were picked and analyzed for peptide toxins. It was also investigated whether there was an association with zooplankton and Nodularia. All the measured seston samples contained nodularin, but other toxins were not detected by the HPLC analysis. In both years, the highest nodularin concentrations were found at the surface water layer. The nodularin concentrations were positively correlated with silicate concentrations in water. High concentrations of silica in surface water may indicate recent upwelling, which in turn renders surface water rich in nutrients. This upwelling is likely to intensify cyanobacterial growth and toxin production, which may explain this rather unexpected result. The picked Aphanizomenon colonies did not contain nodularin and the dissolved nodularin concentrations were below detection limit. Thus it was concluded that most of the nodularin was bound to Nodularia cells. The abundances of zooplankton (copepods, rotifers, and cladocerans) were unrelated to Nodularia, but were positively associated with Aphanizomenon

The relationships between N:Si:P molar ratio and coastal marine phytoplankton in Izmir Bay (Eastern Aegean Sea-Turkey)

N:P, Si:N and Si:P ratios are one of the most important factor having a control on the dominance of phytoplankton groups both in oceans and coastal waters. The changes of these ratios have a limiting effect on the growth of the phytoplankton groups. This study aimed that to determine effects of the N:P:Si ratios to coastal phytoplankton groups in Izmir Bay on a weekly basis after activated the Big Channel Waste Water Treatment project. For this purpose, nutrients and Chl-a levels were analyzed from sea water which were taken from 0, 5, 10 m and bottom depths of the Gulf of Izmir on a weekly basis between 2003-2004. At the end of the study, results of analysis from water samples which were taken from three stations on a weekly basis between 2003-2004 from the Gulf of Izmir the ratios of nutrient values (N:P, Si:P, Si:N and C:Chl a) were compared. In conclusion, the average N:P, Si:P, Si:N and Chl a:C values were 2.55±0.31, 4.19 ± 0.56, 2.78±0.41, 0.0080±0.0011 for the Meles station (Station 1), 2.31+0.29, 4:39 ± 0.67, 3.74±0.58, 0.0083±0.O011 for the Yacht harbor station (Station 2) and 1.99±0.32, 4.56 ± 0.59, 4.35±0.71, 0.0067±0.0009 for the Cigli station (Station 3), respectively. The emergence of processes acting on Reactive Phosphate and TIN in different times reveal a great difference onto the temporal distribution of these two nutrients in the Inner part of İzmir Bay. Thus, indirect evidences about these processes have been obtained from the nutrients and their rates of distribution. © by PSP

BASIC: Baltic Sea cyanobacteria. An investigation of the structure and dynamics of water blooms of cyanobacteria in the Baltic Sea responses to a changing environment.

The blooms of cyanobacteria that develop each summer in the Baltic Sea are composed of two functional groups, namely the small-sized picocyanobacteria (Synechococcus sp.) and the larger, colony-forming, filamentous N2-fixing cyanobacteria. The former encompassed both red (phycoerythrin-rich) and blue-green (phycocyanin-rich) species. The majority of the picocyanobacteria measured less than 1 μm and this size fraction comprised as much as 80% of the total cyanobacterial biomass and contributed as much as 50% of the total primary production of a cyanobacterial bloom. The picocyanobacteria are incapable of fixing N2, do not possess gas vesicles and are not toxic. However, a small filamentous Pseudanabaena sp. that could potentially fix N2 was isolated from the picocyanobacteria fraction. The larger cyanobacteria may form surface scums because they possess gas vesicles that make them buoyant. Although their biomass was less than the picocyanobacteria, they therefore form the more conspicuous and nuisance-forming part of the bloom. The larger cyanobacteria were composed mainly of three different species: Nodularia spumigena, Aphanizomenon flos-aquae and Anabaena sp. These all belong to the heterocystous, N2-fixing cyanobacteria. N. spumigena and A. flos-aquae were the dominant species; only N. spumigena was toxic. Although individual Nodularia filaments showed a range of different phenotypes, they all belong to one species as judged from 16S rDNA sequencing. Through determination of the genotypes of many individual Nodularia filaments, it was shown that this population was not clonal and that horizontal exchange of genetic information occurs. N. spumigena and A. flos-aquae were different with respect to their photosynthetic and N2-fixing potentials. Depending on prevailing environmental conditions, these differences would promote the proliferation of one species over the other and hence would determine overall the toxicity of a bloom. Daily integrals of photon irradiance rather than temperature determined the onset of bloom formation. During a bloom, the diazotrophic cyanobacteria fixed N2 at a rate that was 10–20% in excess of their own demand for N. Picocyanobacteria assimilated most of this excess N as shown by 15N incorporation. During bloom conditions, the diazotrophic cyanobacteria met about 50% of the N demand of the total cyanobacterial community. The picocyanobacteria were predominantly N-limited while the diazotrophic cyanobacteria were probably iron limited. These findings allow us to understand the formation of toxic cyanobacterial blooms and also to develop tools to predict bloom formation

Chemical and Biological Composition of Suspended Particles and Aggregates in the Baltic Sea in Summer (1999)

Suspended particles and particle aggregates, which formed from concentrated field samples on the roller table, were characterized biologically and chemically along a transect through the Baltic Sea in summer 1999. Phytoplankton composition in field samples was dominated by cyanobacteria, including the filamentous diazotrophic cyanobacteria Aphanizomenon ‘ baltica’, Nodularia spumigena and Anabaena spp. These species formed aggregates together with diatoms, mainly Skeletonema costatum and Chaetoceros spp. and with dinoflagellates, mainly withDinophysis norvegica . Compared to the Redfield ratio, concentration ratios of particulate organic carbon, nitrogen and phosphorus, [POC]:[PON]:[POP], indicated an enrichment of carbon, especially in aggregates. However, regression analysis indicated a higher production rate of PON relative to POP and POC and significant background concentrations of POC. In field samples the concentration of transparent exopolymer particles (TEP) varied around 200 μg Xanthan Equiv. l−1 and comprised a volume fraction of 2–7 ppm and an abundance of about 105 TEP ml−1. TEP were enriched in aggregates as inferred from volume ratios of TEP to conventional particles. It is suggested, that TEP contribute substantially to the background concentration of POC, while the high production rate of PON is attributed to nitrogen fixation of diazotrophic cyanobacteria