Cryptomonas Marssonii Research Articles

Succession Characteristics and Influencing Factors of Phytoplankton Communities in Qionghai Lake

The phytoplankton population of Qionghai Lake was surveyed in December 2015, March 2016, June 2016, September 2016, and March 2017. A total of 196 species (including varieties) belonging to 77 genera of 7 phyla were identified. The phytoplankton communities were dominated by Chlorophyta and diatoms, and there were significant differences across the five sampling sites. The phytoplankton abundance, which ranged between 13.85 × 104 and 335.54 × 104 cells·L−1, was significantly higher in spring and summer than in autumn and winter. Chlorella sp. and Cyclotella sp. were the dominant populations, and their dominance degree reached as high as 0.54 and 0.33, respectively. The diversity of the phytoplankton populations was significantly higher in spring and summer than in autumn and winter, and the Shannon–Wiener index and Margalef index ranged from 2.49–3.65 and 2.47–3.10, respectively. The water quality of Qionghai Lake was generally good. The trophic level index was between 30 and 60, showing that the water body was overall in a mesotrophic to slightly eutrophic state. The Spearman correlation analyses revealed that ammonium nitrogen (NH4+-N), water temperature (WT), permanganate index (CODMn), and transparency (SD) were the most important environmental factors that influenced the phytoplankton communities. For example, NH4+-N was significantly correlated with Chroococcus sp. (r = 0.41, p < 0.05) and Cryptomonas ovata Ehrenberg (r = 0.45, p < 0.05), and WT was significantly correlated with Cryptomonas marssonii Skuja (r = 0.43, p < 0.05) and Cryptomonas ovata (r = 0.53, p < 0.01).

Phytoplankton phagotrophy across nutrients and light gradients using different measurement techniques

Abstract Mixotrophy is important to ecosystems functioning. Assuming that limiting resources induce phagotrophy in mixotrophs, we used a factorial experimental design to evaluate how nutrient and light affects phagotrophy in two mixotrophic phytoflagellates belonging to different lineages. We estimated cell-specific grazing rates (CSGR) by analyzing prey ingestion using microscopy and flow cytometry (FC). Furthermore, we tested if the acidotropic probe LysoTracker green (LyTG) can be used to differentiate autotrophs from mixotrophs. Cryptomonas marssonii (cryptophyte) had higher CSGR in high-nutrient treatments. Although it seems counterintuitive, phytoflagellates likely uses phagotrophy to obtain organic growth factors instead of inorganic nutrients when photosynthesis is more favorable. In contrast, CSGR in Ochromonas tuberculata (chrysophyte) increased when light decreased, suggesting that it uses phagotrophy to supplement carbon when autotrophic growth conditions are suboptimal. Measurements of CSGR obtained by FC and microscopy were significantly correlated and displayed the same trend among treatments, although FC rates tended to be higher. Fluorescence with LyTG did not differ from the control in the non-phagotrophic chlorophyte. Contrarily, addition of LyTG significantly increased the fluorescence in chrysophytes and cryptophytes, although no differences were observed among treatments. This approach allowed for differentiation between phagotrophic and non-phagotrophic flagellates but failed to quantify mixotrophy.

Functional Groups of Phytoplankton and Their Relationship with Environmental Factors in the Restored Uzarzewskie Lake

