Morphological,biochemical and phylogenetic assessments of water‐bloom‐forming tropical morphospecies of Microcystis (Chroococcales,Cyanobacteria)

Previous polyphasic analyses of five morphospecies of the water‐bloom‐forming cyanobacterial genus Microcystis, Microcystis aeruginosa (Kützing) Lemmermann (=Microcystis aeruginosa (Kützing) Kützing), Microcystis ichthyoblabe Kützing, Microcystis novacekii (Komárek) Compère, Microcystis viridis (A. Braun) Lemmermann, and Microcystis wesenbergii (Komárek) Komárek in Kondratieva, have shown them to be conspecific and they have been proposed to be included under the binomial Microcystis aeruginosa (Kützing) Lemmermann. However, several morphospecies from tropical regions, such as Microcystis bengalensis Banerji, Microcystis panniformis Komárek, Komárková‐Legnerová, Sant'anna, Azevedo & Senna, Microcystis protocystis Crow, Microcystis pseudofilamentosa Crow, Microcystis ramosa Bharadwaya, and Microcystis robusta (Clark) Nygaard, have never been analyzed biochemically or phylogenetically; consequently, their taxonomic status is uncertain. To resolve this issue, we collected 57 strains of Microcystis from Vietnam for taxonomic analysis using a polyphasic approach. Strains were assigned to the six tropical morphospecies listed above or to four morphospecies with cosmopolitan distributions (M. aeruginosa, M. ichthyoblabe, M. novacekii, and M. wesenbergii). Several strains produced colony variants in different culture media; some of these variants had forms that overlapped with those of other morphospecies. Cell diameters varied widely between strains (2.6–9.3 µm) and were unrelated to morphospecies discrimination criteria. Strains of the 10 morphospecies examined had similar fatty acid compositions and closely similar 16S rRNA gene sequences (>99.2% similar). Phylogenetic analyses using 16S rRNA gene and 16S–23S internal transcribed spacer sequences did not identify any clear separations corresponding to morphospecies concepts or microcystin‐producing abilities. Thus, the six tropical morphospecies (M. bengalensis, M. panniformis, M. protocystis, M. pseudofilamentosa, M. ramosa, and M. robusta) are not natural taxonomic units within the genus Microcystis and should be included under M. aeruginosa.     

ITS1 sequences of type specimens of Gigartina and Sarcothalia and their significance for the classification of South African Gigartinaceae (Gigartinales,Rhodophyta)

Uncertainties about the identity of type specimens of red algae have frequently led to taxonomic and nomenclatural confusion. A procedure for extracting PCR-amplifiable DNA from formalin-fixed material and herbarium specimens was used to investigate the taxonomic status of several South African Gigartinaceae. We compared nucleotide sequences in the internal transcribed spacer 1 (ITS1) region in type specimens and other historically important collections presently referred to Gigartina bracteata, G. radula and G. stiriata. The following opinions are supported: (1) Fucus bracteatus S.G. Gmelin, Chondrodictyon capense Kützing and Iridaea clathrata Decaisne represent a single species of South African Gigartina (G. bracteata (S.G. Gmelin) Setchell & Gardner) in which the disintegration of tetrasporangial sori results in a reticulate thallus. (2) Mastocarpus polycarpus Kützing, M. incrassatus Kützing and Iridaea lapathifolia Kützing represent a single species of South African Gigartina (G. polycarpa (Kützing) Setchell & Gardner) that has often, but erroneously, been called G. radula (Esper) J. Agardh. (3) Mastocarpus verrucosus Kützing is a later heterotypic synonym of Iridaea papillosa Bory (Sarcothalia papillosa (Bory) Leister) and was based on material that probably came from southern South America rather than from South Africa, the provenance given by Kützing. (4) Fucus stiriatus Turner and Sphaerococcus burmannii C. Agardh represent a single species of South African Sarcothalia (S. stiriata (Turner) Leister).     

