Epithemia Turgida Research Articles

Algal Blooms and their Importance in Xochimilco and San Gregorio Atlapulco, Mexico

Algal blooms refer to the massive development of photosynthetic microorganisms in aquatic environments. Microalgae are an important source of food for the primary consumers of these ecosystems, purify water, capture atmospheric CO2 and from them a large number of products for industrial use are obtained; however, in Mexico its study is still incipient, especially with regard to blooms of freshwater species. This paper presents the results obtained from the most abundant and important algal blooms of the Ejidos de Xochimilco and San Gregorio Atlapulco Protected Natural Area. 12 samplings were carried out between the years 2012 to 2022. The samples were collected with 54 μm mesh aperture trawl and van Dorn bottle and were fixed with 4% final formalin and 1% lugol, respectively. 17 algal blooms were recorded, among the Cyanoprokaryotes are: Anabaenopsis circularis, Limnospira maxima, Microcystis aeruginosa, Planktothrix agardhii; among the Chlorophytes Monoraphidium convolutum, Ankistrodesmus falcatus, Closterium acutum, Lemmermannia tetrapedia; among the Euglenophytes Euglena viridis y Phacus pleuronectes and between the Diatoms Cocconeis placentula var. placentula, Stephanocyclus meneghinianus, Epithemia turgida var. turgida, Gomphonema olivaceum, Gomphonema parvulum var. capitata, Hantzschia amphioxys y Craticula cuspidata. Of these species, Limnospira maxima has very high nutritional value, Anabaenopsis circularis, Microcystis aeruginosa y Planktothrix agardhii are potentially toxic or carcinogenic. It should be noted that all the registered species presented great spatiotemporal variations, for the above and given their great importance, it is necessary to expand their knowledge and carry out constant monitoring, as a tool for their understanding, use and management.

Diatom community composition on submerged macrophyte species from an Ontario (Canada) lake.

The introduction of invasive macrophyte species can affect submerged macrophyte community composition and abundance, which in turn can alter the functions of lake ecosystems. Knowing when and how invasive macrophytes arrive and spread can help disentangle the effects of invasive species from other stressors on lake ecosystems. This requires a long-term (decades) perspective of macrophyte community composition, which is rarely available. An alternative is paleolimnological inferences of macrophyte community composition from fossil diatom assemblages, which requires knowledge of epiphytic diatom communities. Here, we investigated the epiphytic diatom community composition of three common submerged macrophyte species (Chara sp., Potamogeton robbinsii, and the invasive Myriophyllum spicatum) in a typical temperate, mixed forest lake, Chandos Lake, Ontario, Canada, to provide a basis for future paleolimnological research. Non-parametric, multivariate analysis of variance indicated a statistically significant difference in the epiphytic diatom communities of different macrophyte species, despite principal components analysis showing some overlap among the diatom communities. Diatom community composition of all macrophytes had abundant Achnanthidium minutissimum and Cocconeis placentula. Generalized linear models and univariate analysis of variance identified six diatoms (Encyonopsis microcephala, Epithemia turgida, Gomphonema parvulius, Navicula gerloffi, Rhopalodia gibba, and Rossithidium anastasiae) that were significantly different among macrophyte species. Although it remains uncertain whether these differences are sufficient to infer historical macrophyte community composition from epiphytic diatom fossil assemblages, our results indicate the potential of such an approach and offer suggestions for future research.

