Chrysophyte Species Research Articles

Seasonal Dynamics of the Silica-Scaled Chrysophytes as Potential Markers of Climate Change in Natural Model: Deep Cold Lake–Shallow Warmer Reservoir

In the context of global climate changes, it is important to assess the sustainability perspective of aquatic ecosystems based on marker organisms. In this work, we analyzed seasonal dynamics of silica-scaled chrysophytes in freshwater communicating environments which have considerable differences in water temperature between two ecosystems: the deep and cold oligotrophic Lake Baikal versus the shallower and warmer downstream Irkutsk Reservoir having mesotrophic features. During three seasons of the open water period of 2023, 38 species of silica-scaled chrysophytes were observed at 17 stations using scanning and transmission microscopy. The distribution of silica-scaled chrysophytes was shown to correlate with the water temperature. The greatest species richness was observed in the spring season in a large bay of the Irkutsk Reservoir (23 species), the smallest in the cold spring waters of Southern Baikal (up to 7 species). Widespread species living in Southern Baikal continued to grow in warmer waters of the reservoir. Using the example of silica-scaled chrysophytes, the stability of the high-latitudinal freshwater ecosystems affected by climate change is discussed. Continuous increment of the water temperature can lead to an increased abundance of widespread species and the displacement of psychrophilic species, affecting the overall biodiversity in such ecosystems.

The Impact of Environmental Factors on the Spatiotemporal Heterogeneity of Phytoplankton Community Structure and Biodiversity in the Qiongzhou Strait

The distribution and variation in environmental factors and the phytoplankton community in the Qiongzhou Strait were investigated in autumn 2015 and spring 2016. The environmental factors were different in the two seasons, as seen when using one-way ANOVA testing, principal component analysis, and cluster analysis. The temperature and levels of dissolved oxygen and soluble solids were higher in autumn, and the ammonia (NH4-N) level was much higher in spring (4.66 ± 0.97 µmol/L), which led to a higher concentration of dissolved inorganic nitrogen in the northeast area. A total of 118 species of phytoplankton were found, with 47 common species in both seasons and more species in spring. Bacillariophyta (diatom) contributed to over 80% of the relative abundance in both seasons. The species of Chrysophyta and Xanthophyta were endemic species in autumn and spring, respectively. Skeletonema costatum and Chaetoceros curvisetus were the common dominant species, with nine dominant species in both seasons. Higher abundance and biodiversity of phytoplankton appeared in spring, and their differences were mostly determined by NH4-N level, hydrodynamic conditions and artificial activities in the coastal area in the Qiongzhou Strait.

Changes in Diversity of Silica-Scaled Chrysophytes during Lake-River-Reservoir Transition (Baikal-Angara-Irkutsk Reservoir).

Hydroelectric dams create new ecosystems such as reservoirs. Several hydroelectric dams forming shallow reservoirs were built on the Angara River flowing out of Lake Baikal. The first of them in downstream Angara is Irkutsk Reservoir, with several shallow bays. Since silica-scaled chrysophytes are effective bioindicators for aquatic ecosystems, this paper aimed to determine their distribution, taxonomic structure and species richness in South Baikal and Irkutsk Reservoir, which have different environmental parameters. Thirty-one species were found using scanning and transmission electron microscopy. Only seven of them inhabited South Baikal in June 2023 at 3.66-4.51 °C and pH 7.80-8.24, with Chrysosphaerella baicalensis, Spiniferomonas trioralis f. cuspidata and Mallomonas alpina being prevalent. Only one species (M. alpina) was dominant in Irkutsk Reservoir at all stations at a water temperature of 5.33-11.55 °C and pH 8.10-8.52, alongside three other abundant species, Synura cf. glabra, Mallomonas acaroides and M. crassisquama. The maximum number of species (23) was found in a shallow bay of the reservoir at maximal values of temperature (11.5 °C) and pH (8.57) and minimal values of phosphate and nitrate concentrations during the study. The enrichment of Irkutsk Reservoir in species of silica-scaled chrysophytes was due both to cosmopolitan widespread and polyzonal species as well as to rare boreal, arctic-boreal, and unknown, possibly new species.