Benthic algal response to hyporheic-surface water exchange in an alluvial river

We studied the response of benthic algae to points of hyporheic-surface water exchange in the main channel of the Middle Fork Flathead River within the Nyack Flood Plain, Montana. We examined hyporheic exchange at 120 sites using piezometers and measuring vertical hydraulic gradient (VHG), hydraulic conductivity, and vertical discharge. We removed benthic algae from a single cobble at each site, and we used VHG to group sampling sites for statistical analysis. Algal cell density and chlorophyll a concentration were significantly higher at sites with hyporheic discharge (+VHG, upwelling) compared to both sites with hyporheic recharge (−VHG, downwelling) and sites with no hyporheic-surface water exchange (=VHG, neutral) (ANOVA, P < 0.05). The assemblages of algae at upwelling sites were also significantly different from downwelling and neutral exchange sites (ANOSIM, P < 0.05). Filamentous green algae Stigeoclonium sp. and Zygnema sp. and a chrysophyte, Hydrurus foetidus (Villars) Trevisan were abundant at upwelling sites, whereas an assemblage of diatoms Achnanthidium minutissimum (Kützing) Czarnecki, Cymbella excisa Kützing, Diatoma moniliformis Kützing, and Gomphonema olivaceoides Hustedt, were the most abundant taxa at downwelling and neutral exchange sites, occurring attached to, or in close association with the stalks of Didymosphenia geminata (Lyngbye) Schmidt. These data show that benthic algal communities are structured differently depending on the direction of hyporheic flux in the main channel of a large alluvial river, suggesting that hyporheic-surface exchange may influence the spatial distribution of main-channel benthic algae in rivers with hyporheic-surface water connectivity. Handling editor: J. Padisak     

Spatial and temporal variation of phytoplankton in two subtropical Brazilian reservoirs

The purpose of this study was to verify the longitudinal distribution of phytoplankton biomass in two subtropical Brazilian reservoirs in the State of Paraná and investigate intervening factors on changes in phytoplankton biomass according to functional groups. In the Capivari and Segredo reservoirs, samples were obtained every 3 months during 2002, along a longitudinal axis (fluvial, transition, and lacustrine zones) at different depths. One hundred and eighteen taxa were identified, with Chlorophyceae as the most specious group. During the study period, both reservoirs had mostly low biomass values (less than 1 mm³ l⁻¹). The short retention time of these reservoirs constituted the principal limiting factor to phytoplankton development. Biomass values above 1 mm³ l⁻¹ were observed in the Capivari fluvial zone in March and in the Segredo lacustrine zone in December, with dominance by Microcystis aeruginosa Kütz (L_M) and Anabaena circinalis Rab. (H₁), respectively. Vertical and horizontal gradients of analyzed abiotic variables and phytoplankton biomass were observed. Considering the phytoplankton biomass values, both reservoirs were oligotrophic for the duration of the study. The Canonical Correspondence Analysis (CCA) evidenced temporal and spatial gradients of phytoplankton biomass; nevertheless, it did not follow the classic model proposed for deep reservoirs, since higher biomass was registered in the lacustrine zone during some months and in fluvial zones during other months. Distinct functional groups of phytoplankton characterized both studied reservoirs. Capivari Reservoir was best characterized by L_M and Y groups, indicative of its greater water column stability and higher phosphorus concentration, whereas Segredo Reservoir was principally characterized by the MP functional group, indicative of its greater mixing zone extension and higher nitrate concentration. The obtained results also evidenced the influence of morphometric conditions and watershed purposes as important structuring factors of phytoplankton biomass in these reservoirs. Handling editor: L. Naselli-Flores     

桥弯藻科和异极藻科（硅藻门）植物中国7种新记录

对采自黑龙江省东南部兴凯湖湿地的100余号硅藻标本进行分类研究,共发现桥弯藻科、异极藻科（硅藻门）中国新记录植物5种2变种,分别为亚粗糙桥弯藻（Cymbella peraspera Krammer）、尖头弯肋藻［Cymbopleura cuspidata (Kützing) Krammer］、不显内丝藻高山变种（Encyonema obscurum var.alpina Krammer）、西里西亚内丝藻翼形变种（Encyonema silesiacum var.lata Krammer）、耳状异极藻（Gomphonema auritum Braun & Kützing）、棍棒异极藻（Gomphonema clava Reichardt）、极细异极藻［Gomphonema exilissimum (Grunow) Lange-Bertalot & Reichardt］。对其分类学特征进行了详细的描述,与同属中相似的种类进行了比较与讨论,为今后该区域的藻类研究提供了基础的资料。     