Forensic studies of phytoplankton ecology of two water bodies of Kurukshetra area of Haryana, State in India

BackgroundIn forensic investigations of death cases in which the body has been recovered from a water body, there is an urgent need to prove whether the death is due to drowning or not. Moreover, another important issue arises, whether a person was alive at the time of drowning (anti-mortem drowning) or he was thrown dead into the water body (post-mortem drowning) To answer these questions, phytoplankton species of forensic importance from two water bodies (Braham Sarovar and Prithus Pools) were analyzed to develop the Phytoplankton maps (P-maps). The P-maps are basically a detailed list of categories of species which are common, site-specific, rare and seasonally occurring phytoplanktons along with their photomicrographs.MethodsIn the present study, water samples have been collected from Braham Sarovar and Prithus Pools situated at Kurukshetra area of Haryana state, India. The phytoplankton species present in both ponds were extracted by mild acid digestion (5% HCl). The physico-chemical properties of these water bodies such as pH, water temperature, total dissolved solids, electrical conductivity, hardness, alkalinity, calcium, sodium, potassium, and chloride ions have been recorded to establish a correlation with the distribution of phytoplankton using principal component analysis.ResultsTotal 138 species of 59 genera of phytoplanktons belonging to Cyanophyceae, Chlorophyceae, Bacillariophyceae, Euglenophyceae and Dinophyceae have been observed. In Braham Sarovar, Cylindrospermum sp., Epithemia turgida, Eunotia rhomboidea, and Westella botryoides were the site-specific phytoplanktons whereas in Prithus pool, the site specific phytoplanktons were Leptolynbya granulifera, Arthospira jenerii, Cymbella cymbiformis, Frustulia vulgaris.ConclusionIt is hoped that results/data obtained from the present study (P-maps) may go a long way in solving the mysteries related to the deaths due to drowning and can be usefully used as a reference data for determining the exact site of drowning.

Genomic divergence within non-photosynthetic cyanobacterial endosymbionts in rhopalodiacean diatoms

Organelle acquisitions via endosymbioses with prokaryotes were milestones in the evolution of eukaryotes. Still, quite a few uncertainties have remained for the evolution in the early stage of organellogenesis. In this respect, rhopalodiacean diatoms and their obligate cyanobacterial endosymbionts, called spheroid bodies, are emerging as new models for the study of organellogenesis. The genome for the spheroid body of Epithemia turgida, a rhopalodiacean diatom, has unveiled its unique metabolic nature lacking the photosynthetic ability. Nevertheless, the genome sequence of a spheroid body from a single lineage may not be sufficient to depict the evolution of these cyanobacterium-derived intracellular structures as a whole. Here, we report on the complete genome for the spheroid body of Rhopalodia gibberula, a lineage distinct from E. turgida, of which genome has been fully determined. Overall, features in genome structure and metabolic capacity, including a lack of photosynthetic ability, were highly conserved between the two spheroid bodies. However, our comparative genomic analyses revealed that the genome of the R. gibberula spheroid body exhibits a lower non-synonymous substitution rate and a slower progression of pseudogenisation than those of E. turgida, suggesting that a certain degree of diversity exists amongst the genomes of obligate endosymbionts in unicellular eukaryotes.

Fauna and flora of drilling and core data from the İznik Lake: The Marmara and the Black Sea connection