Uzarzewskie Lake is a small, postglacial lake, located in western Poland. The lake is under restoration treatment since 2006. At first, iron treatment was done for 2 years. In the second stage, spring water was directed into the hypolimnion in order to improve water oxygenation near the bottom sediments. The purpose of our research was to determine changes in the contribution of functional groups to the total number of taxa and total biomass of phytoplankton due to changes in the physical and chemical characteristics of the restored lake. Phytoplankton composition was analyzed in three periods: (1) before restoration; (2) during the first method of restoration; and (3) when the second method was implemented in the lake. Epilimnetic phytoplankton was sampled every year monthly from March to November. The relationship between phytoplankton groups and environmental factors (water temperature, ammonium nitrogen, nitrate nitrogen, dissolved phosphorus, conductivity and pH) was examined, using the canonical analyses. The redundancy analysis indicated that the temperature, dissolved phosphates concentration, ammonium nitrogen and pH were the main determining factors of the phytoplankton community dynamics. During the study, 13 coda dominated the phytoplankton biomass. Cyanobacteria of the codon H1 with such species as Aphanizomenon gracile, Dolichospermum planctonicum, D. viguieri dominated the phytoplankton community before restoration. S1 group consisting of Planktolyngbya limnetica, Limnothrix redekei and Planktothrix agardhii mostly dominated during the period in which the first method was used. Improvement of water quality due to restoration efforts in the third period caused dominance of other groups, especially J (Actinastrum hantzschii and other Chlorococcales), C (Asterionella formosa and other diatoms), Y (Cryptomonas marssonii and other cryptophytes), Lo (Peridiniopsis cunningtonii and other dinophytes) and X2 (Rhodomonas lacustris).

Phytoplankton composition and physicochemical properties in Lake Swarzędzkie (midwestern Poland) during restoration: Preliminary results

Abstract This paper presents the preliminary results of a study of the phytoplankton structure and dynamics and physicochemical properties of Lake Swarzędzkie in 2011. The subject of the study is a shallow, elongated, post-glacial lake located in western Poland. The surface area is 93.7 ha with a maximum depth of 7.2 m. Its poor water quality led to the implementation of chemical and biological restoration procedures in an attempt to improve it. The highest concentration of total nitrogen was 13.07 mg l-1 N. Secchi depth (SD) was low in the summer with a minimum value of 0.5 m in September. The most abundant group of phytoplankton were cyanobacteria, and the maximum value of chlorophyll a concentration was 278.0 μg l-1. The dominant species were Pseudanabaena limnetica and Aphanizomenon gracile. Cyanobacteria were the most abundant phytoplankton until November. Maximum diatom, cryptophyte, and chrysophyte density was noted in the spring, and the most abundant were Nitzschia acicularis, Cryptomonas marssonii, Rhodomonas lacustris, Erkenia subaequiciliata, and Dinobryon sociale. One-hundred and thirty-six phytoplankton taxa belonging to nine taxonomic groups were identified in Lake Swarzędzkie. The highest number of taxa was noted among chlorophytes (57 taxa), cyanobacteria (19), diatoms (16), and chrysophytes (12), while other taxonomic groups were represented by smaller number of taxa.

Differing Daphnia magna assimilation efficiencies for terrestrial, bacterial, and algal carbon and fatty acids

There is considerable interest in the pathways by which carbon and growth-limiting elemental and biochemical nutrients are supplied to upper trophic levels. Fatty acids and sterols are among the most important molecules transferred across the plant-animal interface of food webs. In lake ecosystems, in addition to phytoplankton, bacteria and terrestrial organic matter are potential trophic resources for zooplankton, especially in those receiving high terrestrial organic matter inputs. We therefore tested carbon, nitrogen, and fatty acid assimilation by the crustacean Daphnia magna when consuming these resources. We fed Daphnia with monospecific diets of high-quality (Cryptomonas marssonii) and intermediate-quality (Chlamydomonas sp. and Scenedesmus gracilis) phytoplankton species, two heterotrophic bacterial strains, and particles from the globally dispersed riparian grass, Phragmites australis, representing terrestrial particulate organic carbon (t-POC). We also fed Daphnia with various mixed diets, and compared Daphnia fatty acid, carbon, and nitrogen assimilation across treatments. Our results suggest that bacteria were nutritionally inadequate diets because they lacked sterols and polyunsaturated omega-3 and omega-6 (omega-3 and omega-6) fatty acids (PUFAs). However, Daphnia were able to effectively use carbon and nitrogen from Actinobacteria, if their basal needs for essential fatty acids and sterols were met by phytoplankton. In contrast to bacteria, t-POC contained sterols and omega-6 and omega-3 fatty acids, but only at 22%, 1.4%, and 0.2% of phytoplankton levels, respectively, which indicated that t-POC food quality was especially restricted with regard to omega-3 PUFAs. Our results also showed higher assimilation of carbon than fatty acids from t-POC and bacteria into Daphnia, based on stable-isotope and fatty acids analysis, respectively. A relatively high (>20%) assimilation of carbon and fatty acids from t-POC was observed only when the proportion of t-POC was >60%, but due to low PUFA to carbon ratio, these conditions yielded poor Daphnia growth. Because of lower assimilation for carbon, nitrogen, and fatty acids from t-POC relative to diets of bacteria mixed with phytoplankton, we conclude that the microbial food web, supported by phytoplankton, and not direct t-POC consumption, may support zooplankton production. Our results suggest that terrestrial particulate organic carbon poorly supports upper trophic levels of the lakes.

