Colonial Algae Research Articles

Effects of tire wear particle on growth, extracellular polymeric substance production and oxidation stress of algae Chlorella vulgaris: Performance and mechanism

Tire wear particles (TWP) represent a distinctive form of microplastics (MPs) that are widely distributed in aquatic ecosystems. However, the toxicity of various types of TWP on phytoplankton remain to be further explored. Thus, three different TWPs originating from replaced bicycle, car, and electro-mobile tire (marked as BTWP, CTWP, and ETWP) were selected and their long-term biological influences on Chlorella vulgaris were investigated. Results demonstrated TWPs showed a concentration-dependent growth promotion of Chlorella vulgaris, with a maximum promotion rate reached to 40.51 % (10 mg/L, 10 d), 23.5 % (80 mg/L, 12 d), and 28.7 % (20 mg/L, 12 d) in the presence of BTWP, CTWP and ETWP, respectively. Meanwhile, TWPs could stimulate the secretion of EPS and induce oxidative stress. EPS analysis revealed the increase of polysaccharides could protect the cell from the direct contact with TWP particles. Moreover, the increased concentration of EPS also helps to induce the settlement of TWP and reduce the leachate release. The release of TWP into the environment could act as an accelerator for the growth of Chlorella vulgaris, which might further change the normal physicochemical behaviors of algae colony in aquatic system. Our findings provide new insights into the toxicity mechanism of TWPs on freshwater algae and valuable data on environmental risk assessment of TWPs.

Optimized medium conditions maximize colony regeneration from a single cell of Botryococcus braunii NIES836

Botryococcus braunii is a colonial alga recognized for its slow growth but high hydrocarbon accumulation. Although using genetic engineering to increase the growth rate and hydrocarbon yield of B. braunii is desirable, the presence of an extracellular matrix (ECM) significantly hinders the emergence of a homogeneous colony from a single DNA-transformed cell. Previously, we developed a method to isolate single cells without ECM from colonies. However, following the isolation of single cells, several months are required to regenerate colonies with a sufficient cell mass for subsequent analysis. To shorten the colony regeneration period, we investigated basal media and medium components, along with growth-promoting additives, in a series of single-factor experiments and optimized the concentrations of the medium constituents via response surface methodology (RSM). The results of the single-factor experiments revealed that the nitrogen source (a mixture of NaNO3 and NH4NO3), 1-naphthylacetic acid (NAA) and Fe(III)-citrate significantly increased the growth of B. braunii single cells into colonies. The optimal medium composition identified by RSM included 151.6 mg/L nitrogen source, 2.419 mg/L NAA and 15.3 mg/L Fe(III)-citrate. Verification experiments showed that the optimized medium resulted in a 1.75-fold increase in colony size compared with that of colonies grown in nonoptimized AF6 medium. This is the first report of the optimal medium composition for the regeneration of B. braunii colonies from single cells.

Modeling the reactive oxygen species (ROS) wave in Chlamydomonas reinhardtii colonies

Reactive oxygen species (ROS) play a crucial role as signaling molecules in both plant and animal cells, enabling rapid responses to various stimuli. Among the many cellular mechanisms used to generate and transduce ROS signals, ROS-induced-ROS release (RIRR) is emerging as an important pathway involved in the responses of various multicellular and unicellular organisms to environmental stresses. In RIRR, one cellular compartment, organelle, or cell generates or releases ROS, triggering an increased ROS production and release by another compartment, organelle, or cell, thereby giving rise to a fast propagating ROS wave. This RIRR-based signal relay has been demonstrated to facilitate mitochondria-to-mitochondria communication in animal cells and long-distance systemic signaling in plants in response to biotic and abiotic stresses. More recently, it has been discovered that different unicellular microorganism communities also exhibit a RIRR cell-to-cell signaling process triggered by a localized stress treatment. However, the precise mechanism underlying the propagation of the ROS signal among cells within these unicellular communities remained elusive. In this study, we employed a reaction-diffusion model incorporating the RIRR mechanism to analyze the propagation of ROS-mediated signals. By effectively balancing production and scavenging processes, our model successfully reproduces the experimental ROS signal velocities observed in unicellular green algae (Chlamydomonas reinhardtii) colonies grown on agar plates, furthering our understanding of intercellular ROS communication.

