Life history of Cladophora surera sp. nov. (Cladophorales, Ulvophyceae)

The life history of Cladophora surera sp. Nov., described from the south of the province of Buenos Aires, Argentina, was found to be diplobiontic and isomorphic with haploid gametophytic (n= 24) and sporophytic (2n= 48) plants. Other freshwater species, namely C, suhriana Kutz, and C. callicoma Kütz. have also been reported to be diplobiontic and isomorphic but differing from C. surera by their ploidy level. Plants exhibit great morphological variation, as the number of branches/mm² tends to increase with higher water velocity, thus adopting morphotypes that resemble very different species, that is, C. vagabunda (L.) Hoek, C. glomerata (L.) Kutz., C, laetevirens (Dillw.) Kutz., C. brasiliana Martens, C. dalmatica Kütz., C. vadorum (Aresch.) Kütz. and C. rivularis (L.) Hoek., but clearly differing from them by other morphological parameters; apical cell diameters, The ploidy level 24/48 has not been established for a species of Cladophora. Autogamy is the normal conjugation method and can take place even inside the gametangia before the gametes are released. Isogametes conjugate in a slow behavioral anisogamy, in which the contents of one migrate to the other. Tetra-flagellate zoospores result from meiosis.     

Morphology of Cell Wall Pore Channels in the Genus <Emphasis Type="Italic">Euastrum</Emphasis> Ralfs (Desmidiales)

The study of the cell wall structure was performed for ten species of Euastrum: E. ansatum (Ehrenb.) Ralfs, E. bidentatum Näg., E. binale (Turp.) Ehrenb. ex Ralfs, E. dubium Näg., E. elegans (Bréb.) Kütz. ex Ralfs, E. germanicum (Schmidle) W. Krieger, E. oblongum (Grev.) Ralfs ex Ralfs, E. pectinatum Bréb. ex Bréb. in Ralfs, E. validum West et G.S.West, E. verrucosum (Ehrenb.) ex Ralfs. The investigation of the cell wall ultrastructure has established for the first time that the pore canal in 6 of 10 species always has a coiled form to some degree. Three species (E. germanicum, E. pectinatum, and E. verrucosum) have both coiled and straight canals, and E. ansatum has only straight ones. A new type of pores (P7), typical only for representatives of the genus Euastrum, was also noted. In addition, a simple and effective method of preparing desmidium algal cells for investigation with transmission electron microscope has been developed.     

Examination of the type material of Synedra rumpens =Fragilaria rumpens, Bacillariophyceae

Fragilaria rumpens (Kütz.) G. W. F. Carlson is assumed to be a cosmopolitan species, and is often reported from ponds and lakes. Nevertheless, this species is similar to both Fragilaria capucina Desm. and Fragilaria vaucheriae (Kütz.) J. B. Petersen and, as a consequence, the taxonomy of all three species has been confusing. In an attempt to solve the taxonomic problems within this group, we have examined the type material of Synedra rumpens and discuss the differences between it and some of those species said to be similar.     

Geothermal diatoms: a comparative study of floras in hot spring systems of Iceland,New Zealand,and Kenya