Two Freshwater Cryptomonads New to Korea: Cryptomonas marssonii and C. pyrenoidifera

We described two brownish freshwater Cryptomonas species, C. marssonii Skuja and C. pyrenoidifera Geitler as first records in Korea. The identification was based on light microscopy, scanning electron microscopy, and nuclear SSU rDNA sequences analysis. Cryptomonas marssonii is characterized by its sigmoid shape with a sharply pointed and dorsally curved antapex, dorso-ventrally flattened cell, two lateral plastids without pyrenoid, and its dimension of 18-25 μm in length and 8-13 μm in width. Cryptomonas pyrenoidifera is characterized by ovoid to elliptical shape with a partially twisted or rounded antapex, dorso-ventrally biconvex cell, lateral plastids with two pyrenoids, and the dimensions of 15-22 μm in length and 10-14 μm in width. Nuclear SSU rDNA sequences between C. marssonii WCK01 from Korea and CCAC0086 from Gernmay, and between C. pyrenoidifera WCK02 from Korea and CCMP152 from Australia were identical, respectively.

Abundance and diversity of phytoplankton in the Paraná River (Argentina) 220 km downstream of the Yacyretá reservoir

Patterns in the temporal composition, abundance and diversity of the phytoplankton community of the Paraná river prior to and after the initial filling phase of the Yacyretá reservoir are analyzed. The study site is located 220 km downstream from the Yacyretá reservoir and 30 km downstream from the confluence with the Paraguay river. Because both rivers remain separate and unmixed at the study site, we compared the possible effects of the impoundment on both river banks (left and right banks) in hydrological periods with similar duration and magnitude of the low and high water phases. Physical and chemical conditions measured on the right bank (water from the Paraguay river) were similar at both periods (pre and post-impoundment) whereas conductivity, pH and orthophosphate concentration increased on the left bank (water from the High Paraná river and Yacyretá reservoir) after the impoundment. Changes in phytoplankton density and diversity were observed only in samples collected from water flowing from the reservoir (left bank). The density of Chlorophyceae (Chloromonas acidophila, Chlamydomonas leptobasis, Choricystis minor, Chlorella vulgaris, Scenedesmus ecornis, Monoraphidium minutum, M. contortum and M. pusillum) and Cryptophyceae (Rhodomonas minuta, Cryptomonas marssonii and C. ovata) increased while Cyanophyceae (Cylindrospermopsis raciborskii, Raphidiopsis mediterranea and Planktolyngbya subtilis) and Bacillariophyceae (Aulacoseira granulata and its bioforms) decreased compared to previous studies conducted on the left bank of the Paraná river. Phytoplankton collected from the right bank of the river did not differ in pre and post- impoundment samples because they originate from the Paraguay river, which remains relatively unaffected by human activities.