A simple method for the preparation of single cells and regeneration of colonies of Botryococcus braunii NIES836

Botryococcus braunii, a colonial alga, is known for notably slow growth; however, the growth rate and hydrocarbon productivity are expected to be improved using genetic modification techniques. Nevertheless, B. braunii has a hydrocarbon-rich extracellular matrix (ECM), and the ECM is a major barrier to DNA transformation. To analyse and utilize genetically modified B. braunii, it is essential to regenerate genetically homogeneous colonies derived from single cells. In this study, we developed a novel, simple method for harvesting viable single cells of B. braunii by centrifugation of the culture and subsequent filtration alone. The harvest of single cells was made possible by culturing B. braunii colonies in AF6 medium until the depletion of nitrogen and phosphorus sources and then releasing the single cells in colonies into the medium. Twenty-day culture of single cells in a 96-well plate resulted in 96% regeneration of colonies, and the regeneration of colonies was also confirmed on agar medium. This is the first report of colony regeneration from single cells of B. braunii. We believe that our method developed in this study will contribute greatly to the advancement of genetic modification techniques for B. braunii.

New insights into Coniacian-Santonian palynology in the Neo-Tethys (Egypt), with special emphasis on the ecological and depositional significance of the freshwater alga Pediastrum

Integrated palynological and palynofacies investigation based on hundreds of samples recovered from surface and subsurface successions in Sinai and the Gulf of Suez, Egypt, offer reliable data on the depositional framework of the Coniacian-Santonian Matulla Formation. The results reveal that the palynofacies contents of the three members of the Matulla Formation differ in that the lower Matulla-3 Member is Pediastrum-dominated, Matulla-2 Member is phytoclast-dominated, and the upper Mautalla-1 Member is AOM-dominated. However, some gradational mixing is observed. The assumed subdivision is very important as the Matulla Formation is a significant hydrocarbon reservoir in the Gulf of Suez, especially since this subdivision is strongly correlated with previous informal lithostratigraphic units.Furthermore, the peak occurrence of Pediastrum and its allied colonial algae that dominate the palynological assemblage, especially in the lower member of the Matulla Formation (Matulla-3), which is marginal marine, clearly implies freshwater incursions. Hence, these fossil algae are useful tracers of river runoffs as well as suspended load, enabling reconstruction of paleo-river discharge and sediment source area determination, especially if they have a promising reservoir potential, as in this case. This noteworthy record may specify an important ecozone at this time, not only in Egypt but also regionally, based on similar records from neighboring North African regions. Ultimately, the presence of Pediastrum demonstrates a sea level fall and its good preservation argues for a deposition in lowstand system tracts, which greatly conforms to sequence stratigraphic data.

Sulzbacheromyces leucodontium (Basidiomycota, Lepidostromataceae), a new species of basidiolichen widely distributed in the Neotropics

As a result of botanical and lichenological expeditions in the Colombian Andean-Amazonian Piedmont, in the Brazilian Amazon, and in Veracruz, Mexico, a new species of Sulzbacheromyces was discovered and is here described based on morphological, anatomical, and molecular characters. S. leucodontium differs from other neotropical species in the genus by having white basidiomata and colonial algae in the thallus and represents the species with the widest distribution of the genus in the Americas, from Mexico to Brazil. In addition, the most complete phylogenetic reconstruction of the genus to date is presented as well as a key to the known species of Sulzbacheromyces in the Neotropics.

