RECENT APPEARANCE OF CYLINDROSPEMOPSIS (CYANOBACTEIUA) IN FIVE HYPEREUTROPHIC FLORIDA LAKES1

Observations of historical and recent phytoplankton samples from five hypereutrophic Florida lakes indicate that nitrogen-fixing cyanobacteria in the genus Cylindrospermopsis Seenayya et Subba Raju have entered these water-bodies sometime in the last 30 years. Cylindrospermopsis forms a year-round bloom in one of the five lakes, dominates seasonally in another, and is at least at times an important component of the phytoplankton community in the remaining three. The increase in abundance of Cylindrospermopsis in Florida lakes could have implications for water management.     

Phytoplankton assemblages and steady state in deep and shallow eutrophic lakes – an approach to differentiate the habitat properties of Oscillatoriales

Ecological conditions and phytoplankton succession in two shallow hypertrophic lakes (Langer See and Melangsee) and a dimictic, eutrophic lake (Scharmützelsee) in a lake chain in Eastern Germany were analyzed from 1999 to 2001 in order to find situations of phytoplankton steady state assemblages and variables controlling the phytoplankton composition according to Reynolds et al. (2002). Long term background data from 1993 to 2001 suggest steady state conditions in shallow lakes, whereas the deep lake exhibited irregular fluctuations between various phytoplankton stages. Since the phytoplankton composition in the shallow lakes was similar in all the 3 years, it was highly predictable. Steady state conditions dominated by different species of Oscillatoriales were detected during the summer period 1999 and 2000 in Langer See and in Melangsee (see Mischke & Nixdorf, this volume). This dominant assemblage found in both lakes (group S ₁ acc. to Reynolds et al., 2002): Planktothrix agardhii (Gom.) Anagn. et Kom., Limnothrix redekei (Van Goor) Meffert, Pseudanabaena (Lauterb.) is typical in turbid mixed layers with highly light deficient conditions, but it is also regularly dominant in the dimictic lake Scharmützelsee as observed in 1999 and 2001 (Pseudanabaena limnetica (Lemm.) Kom. The Nostocales Cylindrospermopsis raciborskii (Wolz.) Seenayya et Subba Raju and Aphanizomenon gracile (Lemmerm.) Lemmerm. were important in the shallow lakes as well as in lake Scharmützelsee. Nevertheless, the occurrence of filamentous cyanobacteria in the dimictic lake was not regular and an unpredictable change in phytoplankton development was observed in 2000. It is discussed, whether this phenomenon of regular succession in shallow hypertrophic lakes is caused by adaptation to a resilient and an extreme environment or by the pool of species that can live or survive in that environment. This was checked through comparison of the depth of the mixed layer, the mean daily irradiance within this layer and the nutrient resources. Although the nutrient resources in both types of lake are near threshold levels, indicating growth inhibition by dissolved nutrients (DIP, DIN, TIC, DSi), the under water light supply seems to be the key factor favoring the dominance of filamentous cyanobacteria belonging to the functional group S ₁.     

The efficiency of combined coagulant and ballast to remove harmful cyanobacterial blooms in a tropical shallow system

We tested the hypothesis that a combination of coagulant and ballast could be efficient for removal of positively buoyant harmful cyanobacteria in shallow tropical waterbodies, and will not promote the release of cyanotoxins. This laboratory study examined the efficacy of coagulants [polyaluminium chloride (PAC) and chitosan (made of shrimp shells)] alone, and combined with ballast (lanthanum modified bentonite, red soil or gravel) to remove the natural populations of cyanobacteria collected from a shallow eutrophic urban reservoir with alternating blooms of Cylindrospermopsis and Microcystis. PAC combined with ballast was effective in settling blooms dominated by Microcystis or Cylindrospermopsis. Contrary to our expectation, chitosan combined with ballast was only effective in settling Cylindrospermopsis-dominated blooms at low pH, whereas at pH ≥ 8 no effective flocculation and settling could be evoked. Chitosan also had a detrimental effect on Cylindrospermopsis causing the release of saxitoxins. In contrast, no detrimental effect on Microcystis was observed and all coagulant-ballast treatments were effective in not only settling the Microcystis dominated bloom, but also lowering dissolved microcystin concentrations. Our data show that the best procedure for biomass reduction also depends on the dominant species.     

