Melosira Species Research Articles

A morphology-based phylogeny of the diatoms formerly assigned to the Orthoseiraceae (Bacillariophyta): phylogenetic relationships, character analysis and classification

ABSTRACT A formal cladistic analysis of the morphological features of taxa assigned to the Orthoseiraceae, including Phycavernosa, Guarreraea and species of the genus Orthoseira is developed for 35 taxa based on 16 characters along with two Melosira species and four biddulphioid species as ingroup taxa as well as Leptocylindrus danicus as the outgroup. A consensus tree of 266 843 most parsimonious topologies suggests that the Orthoseiraceae is monophyletic, and that Guarreraea plus all former species of Orthoseira represent a monophyletic group. This analysis of morphological data did not provide support for the members of the Orthoseiraceae being more closely related to melosiroid or biddulphioid diatoms. Relationships within the monophyletic orthoseiracean group are detailed. Due to the exclusion of the generitype of Orthoseira not possessing carinoportulae which are central tube processes, one of the diagnostic features of the former Orthoseiraceae, other taxon names are described and recognized herein. We recognize and describe a new order, the Liparogyrales, based on the genus Liparogyra for taxa that were previously assigned to Orthoseira. Two families, the Phycavernosaceae, comprising the genus Phycavernosa, and the Liparogyraceae, comprising Guarreraea and taxa formerly assigned to Orthoseira, are described. The genus Liparogyra is composed of three subgenera: the subgenus Liparogyra, the subgenus Porocyclia, and the subgenus Insularis which are diagnosed by synapomorphic features. Based on our analysis, the genus Stephanosira appears to lack synapomorphies. Liparogyra, Porocyclia and Stephanosira had previously been described as genera by Ehrenberg. Guarreraea and one newly proposed genus are also included in the Liparogyraceae. Several other lineages are aphyletic, due to them either being monotypic or without diagnostic features. Thus, a total of 29 species in five genera are recognized within the newly described order and two newly described families. Eighteen new combinations are proposed for the transfer of taxa from Orthoseira to other genera. Homoplasy amongst some of the character states is discussed.

Morphological and phylogenetic analysis of a new Melosira species and revision of freshwater Melosira in China

Morphological and phylogenetic analysis of a new Melosira species and revision of freshwater Melosira in China

Revision of the non-marine centric diatom flora (Bacillariophyta) of the sub-Antarctic Campbell Island (southern Pacific Ocean) with the descriptions of five new species

During a survey of the moss-inhabiting diatom flora of the sub-Antarctic Campbell Island, located in the southern Pacific Ocean, several unknown centric diatoms were observed that could not be identified using the currently available literature. Detailed light and scanning electron microscopical observations and comparisons with the characters of several species of Melosira, Angusticopula, Ferocia and Arcanodiscus worldwide indicated that five of them should be described as new to science: Angusticopula cosmica Goeyers & Van de Vijver sp. nov., Arcanodiscus crawfordianus Goeyers & Van de Vijver sp. nov., A. indistinctus Goeyers & Van de Vijver sp. nov., A. saundersianus Goeyers & Van de Vijver sp. nov. and Ferocia houkiana Goeyers & Van de Vijver sp. nov. A sixth species, Angusticopula chilensis, was illustrated for the first time using SEM and as a result is considered to differ sufficiently from A. dickiei to warrant epitypification as A. chilensis. The new species were first described in genera that formerly were included within the genus Melosira. All six species are morphologically characterized and compared with similar species within their respective genera. Their presence and distribution on Campbell Island are discussed based on the observations made in the available samples.

Melosira jeanbertrandiana, a new Melosira species (Bacillariophyceae) from the sub-Antarctic region

ABSTRACTDuring a survey of the soil diatom flora of the sub-Antarctic Ile de la Possession (Iles Crozet), located in the southern Indian Ocean, an unknown Melosira species was found that could not be identified using the currently available literature on the genus. The species is described as Melosira jeanbertrandiana sp. nov. based on detailed light and scanning electron microscopy observations. The new species is characterized by a relatively high mantle, the presence of several marginal rings of acute, never bifurcating spines and a series of eight rimoportulae near the central area with several others scattered over the rest of the valve face and mantle. The girdle comprising several large, ligulate open copulae and the position of the rimoportulae clearly place this new species within the genus Melosira C.Agardh. The species was observed in bare, moist soil in scratches in cliffs bordering the ocean where the influence of sea spray is obvious. The description of this new species further increases the number of species of the Melosirales compared to other centric freshwater diatoms which are infrequently found on the sub-Antarctic islands.