The study deals with on the Quaternary connection of the Iznik Lake between the Gemlik Gulf and the Black Sea located in the Marmara Region. The core and drilling data were evaluated. They were collected at two locations and depths from drilling cores and at the three deepest locations of the lake. A total of 510 samples were examined from the lake-bottom cores. Ostracod, mollusc, nannoplankton, ascidian spicule, and diatom assemblages observed at different levels of the drillings were studied. No foraminiferal data were recorded. Molluscan association such as Dreissena bugensis, D. caspia, Monodacna pontica, Clathrocaspia makarovi, Euxinipyrgula milachevitchi, Euxinipyrgula lincta indicate Neoeuxinian age. Amnicythere olivia, A. stepanaitysae, A. striatocostata, Tyrrhenocythere amnicola and Loxoconcha immodulata of the ostracod assemblage, exhibiting Ponto-Caspian origin, were found. In addition, fossil ascidian spicules comprising various species of Bonetia, Micrascidites, Monniotia, and Rigaudia genera were encountered, probably representing Late Pleistocene to Holocene ages. Campylodiscus echeneis, Cocconeis placentula var. lineata Epithemia turgida var. granulata, Epithemia adnata, Nitzschia commutate and N. vermicularis, from the diatom assemblage are genera and species also found in the İznik Lake and in the Black Sea. Mollusc and ostracod fauna, the Ponto-Caspian origin indicates that the İznik Lake was connected with the Black Sea and the Marmara Sea in the recent period. Thus, the Ponto-Caspian assemblages indicate the early Neoeuxinian (Surozhian) brackish water inundated the study area.Geochronological ages determined by the 14C method from the deposits occurring at 53–54 m above present sea level in the İznik Lake indicate the periods of connection via Iznik Lake during 33,630 to 32,920 cal BP (SK-1) and BP 27,335 to 27,070 cal BP (SK-2). When the position of the deposits is compared with the previously available Late Pleistocene 14C data obtained from the molluscs identified in the nearby Gemlik Gulf at −76 m present water depth and also with the early Khazarian (Middle Pleistocene) age data on the molusc fauna at 130–150 m heights of uppermost terraces above present sea level to NW of the lake, we suggest the influence of a neo-tectonic regime for the occurrence of comparable age deposits at different levels in the region. It may be proposed that a vertical displacement in the order of a 100 m occurred since the late Pleistocene in the İznik Lake area and the lake acquired its present features as a result of the tectonic movements.

Global analysis of gene expression dynamics within the marine microbial community during the VAHINE mesocosm experiment in the southwest Pacific

Abstract. Microbial gene expression was followed for 23 days within a mesocosm (M1) isolating 50 m3 of seawater and in the surrounding waters in the Nouméa lagoon, New Caledonia, in the southwest Pacific as part of the VAriability of vertical and tropHIc transfer of diazotroph derived N in the south wEst Pacific (VAHINE) experiment. The aim of VAHINE was to examine the fate of diazotroph-derived nitrogen (DDN) in a low-nutrient, low-chlorophyll ecosystem. On day 4 of the experiment, the mesocosm was fertilized with phosphate. In the lagoon, gene expression was dominated by the cyanobacterium Synechococcus, closely followed by Alphaproteobacteria. In contrast, drastic changes in the microbial community composition and transcriptional activity were triggered within the mesocosm within the first 4 days, with transcription bursts from different heterotrophic bacteria in rapid succession. The microbial composition and activity of the surrounding lagoon ecosystem appeared more stable, although following similar temporal trends as in M1. We detected significant gene expression from Chromerida in M1, as well as the Nouméa lagoon, suggesting these photoautotrophic alveolates were present in substantial numbers in the open water. Other groups contributing substantially to the metatranscriptome were affiliated with marine Euryarchaeota Candidatus Thalassoarchaea (inside and outside) and Myoviridae bacteriophages likely infecting Synechococcus, specifically inside M1. High transcript abundances for ammonium transporters and glutamine synthetase in many different taxa (e.g., Pelagibacteraceae, Synechococcus, Prochlorococcus, and Rhodobacteraceae) was consistent with the known preference of most bacteria for this nitrogen source. In contrast, Alteromonadaceae highly expressed urease genes; Rhodobacteraceae and Prochlorococcus showed some urease expression, too. Nitrate reductase transcripts were detected on day 10 very prominently in Synechococcus and in Halomonadaceae. Alkaline phosphatase was expressed prominently only between days 12 and 23 in different organisms, suggesting that the microbial community was not limited by phosphate, even before the fertilization on day 4, whereas the post-fertilization community was. We observed high expression of the Synechococcus sqdB gene, only transiently lowered following phosphate fertilization. SqdB encodes UDP-sulfoquinovose synthase, possibly enabling marine picocyanobacteria to minimize their phosphorus requirements by substitution of phospholipids with sulphur-containing glycerolipids. This result suggests a link between sqdB expression and phosphate availability in situ. Gene expression of diazotrophic cyanobacteria was mainly attributed to Trichodesmium and Richelia intracellularis (diatom–diazotroph association) in the Nouméa lagoon and initially in M1. UCYN-A (Candidatus Atelocyanobacterium) transcripts were the third most abundant and declined both inside and outside after day 4, consistent with 16S- and nifH-based analyses. Transcripts related to the Epithemia turgida endosymbiont and Cyanothece ATCC 51142 increased during the second half of the experiment.