Experimental study on the microbial plankton community in a South American wetland (Lower Paraná River Basin) and the effect of the light deficiency due to the floating macrophytes

An experimental study using microcosms was conducted in a South American wetland, Lower ParanaRiver Basin (Argentina), to analyse the structure of the components of the microbial plankton community and the influence of the light deficiency due to floating macrophytes on this community. Two experiments were run under different light conditions; the decrease of the light penetration due to 20 floating macrophytes was simulated using different nylon mesh covers that resembled natural conditions in the lake. These studies revealed that the light deficiency favoured the replacement of obligate autotrophs by mixotrophic and heterotrophic organisms. Abundances of strictly autotrophic algae along the experiments responded to the light gradient, being maximum in the flasks without cover. Heterotrophic nanoflagellates (HNF) and ciliates increased in the microcosms, probably 25 favoured by the high food availability (picoplankton) and the lack of their predators (zooplankton). The increase of ciliates was higher in the microcosms with more light. In the first experiment, the picoplankton fraction strongly decreased after 24 h in the flasks that included all their potential predators, thus suggesting a grazing pressure on this fraction. Grazing experiments performed with fluorescent-labelled bacteria (FLB) revealed that two Cryptomonas species, which are frequent in the 30 lake (Cryptomonas erosa and Cryptomonas marssonii), can ingest bacteria.

Diversity in the influence of temperature on the growth rates of freshwater algae, and its ecological relevance

Summary1. Growth rates of seven species of planktonic algae were determined in culture over a range of temperature from 2 to 35 °C. Additional observations on growth and viability were made for 13 species in the temperature range 20–35 °C.2. There was a wide range of growth rates between species at their optimal temperatures, from 1.7 divisions day−1 (Asterionella formosa) to 0.3 divisions day−1 (Ceratium furcoides).3. There were considerable differences between species for growth at low and high temperature. Certain algae, including the diatom A. formosa and the flagellates Cryptomonas marssonii, Dinobryon divergens and Eudorina unicocca var. unicocca, had growth rates of 0.4 divisions day−1 or more at 5 °C. The cyanophyte Tychonema (formerly Oscillatoria) bourrellyi, the xanthophyte Tribonema sp., the desmid Staurastrum cingulum and the large dinoflagellate C. furcoides grew poorly or not at all at this temperature. All 21 species tested could grow at 25 °C, but many – including most of the diatoms, some cyanophytes, and all the flagellates – failed to grow persistently at 30 °C. Only Aphanizomenon flos‐aquae survived with moderate increase at 35 °C, a lethal temperature for the other species.4. The applicability was considered of proposed quantitative formulations of the rate‐temperature relationship. Simple exponential relationships applied only to very limited lower ranges of temperature. The relationship proposed by Bĕlehrádek was a better fit over a wider temperature range, but still excluded rate‐decline at high temperature.5. The interspecific differences found are of potential significance for restrictions in natural distributions associated with season, altitude (especially above 500 m) and latitude.

Phytoplankton successions under ice cover in four lakes located in north-eastern Sweden: effects of liming.

Phytoplankton successions under ice cover (January-March) were determined in four oligotrophic lakes (Burtjärn, Aspen, Vialamptjärn and Storkorstjärn) located in North-Eastern Sweden. The total phosphorus concentration in the lakes was less than 10 micrograms/L. Lake Burtjärn (reference lake) had a similar hydrology as Lake Aspen. Storkorstjärn and Vialamptjärn were of similar hydrology and had heavily colored water (> 100 mgpt/L). Aspen as well as vialamptjärn became continuously limed with calcium carbonate annually during the last decades. Biodiversity was considerably higher in the limed lakes (Aspen and Vialamptjärn) than in the untreated lakes (Burtjärn and Storkorstjärn). In Lake Burtjärn the most frequent species were Rhodomonas lacustris, Tabellaria flocculosa and Botryococcus braunii. Cryptophyceae (R. lacustris and Cryptomonas marssonii) and Dinophyceae (especially Gymnodinium lantzschii) were common phytoplankton groups in Lake Aspen. Tabellaria flocculosa was also the most common organism in both humic lakes Storkorstjärn and Vialamptjärn, other phytoplankton groups were in the humic lakes scarce. Liming was found to have profound effects on phytoplankton communities studied.

