The production of extracellular carbohydrates by estuarine benthic diatoms: the effects of growth phase and light and dark treatment

Epipelic diatoms are important constituents of estuarine microphytobenthic biofilms. Field‐based investigations have shown that the production of carbohydrates by such taxa is ecologically important. However, limited information exists on the dynamics of carbohydrate production by individual species of epipelic diatoms. The production of low and high molecular weight extracellular carbohydrates in axenic cultures of five species of benthic estuarine diatoms, Cylindrotheca closterium (Ehrenberg), Navicula perminuta (Grun.) in Van Heurck, Nitzschia frustulum (Kütz.) Grunow, Nitzschia sigma (Kütz.) Grunow, and Surirella ovata (Kütz.) Grunow, were investigated. All species produced colloidal (water‐soluble) carbohydrates during growth, with maximal production occurring during stationary phase. During logarithmic growth, approximately 20% of extracellular carbohydrates consisted of polymeric material (extracellular polymeric substances [EPS]), but during stationary phase, EPS content increased to 34%–50%. Pyrolysis–mass spectrophotometry analysis showed differences in the composition of EPS produced during logarithmic and stationary phase. All species synthesized glucan as a storage carbohydrate, with maximum glucan accumulation during the transition from log to stationary phase. Short‐term labeling with ¹⁴C‐bicarbonate found that between 30 and 60% of photoassimilates were released as colloidal carbohydrate, with EPS consisting of approximately 16% of this colloidal fraction. When cells were placed in darkness, EPS production increased, and between 85 and 99% of extracellular carbohydrate produced was polymeric. Glucan reserves were utilized in dark conditions, with significant negative correlations between EPS and glucan for N. perminuta and S. ovata. Under dark conditions, cells continued to produce EPS for up to 3 days, although release of low molecular weight carbohydrates rapidly ceased when cells were dark treated. Three aspects of EPS production have been identified during this investigation: (1) production during rapid growth, which differs in composition from (2) EPS directly produced as a result of photosynthetic overflow during growth limiting conditions and (3) EPS produced for up to 3 days in the dark using intracellular storage reserves (glucans). The ecological implications of these patterns of production and utilization are discussed.     

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     

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.     

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     

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.     

OCCURRENCE OF THREE NITZSCHIA (BACILLARIOPHYCEAE) TAXA WITHIN COLONIES OF TUBE-FORMING DIATOMS1

In benthic samples from the unchannelized Missouri River, the diatoms Nitzschia dissipata (Kütz.) Grun., N. filiformis (W.Sm.) Schütt and N. pseudofonticola Hust. were observed within the mucilage tubes of four tube-forming diatoms: Cymbella prostrata (Berk.) Cl., C. prostrata var. auerswaldii (Rabh.) Reim., Navicula tripunctata var. schizonemoides (V.H.) Patr., and Nitzschia filiformis. Microscopical observations of live and preserved specimens indicated that “invasion” by Nitzschia occurred primarily in older tubes. Data are presented on the environmental conditions in which the tube-formers and their cohabitants have been found.     

EFFECT OF GROWTH AND LIGHT/DARK CYCLES ON DIATOM LIPID CONTENT AND COMPOSITION1

Total extractable lipid (TEL) and lipid composition were studied throughout the growth cycle in three freshwater diatoms-Cyclotella meneghiniana Kütz., Melosira varians C. A. Ag., and Stephanodiscus binderanus (Kütz.) Krieg under three light regimes (16:8 h LD, 20:4 h LD, and 12:12 h LD) at 20°C. Two of the diatoms demonstrated strong daylength preferences for growth; C. meneghiniana grew best under long-day (20: 4-h LD) conditions, whereas S. binderanus grew best under short-day (12:12-h LD) conditions. The lipid composition of the diatoms was similar throughout the growth cycle. Aged (2-month-old) cells were high in total lipid and triacylglycerols. Before the onset of active growth and during the early part of active growth, there was a reduction in total neutral lipids, primarily triacylglycerols, and an increase in all polar lipids, including chlorophyll a, acetone-mobile polar lipids, and phospholipids. While cell numbers were still increasing, triacylglycerols increased and polar lipids decreased to levels near those found in aged cultures, Results suggest that increased triacylglycerol content of freshwater diatoms is not necessarily indicative of senescent populations.     