Spatial and temporal variability of river periphyton below a hypereutrophic lake and a series of dams

Klamath River is described as an “upside-down” river due to its origins from the hypereutrophic Upper Klamath Lake (UKL) and hydrology that is heavily regulated by upstream dams. Understanding the lake and reservoir effects on benthic communities in the river can inform important aspects of its water quality dynamics. Periphyton samples were collected in May–November from 2004, 2006–2013 at nine long-term monitoring sites along 306riverkm below UKL and a series of dams (n=299). Cluster analysis of periphyton assemblages identified three statistically different periphyton groups (denoted Groups 1–3). Group 1 occurred primarily in the upstream reach for June–October and had a higher percentage of sestonic species, including the cyanobacteria Aphanizomenon flos-aquae and Microcystis aeruginosa, consistent with the presence of upstream reservoirs. Group 2 had the highest relative biomass of diatoms and lowest relative biomass of cyanobacteria. Sites in the lower reach of the Klamath River fell into Group 2 in May–June and transitioning into Group 3 for July–October. Group 3 was dominated by nitrogen (N)-fixing species, including three diatoms (Epithemia sorex, Epithemia turgida, and Rhopalodia gibba) with cyanobacterial endosymbionts and the cyanobacterium Calothrix sp. Periphyton assemblages were strongly associated with temporal variations in flow conditions (e.g., decreasing flow from spring to fall) and spatial gradients in nutrient concentrations (e.g., decreasing from upstream to downstream). The inverse longitudinal relationship between periphyton biomass and nutrients may be explained by the ability of benthic N-fixers (Group 3) to overcome N limitation. Overall results showed a strong inverse relationship between the relative biomass of N-fixers and nitrogen concentrations and flow. This long-term dataset provides valuable insight into Klamath River's seasonal and longitudinal patterns of benthic algal communities and associated environmental variables. Our findings can inform river management decisions such as reducing upstream nutrient loads, setting flow regimes, and potential dam removals.

Diatoms in Sub-Surface Sediment Cores from Mangrove Forest Floors of Deltaic Islands in Sundarbans, India

Species constituting diatom assemblages in sediments provide important information regarding the past and present environmental conditions related to soil and water physico-chemistry and also biodiversity dynamics data. This information can reveal the developmental history of the region. Diatoms are sensitive to stochastic changes in the environment, making them extremely reliable bio-indicators. The purpose of the present study was to decipher such biodiversity related information provided by the diatom assemblages from the Indian Sundarbans. Diatoms were identified in the top 50 cm layer of two sediment cores: a newly silted up deltaic landmass with mangroves in early succession stage, and an island within the Protected Area Network with mangroves in late succession stage. Fifteen diatom species, with no past records in the sediments of Indian Sundarbans were identified and described. Four species among them are sporadically mentioned in previous phytoplankton records fi-om the Sundarbans, but these are not confirmed taxonomically. This paper provides identification and nomenclatural notes on all 15 species. High abundance and species richness of the centric forms Coscinodiscus spp., Cyclotella spp., and Thalassiosira spp. at both the sites is attributed to their proximity to estuarine rivers and their regular inundation, leading to settling of planktonic forms within sediment cores. Many pennate forms, namely Amphicampa eruca, Amphora holsatica, Diploneis spp. (except Z). smithii), Epithemia turgida, Eunotiapectinalis, Giffenia cocconeiformis , and Rhaphoneis rhombus which are being reported for the first time fi-om this region have never been part of described planktonic communities in estuarine waters, validating their' soil diatom' status. Typical fi-eshwater diatoms, namely Aulacoseira granulata and Epithemia turgida, in the sediments indicate lower salinity in these areas, not much earlier than present times.