Diel Vertical Distribution of Phytoflagellates in a Small Artificial Pond

Diel vertical distribution of phytoflagellates and interactions between the phytoplankton components and environmental and biological factors were studied in a small artificial pond for three days on the December 18, 1998 and April 9 to 10, 1999. The phytoplankton population was dominated by Mallomonas akrokomos of chrysophytes and Cryptomonas marssonii and Chroomonas sp. of cryptophytes. The vertical distribution of these phytoflagellates taxa exhibited clear diel migration pattern. Moreover their migration patterns are showed differential fluctuation between M. akrokomos, C. marssonii and Chroomonas sp. The later two species upward migrated in the evening as well as night, whereas the former species migrated downward. Their distinctive migration pattern was found during the night but was not observed in the morning. During daytime C. marssonii and Chroomonas sp. showed maximum density above 2 m depth but M. akrokomos below 2 m depth. The diel vertical distribution of the dominant phytoflagellates did not show significant correlation between physical, chemical and biotic factors.

Structure and variation of the Paraguay River phytoplankton in two periods of its hydrological cycle

The structure and distribution of the Paraguay River phytoplankton (between 16° 03′ and 26° 53′ S and between 57° 13′ and 58° 23′ W was studied during June–July/95 and December/95–January/96. Phytoplankton density values were lower in winter (mean value between 731 and 878 ind. ml−1) in summer (between 1113 and 1876 ind. ml−1), and mean biomass (biovolume) ranged between 0.215 and 0.372 mm3 l−1 and between 0.586 and 1.223 mm3 respectively. In all, 332 algal taxa were identified: 298 in the upper section (Pantanal) and 143 in the middle and lower sections. They pertained to the Cyanophyta, Chlorophyta, Euglenophyta, Cryptophyta, Pyrrhophyta, Bacillariophyceae, Chrysophyceae and Xanthophyceae. Small Chlorophyta (Chloromonas gracilis, Choricystis minor, Crucigenia quadrata, Scenedesmus ecornis, Monoraphidium contortum and M. minutum) and Cryptophyta (Cryptomonas marssonii, C. ovata and Rhodomonas minuta) dominated. Bacillariophyceae (genera Aulacoseira and Cyclotella) increased in the lower section of the river. Biomass was dominated by centric forms of the genus Aulacoseira (A. granulata and its morphotypes, and A. herzogii). The diversity index varied between 1.99 and 5.0 bits ind.−1 in winter and between 1.49 and 4.87 bits ind.−1 in summer. Species richness (between 4 and 105 taxa per sample) showed a decrease in north–south direction. The presence of one of the largest wetlands of the world may explain the high algal diversity in the upper section. The Bermejo River, with highly mineralized waters and a high content of suspended solids, causes a strong discontinuity in the lower section of the main course, viz, a decrease in water transparency and in the density, biomass, diversity and species richness values of phytoplankton, before its waters meet the Parana River.

Phytoplankton and water chemistry of several alluvial pools and oxbows after the flood event - a process of diversification