ALLELOPATHIC GROWTH INHIBITION OF SELECTED PHYTOPLANKTON SPECIES BY SUBMERGED MACROPHYTES1

Allelopathic effects of submerged macrophytes on the growth and photosynthesis of different unialgal cultures of planktonic cyanobacteria, a diatom, and a green alga were tested in coexistence experiments using dialysis cultures. The method applied allowed measurements under conditions similar to that in lakes but without nutrient and light limitation. Growth and photosynthesis were measured with a pulse amplitude modulated fluorometer as an increase of chl a fluorescence and activity of PSII, respectively. Eurasian water milfoil Myriophyllum spicatum L. and rigid hornwort Ceratophyllum demersum L. proved to inhibit the PSII activity and then growth of the investigated phytoplankton species, whereas sago pondweed Potamogeton pectinatus L. showed no effect. Growth inhibition was dependent on biomass of M. spicatum. Considerable differences between phytoplankton groups and among species of cyanobacteria were found regarding their response to M. spicatum. Members of the Oscillatoriales and Microcystis aeruginosa Kütz. emend. Elenkin were more sensitive than the cyanobacterium Aphanizomenon flos‐aquae Ralfs ex Born. et Flah., the diatom Stephanodiscus minutulus (Kütz) Cleve et Möller, and the green alga Scenedesmus armatus Chodat. A possible contribution of this result to changes in the phytoplankton succession of lakes after loss of macrophytes is discussed.     

New finds of charophytes in Iceland with an update on the distribution of the charophyte flora

Charophyte species new to the flora of Iceland are reported and an update on the distribution of the previously known species is given. Four species are new to Iceland; Chara aspera Willdenow, Chara contraria Braun ex Kützing, Tolypella canadensis Sawa and Tolypella glomerata (Desvaux) Leonhardi, while four species were previously known: Chara globularis Thuiller, Chara virgata Kützing, Nitella flexilis (L.) Agardh and Nitella opaca (Agardh ex Bruzelius) Agardh. The finding of the species new to Iceland add to the hitherto known worldwide distribution of those species, including a significant extension to the north.     

Cryptic speciation in the cosmopolitan <Emphasis Type="Italic">Epiphanes senta</Emphasis> complex (Monogononta,Rotifera) with the description of new species

The phytoplankton species composition and seasonal succession were examined in Lake Kastoria during the period November 1998–October 1999. A total of 67 species and 19 functional groups were identified. Only 4 out of the 67 species, all Cyanobacteria, were dominant (Limnothrix redekei, Microcystis aeruginosa, Cylindrospermopsis raciborskii and Aphanizomenon gracile). Diatoms were rare, not only in terms of species number, but also in terms of biomass (contributing <5% to the total phytoplankton biomass) in relation to the rather low silicon concentrations throughout the year. The functional groups S1, S_N, M and H1 were found dominant in the lake. The species A. gracile (functional group H1) behaved like the species Cylindrospermopsis raciborskii (functional group S_N) which is tolerant to mixing and poor light conditions. The phytoplankton seasonal succession showed similar patterns in all six sampling stations, both at the surface and the bottom water layer, with minor differences during Microcystis aeruginosa dominance. Two steady-state phases were identified within a year lasting for 4 months under relatively stable physical conditions. In these steady-states, the Limnothrix redekei persistent dominance under low light availability and low inorganic nitrogen has been explained by its specific ability such as buoyancy regulation to exploit resources in the water column. Moreover, high population densities over the winter and before the development of daphnids may contribute to the steady-state dominance of Limnothrix. Different niches separated vertically in the water column is one of the explanations for the Limnothrix–Microcystis steady-state when a replacement between the two species was observed in different water layers and areas of the lake. Long lasting steady-states of Cyanobacteria observed in Lake Kastoria and in other Mediterranean and tropical freshwaters may indicate influence of warm climate properties on phytoplankton dynamics. Electronic Supplementary Material Supplementary material is available to authorized users in the online version of this article at http://dx.doi.org/10.1007/s10750-006-0360-4 Handling editor: K. Martens     

Bioaccumulation of Microcystins in Lettuce

The contamination of lettuce (Lactuca sativa L.) by water‐borne crude extracts of the cyanobacterium microcystin‐producing Microcystis aeruginosa (Kützing) Kützing was investigated. The aim of the study was to determine whether bioaccumulation of microcystins occurs in lettuce foliar tissue when sprayed with solutions containing microcystins at concentrations observed in aquatic systems (0.62 to 12.5 μg · L^?1). Microcystins were found in lettuce foliar tissues (8.31 to 177.8 μg per Kg of fresh weight) at all concentrations of crude extracts. Spraying with water containing microcystins and cyanobacteria may contaminate lettuce at levels higher than the daily intake of microcystins recommended by the World Health Organization (WHO), underscoring the need to monitor such food exposure pathways by public authorities.     