The role of heterocytes in the physiology and ecology of bloom-forming harmful cyanobacteria

Dolichospermum flos-aquae and Cylindrospermopsis raciborskii are two cyanobacteria species which cause harmful blooms around the world. Both these species share the capacity to fix atmospheric nitrogen in heterocytes (cell where fixation occurs). While Dolichospermum can express heterocytes at rather regular intervals across the filament, Cylindrospermopsis can only express heterocytes at the end of the filament. The aim of this study was to experimentally assess the role of heterocyte position in the eco-physiological responses of these bloom forming cyanobacteria. Replicated monocultures of each species were grown at different eutrophication scenarios (limiting and sufficient nitrogen and phosphorus concentrations, in factorial design). Dolichospermum reached high biomass regardless of the nitrogen (and phosphorus) provided, suggesting that this species could bloom in situations with and without nitrogen limitation. In contrast, Cylindrospermopsis reached high biomass only when nitrogen supply was high; its biomass was 15-20 times lower when relying on nitrogen fixation. Hence, despite its ability to fix nitrogen, blooms of Cylindrospermopsis would be expected only under high total nitrogen availability. In Dolichospermum heterocytes occurred only in the scenarios without supplied nitrogen while in Cylindrospermopsis heterocytes occurred regardless of nitrogen availability. Yet, in both species nitrogen fixation occurred (heterocytes were functional) only when nitrogen was limiting, and nitrogen fixation increased significantly at higher phosphorus concentration. Finally, in the absence of supplied nitrogen, filament length in Dolichospermum was the longest, while filaments in Cylindrospermopsis were the shortest (up to 13 times shorter than at nitrogen sufficiency). Therefore, heterocyte expression in Dolichospermum, and filament length in Cylindrospermopsis seem good proxies of nitrogen fixation. The eco-physiological responses recorded here help understand the distribution of these species along nutrient gradients in nature.     

Host-Specificity and Dynamics in Bacterial Communities Associated with Bloom-Forming Freshwater Phytoplankton

Many freshwater phytoplankton species have the potential to form transient nuisance blooms that affect water quality and other aquatic biota. Heterotrophic bacteria can influence such blooms via nutrient regeneration but also via antagonism and other biotic interactions. We studied the composition of bacterial communities associated with three bloom-forming freshwater phytoplankton species, the diatom Aulacoseira granulata and the cyanobacteria Microcystis aeruginosa and Cylindrospermopsis raciborskii. Experimental cultures incubated with and without lake bacteria were sampled in three different growth phases and bacterial community composition was assessed by 454-Pyrosequencing of 16S rRNA gene amplicons. Betaproteobacteria were dominant in all cultures inoculated with lake bacteria, but decreased during the experiment. In contrast, Alphaproteobacteria, which made up the second most abundant class of bacteria, increased overall during the course of the experiment. Other bacterial classes responded in contrasting ways to the experimental incubations causing significantly different bacterial communities to develop in response to host phytoplankton species, growth phase and between attached and free-living fractions. Differences in bacterial community composition between cyanobacteria and diatom cultures were greater than between the two cyanobacteria. Despite the significance, major differences between phytoplankton cultures were in the proportion of the OTUs rather than in the absence or presence of specific taxa. Different phytoplankton species favoring different bacterial communities may have important consequences for the fate of organic matter in systems where these bloom forming species occur. The dynamics and development of transient blooms may also be affected as bacterial communities seem to influence phytoplankton species growth in contrasting ways.     

Seasonal variation in the composition and rate of change of the phytoplankton community in a deep subalpine lake (Lake Garda, Northern Italy). An application of nonmetric multidimensional scaling and cluster analysis