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.     

OCCURRENCE OF THREE NITZSCHIA (BACILLARIOPHYCEAE) TAXA WITHIN COLONIES OF TUBE-FORMING DIATOMS1

In benthic samples from the unchannelized Missouri River, the diatoms Nitzschia dissipata (Kütz.) Grun., N. filiformis (W. Sm.) Schütt and N. pseudofonticola Hust. were observed within the mucilage tubes of four tube-forming diatoms: Cymbella prostrata (Berk.) Cl., C. prostrata var. auerswaldii (Rabh.) Reim., Navicula tripunctata var. schizonemoides (V.H.) Patr., and Nitzschia filiformis. Microscopical observations of live and preserved specimens indicated that “invasion” by Nitzschia occurred primarily in older tubes. Data are presented on the environmental conditions in which the tube-formers and their cohabitants have been 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.     

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.     

ABSOLUTE CONFIGURATION ANALYSIS OF THE FLAGELLAR APPARATUS IN CLADOPHORA AND CHAETOMORPHA MOTILE CELLS,WITH AN ASSESSMENT OF THE PHYLOGENETIC POSITION OF THE CLADOPHORACEAE (ULVOPHYCEAE,CHLOROPHYTA)

Absolute configurational analyses of flagellar apparatus components were performed on the motile cells produced by three species of Cladophora, Cl. dalmatica Kütz., Cl. flexuosa (Dillw.) Harv., and Cl. glomerata (L.) Kütz., and by Chaetomorpha aerea (Dillw.) Kütz. There was little variation among the species. All of the flagellar apparatuses demonstrated the ulvophyceous features of 180° rotational symmetry, counterclockwise absolute orientation, and basal body overlap, as well as the alignment of the basal bodies perpendicular to the long axis of the cell. Diagnostic features included the nearly complete absence of C tubules from the basal bodies and the presence of a coarsely striated component dorsal to the two-membered rootlets in all cells, as well as, in quadriflagellate cells, a tetralobate distal fiber, the coaxial arrangement of the lowermost pair of basal bodies, and the presence of a characteristic array of basal-body-associated striated bands. The distal fiber architecture, the presence of a “wing” in the X-membered rootlets, and the “flattening” of the flagellar apparatus components suggests a close relationship of the Cladophoraceae to the Dasycladales, and indicates that these two groups may have shared a common ancestor, possibly ancient in terms of the geological time scale but relatively recent in the context of ulvophyceous evolution. A sizeable phylogenetic gap exists between the Cladophoraceae and uninucleate-celled, presumably primitive members of the Ulvophyceae.     

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.     

POLYMORPHISM IN THE DESMID MICRASTERIAS PINNATIFIDA AND ITS TAXONOMICAL IMPLICATIONS1

A case of polymorphism in the desmid Micrasterias pinnatifida (Kütz.) Ralfs is described. It is based on material collected from the overflow channel of a dam in Caeté, Minas Gerais State. After careful examination of nearly 500 specimens, 26 different morphological expressions of the alga were found which led the authors to make the following deductions: (1) for delimitation of species and infraspecific taxa in desmids it is absolutely necessary to analyze sample populations; (2) the morphological characteristics presently used, for delimination of some varieties of M. Pinnatifida (Kütz.) Ralfs seem to have no taxonomical value if only isolated individuals are examined; (3) the varieties granulata, inflata, and tridentata must be considered with some caution, until further studies are carried out, because they can be merely distinct morphological expressions of M. pinnatifida (Kütz.) Ralfs var. pinnatifida.     