CHANGES IN THE MORPHOLOGY AND POLYSACCHARIDE CONTENT OF MICROCYSTIS AERUGINOSA (CYANOBACTERIA) DURING FLAGELLATE GRAZING1

To investigate the changes in the morphology and polysaccharide content of Microcystis aeruginosa (Kütz.) Kütz. during flagellate grazing, cultures of M. aeruginosa were exposed to grazing Ochromonas sp. for a period of 9 d under controlled laboratory conditions. M. aeruginosa responded actively to flagellate grazing and formed colonies, most of which were made up of several or dozens of cells, suggesting that flagellate grazing may be one of the biotic factors responsible for colony formation in M. aeruginosa. When colonies were formed, the cell surface ultrastructure changed, and the polysaccharide layer on the surface of the cell wall became thicker. This change indicated that synthesis and secretion of extracellular polysaccharide (EPS) of M. aeruginosa cells increased under flagellate grazing pressure. The contents of soluble extracellular polysaccharide (sEPS), bound extracellular polysaccharide (bEPS), and total polysaccharide (TPS) in colonial cells of M. aeruginosa increased significantly compared with those in single cells. This finding suggested that the increased amount of EPS on the cell surface may play a role in keeping M. aeruginosa cells together to form colonies.     

Phytoplankton composition,dominance and abundance as indicators of environmental compartmentalization in Jurumirim Reservoir (Paranapanema River), São Paulo,Brazil

Patterns in the spatial and temporal composition, dominance and abundance of the phytoplankton community of the Jurumirim Reservoir (Brazil) were studied during one year at ten different sampling stations. The main phytoplankton associations were characterized by diatoms and blue-green algae, in distinctive patterns of dominance. The main species were Microcystis aeruginosa Küetz, Anabaena circinalis Rabenhorst, A. spiroides Kleb., A. solitaria Kleb., Aulacoseira cf. italica Grunow and A. granulata (Ehr.) Simon. A high growth of Aulacoseira was observed in the upstream zones of the reservoir in spring, at the beginning of the seasonal rainy period. This growth was a response to increased flow rates and input of fresh nutrients by the main feeder rivers. A high concentration of blue-green algae, especially Anabaena circinalis and A. spiroides, was observed in winter (dry season) in the lacustrine part of the reservoir, towards the dam. These algae benefitted from the longer water retention times and greater internal circulation of nutrients in the absence of a thermocline at this time of the year. Among the Cyanophyceae, there was an alternation between M. aeruginosa, more abundant in summer, and Anabaena, dominant in autumn and winter. A conspicuous growth of Anabaena occurred in a diverticle of the reservoir, sheltered from the main advective processes that predominate in the central channel. Higher phytoplankton diversity was associated with the contact zone between riverine and lacustrine systems.     

Contrasting effects of the cyanobacterium Microcystis aeruginosa on the growth and physiology of two green algae,Oocystis marsonii and Scenedesmus obliquus,revealed by flow cytometry

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Occurrence of cell-associated mucilage and soluble extracellular polysaccharides in Rostherne Mere and their possible significance

The cell-associated mucilage and soluble extracellular polysaccharides (EPS) were investigated in a eutrophic freshwater lake (Rostherne Mere, Cheshire, U.K.) over up to 2 year annual cycles. Five particular lake algae (Anabaena spiroides Klebahn, Anabaena flos-aquae Brébisson ex Bornet & Flahault,Anabaena circinalis Rabenhorst, Microcystis aeruginosa Kützing emend. Elenkin and Eudorina elegans Ehrenberg) were found to be the major contributors to cell-associated mucilage, particularly M. aeruginosa. Calculation of the total amount of cell-associated mucilage in the phytoplankton samples showed that it occupied 0.0001–0.007% (the latter during a bloom of Microcystis) of lake water volume within the epilimnion. Seasonal changes in the total volume of associated mucilage reflected the succession of mucilage-producing algal species in Rostherne Mere, which was closely correlated with the physico-chemical (temperature, oxygen, pH, nutrients) and biological (Secchi depth, phytoplankton) parameters within the lake. High levels of cell-associated mucilage present in the lake may have potential for binding metals or other ions in the aquatic environment. Colourimetric determination of the concentration of soluble EPS revealed concentrations of between 2.5 and 60 mg l^–1, with peak levels during the bacillariophyceaen bloom and late clear water phase. The second phase did not appear to relate directly to changes in algal population, and may result from bacterial activity, algal lysis or zooplankton activity. As soluble EPS forms a major component of the total amount of dissolved carbon in lakes, the study of the soluble EPS is important to understand the carbon cycle in freshwaters. No direct correlation occurred between algal-associated mucilage and soluble EPS over a single annual cycle.     