Seasonal variations and spatial homogeneity of the phytoplankton community were followed, from spring 1991 to spring 1992, in four pelagic stations of a large deep subalpine lake (Lake Garda, Northern Italy). Both cluster analysis and nonmetric multidimensional scaling (NMDS) applied to Bray & Curtis' dissimilarity matrices computed on density and biovolume data were employed; the Bray & Curtis index, calculated between pairs of chronologically contiguous samples, was also used as a measure of the community change rate over the temporal succession. In the tree diagrams obtained both from density and biovolume data, six groups of different size have been identified, with ordered sequences of samples within them. Superimposition of the results of cluster analysis on the NMDS configurations has allowed interpretations of the trajectories of the samples as a chronological and cyclical succession of compositionally homogeneous groups. A clear relationship between the community change rate and stability of the water column has been assessed. The specific composition of the six groups has been discussed in relation to environmental variables and in terms of adaptive strategies. During winter (winter-spring group) the turbulence of the water and the availability of nutrients favour the development of colonial Bacillariophyceae (Fragilaria crotonensis Kitton, Tabellaria fenestrata (Lyngb.) Kütz., Aulacoseira spp.), Cyanophyceae (Planktothrix agardhii (Gom.) Anagn. et Kom. and Planktolyngbya limnetica (Lemur.) Kom.-Legn. et Cronb.) and Cryptophyceae. In late spring group, with the stabilisation of the water column and silicon depletion, the diatoms give way to small, opportunistic species (Ankyra judayi (G. M. Smith) Fott, Cyclotella spp., Chroomonas acuta Utermhöl) and larger species (Ceratium hirundinella (O. F. Müll.) Dujardin). The three summer groups are characterised by a development of Chlorophyceae (chiefly Chlorococcales), Cyanophyceae (mainly Chroococcales), Cyclotella spp. and Dinophyceae. With the autumn destratification the summer community undergoes a rearrangement principally in favour of Cyanophyceae and Cryptophyceae.     

EPIPELIC AND EPILITHIC DIATOM ASSEMBLAGES IN MONTEZUMA WELL NATIONAL MONUMENT,ARIZONA1

Epipelic and epilithic diatom assemblages in Montezuma Well National Monument, Arizona, were identified and analyzed by H' (species diversity), species number, J' (evenness), relative abundance, SIMI (similarity index), and DI (dissimilarity index) values. The epipelic assemblage was found to be a tri-dominant association of Cyclotella pseudostelligera f. parva Czar. & Blinn, Cocconeis placentula var. lineata (Ehr.) V.H. and Achnanthes linearis (W. Sm.) Grun. The epilithic assemblage was a tri-dominant association of Rhoicosphenia curvata (Kütz.) Grun. ex Rabh., Cy. Pseudostelligera f. parva and Synedra ulna (Nitz.) Ehr. Both associations persisted throughout the year. Of the 83 taxa observed, 51 were common to both assemblages, 24 were restricted to the epipelon, and 8 were restricted to the epilithon. On a yearly basis, the epipelic assemblage exhibited less diversity (H') than the epilithon, even though the latter exhibited fewer taxa. The use of mean diversity values was also determined to be unacceptable. Cy. Pseudostelligera f. parva and S. ulna appeared more abundant under high light intensity and duration, Fragilaria construens var. venter (Ehr.) Grun. favored low light intensity and duration, whereas A. linearis, R. curvata and Co. placentula var. lineata were tolerant of a variety of intensities and durations. On a yearly basis, both assemblages exhibited slight similarity (SIMI, DI). The use of SIMI values for comparing assemblages with few highly abundant taxa was determined to be unacceptable and under these conditions, the use of DI was recommended.     

Relationship between phytoplankton and environmental factors in landscape water supplemented with reclaimed water

The water quality of Feng-qing Lake, which is a landscape lake supplemented with reclaimed water, was surveyed to investigate the relationship between phytoplankton and environmental variables. A total of 29 water samples were collected to analyze temporal variations of phytoplankton and environmental factors from July 2013 to June 2014. Six phyla and 39 genera of phytoplankton were identified when the lake was supplied with reclaimed water. Among these, Cyanophyta and Chlorophyta account for 38.46% and 30.77% of phytoplankton, respectively. The dominant species in the lake are Pseudanabaena limnetica and Chlorella vulgaris, which are present the entire year. Other leading species include Cosmarium sp. and Raphidiopsis curvata. Principal component analysis (PCA) was conducted to analyze the relationship among environmental factors. Canonical correspondence analysis (CCA) was performed to investigate the relationship between environment factors and dominant species. The PCA result showed that temperature (T), total phosphorus (TP), total nitrogen (TN), transparency, and dissolved oxygen are the main factors that affect the eutrophication level of the lake. The CCA result revealed that TN, PO₄³⁻–P, chemical oxygen demand (COD), T, and chlorophyll a exhibit a close relation with dominant species. In particular, TN, salinity, and COD influence the growth of P. limnetica; T and COD influence the growth of R. curvata; and T, PO₄³⁻–P, NH₃–N, and pH influence the growth of C. vulgaris and Cosmarium sp.     