Effects of nutrient limitation on cell growth, exopolysaccharide secretion and TEP production of Phaeocystis globosa

Phaeocystis globosa (P. globosa) often colonizes and produces mucus, which may cause massive blooms in coastal areas. To understand mechanism of the growth and the impact factors for better control of the bloom, we conducted a laboratory experiment on the effect of nitrogen (N) or phosphorus (P) limitation on the cell growth, production of exopolysaccharide (EPS), and transparent exopolymeric particles (TEP) of P. globosa. Results show no obvious differences in the N- and/or P-limitation in TEP production, polysaccharide secretion, and colony growth of P. globosa. Particularly in the death phase of the algae growth, the TEP production level in the experiment differed significantly, and was higher in the P-limitation group than that in the N-limitation group; additionally, the P-limitation group produced a relatively higher amount of EPS than N-limitation group, with greater cellular chlorophyll-a content, and in greater photosynthetic reaction rate of P. globosa cells, than those of the N-limitation group. However, under N-limited conditions, the algae colony survived longer. Under P-limited condition, P. globosa cells spend the photosynthesis-produced substances and energy for the secretion of extracellular substances but for cell reproduction, which was indicated by P. globosa cell growth and carbon content ratio between TEP and biomass.

Optimization of Microalgae–Bacteria Consortium in the Treatment of Paper Pulp Wastewater

The microalgae–bacteria consortium is a promising and sustainable alternative for industrial wastewater treatment, since it may allow good removal of organic matter and nutrients, as well as the possibility of producing products with added value from the algae biomass. This research investigated the best bacterial and microalgae inoculation ratio for system start-up and evaluation of removing organic matter (as chemical oxygen demand (COD)), ammoniacal nitrogen (NH4+–N), nitrite nitrogen (NO2−–N), nitrate nitrogen (NO3−–N), phosphate phosphorus (PO43−–P) and biomass formation parameters in six photobioreactors with a total volume of 1000 mL. Reactors were operated for 14 days with the following ratios of pulp mill biomass aerobic (BA) and Scenedesmus sp. microalgae (MA): 0:1 (PBR1), 1:0 (PBR2), 1:1 (PBR3), 3:1 (PBR4), 5:1 (PBR5), and 1:3 (PBR6). Results show that COD removal was observed in just two days of operation in PBR4, PBR5, and PBR6, whereas for the other reactors (with a lower rate of initial inoculation) it took five days. The PBR5 and PBR6 performed better in terms of NH4+–N removal, with 86.81% and 77.11%, respectively, which can be attributed to assimilation by microalgae and nitrification by bacteria. PBR6, with the highest concentration of microalgae, had the higher PO43−–P removal (86%), showing the advantage of algae in consortium with bacteria for phosphorus uptake. PBR4 and PBR5, with the highest BA, led to a better biomass production and sedimentability on the second day of operation, with flocculation efficiencies values over 90%. Regarding the formation of extracellular polymeric substances (EPS), protein production was substantially higher in PBR4 and PBR5, with more BA, with average concentrations of 49.90 mg/L and 49.05 mg/L, respectively. The presence of cyanobacteria and Chlorophyceae was identified in all reactors except PBR1 (only MA), which may indicate a good formation and structuring of the microalgae–bacteria consortium. Scanning electron microscopy (SEM) analysis revealed that filamentous microalgae were employed as a foundation for the fixation of bacteria and other algae colonies.

New data on the problem of the origin of Griva and Lake landscapes in the south of Western Siberia

The characteristic of the upper part of the borehole 486 drilled in 1981 on the Tyumensky Peninsula, located in the center of the Chany Reaches agglomeration is given. The main feature of the section is the presence of a horizon of large frost cracks in the roof of clays of the Lower Pliocene Novostanichnaya Formation, on which the upper Quaternary cover of Griva deposits occurs. The nature of the filling of cracks by the sediments of the overlying layer indicates that they were constantly filled with ice, which had already melted under the influence of the Grosswald Flow. This horizon is important for the reconstruction of the paleoclimate and paleogeography of the region. For the first time, data of palynological study of sediments of a typical Griva in the south of Western Siberia on the example of a section on the Cape Kazantsevsky Peninsula (the northern part of Lake Chany) are presented. Sediments contain pollen of woody and herbaceous plants, single spores of mosses and ferns, as well as microphytoplankton. The presence of cells of colonial algae of the genus Pediastrum suggests the accumulation of sediments in lacustrine conditions.