广州市景观湖微囊藻的分类学研究

于2008年3月至2009年4月,对广州市区若干景观湖水体的微囊藻属(Microcystis)进行分类学研究。共观察到11种微囊藻,分别是铜绿微囊藻(M. aeruginosa Kützing)、放射微囊藻(M. botrys Teiling)、坚实微囊藻(M. firma Kützing)、水华微囊藻(M. flosaquae Wittrock)、鱼害微囊藻(M. ichthyoblabe Kützing)、挪氏微囊藻(M. novacekii Komárek)、苍白微囊藻(M. pallida (Farlow) Lemm.)、假丝微囊藻(M. pseudofilamentosa Crow)、史密斯微囊藻(M. smithii Komárek & Anagnostidis)、绿色微囊藻(M. viridis A. Braun)和惠氏微囊藻(M. wesenbergii Komárek),对它们的形态学特征进行描述,并比较这些种类间的形态区别。     

MOLECULAR PHYLOGENY OF ANTARCTIC PRASIOLA (PRASIOLALES,TREBOUXIOPHYCEAE) REVEALS EXTENSIVE CRYPTIC DIVERSITY1

Trebouxiophytes of the genus Prasiola are well known in Antarctica, where they are among the most important primary producers. Although many aspects of their biology have been thoroughly investigated, the scarcity of molecular data has so far prevented an accurate assessment of their taxonomy and phylogenetic position. Using sequences of the chloroplast genes rbcL and psaB, we demonstrate the existence of three cryptic species that were previously confused under Prasiola crispa (Lightfoot) Kützing. Genuine P. crispa occurs in Antarctica; its presence was confirmed by comparison with the rbcL sequence of the type specimen (from the Isle of Skye, Scotland). Prasiola antarctica Kützing is resurrected as an independent species to designate algae with gross morphology identical to P. crispa but robustly placed in a separate lineage. The third species is represented by specimens identified as P. calophylla (Carmichael ex Greville) Kützing in previous studies, but clearly separated from European P. calophylla (type locality: Argyll, Scotland); this alga is described as P. glacialis sp. nov. The molecular data demonstrated the presence of P. crispa in Maritime and Continental Antarctica. P. antarctica was recorded from the Antarctic Peninsula and Shetland Islands, and P. glacialis from the Southern Ocean islands and coast. Such unexpected cryptic diversity highlights the need for a taxonomic reassessment of many published Antarctic records of P. crispa. The results also indicate that marine species of Prasiola form a well‐supported monophyletic group, whereas the phylogenetic diversity of freshwater species is higher than previously suspected (at least three separate lineages within the genus include species living in this type of environments).     

PRODUCTION OF NATURAL BUTYLATED HYDROXYTOLUENE AS AN ANTIOXIDANT BY FRESHWATER PHYTOPLANKTON1

Butylated hydroxytoluene (BHT) is one of the synthetic antioxidant agents commonly used for food additives. In the present study, we determined that four freshwater phytoplankton, including a green alga (Botryococcus braunii Kütz.) and three cyanobacteria [Cylindrospermopsis raciborskii (Wol?osz.) Seenaya et Sabba Raju, Microcystis aeruginosa (Kütz.) and Oscillatoria sp.] were capable of producing this compound. Hexane extracts from all the studied species exhibited various degrees of antioxidative properties when they were tested with the β‐carotene‐linoleate (β‐CL) assay and the 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) free‐radical‐scavenging assay. The highest antioxidant activity was observed in the crude extracts of M. aeruginosa and B. braunii, which displayed a similar activity to synthetic BHT. Gas chromatography/mass spectroscopy (GC‐MS) analysis of the purified fractions revealed that the active compound was identical to synthetic BHT. Culturing under various irradiances gave rise to different magnitudes of BHT production in cyanobacterial cells, showing that more BHT was produced in the cells irradiated with a higher light intensity, and its production was irradiance dependent. Moreover, the quantity of cellular BHT displayed a positive correlation with the antioxidative activity of the tested species. The present study confirms the production of BHT in all four of the studied freshwater phytoplankton and suggests that these species constitute a potential source for producing natural BHT.     