The process of diversification of six small floodplain pools after the flood event was investigated in the Lužnice river, floodplain, South Bohemia, Czech Republic. Water chemistry and the rapid phytoplankton development were studied in the spring for one month. Large ecosystem diversity of floodplain lentic localities is maintained by following factors: (i) different disposition of locality towards the flooding, (ii) different level of shade, caused by terrestrial vegetation and (iii) different Water basin morphology Phytoflagellate bloom (250 μg.l -1 chlorophyll a, Cryptomonas marssonii, Rhodomonas lacustris) developed in the shallow place of overflooded floodplain before its separation from the river. This bloom was horizontally heterogenous, having its maximum density in places protected from direct water current. After the separation of studied pools, their mutual differences rose: underground water from the river terrace, rich in NO 3 - , Cl - and SO 4 2- , seeped into some localities, while others were supplied by only river water, seeping through the permeable floodplain sediments. Different level of shading by surrounding vegetation resulted in different oxygen regime: oxygen concentration decreased in shaded pools, where photosynthesis was restricted. Only species-poor flagellate communities (Cryptophyceae), tolerant to low light intensities, developed there. On the other hand, high phytoplankton biomass (1200 μg.l -1 of chlorophyll a) developed in unshaded and shallow pools. Phytoplankton was dominated by Cryptophyceae, but also represented by Chrysophyceae and coccal forms (especially Chlorococales) in these pools. Hence, the water was well oxygenated there. The decrease ofwater level, typical for this spring time, enhance the role of bottom sediment processes in the whole pool ecosystem. The remarkable dominance of Cryptophyceae group in almost all localities seem to be related generally to the poor-light conditions and stable unmixed water column of pools. These characteristics are suitable for this mobile, low-light tolerant, and rapidly growing flagellates.

Diurnal vertical migration study during a winter bloom of Cryptophyceae in a floodplain pool

AbstractThe diurnal vertical migration (DVM) of the phytoplankton community was studied in a small (270m2), shallow (1.8m), and frozen floodplain pool. Steep vertical gradients were detected in O2, NH4+‐N, NO3−‐N and PO43‐‐P profiles. The phytoplankton of the pool is characterized by year round dominance of Cryptophyceae: Cryptomonas curvata and Cryptomonas marssonii created more than 90% of total phytoplankton biomass during the time of study. DVM was studied by analysing vertical profiles six times during a 24 hour cycle; samples were taken at 20 cm intervals along the profiles. Koliella planktonica, the only non‐motile alga, showed a stable uniform distribution. Dinobryon divergens and Chrysococcus rufescens created a stable distinct concentration maximum at 40cm. Unlike these three species, both Cryptomonas spp. actively changed their position during the 24 hour cycle with distinctive evening downward and morning upward migration. The absence of filtering zooplankton excluded its influence on the patterns of phytoplankton DVM. The results showed the key role of PhAR (Photosynthetic active irradiance) in day ‐ positioning of Cryptomonas. Night‐time uptake of phosphate and/or ammonium at the bottom is probable, although direct evidence is lacking.

Observations on some new and interesting Cryptophyceae

Three new varieties and two new combinations of marine Cryptophyceae are described: Proteomonas pseudobaltica comb, nov., P. pseudobaltica var. leonardiana var. nov., Pyrenomonas salina var. curvata var. nov., Rhinomonas reticulata var. atrorosea comb, et stat. nov., and R. reticulata var. compressa var. nov. Proteomonas is compared to the freshwater Cryptomonas marssonii. Planktonic specimens collected from the southern North Sea during the NERC North Sea Project 1988/89, tentatively identified as Cryptomonas acuta and Plagioselmis sp., are also examined. Characters having taxonomic significance at various levels include cell compression, periplast features, chloroplast number, nucleomorph position, and phycoerythrin type. Comments are made on cell shrinkage occuring during preparation for scanning electron microscopy (up to about 23%). The appearance af trie vestibular region from which the flagella emerge is also discussed. It is suggested that the term ‘furrow’ may encompass a variety of structures. Of these, only one appears to be non‐artefactual; this seems to be taxonomically significant at most at the species level.

Seasonal and spatial distribution of cryptophycean species in the deep, stratifying, alpine lake Mondsee and their role in the food web

Quantitative data are presented on the depth-time distribution of four cryptophycean species (Cryptomonas marssonii, C. cf. ovata, C. pusilla and Rhodomonas minuta var. nannoplanktica) over a three year investigation period in Mondsee, Austria, a deep, stratifying alpine lake. Net rates of population increase and decrease are calculated and related to environmental variables (temperature, light, turbulence) and impact by herbivorous zooplankton. Although cryptophyceans rarely comprise more than 15 – 20% of total phytoplankton biovolume they contribute considerably to plankton community dynamics.