Contribution à la paléolimnologie du Plio-Pléistocène du bassin de Baza (SE Espagne) à partir de l’étude des diatomées

Several outcrops with diatoms have been identified in the Neogene-Quaternary Baza basin. The most relevant two are located in the NE margin, in different lithostratigraphic units. Their diatom flora is dominated by Epithemia adnata and Epithemia turgida, a littoral epiphytic aquatic plants. These diatom assemblages are typical of fresh to slightly brackish waters in shallow and alkaline lakes. Those two diatomitic deposits are interstratified between alluvial sediments and represent permanent shallow lakes developed during two wet periods of time. Barranco de las Lumbres is the oldest of these lake events and is dated by fauna and paleomagnetism as late Miocene (Turolian). The upper beds of the younger lake episode (Rincon de la Losa) is dated by paleomagnetism and mammals at 1.9 Ma. In addition to these marginal diatomitic deposits, other outcrops with diatoms have been identified in more central areas of the Basin in Galera village, the lower part of Barranco del Agua section is composed of gypsum, carbonates and dark-brown clays and marls. Here epiphytic shallow-water diatoms Epithemia adnata, Epithemia turgida and some planktonic littoral forms (Fragilaria sp.) suggest a shallow fresh to oligosaline water environment. Additional diatomaceous deposits were located in a more evaporitic zone of the basin near the town of Castillejar. This outcrop presents species (Navicula digitoradiata and Surirella ovalis), which indicate distinctive more saline waters and environment. The distribution of the diatom flora in the Baza basin is consistent with stratigraphic data, which indicates an increase of evaporitic facies towards the center of the basin and the occurrence of different kinds of waters within the lake system. The isotopic composition (δ34S, δ18O) of the gypsum samples of Baza basin (Gibert et al.,2007a) is consistent with a Triassic origin of the sulphate as a result of chemical recycling. These data also suggest that a similar recycling mechanism operated in the saline lake system, where the gypsum sediments from the margins were coevally recycled towards the inner part.

Late Miocene lacustrine sedimentation in the Mytilinii Basin, Samos Island, Greece

The Mytilinii Basin, eastern Samos Island, Greece, is one of many basins that developed in southeastern Europe during the Upper Neogene. The oldest lacustrine portion is of Late Miocene age, and besides tuffs, includes bituminous limestones, marlstones, dolostones and porcelanites of the Pythagorion Formation, and the limestones and diatomites of the overlying Hora Beds. Younger sedimentary rocks of Turolian through Pliocene age partially covered the Pythagorion Formation and Hora Beds (PFHB). Diatom floras range from well preserved to highly corroded and from sparse to abundant. The main taxa include Cyclotella aegaea, C. aegaea var. pythagoria, an unidentified Cyclotella and Nitzschia frustulum, and less common Epithemia turgida, E. reichelti, Synedra ulna, Tryblionella granulata, Encyonema silesiaca, Diploneis ovalis and Cocconeis placentula. Chrysophyte cysts, Hydrobia molluscs and trace fossils occur sporadically. The environmental evolution of the PFHB can be divided into three major stages. Fluctuating shallow to deeper waters in a saline lake characterized Stage A. Saline lake and playa environments with evidence for frequent earthquake events in the form of convolute bedding, drape folds and brecciated sediments characterized Stage B. During Stage C, the lake may have partially or completely split into two separate lakes. In the southeast, a saline playa passed laterally into a deeper-water lake. Locally, fresher-water ponds occurred. Subsequently, a deeper, possibly oligotrophic lake developed. In contrast, a saline lake with abundant diatoms formed in the northwest of the basin, in which diatom blooms led to whiting events and deposition of carbonate laminae. Cyclotella dominated the early floras in this water body, with later assemblages being co-dominated by Cyclotella and Nitzschia frustulum, possibly reflecting seasonal changes. Sedimentation was terminated by uplift and (or) increasing aridity associated with the Messinian Salinity Crisis.