Diatom floras were examined from geothermal environments in three contrasting tectonic settings. These included subduction-related acid and alkaline springs in New Zealand; alkaline springs along a divergent plate boundary on Iceland; and alkaline springs in the Kenya Rift. These shallow (<1 cm) aquatic environments vary considerably (e.g., temperature: 21.3–99°C; pH: 2.1–9.65; 56.41–643 mg l⁻¹ SiO₂). Diatoms form an important component of geothermal floras at temperatures of <45°C. The floras from New Zealand are distinguished by the common occurrence of Pinnularia. Icelandic springs have a variety of Fragilariaceae. Navicula and Anomoeoneis are most common in the Kenyan springs. Statistical analyses suggest that the diatoms cluster into seven major groups. The most common taxa include: Achnanthidium exiguum v. heterovalvum (Kras.) Czarn., Anomoeoneis sphaerophora (Ehrenb.) Pfitz, Brachysira brebissonii f. thermalis Grun., Caloneis bacillum (Grun.) Cl., Craticula cuspidata (Kütz.) Mann, Diadesmis confervacea Kütz., Epithemia argus (Ehrenb.) Kütz., Frustulia rhomboides (Ehrenb.) DeT., Hantzschia amphioxys (Ehrenb.) Grun., Navicula tenelloides Hust., Nitzschia amphibia Grun., Nitzschia inconspicua Grun., Nitzschia invisitata Hust., Nitzschia frustulum (Kütz.) Grun., Nitzschia sigma (Kütz.) W, Smith., Pinnularia chapmaniana Fog., Pinnularia appendiculata (Ag.) Cl., Pinnularia molaris (Grun.) Cl., Pinnularia acoricola Hust., Rhopalodia gibberula (Ehrenb.) O. Müll., Staurosira construens v. venter (Ehrenb.) Ham., Staurosira elliptica (Schum.) Will. & Round, and Staurosirella pinnata (Ehrenb.) Will. & Round. Canonical correspondence analysis shows clear correlations between species, alkalinity, pH, and conductivity, with less strong correlations for silica and temperature. Other factors include substrate type, current velocity, and light conditions. The preservation potential of host deposits varies considerably, being lowest for springs on clastic deltas and highest where travertine or sinter is accumulating. Handling editor: J. Padisak     

SCANNING ELECTRON MICROSCOPY OBSERVATIONS OF DEFORMITIES IN SMALL PENNATE DIATOMS EXPOSED TO HIGH CADMIUM CONCENTRATIONS1

Different types of malformations are likely to affect the morphology of diatoms when exposed to particularly unstable environmental conditions, the most easily identifiable being distortion of the whole frustule. In the present study, we investigated, by means of SEM, valve abnormalities induced by high cadmium contamination (100 μg · L^?1) in small pennate diatoms. Changes in the shape of Amphora pediculus (Kütz.) Grunow and anomalous sculpturing of the cell wall of many species, such as Encyonema minutum (Hilse) D. G. Mann, Mayamaea agrestris (Hust.) Lange‐Bert., Gomphonema parvulum (Kütz.) Kütz., or Eolimna minima (Grunow) Lange‐Bert., were observed, which were not, or almost not, noticeable in the LM. With consideration to current knowledge of diatom morphogenesis, metal uptake by the cell would induce, directly or indirectly, damage to many cytoplasmic components (e.g., microtubules, cytoskeleton, Golgi‐derived vesicles) involved in the precisely organized silica deposition. This study confirms that many species, whatever their size, are likely to exhibit morphological abnormalities under cadmium stress, and that this indicator may be valuable for the biomonitoring of metal contamination, even if SEM observations are not necessary for routine studies.     

ALLELOPATHIC GROWTH INHIBITION OF SELECTED PHYTOPLANKTON SPECIES BY SUBMERGED MACROPHYTES1

Allelopathic effects of submerged macrophytes on the growth and photosynthesis of different unialgal cultures of planktonic cyanobacteria, a diatom, and a green alga were tested in coexistence experiments using dialysis cultures. The method applied allowed measurements under conditions similar to that in lakes but without nutrient and light limitation. Growth and photosynthesis were measured with a pulse amplitude modulated fluorometer as an increase of chl a fluorescence and activity of PSII, respectively. Eurasian water milfoil Myriophyllum spicatum L. and rigid hornwort Ceratophyllum demersum L. proved to inhibit the PSII activity and then growth of the investigated phytoplankton species, whereas sago pondweed Potamogeton pectinatus L. showed no effect. Growth inhibition was dependent on biomass of M. spicatum. Considerable differences between phytoplankton groups and among species of cyanobacteria were found regarding their response to M. spicatum. Members of the Oscillatoriales and Microcystis aeruginosa Kütz. emend. Elenkin were more sensitive than the cyanobacterium Aphanizomenon flos‐aquae Ralfs ex Born. et Flah., the diatom Stephanodiscus minutulus (Kütz) Cleve et Möller, and the green alga Scenedesmus armatus Chodat. A possible contribution of this result to changes in the phytoplankton succession of lakes after loss of macrophytes is discussed.     

