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.     

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.     

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.     

COMPARISON OF ATTACHED DIATOM COMMUNITIES ON NATURAL AND ARTIFICIAL SUBSTRATES1

A study of attached diatom communities on artificial and natural substrates was conducted in Wheelwright Pond, New Hampshire, during 1975. There were differences in the species composition growing on artificial glass slides and natural substrates. The slides favored the accumulation of Achnanthes minutissima Kütz. and decreased the relative abundance of Eunotia incisa W. Sm. ex. Greg. and Cocconeis placentula v. euglypta (Ehr.) Cleve. Large growths of planktonic species were also noted on the slides. Compositional differences between slides positioned at 15–30 cm (upper) and 1 m (lower) from the surface of the water were minimal. A similar community composition of periphytic diatoms was found on five aquatic macrophytes.     

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     

Structural and functional characteristics of epiphyton and epipelon in relation to their distribution in Lake Vechten

Epiphyton and epipelon were quantitatively collected, respectively, from the submerged macrophytes and the sandy lake bottom of Lake Vechten (The Netherlands). On a weight basis, epiphyton was maximal in autumn and epipelon in summer. In winter the chemical composition of epiphyton and epipelon was similar. In summer the epiphyton had on a unit weight basis more organic matter and carbonate, and had per unit organic matter a higher algal number, nitrogen and energy content than the epipelon. Algae predominating the epiphyton were filamentous greens and pennate diatoms; those in the epipelon were pennate diatoms and blue-green algae. In both cases, species known to frequent the phytoplankton were abundant. The diatoms were quantified using paper chromatographic pigment analyses. Both the epiphyton and the epipelon exhibited maximal photosynthesis in mid summer. That light was generally the limiting factor was evident from periphyton developed on artificial substrates. This periphyton differed widely in its composition from that on the natural substrates, mainly because the latter collected much more sedimenting matter.In dense Ceratophyllum stands light was severely attenuated and the significant gradients in oxygen and pH were caused by the differences with depth in the proportions of photosynthesis and respiration. The oxygen content and pH at the bottom decreased owing to epipelic respiration. The epiphytic composition depended greatly on the degree of light attenuation. The epiphytic and epipelic respiration, except during part of the early summer, exceeded photosynthesis on a 24 h basis; this included the macrophytic photosynthesis during the time the vegetation was maximally developed. During the growing season import of organic matter, i.e. deposited seston, greatly exceeded that due to the photosynthetic production. After the summer maximum, the epipelon decreased faster than predicted from its oxygen exchange. It was concluded that sedimentation and resuspension determined mainly the changes in epiphyton and epipelon. Especially when covered with vegetation, the lower littoral of Lake Vechten plays a large part in the aerobic decomposition of sestonic organic matter.     

SOME MORPHOLOGICAL VARIATIONS IN THE DIATOM CYMBELLA CISTULA1,2

Several populations of Cymbella cistula (Ehr.) Kirchn. were studied. An epiphytic population contained smaller specimens than any reported by recent authors. The size range of members of the epiphytic population included specimens as small as 24 μ long by 11 μ wide. These small specimens could be mistaken for C. cistula var. maculata (Kütz.) V. H., but differ in having isolated puncta, which, may be indistinct, and somewhat coarser striae.     

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.     

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.     

Structure of Periphytic Community on Artificial Substrata: Influence of Depth, Slide Orientation and Colonization Time in Karstic Lake Visovačko, Croatia

This study determined the potential for periphyton growth on artificial surfaces using plexiglas slides exposed for different lengths of time, orientations and depths in the lower, lentic area of River Krka during the summer of 1995. During the research period, 88 taxa were identified. The most abundant group was Bacillariophyceae with 57 taxa. Species Cyclotella comta (Ehr.) Kutz., Achnanthidium affine (Grunow) Czarn., Cocconeis placentula Ehr. and Eolimna minima (Grunow) Lange-Bertalot were present in all samples. The results show significant differences in abundance, number and composition of algae between growth surfaces and depths. The number of species present shows statistically significant differences with respect to all three variables (days of colonization, depth and orientation), while the total number of cells per square centimeter varies with respect to the days of colonization and the depth only. The highest growth potential was observed after 60 days of exposition on the upper side of the horizontally placed surface at a depth of 1 m. During the same exposition time, the lowest growth potential was noted on the vertical slide at a depth of 18 m. Physical and chemical parameters and their relations to algal periphyton assemblages were also monitored.     

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.     

Natural community bioassays to determine the abiotic factors that control phytoplankton growth and succession

SUMMARY. 1. The successional patterns of the dominant phytoplankton species in Lake Maarsseveen (The Netherlands) were very similar in 1980 and 1981. In December/January the diatoms Stephanodiscus hantzschii Grun., Stephanodiscus astraea (Ehr.) Grun. and Asterionella formosa Hass. dominated the algal community (A. formosa had several further population increases during the year). Fragilaria crotonensis Kitt. came to dominance in March/April, followed by the chrysophyte Dinobryon divergens Imhof and the diatom Cyclotella comta (Ehr.) Kütz in May/June. A second appearance of D. divergens was observed in July/August, followed in 1980 by F. crotonensis and a third small increase of D. divergens. In both years S. astraea and S. hantzschii started to grow again in November/December. Cryptophyceae and Chlorophyta were present throughout the year, but did not show a distinct succession. 2. Natural community bioassays, performed under natural light and temperature conditions in a newly developed outdoor bioassay apparatus, showed that phosphate was the major nutrient limiting the growth rate of the phytoplankton. From January till June, during the decline in phosphorus concentration, the diatoms became successively phosphate limited in the sequence: S. hantzschii, S. astraea, F. crotonensis, A. formosa and C. comta. Light limitation was probably the major cause of the relatively late start of F. crotonensis in early spring. 3. D. divergens, increasing after the diatoms from June till September, was stimulated by the addition of a chelator (EDTA). The chelator might stimulate the formation of trace metal species favouring their uptake (e.g. iron). 4. The patterns of succession of the diatoms observed from January till June and from July till December were to a large extent symmetrical. The controlling factors followed opposite trends: declining phosphorus concentrations with increasing irradiance from winter till spring and increasing phosphorus concentrations with decreasing irradiance from summer till late winter.     