Two new species of silica-scaled chrysophytes (Chrysophyceae, Synurales) Mallomonas kicherica and M. sibirica water bodies of Eastern Siberia, Russia

Two new species of Chrysophytes, Mallomonas kicherica and M. sibirica (order Synurales) were described in several water bodies in Eastern Siberia based on the ultrastructure of silica scales. These species belong to section Striatae. M. kicherica is characterised by scales with labyrinth-like reticulation on the dome and transverse ribs connected by short ribs-jumpers. This species is most similar in scale ultrastructure to M. striata var. balonovii. M. kicherica was found in the mouth of Kichera River, a tributary of Lake Baikal. M. sibirica is characterised by scales with a well-developed secondary layer on the shield in which rounded depressions are located. This species is most similar in scale ultrastructure to M. pechlaneri. M. sibirica was registered in different waters of Eastern Siberia under various ecological parameters—in the mixing zone of the Yenisei River and the Kara Sea, Lake Baikal, and in lakes Ulu, Vorota and Labynkyr (Yakutia).

Two New Species, Mallomonas baicalensis sp. nov. and M. grachevii sp. nov. (Synurales Chrysophyceae), Found under the Ice of Lake Baikal

Two new species of silica-scaled chrysophytes (order Synurales) from the genus Mallomonas and sections Striatae Mallomonas baicalensis sp. nov. and M. grachevii sp. nov. found at the bottom surface of the ice of Lake Baikal, with a structure of siliceous scales, are described using electron microscopy. The main and unique distinctive feature of M. baicalensis is its dome with a long spine and the slightly asymmetrical shape of its scales, regardless of their position on the cell. We could not find the bristles, and if there are spines on the dome, we can assume that they may be missing. The main distinguishing feature of M. grachevii is the presence of a secondary layer on the shield except at the angle of the V-rib, in which an area without the secondary layer, a “window”, is present with numerous pores, and the first transverse rib closest to the dome is thickened. Among the Mallomonas species from the section Striatae, only M. siveri and M. baicalensis have a group of rimmed pores in the corner of the V-rib. As a result of our research, the number of Mallomonas species of the section Striatae found in Lake Baikal has increased to eight, of which, in addition to the new species, only one species is widespread, and the rest are rare, previously foundin oligotrophic/mountain water bodies.

Additions to chrysophycean stomatocyst flora from South Urals shallow lake including descriptions of three new morphotypes

In this study we observed 17 additional morphotypes of chrysophycean stomatocysts from the shallow lake Zhurmankol which is located in a protected zone of South Urals steppes (Russia). Including our new records, the number of known chrysophycean stomatocysts from the Lake Zhurmankol increased to 32 morphotypes. Three morphotypes are described as new to science. Their similarity and difference from previously described morphotypes are discussed. While the biological affinity of two new morphotypes remains unknown, the third stomatocyst was produced by a heterotrophic chrysophyte species, Paraphysomonas bandaiensis. Critical analysis of the published micrographs of P. bandaiensis siliceous scales from Russia revealed that they belong to another, yet undescribed, taxon (or taxa). So, our report on P. bandaiensis is the first confirmed record of this species in Russia.

Light-dependent niche differentiation in two mixotrophic bacterivores.