Spheroid bodies in rhopalodiacean diatoms were derived from a single endosymbiotic cyanobacterium

Members of the diatom family rhopalodiaceae possess cyanobacteria-derived intracellular structures called spheroid bodies (SBs) that very likely carry out nitrogen fixation. Due to the shortage of molecular data from SBs and rhopalodiacean diatoms, it remains unclear how SBs were established and spread in rhopalodiacean diatoms. We here amplified the small subunit ribosomal DNA sequences from both host and SB in three rhopalodiacean diatom species, Epithemia turgida, E. sorex, and Rhopalodia gibba. Phylogenetic analyses considering these new sequences clearly indicate that the SBs were acquired by a common ancestor of rhopalodiacean diatoms and have been retained during host speciation.

Algal mats and insect emergence in rivers under Mediterranean climates: towards photogrammetric surveillance

Summary1. In a nitrogen (N)‐limited river subject to Mediterranean summer drought hydrology, the colour of macroalgal proliferations changed with successional and seasonal changes in epiphyte assemblages. New growth of the dominant macroalga,Cladophora glomerata, was green, as were proliferations ofOedogonium,MougeotiaandSpirogyra, which did not become heavily colonized with diatoms. GreenCladophoraturned yellow asCladophorafilaments became colonized by diatoms that were not N fixers, and turned rust‐coloured as later‐successional epiphyte assemblages became dominated by denseEpithemia turgidaandE. sorex, which both contain N‐fixing cyanobacterial endosymbionts.2. The rate and composition of insect emergence from floating algal mats differed among proliferations of different colour. The rates of emergence (individuals day−1 500 cm−2) of nematoceran flies were three to 25 times greater from yellow or rusty‐colouredCladophoramats than from greenCladophora,OedogoniumorMougeotiamats that had lower epiphyte densities. Biomass emergence fromCladophoramats that were rusty in colour was eight to 10 times greater than from yellowCladophoramats, because larger nematocerans dominated in rusty mats (Chironominae versus Ceratopogonidae in yellow mats).3. Proliferations ofEpithemia‐infestedCladophoraoccur at and above drainage areas of about 100 km2(channel widths of 25–30 m) in this river network, coinciding with the drainage area threshold where a step increase in concentration of total dissolved N is observed during summer.4. In rivers under Mediterranean climate regimes, algal succession during the prolonged low flow season is less subject to stochastic interruption by spates than in rivers under more continental climates. Under these summer drought conditions, photogrammetric detection of colour changes in algal proliferations may help us track reach or basin‐scale change in their ecological functions.

EFFECTS OF WATER VELOCITY ON THE ARCHITECTURE AND EPIPHYTES OF CLADOPHORA GLOMERATA (CHLOROPHYTA)1

ABSTRACT 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.

Heterogeneous Spatial Distribution of Periphytic Diatoms on Vertical Artificial Substrata

Traditional techniques for algal enumeration on substrata may ignore variation along microenvironmental gradients. To examine microdistributional patterns of diatoms on such surfaces, topographically simple, nutritionally inert artificial substrata were positioned in a duckweed-covered canal and in the littoral zone of a prairie lake. After a period of colonization, substrata were sampled using a surficial peel technique along a short section suspected to traverse sharp microenvironmental gradients of irradiance and nutrient concentration. At both sites, significant horizontal and vertical microheterogeneity in diatom species abundance was observed on a single substratum. A zonation of diatom species occurred with depth in the duckweed mat; Achnanthes hungarica, an apparently host-specific taxon, was distributed mostly in the leaf zone of the mat. Join-count analysis of a peel sample from the lake demonstrated that the major diatom taxa were significantly more abundant on some parts of the substratum than others. Refined nearest-neighbor analysis of mapped populations of Cocconeis diminute and Epithemia turgida in these peels showed that they were significantly aggregated in the distance range of a few cell lengths, suggesting that their progeny were only weakly motile after cell division. A relatively motile diatom, Achnanthes hungarica, was distributed randomly at low cell density; a more dense A. hungarica population was distributed regularly. These results illustrate the importance of examining microdistributional patterns of diatoms on substrata as the genesis of ultimate community development and macrodistribution.