Resposta taxonômica e morfofuncional do fitoplâncton à variabilidade ambiental em rios de diferentes bacias hidrográficas no sul do Brasil

Abstract Aim Urbanization, agriculture, and deforestation are the main anthropogenic factors that modify the soil, altering the quality of water, and influencing limnological aspects and the aquatic biota in rivers. We investigated the morphology-based taxonomic and functional response (MBFG) of the phytoplankton community among different public supply rivers in distinct hydrographic basins with ultraoligotrophic, oligotrophic, and mesotrophic characteristics. Methods We sampled the phytoplankton community and environmental variables in nine rivers along three hydrographic basins in western Paraná. In order to evaluate the taxonomic and functional relationship of the community with the environmental variables, we applied both variance and redundancy analyses. Results Differences in temperature, pH, turbidity, total phosphorus, chemical oxygen demand, and total dissolved solids were identified among river basins and/or trophic states. The highest taxonomic contributions to richness and biovolume were from green algae and diatoms, while the highest functional contributions were from MBFG IV (algae without specialized traits), MBFG V (unicellular flagellated algae), MBFG VI (algae with a siliceous exoskeleton) and MBFG (large colonial algae). The taxonomic approach was sensitive to environmental variability in the rivers, while for the functional approach no relationship to environmental variability was identified. Conclusions The taxonomic approach of the phytoplankton community was more sensitive to the environmental variability of the studied rivers than the functional approach based on morphology. Therefore, we reinforce the importance of biological indicators for understanding the dynamics in aquatic ecosystems, providing crucial information for the management of water resources used for public supply.

Colony Formation in Three Species of the Family Scenedesmaceae (Desmodesmus subspicatus, Scenedesmus Acutus, Tetradesmus Dimorphus) Exposed to Sodium Dodecyl Sulfate and its Interference with Grazing of DAPHNIA Galeata.

By mimicking the info-chemicals emitted by grazers, the common anionic surfactant sodium dodecyl sulfate (SDS) can induce colony formation in the green algal genus Scenedesmus at environmentally relevant concentrations. The morphometric effects can hinder the feeding efficiency of grazers, reducing energy flow along the pelagic food chain from Scenedesmus to consumers. Despite this potential ecological risk, few studies exist on whether the SDS-triggered induction of colonies is common in other species of the family Scenedesmaceae. Here, we investigated the effects of SDS on the growth and morphology of three species of Scenedesmaceae (Desmodesmus subspicatus, Scenedesmus acutus, and Tetradesmus dimorphus) and on the clearance rates of Daphnia galeata grazing on the SDS-induced colonies. SDS triggered colony formation in all algal species at concentrations nonlethal to them (0.1-10mg L-1) in 72h; however, the induction levels of colony formation were generally lower than for those in the Daphnia culture medium. We also found that the SDS-induced colonial algae reduced D. galeata clearance rates. Our results highlight the potential effect of SDS on the Daphnia-Scenedesmaceae system by triggering the morphological response of Scenedesmaceae at concentrations below those that exert toxicity. Such disruptive effects of pollutants on predator-prey interactions should be considered within the framework of ecological risk assessments.

Evaluation of Syndromic Surveillance Data for Studying Harmful Algal Bloom-Associated Illnesses - United States, 2017-2019.