PERIPHYTON COLONIZATION OF ROCK SURFACES IN A BOREAL FOREST STREAM STUDIED BY SCANNING ELECTRON MICROSCOPY AND TRACK AUTORADIOGRAPHY1

Periphyton colonization of natural rock surfaces and granite tiles was followed experimentally in the Matamek River, an acidic (pH 5.5) sixth order boreal stream in northeast Quebec, Canada. Accumulation of chlorophyll a and freshweight algal biomass was logarithmic over a 25 day colonization period. The major colonizers were Tabellaria flocculosa (Roth) Kütz., T. fenestrata (Lyngb.) Kütz., Mougeotia sp., and Eunotia pectinalis (Kütz) Rabh., and its varieties. The microcolonization sequence on granite tiles, followed over 27 days with scanning electron microscopy, showed an initial accumulation of algal cells on the upstream and downstream margins and in depressions, followed by a gradual filling-in of the flat surfaces. It is hypothesized that the observed slow rate of colonization was due to the high surface tension of the granite substratum and the absence of preconditioning by an organic film. It is further hypothesized that the increase in cellular carbon fixation rates of T. flocculosa measured over a 23 day period using nuclear track autoradiography parallels the development of an algal-detrital microcosm on the granite tile, and is evidence for the establishment of localized tight nutrient spiralling. It is suggested that the periphyton community may be regarded as a nutrient recycling system at a microenvironmental level which may be especially important in oligotrophic systems.     

SCHIZOMERIS—A GROWTH FORM OF STIGEOCLONIUM TENUE (CHLOROPHYTA:CHAETOPHORACEAE)1

Schizomeris leibleinii Kütz. was found as an ecophene of Stigeoclonium tenue (Ag.) Kütz. in Centennial Lake, Palmerston North, New Zealand. The Schizomeris form occurred in autumn when the water was polluted by a large number of ducks. Sampling of the plant population of the lake and culture work showed that S. tenue has a high degree of polymorphism. Other forms of it which developed both in the lake and in culture were indistinguishable from Protoderma Kütz. emend. Borzi, from Uronema Lagerheim, or from Pearsoniella Fritsch and Rich, respectively.     

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.     

COMPARATIVE ULTRASTRUCTURE OF THE VALVES OF SOME CYCLOTELLA SPECIES (BACILLARIOPHYCEAE)1

Cyclotella atomus Hust., C. meneghiniana Kütz., C. comta (Ehr.) Kütz., C. antiqua W. Sm., C. michiganiana Skv., C. ocellata Pant., C. glomerata Bachmann, C. pseudostelligera Hust., and C. stelligera (Cleve et Grun.) V. H., were selected for ultrastructure investigations on the basis of their ready availability. Specimens were examined employing both transmission and scanning electron microscopy. Strutted processes, labiate processes, spines and other special features were surveyed in all species. On the basis of these observations the species of Cyclotella observed seem to be in one of 3 morphological groups, the meneghiniana group, the comta group, and the stelligera group.     

STRUCTURE,LIFE HISTORY AND SYSTEMATICS OF RHOICOSPHENIA (BACILLARIOPHYTA). IV. CORRELATION OF SIZE REDUCTION WITH CHANGES IN VALVE MORPHOLOGY OF RH. GENUFLEXA1

Rhoicosphenia Grun. is a relatively isolated genus among the biraphid diatoms. Morphological changes in an isopolar member of the genus, Rh. genuflexa (Kütz.) Medlin, were investigated using light and scanning electron microscopy. The fully raphid valve showed changes in its flexure that could be correlated with size reduction during its life history from the initial cells to the smallest cells found in the population. Bands showed changes in number (from three to one) related to size reduction. Rh. genuflexa is morphologically similar to Rh. abbreviata (C. Ag.) Lange-Bert. (=Rh. curvata (Kütz.) Grun.), although the two are distinct taxa. These observations support previous contentions that Rhoicosphenia is a natural taxonomic grouping.     