SummaryMixotrophy usually is considered with respect to the advantages gained and the associated trade‐offs of this form of nutrition, compared to specialized competitors, strict photoautotrophs and heterotrophs. However, we currently have an incomplete understanding of the functional diversity of mixotrophs and the factors controlling niche differentiation in different mixotrophic species. Here we experimentally studied the light‐dependent niche differentiation in two chrysophyte species. We show that the newly isolated Ochromonas sp. is an obligate phototroph and possibly an obligate mixotroph. In contrast, Poterioochromonas malhamensis is a facultative mixotroph; photosynthesis and heterotrophy in this species represent substitutable routes of resource acquisition. We further hypothesize that the variable plasticity in the considered traits of the here tested species may result in different niche differentiation with regard to a vertical light gradient. Ochromonas sp. should perform better in stable stratified surface water layers, where light is available, but prey abundances might be low. However, P. malhamensis should be able to also successfully grow in deeper water layers, benefiting from higher bacterial production. This study represents a first step towards understanding competition between mixotrophs engaging in different physiological strategies, and consequently their potential co‐occurrence due to niche differentiation.

Diversity Variation of Silica-Scaled Chrysophytes Related to Differences in Physicochemical Variables in Estuaries of Rivers in an Arctic Watershed

The present study examined the taxonomic diversity of silica-scaled chrysophytes in the estuaries of the Arctic watershed of Yakutia in the context of global climate change, as these aquatic organisms are highly sensitive to environmental changes. Previously, 41 species of silica-scaled chrysophytes were recorded in the waters of Yakutia. In the present study, we supplemented this list with 55 species. We observed a high species richness (82 taxa) of silica-scaled chrysophytes in the study area. Of these, eight species were recorded in the waters of Russia for the first time. At present, the study area represents the northernmost habitat for most species observed during the study. The diversity of silica-scaled chrysophytes in Arctic rivers is comparable to or even greater than the diversity of chrysophycean flora at the middle latitudes. Most of these chrysophytes are represented by polyzonal and ubiquitous species. During 2008–2010, we noted increased relative numbers of boreal species in northern waters compared with data obtained during the previous 30 years. Overall, the species richness of silica-scaled chrysophytes in the studied rivers increased with increase in water transparency, temperature, and magnesium ion concentration, but decreased with increase in surfactant concentration. The origin of samples from a certain river; distance of the sampling site from the estuary; water temperature, transparency, and colour; and concentration of carbon dioxide, magnesium ions, total iron, surfactants, and oil products affect the species composition of silica-scaled chrysophytes in the study area. Our findings are fundamental to evaluate the current status of Arctic aquatic microflora and its further monitoring in the context of anthropogenic and climatic impacts.

From adverse to beneficial: Contrasting dietary effects of freshwater mixotrophs on zooplankton

Abstract The importance of mixotrophic algae as key bacterivores in microbial food webs is increasingly acknowledged, but their effects on the next trophic level remain poorly understood. Their high stoichiometric food quality is contrasted by anti‐grazing strategies. We tested the quality of freshwater mixotrophs as prey for zooplankton, using four non‐colonial chrysophyte species and a cryptophyte as a high quality reference food. We (1) analyzed the stoichiometric and biochemical (fatty acid) composition of the mixotrophs, and (2) quantified their dietary effects on Daphnia longispina survival. Survival of D. longispina significantly depended on the identity of species provided as food, ranging from higher to lower as compared to starvation. This was not reflected in differences in cellular stoichiometry or fatty acid profiles of the mixotrophs. We suggest that toxicity may be the driver for the observed differences. Generalization of the dietary effects of mixotrophic chrysophytes does not appear straightforward. Besides fundamental species‐specific differences, potential toxic effects may vary depending on environmental cues or physiological strategies. Notably in our study, Ochromonas tuberculata, a species previously reported to be deleterious, turned out to be a beneficial food source in terms of enabling high survival of D. longispina. We challenge the generality of the assumption that chrysophytes are of low value as food for zooplankton. We recommend that future studies test how environmental conditions and physiological strategies shape the quality of mixotrophs as food for consumers at higher trophic levels, specifically focusing on effects of dietary toxicity.

