NOTES ON CLADOPHORA (CHLOROPHYCEAE). II. CLADOPHORA CATENATA (LINNAEUS) KÜTZ., 1843, EMEND. V. D. HOEK, 1963

The species name Cladophora catenata (L.) Kütz. emend, van den Hoek has priority over Cladophora fuliginosa Kütz.     

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.     

ON THE LIFE CYCLE,CYTOLOGY AND TAXONOMY OF CLADOPHORA CALLICOMA FROM INDIA

The present investigation deals with the cultural observations on the morphology, reproduction, life cycle, cytology and taxonomy of a freshwater Cladophora, C. callicoma (L.) Kütz, from India. There is a regular isomorphic alternation of generations between quadriflagellate zoospore-producing diploid plants and biflagellate isogamete-producing haploid plants, coupled with heterothallism in the latter. Chromosome numbers of n = 12 and 2n = 24 were determined respectively for gametophytes and sporophytes. Twelve bivalents were counted in meiosis where chiasmata varied from one to three. In light of above observations, the affinity of C. callicoma with C. glomerata, to which the former has often been assigned, has been discussed. It is proposed that the C. glomerata complex, which consists of intraspecific polyploid races, might have two distinct lines of evolution with regard to life cycle; one with forms having higher ploidy levels and lacking an alternation of generations, and the other with forms having low ploidy levels and alternation of generations.     

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.     

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.     

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.     

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.     

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.     

Temperature responses of macroalgae from the tropical island Hainan (P.R. China)

The temperature tolerances of 24 tropical macroalgae collected on Hainan Island (P.R. China) were investigated. For some isolates, growth response curves were also determined. The upper survival temperatures (USTs, 32–37°C) of these tropical west Pacific strains are similiar to those of tropical Atlantic species. With regard to their lower survival temperatures (LSTs) the species investigated show high variations: 12 species have LSTs between 16 and 7°C (Hypnea musciformis (Wulfen) Lamx. var esperi J, Ag., Centroceras clavulatum (C. Ag) Mont., Falkenbergia hillebrandii (Bornet) Falkenberg, Gelidiopsis intricata (Ag.) Vickers, Halymenia maculata J. Ag., Hypnea cenomyce J. Ag., Hypnea spinella (C. Ag.) Kütz., Gracilaria changii (Xia et Abott) Abott, Chang et Xia, Dictyopteris repens (Okam.) Boerg., Laurencia cartilaginea Yamada, Gelidium pusillum (Stackh.) Le Jol., Laurencia sp.). Their LSTs and temperature requirements for growth (range: 15–30 °C, optimum: 25–30 °C) are mostly similar to those of tropical west Atlantic and amphi-Atlantic (sub)tropical macroalgae as well as to tropical isolates of species with an Atlantic tropical to warm-temperate distribution. The remaining 12 species have LSTs between 6 and 1 °C (Ulva conglobata Kjellm., Ulva fasciata Delile, Padina boryana Thivy, Dictyosphaeria cavernosa (Forssk.) Boerg., Boodlea composita (Harv.) Brand, Boergesenia forbesii (Harv.) Feldm., Cladophora vagabunda (L.) van den Hoek, Enteromorpha compressa (L,) Grev., Enteromorpha intestinalis (L.) Link, Gracilaria tenuistipitata Chang et Xia, var liui Chang et Xia, Monostroma nitidum Wittr. and Valonia aegagropila C. Ag.). Their LSTs are mostly similar to those of Atlantic macroalgae with a tropical to (warm-) temperate distribution. The results are discussed with respect to the factors which may have triggered the development of the temperature requirements of the various species.     

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.     

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.     

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.     

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     

EVOLUTIONARY RELATIONSHIPS BETWEEN FOUR SPECIES OF CLADOPHORA (CLADOPHORALES,CHLOROPHYTA) BASED ON DNA–DNA HYBRIDIZATION1

Analysis of the reassociation kinetics of the DNA from Cladophora pellucida (Huds.) Kütz. indicates that the genome of this benthic alga is comprised of approximately 75% repetitive sequences. Single-copy sequences reassociated with a rate constant of 1.8 × 10^?3 M^?1· s^?1, which corresponds to a haploid genome size of 4.7 × 10⁸ bp. Genotypic relationships between members of the form section Longiarticulatae were determined by the method of DNA–DNA hybridization. No significant divergence was observed between the single-copy sequences of C. pellucida isolates from the East Atlantic coast and Mediterranean Sea. Cladophora feredayi Harv. and C. att. ad pellucida from Australia and C. pellucidoidea van den Hoek from the West Atlantic coast were highly and about equally divergent from C. pellucida. The data support the hypothesis that the West Atlantic–West Pacific divergence reflects the middle Miocene closure of the Mediterranean–Indo-Pacific seaways, and the hypothesis that the Northwest Atlantic–Northeast Atlantic divergence reflects the middle Miocene thermal separation of these coasts.     