Harmful algal and cyanobacterial blooms (harmful algal blooms) are large colonies of algae or cyanobacteria that can harm humans, animals, and the environment (1-3). The number of algal blooms has been increasing in the United States, augmented by increasing water temperatures and nutrients in water from industry and agricultural run-off (4,5). The extent to which harmful algal bloom exposures cause human illness or long-term health effects is unknown. As the number of blooms increases annually, the likelihood of negative health outcomes (e.g., respiratory or gastrointestinal illness) from exposure also increases (4,5). To explore the utility of syndromic surveillance data for studying health effects from harmful algal bloom exposures, CDC queried emergency department (ED) visit data from the National Syndromic Surveillance Program (NSSP) for harmful algal bloom exposure-associated administrative discharge diagnosis codes and chief complaint text terms related to harmful algal bloom exposure (6). A total of 321 harmful algal bloom-associated ED visits were identified during January 1, 2017-December 31, 2019. An increase in harmful algal bloom-associated ED visits occurred during warmer months (June-October), consistent with seasonal fluctuations of blooms and recent publications (6,7). Although syndromic surveillance data are helpful for understanding harmful algal bloom-associated ED visits in the United States, exposures were documented infrequently with discharge diagnosis codes; 67% of harmful algal bloom-associated ED visits were identified through querying chief complaint text. Improving the documentation of harmful algal bloom exposures in medical records would further benefit future health studies.

Control of variability of primary grain assemblages on the stratigraphic differences in diagenetic processes and products in organic-rich sediments

Diagenesis exerts a key control on the evolution of mineralogical systems in shales, and by extension, on the development of rock properties amenable to unconventional reservoir prospectivity. To develop an understanding of the control of primary grain assemblage on the diagenetic pathways and products in shales, integrated high-resolution petrographic and multiple geochemical studies were conducted on samples from a vertical transect of oil-gas mature (vitrinite reflectance ranging from 0.98 to 2.72%) Whitehill Formation, a shale unit identified as the main potential gas reservoir in South Africa. Results show that the formation comprises three intervals with contrasting primary grain assemblages, including organic matter content, maceral type, and detrital mineral grains, as well as the submillimeter-scale arrangement of these constituents. The lower interval occurs as parallel-laminated black shale dominated by components derived from primary production, such as Tasmanites cysts, colonial algae, radiolarian tests, and amorphous organic matter with up to 5.78% TOC, and depleted in siliciclastic detritus. The mid and upper intervals contain biologically produced components (up to 16.57% TOC) and high quantities of siliciclastic mud dominated by clay minerals and micas, and are organized into thick discontinuous gray laminae. Petrographic data suggest that the high organic content supported a variety of bacterial metabolic pathways, which caused the precipitation of mineral cements in the sediment pore spaces prior to compaction. However, the early diagenetic reactions and products in these intervals display systematic variations that reflect heterogeneity in their primary grain assemblages. The presence of framboidal pyrite throughout the lower interval suggests sulfate reduction as the predominant metabolic pathway. In absence of significant volumes of siliciclastics, the acidity associated with this process was poorly buffered, and the pore waters were reducing. These conditions led to the dissolution of opaline radiolarian tests, which recrystallized within Tasmanites cysts and interstitial pores to quartz. On the contrary, carbon isotopes indicate that organic oxidation in the mid and upper sections was mainly promoted by methanogenic archaea and that the associated acidity was effectively buffered by the detrital aluminosilicates. The resulting bicarbonate alkalinities allowed for the formation of interstitial carbonate cements (dolomite, calcite). Aluminum released during the acid-consumption reactions recrystallized within sheltered and interstitial pores to chlorite. Considering that many other shale successions exhibit similar stratigraphic variability of primary grain assemblages as the Whitehill Formation, this type of study will improve the characterization of shale mineralogical systems and bulk properties amenable to sustainable unconventional exploration.