EFFECTS OF NITROGEN AND PHOSPHORUS ON THE ENDOSYMBIONT LOAD OF RHOPALODIA GIBBA AND EPITHEMIA TURGIDA (BACILLARIOPHYCEAE)1

ABSTRACTDiatoms of the family Epithemiaceae possess a unicellular nitrogen‐fixing cyanobacterial endosymbiont. We investigated the potential of extracellular nitrogen and phosphorus concentrations to affect the endosymbiont load of Rhopalodia gibba O. Müll, and Epithemia turgida Ehr. in field and culture populations. In a growth chamber experiment, monoclonal cultures of R. gibba were exposed to three levels of nitrate‐nitrogen. Nutrient‐diffusing substrates were used in a lake environment to create nine microhabitats of varying nitrogen and phosphorus ratios for natural populations of R. gibba and E. turgida. The number of endosymbionts per diatom increased as ambient nitrogen became limiting; mean endosymbiont volume increased as nitrogen increased. The mean endosymbiont surface area: volume ratio decreased with increasing nitrogen. Total endosymbiont volume per diatom (the product of the number of endosymbionts per diatom and their individual biovolumes) did not have a simple response to increasing nitrogen. Phosphorus limitation uncoupled the relationship between endosymbiont load and nitrogen. We suspect that flexibility of the endosymbiont load can reduce the metabolic cost to the diatom if the endosymbionts are dependent on the diatom for a resource.

The impact of atrazine on lake periphyton communities, including carbon uptake dynamics using track autoradiography

Chlorophyll a, freshweight biomass, ash-free dry weight, cell numbers, species richness, community carbon uptake and species-specific carbon uptake were used to monitor the impact of atrazine (2 chloro-4-ethylamino-6-isopropylamino- s-triazine) on an in situ, enclosed periphyton community. Atrazine concentrations ranging from 0·08 to 1·56 mg litre −1 were used during the 2 years of study. In both 1982 and 1983, there was a shift from a chlorophyte- to a diatom-dominated community. In 1982 the cyanobacterium Cylindrospermum stagnale and the chlorophyte Tetraspora cylindrica developed isolated colonies in the 1·56 mg litre −1 treatment, indicating resistance to atrazine at this concentration. After atrazine exposure, community productivity was reduced by 21% to 82% in the low to high exposures, respectively. After day 21 productivity returned to control levels. It was shown, using track autoradiography, that the productivities of the larger algae Mougeotia sp., Oedogonium sp., Tolypothrix limbata and Epithemia turgida were the most affected, with reductions of 74·3% to 93·1% that of the controls. All the biotic measures indicated reduced growth after herbicide exposure.

Seasonal Physical, Chemical and Algal Changes in Five Rivers Flowing Through the Oil Sands Region of Alberta, Canada

AbstractSeasonal studies concentrating upon physical and chemical parameters and the epilithic algal community were conducted at specific sites in five tributary rivers flowing through the oil sands region of northeastern Alberta, Canada into the Athabasca River. Numerically cyanophycean algae (Lyngbya aerugineo‐caerulea, Phormidium sp., Calothrix braunii, Nostoc spp. and Anabaena affinis) dominated followed by diatoms (Achnanthes lanceolata, Cocconeis pediculus, Cocconeis placentula, Epithemia sorex, Epithemia turgida, Gomphonema acuminatum, Gomphonema longiceps v. subclavata, Gomphonema olivaceum, Nitzschia fonticola, Nitzschia palea, Synedra rumpens, and Synedra ulna). One exception was the Hangingstone River where chlorophycean algae (Stigeoclonium pachydermum and Cladophora glomerata) were next in importance to the cyanophytes. Seasonal fluctuations in algal species and numbers were influenced by a myriad of interacting parameters. Physically disruptive forces (current velocity and discharge) appeared more important than dissolved nutrients. They were also responsible for affecting the chemical composition of the water itself.