MEASUREMENT OF IN SITU SPECIFIC GROWTH RATES OF MICROCYSTIS (CYANOBACTERIA) FROM THE FREQUENCY OF DIVIDING CELLS1

Diel changes in the frequency of dividing cells (FDC) of three Microcystis species were investigated in a small eutrophic pond from July to October 2005. The representative species was M. aeruginosa (Kütz.) Kütz., constituting 57%–86% of the Microcystis population throughout the study period, and the remainder were M. viridis (A. Braun) Lemmerm. and M. wesenbergii (Komárek) Komárek. The FDC of M. aeruginosa and M. wesenbergii increased in the daytime and fell in the nighttime in July and August, but this regular variation was not observed in September or October. The in situ specific growth rates of Microcystis species were estimated based on the assumption that the specific growth rate can be given as an absolute value of the derivative of FDC with respect to time. The calculated values were similar among species—0.15–0.38 · d^?1 for M. aeruginosa, 0.14–0.63 · d^?1 for M. viridis, and 0.18–0.61 · d^?1 for M. wesenbergii. The specific growth rates in July and August slightly exceeded those in September and October. The analysis of the in situ specific growth rate of Microcystis indicated that recruitment of the benthic population or morphological change, rather than massive growth, was at least partly responsible for the dominance of M. aeruginosa in the study pond.     

COMMUNITY STRUCTURE DYNAMICS OF EPILITHIC AND EPIPHYTIC DIATOMS IN A MISSISSIPPI STREAM1

Epilithic and epiphytic diatoms were collected monthly from 18 June 1979 through 19 May 1980 from both shaded and unshaded sites of Sessums Creek, a shallow, oligotrophic and strongly alkaline stream in northeastern Mississippi. The dominant macroalgae were filamentous green algae belonging to the non-mucilage producing genera Cladophora and Rhizoclonium. Ninety taxa were identified with Navicula minima Grun. and Nitzschia dissipata (Kütz.) Grun. accounting for 50% of all valves counted. Other important taxa were Navicula menisculus var. upsaliensis (Grun.) Grun., N. cryptocephala var. veneta (Kütz.) Rabh., Achnanthes minutissima Kütz. and Cymbella turgida (Greg.) Cl. With few exceptions, the more dominant taxa were equally abundant in the shaded and unshaded sites and also in the epilithon and epiphyton. Species diversity (H') and the number of taxa in a sample in all four habitats showed an identical pattern, being lowest in winter and highest in fall. No one pair of habitats was more structurally similar than any-other pair when compared by a similarity index (SIMI). Apparently, differences in light intensity and substrate type had little effect on diatom distribution in Sessums Creek and it was concluded that the locality sampled supported a single, nearly homogeneous diatom community.     

PHYLOGENETIC RELATIONSHIPS WITHIN CLADOPHORALES (ULVOPHYCEAE,CHLOROPHYTA) INFERRED FROM 18S rRNA GENE SEQUENCES,WITH SPECIAL REFERENCE TO AEGAGROPILA LINNAEI 1

The phylogenetic position of a freshwater green alga, Aegagropila linnaei (Cladophorales, Ulvophyceae), was investigated using nuclear 18S rRNA gene sequences. This alga has usually been called Cladophora aegagropila (L.) Rabenhorst or Cladophora sauteri (Nees ex Kütz.) Kütz. Based on morphology, it was formerly classified into the section Aegagropila or into the subgenus Aegagropila, together with several marine species of the genus Cladophora. This classification is not supported by the present phylogenetic analyses in which two very distinct Cladophorales clades are recognized. Aegagropila linnaei groups together in a well‐supported clade with Cladophora sp., Pithophora sp., Chaetomorpha okamurae, Arnoldiella conchophila, Wittrockiella lyallii, and Cladophora conchopheria. Aegagropila linnaei and its closely related species share some ultrastructural and biochemical characteristics, like pyrenoid structure, carotenoid composition, and cell wall composition. Freshwater species, included in the analysis, were located in two distantly related lineages, indicating that adaptation from a marine to a freshwater habitat has happened at least twice independently in the Cladophorales.     