On the flora of chrysophytes from the state nature reserve “Pasvik”

In June 2019 16 species of chrysophytes from Paz river and a sphagnum bog were recorded. Among them several species, Neotessella lapponica, Kephyrion starmachii and Chrysastrella paradoxa, are rare for Russian algal flora and they are the new records for Murmansk Region. Some taxa (e.g., Synura sp. and Chrysosphaerella sp.) were not identified and probably they are new species for science.

A checklist of freshwater algae from Mt. Sinbul alpine wetlands in South Korea

The present study summarized the freshwater algal diversity from Mt. Sinbul alpine wetlands in South Korea from March 2013 to December 2019. We identified a total of 183 taxa belong to seven main algal groups (Charophyta, Chlorophyta, Cyanophyta, Chrysophyta, Cryptophyta, Dinophyta and Euglenophyta). The algal communities were characterized by high species numbers of the desmids making up 108 taxa. It was examined that the number of species was higher during late spring and summer. Among them, a total of 53 taxa of 40 desmid species (Charophyta) including 4 new taxa (Actinotaenium crassiusculum var. minutum var. nov., Cosmarium vitiosum var. koreanum var. nov., Groenbladia neglecta var. longa var. nov., Staurodesmus koreanus sp. nov.), 5 species of Chlorophyta, 7 species of Chrysophyta and 1 species of Cyanophyta have been recorded for the first time in Korea.

Interaction-Specific Changes in the Transcriptome of Polynucleobacter asymbioticus Caused by Varying Protistan Communities.

We studied the impact of protist grazing and exudation on the growth and transcriptomic response of the prokaryotic prey species Polynucleobacter asymbioticus. Different single- and multi-species communities of chrysophytes were used to determine a species-specific response to the predators and the effect of chrysophyte diversity. We sequenced the mRNA of Pn. asymbioticus in communities with three single chrysophyte species (Chlorochromonas danica, Poterioochromonas malhamensis and Poteriospumella lacustris) and all combinations. The molecular responses of Pn. asymbioticus significantly changed in the presence of predators with different trophic modes and combinations of species. In the single-species samples we observed significant differences related to the relative importance of grazing and exudation in the protist-bacteria interaction, i.e., to the presence of either the heterotrophic Ps. lacustris or the mixotrophic C. danica. When grazing dominates the interaction, as in the presence of Ps. lacustris, genes acting in stress response are up-regulated. Further genes associated with transcription and translation are down-regulated indicating a reduced growth of Pn. asymbioticus. In contrast, when the potential use of algal exudates dominates the interaction, genes affiliated with iron transport are up-regulated. Rapid phototrophic growth of chrysophytes, with a high demand on soluble iron, could thus lead to iron-limitation and cause changes in the iron metabolism of Pn. asymbioticus. Additionally, we observe a benefit for Pn. asymbioticus from a more diverse protistan community, which could be due to shifts in the relative importance of phototrophy in the mixotrophic chrysophytes when competing for food with other species. Our study highlights the importance of biotic interactions and the specificity of such interactions, in particular the differential effect of grazing and algal exudation in the interaction of bacteria with mixotrophic protists.

Production and fate of fishy odorants produced by two freshwater chrysophyte species under different temperature and light conditions

Fishy odor has become one of the most often encountered aesthetic water quality problems in drinking water. While fresh water algae living in colder water can produce offensive fishy odors, their environmental behaviors remain poorly understood. In this study, two chrysophyte species (Synura uvella and Ochromonas sp.), which are often associated with fishy odor events, were selected to investigate the effect of temperature (8, 16, and 24 °C) and light intensity (10, 41, and 185 μmol photons m−2 s−1) on algal growth and odorant production. Five polyunsaturated aldehyde derivatives, including 2,4-heptadienal, 2-octenal, 2,4-octadienal, 2,4-decadienal, and 2,4,7-dectridienal, were identified as fishy/cod liver oil/fatty/rancid descriptors in the cultures of the two algae based on gas chromatography-olfactometry-mass spectrometry and comprehensive two-dimensional gas chromatography mass spectrometry. While biomass yield increased with the increase in temperature for both species, significantly higher odorant yields (production of odorants per cell) were obtained at 8 °C. The total odorant production and cell yield of the odorants decreased with the increase in light intensity from 10 to 185 μmol photons m−2 s−1. The biodegradation half-lives for the released odorants were 6–10 h at 8 °C and 2–4 h at 24 °C, whereas the volatilization half-lives were 36–97 d at 8 °C and 6–17 d at 24 °C, suggesting that temperature-dependent biodegradation was an important factor controlling the fate of fishy compounds in aquatic environments. The results of this study will help clarify why most fishy odor events occur in cooler seasons, and provide knowledge related to cold water persistence for the management of fishy odor problems associated with algae.