Ecological scheduling of the middle route of south-to-north water diversion project based on a reinforcement learning model

The Middle Route of the South-to-North Water Diversion project (MRP) effectively alleviates the problem of serious shortage of water resources in North China. However, owing to the long-term operation of this project, abnormal algal proliferation has occurred in the upper reaches of the main canal, and the water diversion outlet is easily blocked by the large colonies of algae falling into the canal, which has seriously threatened the water quality and water supply safety of the canal. In light of this issue, this study coupled the reinforcement learning model with the one-dimensional hydrodynamic model of the series sluice group to build an ecological scheduling model for prevention and control of algal proliferation in the MRP. The model was applied to the canal section (approximately 300 km long, from No. G2 to No. G17) where in algae grows easily. The results show that: (1) The model can achieve the desired reciprocating adjustment of the canal water level in the process of decline stability rise within 0.8 m and stably maintain the low water level for more than 72 h; (2) during the process of ecological scheduling, the maximum drawdown of water level satisfying the safety regulation and control constraints of the MRP is 1.0 m; (3) for an ecological regulation water level drop greater than 0.3 m, it is more difficult to restore the initial water level, and the water level rise range should therefore be greater than the decrease range; (4) the constructed model exhibits high robustness. Even for an observation error level less than 0.08 m, the success rate of the model can still exceed 80%. The ecological scheduling scheme generated by the model can be used to destroy the algal habitat conditions through hydrodynamic dynamic regulation, whereby decisional support can be provided for the prevention and control of abnormal proliferation of algae in the main canal.

New pelagophytes show a novel mode of algal colony development and reveal a perforated theca that may define the class.

Pelagophytes (Heterokonta) are a morphologically diverse class of marine algae historically united only by DNA sequences. We established clonal cultures of sand-dwelling pelagophytes collected from intertidal pools around Australia. Phylogenetic trees based on nuclear 18S rDNA and plastid rbcL, psaA, psaB, psbA, and psbC sequences revealed two new genera, Gazia and Glomerochrysis, related to Aureoumbra in a distinct lineage within the Sarcinochrysidaceae (Pelagophyceae). The three new species (Gazia saundersii, Gazia australica, and Glomerochrysis psammophila), along with an Australian strain of Aureoumbra geitleri, are characterized by dominant benthic stages that differ significantly from one another, while occasionally producing classic heterokont zoospores. The benthic stage of Ga. saundersii has a novel development not observed in any other colonial alga, consisting of large, spherical colonies (up to 140μm in diameter) containing c. 2,500 cells that eventually differentiate and segregate into a large number of daughter colonies that are subsequently liberated. Alternatively, colonies may differentiate into a mass of zoospores that escape and settle to develop into new colonies. In Gl. psammophila, cubic packets of cells form large sticky clusters that bind sand together, while Ga. australica and A. geitleri are unicellular species. Using fixation by high-pressure freezing, a distinctive perforated theca was observed by TEM in all genera of this lineage, and we hypothesize this unique covering may be the first morphological feature to characterize most, if not all, pelagophytes. This study substantiates the diverse nature of sand-dwelling pelagophytes as well as their mechanisms for thriving in a dynamic habitat.

ESTIMATION THE FACTORS AFFECTING ON GROWTH OF ALGAE IN UM EL-NAAJ LAKE BY USING REMOTE SENSING TECHNIQUES

Epiphytic algae adherent to aquatic plants are an essential link in the composition of the food chain of any ecosystem. Epiphytic algae act as primary producers of the food chain in the aquatic ecosystem and as natural food for herbivorous zooplankton and fish. This study aimed to detect the presence of algae colonies through remote sensing and to analyze factors that affect the growth of algae through field survey and visual interpretation of satellite images in Lake Um El-Naaj. Samples were collected from six locations on Lake Um El-Naaj from November 2018 to June 2019. The algae samples were collected from submerged parts of emerging aquatic plants (aquatic macrophytes Phragmites australis) and stored in plastic bags with little ambient water and solutions for preservation in the field and the laboratory. Water samples were collected to study the nutritional factors that influence the growth of algae, including the concentration of Phosphate, Nitrate, and Silica (silicon dioxide). The results showed that the values of total phosphorus increased by 1.0, 0.9, and 0.8 mg/L, in January, in places 2, 5, and 6, respectively. The highest nitrate value was 11.2 mg/L in December at site 5, while the lowest concentration values were in November (2.2 mg/L at site 6 and 3.7 mg/L at site 4). Besides, the lowest silicate concentration was 0.4 mg/L in November at site 2, while the highest was 2.4 mg/L in June 2019 at site 6. Based on the findings, it is possible to conclude that, during the winter, the water level increased due to the rain. For this reason, nutrient concentrations were low during the last period. Also, with the use of maps and remote sensing techniques, it is possible to determine the expected values around the station's location as future predictive readings that compensate for the difficulty of reaching these areas.

