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In July and August 2008, we performed two experiments examining the effect of glucose addition (final concentration 100 kmol l super(-1)) on silica deposition and growth rates of natural diatom population in a eutrophic Rimov Reservoir (Czech Republic). Silica deposition kinetics was measured at four-hour intervals over 24 hours using the incubation with PDMPO, which fluorescence is proportional to silica deposited. Diatoms represented 58 and 37% of total phytoplankton biomass and were dominated exclusively with Fragilaria croto-nensis. There was a linear increase in PDMPO fluorescence over time, slopes of regression lines significantly differed between the experiments. There was no difference in silica deposition between glucose-amended and control variant till 16 super(th) hour of experiment duration but later on, glucose addition significantly increased PDMPO fluorescence indicating diatom growth stimulation. This was confirmed by direct measurement of growth rates (based on cell counts), which almost doubled in glucose-amended variant (k = 0.61 d super(-1)), compared to control (k = 0.35 d super(-1)). Our results indicate that Fragilaria may subsidize its phototrophic metabolism by glucose uptake; however, there is a 16 hour lack required likely for induction of active transport mechanisms.

Phytoplankton seasonal succession has been linked to a variety of serial environmental changes, especially weather- and climate-induced physical forcing. This study compared spring phytoplankton dynamics after winters of different severity (cold, normal, and warm) in Lake Erken, Sweden. The spring diatom bloom was dominated by different functional groups: group A (centric diatoms 5–10 μm) after cold winters, B (centric diatoms >15 μm) after normal winters, and P ( Aulacoseira granulata , Fragilaria crotonensis ) after warm winters. Our results suggest that weather-related processes were the primary external drivers accounting for differences in spring phytoplankton dynamics in Lake Erken. Spring phytoplankton are influenced by overwintering species from the last autumn that can initiate the following spring bloom. Average taxonomic distinctness of the spring community was assessed using a new biodiversity measurement that incorporates taxonomic relatedness information. This value was lower than expected after warm and cold winters, which had winter air temperature 1°C deviation from an average value calculated over 21 years. Such winters increased the level of disturbance or stress to the lake, resulting in a spring with less diverse phytoplankton by narrowing the niche for species with various ecological requirements.

Two diatom species, Ulnaria acus and Fragilaria radians, are morphologically very similar and often coexist, which makes it difficult to compare their abundances. However, they are easily separated by molecular data; thus, in this work, we attempted to estimate the differences in their spatial and temporal distribution from existing metabarcoding datasets. Reanalyzing published sequences with an ASV-based pipeline and ad hoc classification routine allowed us to estimate the relative abundances of the two species, increasing the precision compared to usual OTU-based analyses. Existing data permit qualitative comparisons between two species that cannot be differentiated by other methods, detecting the distinct seasonal peaks and spatial distributions of F. radians and U. acus.

Background and aims - During phytoplankton surveys of a freshwater pond in Northeastern France, Fragilaria subconstricta (Bacillariophyceae) was observed. This rare diatom was present in large numbers in several plankton samples from Lachaussée Pond in the French Grand Est region. Methods - The morphology of Fragilaria subconstricta was examined in detail using light and scanning electron microscopy. Its identity is discussed and it is compared to the morphologically most similar species, especially Fragilaria capucina, F. mesolepta Rabenhorst, F. neointermedia and F. tenuistriata. Key results - Fragilaria subconstricta produces ribbon-like colonies and has narrow linear-lanceolate valves with slightly rostrate ends. The central area is rectangular, usually small or even absent. Spatulate linking spines are present all along the valve margins and a single rimoportula is located near one apex at the valve face-mantle junction. An amended diagnosis and new synonyms are proposed for this species. Additionally, the type material of Fragilaria mesolepta and a population of the very rare species Fragilaria capucina have been investigated and illustrated. Conclusions - Fragilaria subconstricta and F. tenuistriata are synonyms. Fragilaria capucina s. str. is a rare species in Europe, and the majority of records for this species should be considered part of the Fragilaria capucina \"Sippenkomplex\" sensu Krammer & Lange-Bertalot (1991).

Morpho-functional classifications of phytoplankton are increasingly used in ecological studies of different aquatic ecosystems. The aim was to compare three different classifications: (a) functional groups (FG); (b) morpho-functional groups (MFG); and (c) morphologically based functional groups (MBFG), and to detect how well can the biomass of phytoplankton groups based on different classifications be explained by environmental conditions of two different karstic lakes in the National Park Plitvice Lakes. Phytoplankton biomass in Lake Kozjak was lower than in Lake Prošće (total avg. 1.13 and 2.59 mg l⁻¹, respectively). Several diatoms (Cyclotella spp., Discostella stelligera, Synedra sp., Ulnaria ulna var. acus) with Dinobryon divergens were dominant in Kozjak, while Prošće was characterized by Dinobryon sociale, D. divergens, Cryptomonas sp., Stephanodiscus sp. and Fragilaria crotonensis. The best results in describing the phytoplankton succession were obtained using MBFG approach although it is less sensitive in describing variability of individual descriptive algal groups in this environment than FG and MFG. Nonetheless, because of distinct differences among dominant phytoplankton groups in these systems, MBFG classification was shown to be applicable, as supported by statistical analyses. FG and MFG classifications showed a high level of similarity, thus proving to be applicable to deep karstic lakes.