Spatial-temporal variation of phytoplankton community structure in Jiaozhou Bay, China

To better understand the spatial-temporal variation in phytoplankton community structure and its controlling factors in Jiaozhou Bay, Qingdao, North China, four seasonal sampling were carried out in 2017. The phytoplankton community structure and various environmental parameters were examined. The phytoplankton community in the bay was composed of mainly diatoms and dinoflagellates, and several other species of Chrysophyta were also observed. Diatoms were the most dominant phytoplankton group throughout the year, except in spring and winter, when Noctiluca scintillans was co-dominant. High Si/N ratios in summer and fall reflect the high dominance of diatoms in the two seasons. Temporally, the phytoplankton cell abundance peaked in summer, due mainly to the high temperatures and nutrient concentrations in summer. Spatially, the phytoplankton cell abundance was higher in the northern part of the bay than in the other parts of the bay in four seasons. The diatom cell abundances show significant positive correlations with the nutrient concentrations, while the dinoflagellate cell abundances show no correlation or a negative correlation with the nutrient concentrations but a significant positive correlation with the stratification index. This discrepancy was mainly due to the different survival strategies between diatoms and dinoflagellates. The Shannon-Wiener diversity index (H′) values in the bay ranged from 0.08 to 4.18, which fell in the range reported in historical studies. The distribution pattern of H′ values was quite different from that of chlorophyll a, indicating that the phytoplankton community structure might have high biomass with a low diversity index. Compared with historical studies, we believe that the dominant phytoplankton species have been changed in recent years due mainly to the changing environment in the Jiaozhou Bay in recent 30 years.

Phytoplankton biodiversity and its relationship with aquatic environmental factors in Lake Uvildy, South Urals, Russia

Kostryukova AM, Mashkova V, Krupnova TG, Egorov NO. 2018. Phytoplankton biodiversity and its relationship with aquatic environmental factors in Lake Uvildy, South Urals, Russia. Biodiversitas 19: 1422-1428. Lake Uvildy is one of the largest and the most unique of the South Ural region lakes. This mountain deep lake, which has the status of a natural monument. The purpose of this paper was to study the phytoplankton community structure and the aquatic environmental factors in Lake Uvildy. The phytoplankton samples were collected from 5 sites of Lake Uvildy, then filtered through the plankton net and were preserved in 5% formalin. Species were identified using the handbooks by Sladecek, Yarushina, and Al-Kandari. Water samples were taken for water quality analysis. The several physicochemical parameters were measured in situ by a Portable Meters (Multitest IPL-513 and Multitest KSL-111, Semico Ltd, Russia, Novosibirsk). The others parameters were measured in the laboratory of the Department of Chemistry of the South Ural State University according to the standard methods. The sampling was made during the vegetation period in June-July 2014. The water quality was evaluated using the Shannon biodiversity index. A total of 38 species (11 phyla, 31 genera), including 9 species of Chlorophyta, 13 species of Bacillariophyta, 9 species of Cyanophyta, 4 species of Euglenophyta, 2 species of Chrysophyta, 1 species of Dinophyta, were identified. The phytoplankton species in the lake were mainly represented by Cyanophyta and Bacillariophyta. There were 5 dominant species: Fragilaria crotonensis, Asterionella formosa, Dolichospermum lemmermannii, Microcystis aeruginosa, and Coenococcus planktonicus. The Shannon index value comprised 1.27-2.21. According to the saprobity index values (1.63-2.35), the water in the late is evaluated as satisfactorily clean. Physico-chemical parameters were factors driving the change in phytoplankton community composition in Lake Uvildy.