LOCALIZATION OF MICROCYSTIN SYNTHETASE GENES IN COLONIES OF THE CYANOBACTERIUM MICROCYSTIS USING FLUORESCENCE IN SITU HYBRIDIZATION1

To better understand the production of microcystins (MCs) in Microcystis colonies, fluorescence in situ hybridization (FISH) methods were developed to detect DNA involved in the synthesis of these cyanobacterial hepatotoxins. Using colonies of Microcystis aeruginosa (Kütz.) Kütz. isolated from environmental blooms of cyanobacteria and from a colony‐forming, MC‐producing laboratory strain of Microcystis, amplified PCR products were observed, coincident with positive controls. The total MC content of individual colonies of Microcystis, determined by ELISA, showed a positive correlation with colony cross‐sectional area. FISH analysis of Microcystis colonies gave high fluorescence in comparison to negative controls, indicating the presence of MC synthetase DNA (mcyA) in situ. FISH analysis for MC synthetase genes has the potential to be developed into an effective early warning tool for drinking and recreational water management.     

ULTRASTRUCTURE OF THE FILAMENTOUS HABIT IN THE DIATOM NAVICULA CONFERVACEA (KÜTZ.) GRUN.1

Frustules of the filamentous diatom Navicula confervacea (Kütz.) Grun. are united by the overlapping of marginal teeth located alongside the junction of valve face and mantle. Scanning and transmission electron microscopy show this connecting mechanism to differ from the previously reported inter-digitating spines or teeth in the genera Melosira, Stephanodisus, and Fragilaria.     

Using change-point analysis and weighted averaging approaches to explore the relationships between common benthic diatoms and in-stream environmental variables in mid-atlantic highlands streams,USA

Diatoms are increasingly being used in the bioassessment of aquatic systems. However, autecological information for many common taxa is incomplete. We explored the potential of classification (CT) and regression tree (RT) approaches to identify the hierarchical interaction among water quality variables in predicting the relative abundance of ten common stream diatom taxa in the Mid-Atlantic Highlands ecoregion. RT analysis was also used to identify environmental change points corresponding to major shifts in species abundances. We also used traditional weighted-averaging approaches (WA) to model taxon pH and total phosphorus (TP) optima. RT and WA approaches provided different, yet complementary, information on the complex relationships between common stream diatoms and environmental variables. Both RT and CT highlighted the interaction of stream acidity (pH, acid neutralizing capacity (ANC)), and TP in structuring the stream diatom assemblage. For the RT of taxa, where pH was an important predictor, higher pH predicted higher relative abundances. In contrast, higher TP predicted lower relative abundances for some diatom taxa (e.g., Achnanthidium minutissimum (Kütz.) Czarnecki), while predicting higher relative abundances for other taxa (e.g., Planothidium lanceolatum (Bréb.) Round & Bukht., Gomphonema parvulum (Kütz.) Kütz.). The environmental change point for pH derived from RT analysis was lower than WA optima for all species. We suggest that RT change point analysis can be used to complement traditional WA optima approaches, especially when diatom taxa’s abundances are affected by interactive environmental factors, to provide more refined information on stream diatom environmental preferences. Handling editor: L. Naselli-Flores     

CHANGES IN THE MORPHOLOGY AND POLYSACCHARIDE CONTENT OF MICROCYSTIS AERUGINOSA (CYANOBACTERIA) DURING FLAGELLATE GRAZING1