Phytoplankton associations in a small hypertrophic fishpond in East Hungary during a change from bottom-up to top-down control

Phytoplankton species composition and abundance of a shallow hypertrophic fishpond (Mézeshegyi-tó, East Hungary) was studied for the period 1992–1995. The pond showed a pronounced algal periodicity. High-diversity phytoplankton assemblages occurred in spring and autumn. During the winter period, low diversity values were related either to stable community states, when K-strategist species dominated the plankton, or to a large bloom of r-strategist species. In summer, the stable environment led to low-diversity, high-biomass phytoplankton assemblages, dominated by Cylindrospermopsis raciborskii. At this time, the growth conditions for Cylindrospermopsiswere akin to those prevailing in a continuous fermentor. The overwhelming dominance of this species lasted for more than four months, during which time, the phytoplankton resembled that of one in the tropics. In August, 1993, an unsuccessful chemical treatment for reducing the algal bloom succeeded in killing the pond's entire population of fish. The large fish-stock comprised the planktivorous silver carp. Although the summer of 1994 was one of the warmest summers of this century, the expected Cylindrospermopsis bloom failed to develop probably because of a higher grazing pressure by large zooplankton. In spite of the fact that the temporal and spatial pattern of the phytoplankton is influenced principally by bottom-up effects, changes in cascading trophic interactions may also considerably influence the species composition and biomass.     

Setae thickening in <Emphasis Type="Italic">Daphnia magna</Emphasis> alleviates the food stress caused by the filamentous cyanobacteria

It is assumed that daphnids adjust the filter screen morphology in order to minimize the interference with cyanobacterial filaments. The aim of this study was to investigate the impact of filamentous cyanobacteria (Aphanizomenon gracile Lemmermann, Cylindrospermopsis raciborskii Woloszynska Seenaya et Subba Raju) on the thickness and length of setae of the third pair of thoracic limbs of Daphnia magna. The second objective was to assess whether the setae modifications could improve the performance of daphnids in the presence of cyanobacteria. Three clones of Daphnia magna Straus were cultured with: green algae; green algae with filaments of Cylindrospermopsis; and green algae with filaments of Aphanizomenon. The size and age of animals in the first reproduction cycle as well as the number of offspring were recorded. Setae thickness and length were measured in the central part of each endopodite. Additionally, we analyzed how the changes in setae morphology affect the fitness of experimental animals using the intrinsic rate of population increase calculated with the Euler–Lotka equation. The results showed that the thickness and length of setae increased in the presence of filamentous cyanobacteria. Moreover, cyanobacteria-induced setae thickening was positively correlated to the fitness of daphnids, which may indicate setae thickening as a phenotypic adaptation to cope with food stress caused by filamentous cyanobacteria.     

巢湖蓝藻水华形成原因探索及"优势种光合假说"

为探索蓝藻水华的形成原因,从2007以来对巢湖西区浮游藻类种类、优势种季节变化、初级生产力、水质参数及优势种的光合生理生态学特性作了观测。关于蓝藻水华形成过程中迅猛发展的原因,近80a已提出了10种假说,但对解释巢湖形成的蓝藻水华,尚显不足。本文基于我们对蓝藻水华的了解,提出了如下“优势种光合假说”：（1）蓝藻水华包含各种藻类,蓝藻水华发生不仅与藻细胞浓度有关,还与水体初级生产力直接有关。巢湖中这两者在夏季最大,在冬季最小。但无定量关系。（2）水华藻类中生长最快、细胞密度最大的是优势种,含有多个优势种时可能随季节更替。巢湖几乎整年发生蓝藻水华,已检测出4种优势种都是蓝藻,从早春起先是水华鱼腥藻,以后有绿色微囊藻、惠氏微囊藻和铜绿微囊藻。（3）各种环境因子都影响优势种生长,其中少数主导因子影响较大。在巢湖富营养条件下,光强、温度和pH值是主导因子。（4）主导因子对优势种光合活性的影响,可决定其能否处于优势。巢湖的温度和pH值变化可能促进了惠氏微囊藻取代绿色微囊藻,铜绿微囊藻取代惠氏微囊藻,而光强变化可能调节冬季时水华鱼腥藻取代了绿色微囊藻,春季时正好是相反的取代。     