FOOD RELATIONS BETWEEN WHITEFISH SPECIES IN THE LOWER COURSE OF THE USA RIVER IN THE AUTUMN PERIOD

Feeding characteristics of the Siberian whitefish (pizhyan) and the White Sea least cisco in the Usa River, which is one of the main right-bank tributaries to the Pechora River, are considered. It has been found that while the food spectrum was quite wide (23 groups of food items), the bulk of the diet was made up of invertebrates in various developmental stages, as well as the blue-green colonial algae and indigestible particles. Analysis of the weight shares of the components showed that the biggest contributor to the whitefish diet was aquatic larvae of insects of the Chironomidae family (60.0 %); and in the diet of the least cisco this index was the highest for adult Simuliidae (43.0 %). No significant age-related differences in feeding were found in either of the two species. Their food spectra differ significantly both in terms of the main ontogenetic stages of invertebratesand the main groups of food items, wherefore the trophic tension is low. Low values of the food similarity index and trophic niche overlap indicate a weak competition for food between these fish species in the autumn period. The whitefish acts as a typical benthos feeder with a broad food spectrum, while the least cisco is euryphagous, easily switching between various groups of food item when necessary.

Middle Triassic freshwater green algae and fungi of the Puesto Viejo Basin, central-western Argentina: palaeoenvironmental implications

Diverse freshwater green algal microfossils and dispersed fungal spores among rich terrestrial palynofloras were recovered from the upper part of the Quebrada de los Fósiles Formation, Puesto Viejo Group, cropping-out in the fault-bounded San Rafael Basin, Mendoza Province, Argentina. Sedimentological data suggest that the vegetation recorded from this unit grew in floodplains of high-sinuosity fluvial systems when intense episodic volcanic activity provided great quantities of ash deposits to the sites. Small and temporary shallow lake deposits and thin peat ponds were recorded at two sections, yielding palynofloras composed of variable contents of spores, pollen, freshwater algae and fungal associations. The taxa described and illustrated herein consist of representatives of colonial Chlorophyta algae (Botryococcus), a diverse group of Zygnematales zygospores represented by the genera Lecaniella, Maculatasporites, Mehlisphaeridium, Ovoidites and the incertae sedis algae Leiosphaeridia and Retirotundia as well as representatives of fungi assigned to Microsporonites and Portalites. Two new species of Ovoidites are described herein, Ovoidites tripartitus and Ovoidites circumplicatus, and the new combination Ovoidites scissus is also presented. The terrestrial and aquatic vegetation grew associated with shallow water bodies in floodplain environments developed under warm temperate, strongly seasonal climatic conditions. The environment was stressed by volcanism that probably restricted the colonization and development of the ecosystem. The occurrence of algal microfossils in the Quebrada de los Fósiles Formation suggest shallow and episodic locally restricted aquatic environments inhabited by autochthonous freshwater green algae consistent with the sedimentological evidence. A Middle Triassic age is inferred from recent radiometric dating obtained from the basal and upper ignimbrite beds of the Quebrada de los Fósiles Formation indicate an age of 243.9 ± 2.0 Ma and 235.8 ± 2.0 Ma, respectively, thus mostly constrained to the Ladinian age. The composition of the fossil flora (palynoflora and macroflora) also indicates Middle Triassic age.Ana M. Zavattieri [amz@mendoza-conicet.gob.ar], Unidad de Paleopalinología, Departamento de Paleontología, Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales (IANIGLA), CCT-CONICET-Mendoza, Av. A. Ruíz Leal s/n, Parque General San Martín, M5502IRA Mendoza, Argentina; Pedro Raúl Gutiérrez [pedroraulgutierrez@gmail.com], Museo Argentino de Ciencias Naturales “B. Rivadavia”, CONICET, Sección Paleopalinología, Área Paleontología. Buenos Aires, Argentina, Av. Ángel Gallardo 470, C1405DJR Buenos Aires, Argentina; Mariana Monti [mariana.monti@ypftecnologia.com.ar], YPF Tecnología S.A. (Y-TEC), Avenida del Petróleo s/n, entre 129 y 143, B1924CKU Berisso, Argentina.