Seasonal variation in the diel vertical distribution of the migratory alga Cryptomonas marssonii (Cryptophyceae) in a small, highly humic lake

The diel vertical distribution patterns of a migratory alga Cryptomonas marssonii in a small, steeply stratified humic lake were investigated during a summer season (10 diurnal experiments between May and September) using a close-interval Blakar-type sampler. The results indicate that the cells were phototactic; they were typically concentrated at the surface or subsurface during daylight, while in darkness the highest densities were recorded in deeper water, usually near the upper limit of anoxia. During a dense blue-green bloom in August the cells of C. marssonii were also concentrated by day into the same water layer, where oxygen was depleted. However, the cells seemed to avoid totally anoxic water. Because the vertical distribution pattern of C. marssonii had special diurnal and seasonal characteristics, care is needed when designing a sampling programme for a phytoplankton population dominated by this species.

AN ULTRASTRUCTURAL SURVEY OF CRYPTOMONAD PERIPLASTS USING QUICK‐FREEZING FREEZE FRACTURE TECHNIQUES1

ABSTRACTA quick‐freezing technique for freeze fracturing was used to determine periplast plate types in 20 cryptomonads. With this technique cells are frozen so rapidly that major artifacts are eliminated. We propose that periplast plates are attached to the cell membrane by intramembrane particles (IMP's), consequently plate shapes are outlined by IMP distribution in fractured membranes. Round to oval, sometimes slightly angular, plates occur in Cryptomonas ovata, Cryptomonas tetrapyrenoidosa, Cryptomonas parapyrenoidifera, Cryptomonas obovata, Cryptomonas erosa and two unidentified species of Cryptomonas; large rectangular plates occur in Chroomonas pochmannii, Chroomonas coerulea and Hemiselmis sp.; small rectangular plates were found in Cryptomonas sp. (Strain SDB); square to slightly rounded plates occur in Cryptomonas chrysoidea and a single continuous plate or sheet, perforated by ejectisome pores, was observed in Cryptomonas caudata, Cryptomonas rostratiformis, Cryptomonas marssonii, Cryptomonas platyuris, Cryptomonas curvata, Cryptomonas ozolini, Chilomonas paramecium and Rhodomonas sp. Oval and square plates are described for the first time in Cryptomonas. Plate IMP's may be morphologically modified in size and shape, depending upon their location in relation to the plate, the plate ridges, and ejectisome chambers. Conformational changes in plate shapes, to form hexagons or polygons, may be induced when cells are subjected to fixation, desiccation, cryoprotectants or centrifugation.

Hypolimnetic phosphorus retrieval by diel vertical migrations of lake phytoplankton

SUMMARY. I. Movement of 33P from hypolimnion to epilimnion in a small, dystrophic lake was investigated using small‐diameter experimental tubes enclosing thermally stratified water columns. This approach was made possible by the extremely sharp stratification found in such lakes, in which the euphotic zone closely coincides with the epilimnion.2. The vertical distribution of inorganic phosphorus in the lake showed a sharp increase across the thermocline so that enhanced concentrations were available to phytoplankton just below the thermocline. Inorganic nitrogen concentrations did not show such a marked relation to thermal stratification.3. One abundant motile alga (Cryptomonas marssonii) showed striking and regular vertical migrations in the lake, moving below the thermocline at night and returning to the surface waters in early morning. These migrations took cells across a 10°C temperature gradient. Non‐motile phytoplankton showed constant vertical distributions.4. In the experimental tubes an upward movement of phosphorus took place from hypolimnion to epilimnion which was only attributable to transport by phytoplankton cells undertaking active vertical migrations. No equivalent movement of phosphorus occurred in control tubes from which algae were absent.5. The possible significance of such nutrient retrieval is discussed with reference to plankton phosphorus budgets and competition between phytoplankton species.