The removal of a heated water discharge from a lake and the effect upon an epiphytic algal community

The effects of the removal of a heated water discharge from Lake Wabamun, Alberta (longitudes 114°26′ and 114°44′W; latitudes 53°30′ and 53°35′N) upon epiphytic algae has been documented. Due to the timing of the cessation of flow the first year without elevated temperatures was one of transition. Standing crops returned to normal lake levels the following year. Species composition changes occurred, and species such as Epithemia turgida, Amphipleura pellucida, Nitzschia fonticola, Rhopalodia gibba, Rivularia haematites, and Scytonema alatum, all of which were detrimentally affected by the elevated temperatures, returned to the previously affected area, while species such as Oedogonium sp., Spirogyra sp. and Cladophora glomerata, dominant at times in the heated area, diminished in importance. The ability of Cocconeis placentula to grow at low light intensities (15–110 µEinsteins m−2 s−1) was again demonstrated.

Epipelic and epiphytic algal communities in Great Slave Lake

Seasonal changes in the densities of epiphytic and epipelic algae were determined during 1975 and 1976 at two sites on the north shore of Great Slave Lake. The epiphyton waxed rapidly in May and reached maximum densities of 5–6 × 108 μm3/cm2 in June. Although densities remained high during the summer, they fell rapidly in October, followed by a secondary peak in November. The main species were Tabellaria flocculosa, Achnanthes minutissima, Achnanthes linearis, Gomphonema intricatum, and Lyngbya diguetii. The epipelon, consisting largely of Nitzschia palea, Nitzschia dissipata, Fragilaria construens, and Oscillatoria spp., also showed spring and fall peaks in densities, with maximum populations of 4.2 × 108 μm3/cm2 being recorded in June and July. The growing season for both communities was limited by the formation of ice in the fall, whereas the maximum standing crop of the flora was at least partially restricted by low nutrient levels (total phosphorus, 0.008 mg/L; total alkalinity, 30 mg/L).Seasonal changes in the density of epipelon were monitored during 1977 and 1978 at a third site on the north shore of the lake, where total phosphorus and total alkalinity ranged up to 0.010 and 94 mg/L, respectively. Prevalent taxa included Cymatopleura elliptica, Epithemia turgida, Rhopalodia gibba, Cymbella spp., and Nostoc spp. The growth cycles of the flora were again characterized by spring and fall peaks in numbers. Algal densities were, however, high (up to 2.3 × 109 μm3/cm2), possibly a reflection of nutrient availability.Samples of epiphyton and epipelon were taken at an additional seven sites in the east arm of the lake during June and July 1975. The main epiphytic species were Cocconeis placentula, Achnanthes minutissima, and Tabellaria flocculosa, while prevalent epipelic taxa included Navicula graciloides, Fragilaria vaucheriae, Tabellaria flocculosa, and Achnanthes minutissima. Densities were less than those recorded from the three sites on the north shore, again possibly a reflection of nutrient availability.

Importance of algae in the diet of the oligochaetes Lumbriculus variegatus (MÜller) and Rhyacodrilus sodalis (Eisen).

The importance of algae in the diet of the oligochaetes Lumbriculus variegatus and Rhyacodrilus sodalis was determined from cellections made in a eutrophic bay from April 1977 to April 1978. During the summer, algae represented 70-85% of the gut contents of both species. The most frequently ingested algae were Cymatopleura elliptica, Cymbella spp., Epithemia turgida, Pinnularia spp., and Synedra ulna. Almost all species were consumed in proportion to their abundance in the environment. However, Nostoc pruniforme and Nostoc verrucosum were not eaten due to size selection. The high level of algal consumption exhibited by the oligochaetes was primarily related to the large standing crop of algae on the sediments. During the winter, when algal densities were low in the environment, detritus and associated bacteria were the major food source.