Angusticopula rowlingiana, a new melosiroid diatom (Bacillariophyta) from Ascension Island (South Atlantic Ocean)

During a diatom survey of some samples from Ascension Island, a remote island located in the southern Atlantic Ocean, an unknown melosiroid diatom species was studied using both light and scanning electron microscopy. It proved to be a new species described as Angusticopula rowlingiana sp. nov. and characterized by a large number of narrow copulae in the girdle, a marginal ring of small granules, very small pores covering the entire valve face and occasionally having internal valves. The new species is compared with all Angusticopula species known worldwide and with several Melosira species showing a similar combination of characters. Short notes on its ecology are included.

Novel Widespread Marine Oomycetes Parasitising Diatoms, Including the Toxic Genus Pseudo-nitzschia: Genetic, Morphological, and Ecological Characterisation.

Parasites are key drivers of phytoplankton bloom dynamics and related aquatic ecosystem processes. Yet, the dearth of morphological and molecular information hinders the assessment of their diversity and ecological role. Using single-cell techniques, we characterise morphologically and molecularly, intracellular parasitoids infecting four potentially toxin-producing Pseudo-nitzschia and one Melosira species on the North Atlantic coast. These sequences define two, morphologically indistinguishable clades within the phylum Oomycota, related to the genera of algal parasites Anisolpidium and Olpidiopsis and the diatom parasitoid species Miracula helgolandica. Our morphological data are insufficient to attribute either clade to the still unsequenced genus Ectrogella; hence it is proposed to name the clades OOM_1 and OOM_2. A screening of global databases of the barcode regions V4 and V9 of the 18S rDNA demonstrate the presence of these parasitoids beyond the North Atlantic coastal region. During a biweekly metabarcoding survey (Concarneau Bay, France), reads associated with one sequenced parasitoid coincided with the decline of Cerataulina pelagica bloom, whilst the other parasitoids co-occurred at low abundance with Pseudo-nitzschia. Our data highlight a complex and unexplored diversity of the oomycete parasitoids of diatoms and calls for the investigation of their phenology, evolution, and potential contribution in controlling their host spatial-temporal dynamics.

Phytoplankton and nutrients studies in Magu bay, Speke gulf, Lake Victoria, (Tanzania) following the 2001 principal rain season

Phytoplankton abundance and species composition in relation to some physico-chemical parameters were studied in Magu Bay, Lake Victoria, in May 2001. Investigations on the influence of Simiyu River on the biological and physical characteristics of the Bay were carried out. Surface and bottom currents flowed in the northeast direction close to the river mouth but were completely reversed after about 1.5 km from the river mouth. Most suspended particles brought in by the river were deposited within 0.5 km after entering the lake. Nutrient concentrations were generally high towards the eastern part of the bay as compared to the rest of the bay area probably due to the reversal in the direction of current flow. Phytoplankton were generally dominated by the cyanobacteria Microcystis and Anabaena species though the diatoms Nitzschia and Melosira species were more abundant in some sampling stations. Phytoplankton abundance ranged from 500 cells ml-1 at stations LV36 and LV37 to 1440000 cells ml-1 at station LV1. The high abundance encountered at stations LV1, LV2, and LV3 is assumed to be due to formation of surface scum of the gas vacuolated Microcystis cells as a result of wind action. Phytoplankton production was possibly light limited in areas with simultaneously high nutrient concentrations and high turbidity. More data are required to corroborate the current study and to have a full picture of the influence of the river during different seasons. Tanzania Journal of Science Vol.30(1) 2004: 33-42