Environmental controls on spatial variability of summer phytoplankton structure and biomass in the Bering Sea

The subarctic Bering Sea, one of the most productive regions of the world's oceans, is undergoing significant ecological shifts possibly linked to global climate change. During the Fourth Chinese National Arctic Research Expedition (CHINARE) from July 10 to 20 of 2010, phytoplankton community structure, species diversity, spatial distribution, community types, abundance and biomass variations were investigated in a large scale study extending from the Bering Strait into the open waters down to the subarctic Pacific. These patterns were linked to potential environmental drivers, including effects of water masses and seasonal sea ice retreat. Results showed a marked spatial zonation in the taxonomic composition, abundance and biomass. A total of 149 phytoplankton taxa distributed among 57 genera of 5 phyla were identified, characterized into three ecological groups, namely Arctic, Boreal-temperate and cosmopolitan species. Phytoplankton included 101 species of diatoms, 44 species of dinoflagellates, 2 species of Chrysophyta, 1 species of each Chlorophyta and Euglenophyta. Both abundance and biomass were highest in the Bering Shelf, moderate on the Bering Slope, and lowest on the Bering Basin. Chlorophyll a was found highest in the subsurface chlorophyll maxima (SCM) close to the thermocline and halocline layers but its depth varied regionally. Multi-dimensional scaling (MDS) revealed two types of assemblages, one a deep-sea assemblage associated with the Bering Basin and a neritic assemblage found in the Bering Slope and Shelf. Average abundance (10.22×103cells/L), biomass (0.43mg/m3), species diversity (2.60) and species richness (1.66) were established for deep-sea assemblage with the dominant species ranked as Neodenticula seminae, Chaetoceros atlanticus, Pseudonitzschia delicatissima, and Thalassionema nitzschioides. Neritic assemblage had higher values with 12.73×103cells/L, 2.41mg/m3, and 2.55 species richness but lower (2.41) species diversity, and the community was mainly dominated by Thalassiosira nordenskiöldii, Leptocylindrus danicus, Chaetoceros socialis, Chaetoceros debilis, Fragilariopsis oceanica, Nitzschia closterium and Chaetoceros furcellatus. A diatom bloom was observed near the Bering Strait in the summer of 2010 induced by high availability of nitrate particularly in the Bering Shelf, while water mass transportation mainly influenced communities in the Bering Basin and Slope. The observed fluctuation in both biomass and summer phytoplankton communities in the Bering Sea were mostly influenced by events related to the spring sea ice retreat in 2010.

Adirondack (NY, USA) reference lakes show a pronounced shift in chrysophyte species composition since ca. 1900