Using an online phycocyanin fluorescence probe for rapid monitoring of cyanobacteria in Macau freshwater reservoir

Monitoring of cyanobacteria and their toxins are traditionally conducted by cell counting, chlorophyll-a (chl-a) determination and cyanotoxin measurements, respectively. These methods are tedious, costly, time consuming, and insensitive to rapid changes in water quality and cyanobacterial abundance. We have applied and tested an online phycocyanin (PC) fluorescence probe for rapid monitoring of cyanobacteria in the Macau Storage Reservoir (MSR) that is experiencing cyanobacterial blooms. The relationships among cyanobacterial abundance, biovolume, cylindrospermopsin concentration, and PC fluorescence were analyzed using both laboratory and in-the-field studies. The performance of the probe was compared with traditional methods, and its advantages and limitations were assessed in pure and mixed cyanobacterial cultures in the laboratory. The proposed techniques successfully estimated the species including Microcystis and Cylindrospermopsis, two toxic species recently observed in the MSR. During February–November, 2010, the PC probe detected high correlations between PC and cell numbers (R ² = 0.71). Unlike the chl-a content, which indicates only the total algal biomass, the PC pigment specifically indicates cyanobacteria. These results support the PC parameter as a reliable estimate of cyanobacterial cell number, especially in freshwater bodies where the phytoplankton community and structure are stable. Thus, the PC probe is potentially applicable to online monitoring of cyanobacteria.     

Taxonomic notes on some freshwater planktonic Cryptophyceae based on light microscopy

The cryptomonads sampled frequently from pelagial of large freshwater bodies, lakes and ponds, but also found in littoral regions and in small water bodies covered with vegetation, are often characterized by the sigmoid (S-shaped) form of their cells. According to the quoted findings of electron microscopy it seems that these species should be incorporated into the new genus Campylomonas Hill. Because the EM characteristics have not been proved so far for all species, and the following nomenclatural combinations accomplished, the traditional classification into the genus Cryptomonas is kept here. The correct name for the largest of sigmoid cryptomonads is Cryptomonas curvataEhr. em. Penard. Contrarily, C. rostrata Troitz. em. Kisel. is to be held for later synonyms. The existence of the species C. rostratiformis Skuja remains uncertain. The smaller species of sigmoid shape, i.e. C. reflexa (Marss.) Skuja and C. marssonii Skuja, may also easily be discerned under the light microscope. From the small puddles with H₂S in water, shortened forms of both these species are documented, one of them under the published name C. anas Javorn. The pelagic assemblage of the above sigmoid cryptomonads frequently is completed by Plagioselmis nannoplanctica (Skuja) Novar., Lucas et Morr. and by P. lacustris (Pasch. et Ruttn.) Javorn. These flagellates so far are currently determined as the species of the genus RhodomonasKarsten. In addition to the EM characteristic, they differ from Rhodomonas by the absence of a true gullet (pseudopharynx) having only the ventral furrow with rows of superficial ejectosomes (similar to the genus Cryptochrysis Pascher). The ellipsoidal or ovoid cryptomonads are sampled more frequently from peat pools and small water bodies covered with vegetation than from open pelagial of lakes. An erroneous determination of them causes confusion. Because some strains are wrongly labeled, electron-microscopic characteristics are vaguely determined species. For example, some EM features of Cryptomonas ovata in fact belong to C. pyrenoidifera Geitl. or to C. phaseolus Skuja. Cryptomonas ovata Ehr. em. Stein is not a collective species with a wide dimensional range of ellipsoid cells. It is a large species the typical morphology which is described here in detail. C. splendida Czosn. differs from C. ovata only by the transversal orientation of the cell. Similar to C. ovata but smaller species is C. tatrica Czosn. These species are further compared with the well-defined species C. obovata Skuja and the particularly small C. phaseolus Skuja.     