INFLUENCE OF VARIOUS EXPOSURE PERIODS ON THE BIOMASS AND CHLOROPHYLL A OF CLADOPHORA GLOMERATA (CHLOROPHYTA)1

The biomass of Cladophora glomerata (L.) Kütz. was estimated at selected sites in the Colorado River between Glen Canyon Dam, Arizona, and River Kilometer 354. C. glomerata biomass was significantly higher at sites above Lees Ferry (25 km downstream from the Dam) than sites below the Ferry. Biomass and chlorophyll a were significantly reduced when C. glomerata was subjected to one-time exposures to the atmosphere for 12 daylight h in more. Repeated 12/12 h and 24/24 h (exposure/submergence) cycles over a two-week period also showed a significant reduction in biomass. The adaptations of C. glomerata to “stranding” during regulated flows are discussed.     

A COMPREHENSIVE STUDY OF THE LIFE CYCLE OF A SOUTH AMERICAN POPULATION OF STIGEOCLONIUM TENUE (CHAETOPHORALES,CHLOROPHYTA)1

The diplobiontic–haplodiplontic life cycle with alternating isomorphic generations in Stigeoclonium tenue (C. Agardh) Kütz. is described for the first time. Sporophytes (2n = 10) arise from tetraflagellate zoospores that are produced by meiosis. Sporic meiosis might be inferred from the cruciform divisions formed during zoosporogenesis and is confirmed through observations of prophase I substages. Zoospores do not germinate directly but produce a haploid cyst that germinates to give rise to a gametophyte (n = 5). Gametophytes produce biflagellate isogametes, which fuse to produce zygotes that germinate by mitosis into the sporophytic stage. Gametophytes and sporophytes reproduce asexually both via mitotic tetraflagellate zoospores and by thallus fragmentation. Results from this study indicate that both the cosmopolitan distribution and dominance of S. tenue in many periphytic communities might be due to its multiple reproductive strategies.     

ACCUMULATION OF WATER SOLUBLE PHOSPHORUS AND HYDROLYSIS OF POLYPHOSPHATES BY CLADOPHORA GLOMERATA (CHLOROPHYCEAE)1,2

Concentrations of hot-water extractable phosphorus from most samples of Cladophora glomerata (L.) Kütz. were relatively high (0.06–0.68%) and correlated closely with total dissolved P in ambient Lake Michigan water. Cladophora was able to hydrolyze polyphosphates by enzymes found in intracellular, extracellular and cell wall fractions. The intracellular phosphatase activity is pH dependent with the optimal hydrolysis rate at pH 7.8. Secretion of phosphatases is affected by pH, with maximum rate at 7, but affected little by light intensity. Magnesium is the most effective metallic cofactor required for maximal rates of intracellular phosphatase activities.     

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     

ECOLOGY OF CLADOPHORA GLOMERATA (L.) KÜTZ IN SOUTHERN ONTARIO1

Cladophora glomerata (L.) Kütz. was the dominant attached alga in streams and along lake shores in southern Ontario. Maximum production occurred in summer and resulted from 2 short periods of intensive vegetative growth (June and September). Optimum habitat conditions consist of a firm substrate in shallow alkaline water. These conditions are provided by harbor facilities where man-made structures supplement naturally occurring rock outcrops or cobble beaches and where nutrients are available from tributaries draining agricultural and urban land areas. Periodicity appears to be related to temperature; the interval between the 2 periods of intensive growth during warm weather decreases at successively more northern locations. Frequent observation of Cladophora growing at a single stream station revealed that variations in thallus morphology and relative cell dimensions of C. glomerata are greater than has generally been recognized. These variations can be attributed to changes in environmental conditions and events in the annual life cycle of the alga.     

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.