To investigate the changes in the morphology and polysaccharide content of Microcystis aeruginosa (Kütz.) Kütz. during flagellate grazing, cultures of M. aeruginosa were exposed to grazing Ochromonas sp. for a period of 9 d under controlled laboratory conditions. M. aeruginosa responded actively to flagellate grazing and formed colonies, most of which were made up of several or dozens of cells, suggesting that flagellate grazing may be one of the biotic factors responsible for colony formation in M. aeruginosa. When colonies were formed, the cell surface ultrastructure changed, and the polysaccharide layer on the surface of the cell wall became thicker. This change indicated that synthesis and secretion of extracellular polysaccharide (EPS) of M. aeruginosa cells increased under flagellate grazing pressure. The contents of soluble extracellular polysaccharide (sEPS), bound extracellular polysaccharide (bEPS), and total polysaccharide (TPS) in colonial cells of M. aeruginosa increased significantly compared with those in single cells. This finding suggested that the increased amount of EPS on the cell surface may play a role in keeping M. aeruginosa cells together to form colonies.     

EFFECTS OF WATER VELOCITY ON THE ARCHITECTURE AND EPIPHYTES OF CLADOPHORA GLOMERATA (CHLOROPHYTA)1

The architecture of the filamentous green alga Cladophora glomerata (L.) Kütz. and the composition of this alga's epiphytes [primarily the diatoms Epithemia turgida (Ehrenb.) Kütz., Epithemia sorex Kütz., and Cocconeis pediculus Ehrenb.] were examined in different velocity regimes. After transferring algal-bearing cobbles among velocities, the effects of changes in velocity were also examined. Cladophora branching pattern did not initially differ among slow, medium, and fast velocities, indicating that stable water velocities did not affect branching pattern. Two weeks after cobble transfer, Cladophora in fast velocity had fragmented more (i.e. had fewer filaments and fewer branch points per length of filament and had a higher percentage of unbranched filaments) than Cladophora in slow velocity. Fragmentation was greatest in tufts moved from slow velocity, suggesting velocity-associated differences in susceptibility to breakage. Epiphytic assemblage composition differed among slow, medium, and fast velocities and between locations on the filament (base and apex). Cocconeis pediculus dominated where exposure to high velocity was greater (filament apices in medium and fast velocities), whereas the Epithemia spp. dominated where lower velocities occurred (filament bases in all velocities and apices in slow velocity). Two weeks after the cobble transfer, the translocated diatom assemblages had changed and the original pattern of diatom distribution was restored.     

Polyphasic evaluation of Xanthidium antilopaeum and Xanthidium cristatum (Zygnematophyceae,Streptophyta) species complex

We investigated twenty‐six strains of Xanthidium antilopaeum Kütz. and seven strains of X. cristatum Ralfs isolated from various European localities or obtained from public culture collections. A combination of molecular, geometric morphometric, and morphological data were used to reveal the patterns of the phylogenetic and morphological differentiation of these taxonomically very compli‐cated desmid taxa. The molecular data based on trnG^ucc and ITS rDNA sequences illustrated the monophyly of both the complexes, which indicated that their traditional morphology‐based discriminative criteria, such as the different number of spines, may generally continue to be considered relevant. The single exception was X. antilopaeum var. basiornatum B. Eichler et Raciborski, which was positioned outside the X. antilopaeum/cristatum clade. The independent status of this taxon was also confirmed on the basis of the geometric morphometric data, so that we concluded that it probably represents a separate species. Within X. cristatum complex, the traditional varieties X. cristatum var. cristatum Ralfs, X. cristatum var. uncinatum Ralfs, and X. cristatum var. scrobiculatum Scott et Grönblad turned out to be separate taxa. Conversely, X. cristatum var. bituberculatum Lowe lacked any taxonomical value. Our data on X. antilopaeum illustrated extensive phylogenetic as well as phenotypic variability within this species complex. However, our data did not result in any unambiguous pattern that would allow sound taxonomic classification. Finally, we also found out that the morphologically peculiar Staurastrum tumidum Ralfs belongs to the genus Xanthidium based on the combined rbcL + cox III data set. Consequently, this species was formally transferred to this genus.