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.     

EFFECTS OF HERBIVORE SIZE AND HUNGER LEVEL ON PERIPHYTON COMMUNITIES1

The effects of herbivore size and hunger level were tested on lotic periphyton community structure and ash-free dry mass (AFDM). My hypotheses were 1) that small herbivores would remove more periphyton per unit biomass than large herbivores of the same species because of energetic demands and 2) that within the same size class, starved herbivores would remove more periphyton than nonstarved herbivores. The herbivore used was the prosobranch snail Elimia clavaeformis Lea. Seven treatments were employed: 1) no snails (control); 2) small “starved” snails; 3) large “starved” snails; 4) small and large “starved” snails; 5) small fed snails; 6) large fed snails; and 7) small and large fed snails. Although snails removed significant amounts of periphyton AFDM relative to controls, neither snail size nor degree of starvation had a significant effect on loss of total AFDM. Small snails removed significantly more erect forms of Stigeoclonium tenue (C. A. Ag.) Kütz. than large snails, but snail size had no other significant effect. Starved snails removed significantly more Cocconeis placentula Ehr. than fed snails, suggesting that after the more susceptible growth forms (e.g. erect Stigeoclonium) were removed, Cocconeis cells became more vulnerable to grazing by hungry snails. When small and large snails were combined in chambers, large snails gained weight over time, whereas small snails lost weight. These results suggest that intraspecific competition may occur within populations of Elimia.     

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。     

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.     

THE BENTHIC ALGAE OF SOUTHERN BAFFIN ISLAND. I. EPIPELIC COMMUNITIES IN RIVERS1

The epipelic algae found in 9 rivers of southern Baffin Island were investigated during the 1972 growing season. The overall assemblage consisted of 240 taxa, of which 200 belonged to the Bacillariophyta and, only 17 to the Chlorophyta. Members of the Bacillariophyta accounted for S7–100% by numbers and 44–100% by volume of the algae at most localities. The dominant taxa were Achnanthes kriegeri Krasske, A. marginulata Grun., and Tabellaria flocculosa (Roth.) Kütz. The Chlorophyta comprised. 0–7% by numbers and 0–30% by volume of the algae, with Cosmarium tinctum Ralfs, Cylindrocystis spp., and Mougeotia sp. being most common. The standing crop in the different rivers commonly exceeded 8 × 10⁶ cells/cm² (8 × 10⁹μ³/cm²), and a maximum growth rate of 3.2 × 10⁵ cells/cm²/day (3.2 × 10⁸μ/cm²/day) was observed. Temperature and light are considered important, factors in the regulation of algal numbers, while nutrient supply in the overlying water, grazing by herbivores, wave action, and flooding appeared to have little effect.     

Steady state of phytoplankton assemblage in the tropical Lake Catemaco (Mexico)

Phytoplankton of the tropical lake Catemaco (Veracruz, Mexico) showed similar species composition during samplings from 1993 to 1995. There were two small dominant cyanobacterial species Cylindrospermopsis catemaco Kom.-Legn. et Tavera and Cylindrospermopsis philippinensis (Taylor) Kom., and a group of larger algae and cyanobacteria that were always present, however in smaller numbers: Aulacoseira granulata (Ehr.) Simons morphotype curvata, A. cf. italica (Ehr.) Simons mf. curvata, Fragilaria construens (Her.) Grun., Achnanthes minutissima Kütz., Planktolyngbya circumcreta (G.S.West) Anagn. et Kom., Chroococcus microscopicus Kom.-Legn. et Cronberg. Moreover we found several other scarcely present species. The percentage of total biomass of the two dominant species of Cylindrospermopsis varied between 34 and 81%, but they accounted for 80 to 95% of abundance. Apart from geomorphological features and climate conditions, biological variables played an important role. Fish-stock was formed by filter-feeding native herbivorous species of fish Dorosoma petenense (Günther), Bramocharax caballeroi (Contreras et Rivera), Astyanax mexicanus (Filippi), and an introduced, also herbivore Oreochromis niloticus (L.). Feeding activity of fish removed large species of algae and cyanobacteria as well as detrital remnants and zooplankton from the water. Smaller, inedible cyanobacteria remained in the water and formed the stable portion of the phytoplankton, dominant both in biomass and abundance. CANOCO analysis of samples and species variability demonstrated results of competition between two species of Cylindrospermopsis: steady state during the dominance of C. catemaco lasting probably for the whole year 1993 (one dry and one wet season) and steady state during the dominance of C. philippinensis in 1994 and 1995. According to the functional classification of phytoplankton suggested by Reynolds et al. (2002), Catemaco dominant assemblage would belong to the functional group S _N.