Strategies providing success in a variable habitat: I. Relationships of environmental factors and dominance of Cladophora glomerata

Dominance of macrophytes and their response to environmental factors were studied in the river Ilm, Thuringia/ Germany with special reference to Cladophora glomerata (L.) Kütz. Macroalgae showed a growth peak in spring with C. glomerata, Ulothrix zonata Kütz., Lemanea fluviatilis (L.) C. Agardh and Audouinella sp. being the dominant species. Shortly after this peak, a rapid decline of macrophyte substrate coverage was observed. Only C. glomerata revealed a second growth peak in late summer/early autumn. Frequent disturbances of the macrophyte assemblage by floods resulted repeatedly in an almost complete wash out of benthic organisms. After summer floods C. glomerata was the species that recolonized the substrate. At high‐light sites, faster recovery of C. glomerata was observed as compared to low‐light sites. This is discussed in relation to the life cycle of C. glomerata. Among the physical and chemical parameters that were analysed, irradiance, current velocity, pH, soluble reactive phosphorus and ammonia‐nitrogen accounted for most of the observed patterns of dominance of C. glomerata.     

The occurrence of variant forms in cultures of species of Ectocarpus and Giffordia

Apparent variants, resembling Hecatonema sp., have been isolated from cultures of Ectocarpus fasciculatus Harv., Ectocarpus siliculosus (Dillw.) Lyngb., Giffordia irregularis (Kütz.) Le Jol. and Giffordia mitchellae (Harv.) Hamel. The origin and life history of the hecatonemoid forms is described. Their possible roles are discussed and an argument is presented in support of the hypothesis that they are contaminants.     

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.     

青海省硅藻5种中国新记录

该文报道了采自中国青海省的硅藻中国新记录5种,分别为：亨迪美壁藻(Caloneis hendeyi Lange Bertalot & Genkal)、端聚舟形藻(Navicula digitoconvergens Lange Bertalot)、非洲辐节藻(Stauromis africana Cleve)、埃尔卡布格形藻［Craticula elkab (Müller) Lange Bertalot, Kusber & Cocquyt］和混合海双眉藻［Halamphora hybrida (Grunow) Levkov］,对各个种类的形态特征进行了详细的分类学描述,并附有光镜和扫描电镜图版,给出了各种类的生境分布信息。     

Genetic and ecophysiological diversity of Cladophora (Cladophorales,Ulvophyceae) in various salinity regimes

Although Cladophora species frequently appear in brackish environments, their genetic diversity, phenological patterns and physiological properties have not been well investigated in these environments. Cladophora is distributed throughout Mikata‐goko, an area consisting of five coastal lakes that are directly or indirectly connected to the sea, resulting in a salinity gradient ranging from fully marine to freshwater. To elucidate genetic and ecological variation in Cladophora, we monthly compared ribosomal internal transcribed spacer sequences of Cladophora specimens across six study sites characterized by different salinity regimes for a year. A total of 12 ribotypes were detected and assigned to six species, four of which were restricted to the marine habitat. Ribotype I of C. vagabunda (L.) Hoek was distributed in high‐salinity brackish waters (mean salinity ≤13 psu; maximum salinity ≤31 psu), whereas C. vagabunda ribotype II and C. glomerata were abundant in low‐salinity brackish waters (mean salinity ≤5 psu; maximum salinity ≤10 psu). Although Cladophora albida (Nees) Kütz. and C. glomerata (L.) Kütz. were collected during all four seasons, C. laetevirens (Dillwyn) Kütz., C. oligocladoidea Hoek and Chihara, C. opaca Sakai and C. vagabunda displayed marked seasonal variation. Culture experiments revealed that optimal salinity conditions for vegetative growth vary among ribotypes collected from different salinity regimes, suggesting that Cladophora distributions are controlled by ribotype‐specific ecophysiological adaptations. In contrast, temperature optima and tolerance were similar among ribotypes showing different seasonalities, and thus their phenologies may be controlled by other environmental factors or biotic conditions, such as reproductive maturity and spore germination.