Motility and phototaxis of Gonium, the simplest differentiated colonial alga.

Green algae of the Volvocine lineage, spanning from unicellular Chlamydomonas to vastly larger Volvox, are models for the study of the evolution of multicellularity, flagellar dynamics, and developmental processes. Phototactic steering in these organisms occurs without a central nervous system, driven solely by the response of individual cells. All such algae spin about a body-fixed axis as they swim; directional photosensors on each cell thus receive periodic signals when that axis is not aligned with the light. The flagella of Chlamydomonas and Volvox both exhibit an adaptive response to such signals in a manner that allows for accurate phototaxis, but in the former the two flagella have distinct responses, while the thousands of flagella on the surface of spherical Volvox colonies have essentially identical behavior. The planar 16-cell species Gonium pectorale thus presents a conundrum, for its central 4 cells have a Chlamydomonas-like beat that provide propulsion normal to the plane, while its 12 peripheral cells generate rotation around the normal through a Volvox-like beat. Here we combine experiment, theory, and computations to reveal how Gonium, perhaps the simplest differentiated colonial organism, achieves phototaxis. High-resolution cell tracking, particle image velocimetry of flagellar driven flows, and high-speed imaging of flagella on micropipette-held colonies show how, in the context of a recently introduced model for Chlamydomonas phototaxis, an adaptive response of the peripheral cells alone leads to photoreorientation of the entire colony. The analysis also highlights the importance of local variations in flagellar beat dynamics within a given colony, which can lead to enhanced reorientation dynamics.

Are fluorometric, taxonomic, and functional indicators of phytoplankton community structure linked to environmental typology of urban ponds and lakes?

ABSTRACTPhytoplankton bioindicators were used to assess environmental conditions in urban aquatic systems in a large Canadian city. Sampling was conducted during summers 2010 and 2011 in 20 urban waterbodies on the Island of Montreal (Quebec, Canada). We evaluated 4 indicators: (1) fluorometric estimates of the chlorophyll concentration of the total phytoplankton and of 4 spectral groups, (2) species richness, and (3) biovolumes of taxonomic and (4) functional groups of the microphytoplankton. We assessed how these indicators changed among types of urban waterbodies and determined the limnological features and/or management practices driving their spatial variation. Principal component analysis captured 48% of total environmental heterogeneity, and K-means clustering analyses defined 5 relevant types of waterbodies. Overall, 96 microphytoplankton species (γ diversity) were recorded, and species richness (α diversity) per waterbody varied from 1 to 27. Chlorophyll concentration of the total phytoplankton and the green algae spectral group, as well as the total biovolume of microphytoplankton, dinophytes, and of 2 functional groups (large flagellates, large colonies of green algae, and cyanobacteria) differed among waterbody types. Phytoplankton indicators based on in situ fluorometry and microphytoplankton biovolume of functional and taxonomic groups were fairly coherent and showed potential for monitoring. Implications of our findings are discussed in light of guiding future management practices to sustain biodiversity, ecological integrity, and water quality of urban waterbodies.