The response of a laboratory-raised phytoplankton assemblage to copper and zinc enrichment was studied. Higher intracellular accumulation of both the test metals caused disappearance of metal sensitive species, loss of diversity and species richness, reduced growth rate, Chl a and biovolume; however, the community could recover after 14 days of incubation. Cyanobacteria showed marked sensitivity to both the test metals besides some diatoms, such as, Cyclotella meneghiniana and Melosira granulata. Metal enrichment enhanced the relative abundance of species like Scenedesmus quadricauda, Oocystis borgei, Achnanthes exigua, Fragilaria capucina and Nitzschia amphibia, and these were apparently metal tolerant. Cu and Zn stress induces formation of lipid bodies (bigger in size as well as in number) and morphological abnormalities in diatoms. Among these two metals, Cu impact was higher than Zn despite the fact that the intracellular accumulation of Zn was higher than Cu. Deformed raphe and mixed deformities in diatoms were exclusively found under heavy metal stress which was well supported by regression analysis. Finally the present study gives new insight for using diatoms as an effective tool for biomonitoring and biofuel production.

Global climate change has led to periphytic algal overgrowth in water diversion canals, causing clogging issues and water quality deterioration. Flushes with high water velocity can effectively detach periphytic algae, but little information can be found on the association of flush–periphyton interactions. To fulfill the gap, flush experiments were carried out at the different colonization stages of periphytic algal community (Stage 1: initial colonization stage, Stage 2–1: early community formation stage, Stage 2–2: late community formation stage, and Stage 3: primary succession stage) with varied flushing time (0 d, 2 d, 4 d). The results demonstrated that periphytic algal community at Stage 2–1 had weak resistance to flushing-flows and the lowest biomass accumulation ability after the flush. Besides, flush suppressed the growth of periphytic filamentous algae at Stage 2–1, reducing clogging issues. Short-term (less than 2 days) flushing-flows with high velocities ( v  = 0.8 m/s) inhibited algal proliferation and reduced species diversity with temporary scour effects. The algal species ( Navicula , Achnanthes, and Fragilaria ) with strong scouring resistance became dominant species and proliferated extensively after the flush. This study laid the groundwork for hydraulic regulation, and the flushing strategy would reduce the threat of periphytic algae in the water transportation canals.

We analysed syntype material of Odontidium harrisonii W. Smith, Odontidium mutabile W. Smith, Odontidium tabellaria W. Smith, Odontidium tabellaria var. β W. Smith, Odontidium parasiticum W. Smith, Odontidium parasiticum var. β W. Smith and Fragilaria brevistriata Grunow in Van Heurck. A combination of light and scanning electron microscopy revealed that taxonomic drift led to currently misconstrued concepts of many of these taxa. Preservation of type materials allowed morphological study of each taxon in detail. The following new combinations, new names and new statuses are presented: Staurosirella harrisonii (W. Smith) E. Morales & C.E. Wetzel comb. nov., Staurosirella mutabilis (W. Smith) E. Morales & Van de Vijver comb. nov. and Pseudostaurosira smithii E. Morales & Ector nom. nov. stat. nov. Nomenclatural and ecological discussions, based on historical and current literature, are presented for each taxon. The study of type materials is a necessary task in order to improve current databases used for taxonomic and ecological purposes, and such a study should be an essential component of large-scale palaeo or neo-limnological research programs.

A high abundance of planktonic microalgae is typically thought to be related to their ‘bloom’, that is, to active population growth. Diatom blooms in the photic zone of Lake Baikal generally occur during hydrological spring (April–June); when the summer arrives and the surface water temperature increases, diatoms are replaced by other microalgae. In July 2019, we found a concentration of the diatom Fragilaria radians at a station in South Baikal that was extremely high for that season. This species generally blooms in spring, but in spring (May) of 2019, this alga was nearly absent from the phytoplankton population. Microscopic analysis of the sample taken in July 2019 revealed that the cells were in a dormant stage. The species composition of microalgae in phytoplankton samples from May 2018 and July 2019 was similar. According to the temperature profile analysis, a summer upwelling event from a depth of ca. 100 m occurred in 2019. We hypothesised that this event caused the resuspension of microalgae, including Fragilaria radians, which were deposited on the slopes of the lake in 2018. Hence, the high abundance is not always a ‘bloom’ or an active growth.

Adding fluctuations to models of resource competition provides one solution to Hutchinson's paradox. Fundamental to fluctuation dependent mechanisms of coexistence are differential species' responses to environmental fluctuations through time. The covariance between the environment and competition this generates leads to compensatory population dynamics, now thought to be important for community stability. We tested this theory experimentally using freshwater diatoms. We measured the growth of Cyclotella pseudostelligera and Fragilaria crotonensis over a range of temperatures. Cyclotella showed a higher growth rate and higher silicate assimilation rate between 6° C and 18° C, while Fragilaria showed greater competitive ability above 18° C. These results were used to parameterize a resource competition model. Numerical simulation of this model predicted stable coexistence and compensatory dynamics under fluctuating but not constant temperature. A long-term competition experiment with Cyclotella and Fragilaria confirmed the predictions of the model. These results demonstrate the role abiotic fluctuations may play in maintaining the diversity of natural communities.