Researchers are increasingly tasked with identifying biological recovery targets as ecosystems recover from anthropogenic stressors. Attempts to define such recovery targets are often hampered by two problems: (1) a lack of long-term monitoring data; and (2) the confounding influence of multiple stressors, especially regional stressors like climate warming. Paleolimnological studies of minimally disturbed reference sites can help address both these issues. Using paleoecological techniques, researchers can isolate the long-term impact of regional stressors like climate change on species assemblages largely independent of other confounding stressors such as acidification, eutrophication, and land-use change, thereby providing a framework to assess biological recovery in lakes that are recovering from acid deposition or other stressors. This manuscript provides a theoretical paleolimnological framework for the use of reference lakes in studying biological recovery from acidification, and provides an example of how assemblages of scaled-chrysophytes have changed in Adirondack-region reference lakes (NY, USA) from pre-ca. 1900 to present. The thirty-one reference lakes were selected from a database of over 1400 lakes, using criteria to minimize the influence of acidification, eutrophication, road-salt seepage, and piscivore introductions. As such, these lakes provide a unique opportunity to examine the effects of regional stressors in the Adirondack ecological region, which can inform biological recovery in lakes that have acidified historically. The modern chrysophyte assemblages from the reference lakes were significantly related to modern limnological variables including pH, dissolved organic carbon and ionic concentration as well as important physical variables including lake depth, which were used to help understand changes in the chrysophyte assemblages over the last century. Changes in chrysophyte assemblages from pre-1900 to present were determined by comparing the modern surface assemblages to a sediment interval representing pre-1900 conditions, revealing significant increases in the abundance of colonial chrysophyte taxa, especially S. petersenii, S. sphagnicola, and S. echinulata, and corresponding decreases in the relative abundance of many Mallomonas taxa. These changes suggest that regional warming and/or oligotrophication have influenced the species assemblages of minimally disturbed reference lakes, suggesting that lakes currently recovering from acidification are unlikely to return to their pre-disturbance assemblages.

Mallomonas Camerunensis Sp. Nov. (Chrysophyceae, Stramenopiles) From A Shallow Puddle In The Guineo-Congolian Rainforest (Cameroon)

AbstractA new silica-scaled chrysophyte species, Mallomonas camerunensis J. Piątek, is described and illustrated from a shallow puddle in the Guineo-Congolian rainforest in Cameroon. This species belongs to section Papillosae and series Papillosa. It is similar to other Mallomonas species placed in Papillosa, such as M. binocularis Siver, M. calceolus D. E. Bradley, M. delanciana Siver, M. kalinae Řezáčová, M. papillosa K. Harris & D. E. Bradley, M. paxillata (D. E. Bradley) L. Ş. Péterfi & Momeu, M. rasilis Dürrschm. and M. tropica Dürrschm. & Croome, but differs from them in several morphological characters warranting recognition as a distinct species. The dome of M. camerunensis is clearly delimited and ornamented with papillae and ribs. The scales lack an anterior submarginal rib, while the posterior rim and V-rib are smooth and unornamented. The shield is thickly ornamented with papillae (18–22 papillae per scale width). The species is described and illustrated using light microscopy and scanning electron microscopy.

A fishy odor episode in a north China reservoir: Occurrence, origin, and possible odor causing compounds

A significant outbreak of fishy odor occurred in a reservoir located in Inner Mongolia, China, in the winter of 2011, and the odor rating, algal density and concentrations of some potential odorous compounds were monitored over a period of two months. The peak odor rating of the fishy odor was 7 according to flavor profile analysis. Among the dominant algal species (two diatom and one chrysophyte species) observed during the survey, the chrysophyte Dinobryon sp. was the most abundant species, with the peak density recorded at 88,520 cells/mL. Seven potential algal metabolites including heptanal, 2,4-heptadienal, 2,4-decadienal, nonanal, 2-octenal, 2,6-nonadienal and hexanal were detected. The principal component analysis result showed that n-hexanal, n-heptanal and 2,4-decadienal, possibly the metabolites of diatoms, and 2,4-heptadienal, possibly the metabolite of Dinobryon sp., might have contributed to the fishy odor episode. This study demonstrated that the fishy odor episode in this reservoir might be caused by the abnormal growth of chrysophytes and diatoms under the ice-cover.

Silica-Scaled Chrysophytes (Chrysophyceae and Synurophyceae) from New Zealand Freshwaters. II. Additions to the Flora

Eight species of silica-scaled chrysophytes were observed from collections made between December 1988 and February 1989. The species are cosmopolitan with the exception of one new species, Paraphysomonas preisigii Wujek, described here. Siliceous scales of the colorless free-living flagellate Gyromitus disomatus were also observed.