黑龙江省七星河湿地硅藻植物的初步研究

报道了2004年对黑龙江省七星河湿地国家级自然保护区的硅藻门植物研究的结果,共发现155个分类单位,包括113种39变种3变型,分别隶属于2纲6目9科26属,其中中国新记录2种2变种1变型共计5个分类单位,初步分析了七星河湿地硅藻植物群落的种类组成及生态类型,大部分的硅藻属于普生种类,同时出现了一些喜酸种类如：Eunotia pectinalis var. ventralis(Ehr.)Hust., Tabellaria flocculosa(Roth) Kütz.,Gomphonema augur Ehr.,Navicula subtilissima Cl.等,还有少量的嗜碱性种类出现。     

BENTHIC MARINE DIATOM ASSOCIATIONS: UPPER FLORIDA BAY (FLORIDA) AND ASSOCIATED SOUNDS1

Models of the diatom associations found in upper Florida Bay and adjoining sounds have been constructed utilizing Q modal factor-vector analysis and ecologic diversity indices (Shannon index, number of species, evenness). Four distinct associations were defined using Q-mode factor-vector analysis. Two associations were epiphytic, occurring on Thalassia testudinum König—Association I was characterized by Cocconeis placentula Ehr., Association III by Cylindrotheca closterium (Ehr.) Reim. & Lewin and Cocconeis placentula Ehr. The other two associations were epipelic, occurring on the carbonate mud substratum—Association II was characterized by Cyclotella striata (Kütz.) Grun., Rhopalodia gibberula (Ehr.) O. Müller and Surirella fastuosa (Ehr.) Kütz., Association IV by Fragilaria crotonensis Kitton and Cyclotella striata (Kütz.) Grun. The majority of the 161 species identified were present in both the epiphytic and epipelic assemblages. Only 33 species were restricted to the epiphyton, and 18 species restricted to the epipelon. The epipelic assemblage was significantly more diverse than was the epiphytic assemblage. A general trend of increased diversity away from terrestrial environs toward more open areas of water in both the epipelon and epiphyton was also found.     

PRODUCTION OF NATURAL BUTYLATED HYDROXYTOLUENE AS AN ANTIOXIDANT BY FRESHWATER PHYTOPLANKTON1

Butylated hydroxytoluene (BHT) is one of the synthetic antioxidant agents commonly used for food additives. In the present study, we determined that four freshwater phytoplankton, including a green alga (Botryococcus braunii Kütz.) and three cyanobacteria [Cylindrospermopsis raciborskii (Wol?osz.) Seenaya et Sabba Raju, Microcystis aeruginosa (Kütz.) and Oscillatoria sp.] were capable of producing this compound. Hexane extracts from all the studied species exhibited various degrees of antioxidative properties when they were tested with the β‐carotene‐linoleate (β‐CL) assay and the 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) free‐radical‐scavenging assay. The highest antioxidant activity was observed in the crude extracts of M. aeruginosa and B. braunii, which displayed a similar activity to synthetic BHT. Gas chromatography/mass spectroscopy (GC‐MS) analysis of the purified fractions revealed that the active compound was identical to synthetic BHT. Culturing under various irradiances gave rise to different magnitudes of BHT production in cyanobacterial cells, showing that more BHT was produced in the cells irradiated with a higher light intensity, and its production was irradiance dependent. Moreover, the quantity of cellular BHT displayed a positive correlation with the antioxidative activity of the tested species. The present study confirms the production of BHT in all four of the studied freshwater phytoplankton and suggests that these species constitute a potential source for producing natural BHT.     

DOES ALLELOPATHY CONTRIBUTE TO CYLINDROSPERMOPSIS RACIBORSKII (CYANOBACTERIA) BLOOM OCCURRENCE AND GEOGRAPHIC EXPANSION?1

Cylindrospermopsis raciborskii (Wo?osz.) Seenayya et Subba Raju is a planktonic filamentous cyanobacterium whose sudden worldwide proliferation and ability to produce toxins are a reason for concern. In this paper, we suggest that its ecological dominance might be explained by antagonistic interaction with other phytoplankton species due to production of allelopathic metabolites. To test this hypothesis, experiments were run with exudates of natural phytoplankton and C. raciborskii strains isolated from Lagoa Santa, a small natural lake in southeastern Brazil, where this species has become dominant in recent years. The exudates were added to different algal species obtained from the same environment and maintained in culture. After 24 h incubation, PAM fluorometry was used to compare control and treatment photosynthetic responses (relative electron transport rate) to the dissolved extracellular products. Results indicate that most of the target species were sensitive to C. raciborskii exudates, which showed strong inhibitory effects on their photosynthetic activities. These results provide evidence that allelopathy may offer a competitive benefit to C. raciborskii and contribute to its stable dominance in Lagoa Santa. A potential allelopathic advantage could also help to explain the geographic expansion of this species at midlatitudes.     