Hypothesized resource relationships among African planktonic diatoms

Several hypotheses are advanced for resource relationships among planktonic diatoms in African freshwater lakes that are consistent with the light and nutrient conditions of the lakes and the extant and fossil distributions of the diatom species in them. The hypotheses are all testable and are potentially powerful tools for interpreting past climatic conditions. A ranking is proposed along a Si: P gradient: at the high end are the planktonic Synedra spp. with the highest Si requirements and lowest P requirements (high Si : P), the planktonic Nitzschia spp. are intermediate, and the Stephanodiscus spp. are at the low end with the lowest Si requirements and highest P requirements (low Si : P). Melosira species may be ranked along a light: P gradient. We suggest that Melosira distans and Melosira ambigua grow under high light and have low P requirements, Melosira agassizii and Melosira granulata are intermediate, and Melosira nyassensis has the lowest light and highest P requirements. There also appears to be a relationship between pore size and the light regime for growth among the Melosira species; thus, M. distans and M. ambigua have the smallest pores and highest light requirements, M. nyassensis has the largest pores and lowest light requirements. Melosira granulata is intermediate and seems to be very variable in pore size, depending on the light environment. One diatom, Nitzschia fonticola, lives in and on colonies of Microcystis and is considered to be an obligate nitrogen heterotroph.

The A/C (Araphidineae/Centrales) ratio in high and low alkalinity lakes in eastern Minnesota

SUMMARY. Diatoms from surface sediment samples from lakes on both sides of a glacial drift border in eastern Minnesota show that Araphidinate diatom genera like Fragilaria, Asterionella and Synedra are more common in lakes in drift with lower CaCO3 whereas Stephanodiscus and Melosira species are more abundant in those with high CaCo3. In a lake sediment core from low carbonate drift Fragilaria crotonensis and Asterionella formosa increased when pioneer farmers arrived. These results confirm speculation that high A/C ratios are associated with low‐alkalinity eutrophic lakes.

Diatom associations and succession in Lake Kariba, South Central Africa

Diatom Associations formed by 1% or more of species, found by the Thomasson analysis method are discussed in relation to the morphology and limnology of the four basins of Lake Kariba. A brief comparison is made with associations in two stretches of the Zambesi river. A dominant association formed by certain species of Melosira demonstrated a pattern of succession, in relation to the thermal cycle in the lower, middle and upper lake by variations of the percentage occurrence of species forming it: Melosira granulata dominated during homothermy and remained so throughout stratification in the lacustrine conditions at the barrier or wall; M. granulata v. angustissima dominated during overturn and became the dominant species in the riverine conditions of the two uppermost basins. Results from the Central basin illustrated the intermediate position of this area of the lake. The pattern was disrupted in the far N.E sub-basin of the Sanyati basin, which in general showed individuality and where accidental and ambivalent plankters became co-dominant with the Melosira association during homothermy.

Dynamics of phytoplankton growth in the Waikato River, North Island, New Zealand

The Waikato River (latitude 38°S, longitude 176°E, North Island, New Zealand) is overwhelming y dominated by diatoms (mainly Melosira species) while blue-green and green algae are of minor importance. Both laboratory and in situ nutrient enrichment experiments showed enhanced growth of natural and index blue-green and green algae by addition of phosphate and nitrate. These algae were also shown to require higher temperature and light intensity than the diatoms. On the other hand, Waikato River with its higher silica content, moderate range of temperature and running water habitat was more favourable an environment for diatoms.

The distribution of estuarine diatoms along environmental gradients: A canonical correlation

Multivariate statistical procedures identified groups of non-planktonic diatoms with similar distributions in Yaquina Estuary (Oregon). A clustering algorithm and a canonical analysis of discriminance were used to describe distributional patterns relative to the pattern of sampling, and these patterns were associated with environmental gradients by the method of canonical correlation. There was a distributional continuum of marine and brackish-water diatom taxa that changed location in the estuary with seasonal variation in freshwater discharge. However, the vertical and horizontal gradients of salinity and desiccation were steep enough to manifest three relatively discrete assemblages, one with typical freshwater taxa and two dominated by species of Melosira and Achnanthes. About 41% of the variability in the species data could be associated with salinity, temperature, light energy, and period of exposure to intertidal emergence. Canonical correlation ordered 26 taxa along gradients of mean salinity and mean daily salinity range.