Active release of microcystins controlled by an endogenous rhythm in the cyanobacterium Microcystis aeruginosa

The active release of microcystins in cyanobacterium Microcystis aeruginosa (Kützing) Kützing, strain BCCUSP232 was confirmed. The microcystin release is controlled by an endogenous rhythm, pointing to a biosynthetic pattern of toxins in cyanobacteria. Proofing tests for this active release were carried out by experiments at two independent 24 h cycles, light : dark and continuous light (12:12 h) along the exponential growing phase. Cultivation samples at light, temperature and photoperiod controlled conditions were collected in 2‐h intervals. Microcystin concentrations from the pellet aliquots (intracellular microcystin per cell‐quota –IMC) and supernatant (extracellular microcystin per equivalent cell‐quota – EMC) were quantified with enzyme linked immunosorbent assay. The IMC concentrations showed increases and decreases in both cycles. Decreases of IMC clearly demonstrate that the toxin was actively released to the surrounding medium and not by cell lysis. The total microcystins concentrations (IMC and EMC) between the light : dark and continuous light cycles presented similar variations between the same hours.     

DISTRIBUTION AND SYSTEMATICS OF THE FRESHWATER GENUS TUOMEYA (RHODOPHYTA,BATRACHOSPERMACEAE)1

Twenty-seven populations of Tuomeya, including the types of Tuomeya fluviatilis Harvey and Baileya americana Kützing, were analyzed from the entire known range of the genus: northern Newfoundland to northern Florida and east of the Mississippi River. Key morphological features were examined in detail since it has been recently proposed that Tuomeya should be reduced to a section of the genus Batrachospermum. Our observations confirmed the presence of several characteristics unique to Tuomeya: gametophyte development from a basal mass of undifferentiated cells rather than a chantransia stage, pseudoparenchymatous growth, and carpogonia with obliquely to perpendicularly attached trichogynes. Based on these findings, we conclude that the genus Tuomeya should be retained. Using multivariate morphometrics, two groupings were found that differed significantly in plant length (X = 14.1 and 24.1 mm, respectively). However, since there was no other morphometric, environmental, or geographic basis for separation of the groupings, only one species is recognized, T. americana (Kützing) Papenfuss. Populations tend to occur in large streams (>2.8 m wide) with low ion content (≤ 100 μS · cm^?1).     

USING QUANTITATIVE PCR TO DETERMINE THE DISTRIBUTION OF A SEMICRYPTIC BENTHIC DIATOM,NAVICULA PHYLLEPTA (BACILLARIOPHYCEAE)1

Evidence has accumulated during the last decade showing that many established diatom morpho‐species actually consist of several semicryptic or truly cryptic species. As these species are difficult or even impossible to differentiate by microscopic analysis, there is virtually no information on how they behave in natural environments. In this study, we developed a quantitative real‐time PCR (qPCR) assay using TaqMan probes^® targeted to the internal transcribed spacer 1 (ITS1) to assess the spatial distribution and seasonal dynamics of an important component of the microphytobenthos of intertidal sediments. Navicula phyllepta Kützing is a brackish‐marine morpho‐species with a cosmopolitan distribution. Axenic clones of this species were isolated from natural assemblages of benthic diatoms at different intertidal stations in the Westerschelde estuary (The Netherlands). At least two distinct semicryptic species of N. phyllepta were present, as shown by differences in the quantity of DNA per cell, the ITS1 sequences and the copy number of ITS per cell. DNA and chl a concentrations extracted from sediment surface samples were closely correlated, showing that the DNA used for subsequent analysis mostly belonged to the microalgal community. The results of real‐time qPCR from sites throughout the estuary and over several seasons agreed well with microscopic counts. Additionally, the seasonal pattern of the two forms of N. phyllepta showed an overlapping, but unique distribution along the estuary.