Reduction of marine phytoplankton reproduction rates by copper and cadmium

The reproduction rates of 38 clones of marine phytoplankton were measured in media in which free cupric ion activity was controlled at different levels using a NTA-cupric ion buffer system. The major trend among species in their resistance to copper toxicity was a phylogenetic one, with cyanobacteria being the most sensitive, diatoms the least sensitive, and coccolithophores and dinoflagellates intermediate in sensitivity. The reproduction rates of most of the cyanobacteria were reduced at cupric ion activities above 10⁻¹² M, while most eukaryotic algae still had maximum reproduction rates at 10⁻¹¹ M. Four species, Emiliana huxleyi (Lohm.) Hay & Mohler, Skeletonema costatum (Grev.) Cleve, Thalassiosira pseudonana (Hustedt) Hasle & Heimdal and Thalassiosira oceanica (Hustedt) Hasle were particularly resistant to copper, being able to reproduce well at the highest cupric ion activities tested, 10^−9.5 M and 10^−9.2 M. There was no major difference, however, between neritic and oceanic species in their sensitivity to copper.The sensitivity of 20 species of marine phytoplankton to free cadmium ion activity was measured in a similar manner using an NTA-cadmium ion buffer system. As observed with copper, the prokaryotic cyanobacteria were the most sensitive to cadmium toxicity, diatoms were the least sensitive, and coccolithophores and dinoflagellates were intermediate. All cyanobacteria tested were dead at a cadmium ion activity of 10^−9.3 M whereas the reproduction rates of most of the eukaryotic algae were not reduced significantly until 10^−8.3 M.Comparison of these data with natural concentrations in sea water implies that cadmium is not an important ecological factor in unpolluted waters but natural copper concentrations may inhibit the reproduction of some phytoplankton species, especially cyanobacteria, in upwelled sea water. Copper may influence the seasonal succession of species.     

Genetic Characterization of Cylindrospermopsis raciborskii (Cyanobacteria) Isolates from Diverse Geographic Origins Based on nifH and cpcBA-IGS Nucleotide Sequence Analysis

Isolates of the toxic, N₂-fixing species Cylindrospermopsis raciborskii from various geographic locations were analyzed with respect to their genetic diversity based on the nifH and cpcBA-IGS genes. Gene sequences clustered according to their geographic origin, with the nifH sequences separating into European, Australian, and American groups and the cpcBA-IGS sequences separating into American and European or Australian groups. PCR primers for both genes were designed to exclusively amplify DNA from Cylindrospermopsis species, and an additional primer set for cpcBA-IGS was designed to specifically amplify the American C. raciborskii strains.     

Cyanobacterial dominance in Brazil: distribution and environmental preferences

Based on a literature survey, we evaluated the periods of cyanobacterial dominance in Brazil. We hypothesized that variability of environmental forces along the country will promote or facilitate temporal and spatial mosaic in cyanobacterial dominance. The most striking outcomes are related to the dominance of Cylindrospermopsis, Dolichospermum, and Microcystis. Although they share important adaptive strategies (e.g., aerotopes, large size and toxins production), our findings suggest that they have different environmental preferences. Dolichospermum and Microcystis dominated mainly in warm-rainy periods whereas Cylindrospermopsis was more common during dry periods and in mixed systems, or formed perennial dominance. Maximum phosphorus concentrations were observed in reservoirs dominated by Cylindrospermopsis. Although the main genera reached high biomass levels individually, different abilities to form dominance and co-dominance were observed. The number of co-dominance of Chroococales and Nostocales was almost the same as the individual occurrence of the main genera from these groups. This dataset reveals patterns of dominance of these cyanobacteria and also indicates that physiological features will cause differences in the mechanisms of interactions between species. The understanding of these processes and their relationship to environmental conditions will promote better understanding of cyanobacterial dominance and increase our ability to predict and manage these events.