Phytoplankton of Lake Superior 1973

The horizontal and vertical distribution of Lake Superior phytoplankton was studied from May to November/December 1973 at approximately monthly intervals from 34 stations distributed over the entire lake. Taxonomic identification and enumeration were carried out using the inverted microscope Utermöhl technique. The mean phytoplankton biomass showed a homogeneous distribution with very low biomass concentration across the lake (0.1-0.2 g/m 3). It did not show any inshore/offshore differentiation, although relatively high values were observed in the western end. On a lakewide basis the seasonal composition was dominated by the phy to flagellates (53%) and diatoms (38%), with the bluegreens and greens contributing the least. Among the phytoflagellates, Cryptophyceae (26%), Chrysophyceae (21%), and Dinophyceae (5%) were the main contributors. Lake Superior is characterized by a large number of species. Approximately 285 taxa were identified, the majority of which have not been reported before in Lake Superior or the other Laurentian Great Lakes. The offshore and open lake waters possessed large numbers of common species usually found in oligotrophic environments. However, the western end contained a limited number of common species, dominated by species of Melosira which are often associated with eutrophication. The offshore species succession revealed dominance of species usually found in oligotrophic waters. Several rare species were also identified. Some of them like Stelexmonas dichotoma Lackey and Chrysolykos planctonicus Mack were indicative of a cold-stenothermal oligotrophic environment. Vertical profiles exhibited three types of biomass-temperature relationships, one of which was the presence of a sub-thermocline maximum which appeared to be photosynthetically active. On the basis of biomass and species composition, Lake Superior was classified as an ultra-oligotrophic environment similar to the deep, large, oligotrphic, boreal lakes. Lake Superior results, once again, emphasize the significance of phytoflagellates and nannoplankton in the algal dynamics of the Laurentian Great Lakes and demand the application of the standard Utermöhl technique in all phycological investigations.

Stephanodiscus binderanus (Kütz.) Krieger or Melosira binderana Kütz. (Bacillariophyta, Centrales)

Abstract The centric diatom which has been identified either as a species of Melosira C.A. Ag. or of Stephanodiscus C. G. Ehrenb is an indicator of increasing eutrophication in lakes, and is also responsible for serious problems in water purification plants. Investigation with the light, scanning, and transmission microscopes has yielded the first detailed study of this species and confirmed its position in Stephanodiscus.

Diatom Succession in a Core from Pickerel Lake, Northeastern South Dakota

Percentage analyses of the diatoms from a core of sediment show the changes in the community since the formation of Pickerel Lake. The lake basin is in calcareous drift from the Wisconsin glaciation and is located on the Coteau des Prairies upland. This work supplements earlier studies of the pollen, plant macrofossils, and mollusks made by Watts and Bright (1968), in which they presented evidence for four vegetational stages: (1) spruce forest, (2) deciduous woodland, (3) bluestem prairie, and (4) continued open prairie with the return of some woodland. The diatom core was correlated with the nearby pollen core by pollen analysis. The diatom succession begins in diatom zone I, with an assemblage dominated by Fragilaria and Mastogloia species and containing many taxa of alkaline waters. It also includes several taxa that generally prefer acid environments and only occur in the lower part of this core. This diatom assemblage is correlated primarily with the presence of spruce forest and its associated soils; the change in the diatoms occurs when the deciduous woodland that follows is partly replaced by prairie openings. It is suggested that the changes in the type of material (mainly soil) washed into the lake produced a more alkaline environment, which excluded some of the acidophilous taxa. Diatom zone II is largely transitional to zone III, which is dominated by Melosira species and includes many indicators of a more eutrophic (nutrient-rich) environment, for example Fragilaria crotonensis. More brackish-water taxa also indicate an increase in the mineral content of the water. All of these features are consistent with evidence from the pollen stratigraphy, which indicates that this is the time of maximum prairie development in this area, along with maximum soil erosion and lake-water evaporation. Diatom zone IV is largely transitional, corresponding to the time when woodland was once again developing around the margins of the lake basin. Diatom zone V features increasing percentages of forms characteristic of surf zones in lakes, indicating perhaps a shallowing of the site as a result of sedimentation. There is some indication of recent enrichment, concurrent with an increase in Ambrosia pollen (ragweed), which is possibly due to disturbance by man. The use of a constant volume of material in the diatom preparation makes it possible to draw a diagram of diatom abundance for each level. The diatoms are scarce in samples from the lower part of the core, and four radiocarbon dates bear out a suggestion that more inorganic material was deposited at the core site during the early history of the lake than subsequently. A total of 207 taxa is reported, and ecological notes on all are included in an appendix. A diatom diagram shows curves for 71 of the taxa.

Seasonality and diversity of epipelic diatoms in two wetlands of Banglades

Seasonality and composition of epipelic diatom community were studied for two years in two wetlands of Bangladesh namely, Joysagar and Sitlai Beel. A total 73 diatom taxa were recorded. The average density of epipelic diatom was higher in Sitlai Beel (52.97 × 104/g sediment) than in the Joysagar (3.92 × 104/g sediment). The epipelic diatom community of Joysagar was dominated by the species of Melosira, Synedra, Navicula, Pinnularia, Gomphonema, and Nitzschia, whereas Melosira, Navicula, Pinnularia, Cymbella and Gomphonema dominated in Sitlai Beel. Melosira granulata, Navicula americana, Pinnularia major, and Gomphonema lanceolatum were dominant and expressed distinct seasonality in both wetlands. The concentration of soluble reactive silicate of water and the average density of epipelic diatom did not express any significant relation in both of the water bodies. The concentration of phytoplankton chl a had a positive relationship with epipelic diatoms and was significant in Sitlai Beel. Key words: Epipelic diatoms; Sitlai Beel; Wetlands; Melosira; Bangladesh DOI: 10.3329/bjb.v39i1.5523Bangladesh J. Bot. 39(1): 29-36, 2010 (June)

Sovetskie Riboch. Issledov. v Severo-Zapadnoi Atlant. Okean., VNIRO-PINRO, Moskva : Nesis K.N., 1962. Soviet investigations of benthos in Newfoundland-Labrador fishing area 219–225

The horizontal and vertical distribution of Lake Superior phytoplankton was studied from May to November/December 1973 at approximately monthly intervals from 34 stations distributed over the entire lake. Taxonomic identification and enumeration were carried out using the inverted microscope Utermöhl technique. The mean phytoplankton biomass showed a homogeneous distribution with very low biomass concentration across the lake (0.1-0.2 g/m3). It did not show any inshore/offshore differentiation, although relatively high values were observed in the western end. On a lakewide basis the seasonal composition was dominated by the phy to flagellates (53%) and diatoms (38%), with the bluegreens and greens contributing the least. Among the phytoflagellates, Cryptophyceae (26%), Chrysophyceae (21%), and Dinophyceae (5%) were the main contributors.Lake Superior is characterized by a large number of species. Approximately 285 taxa were identified, the majority of which have not been reported before in Lake Superior or the other Laurentian Great Lakes. The offshore and open lake waters possessed large numbers of common species usually found in oligotrophic environments. However, the western end contained a limited number of common species, dominated by species of Melosira which are often associated with eutrophication. The offshore species succession revealed dominance of species usually found in oligotrophic waters. Several rare species were also identified. Some of them like Stelexmonas dichotoma Lackey and Chrysolykos planctonicus Mack were indicative of a cold-stenothermal oligotrophic environment. Vertical profiles exhibited three types of biomass-temperature relationships, one of which was the presence of a sub-thermocline maximum which appeared to be photosynthetically active. On the basis of biomass and species composition, Lake Superior was classified as an ultra-oligotrophic environment similar to the deep, large, oligotrphic, boreal lakes. Lake Superior results, once again, emphasize the significance of phytoflagellates and nannoplankton in the algal dynamics of the Laurentian Great Lakes and demand the application of the standard Utermöhl technique in all phycological investigations.