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Lake Tovel (Italian Alps, Brenta Dolomites, 1178 m a.s.l.), with a dimictic mixolimnion, is a meromictic and oligotrophic mountain lake, once notorious for the summer reddening of its waters due to dinoflagellate blooms that ceased suddenly in 1964. Since 1997 the Museo Tridentino di Scienze Naturali has been carrying out in situ experiments in order to understand the factors regulating the blooms. Experiments were carried out in different types of enclosures to test the reaction of phytoplankton to phosphorus enrichment and light reduction, with special reference to Glenodinium sanguineum Marchesoni, the dinoflagellate responsible for the reddening. The aim of the present contribution is to study the ecology of other flagellate algae typical of Lake Tovel, by analysing the data from the enclosure experiments. Particular attention is given to competition for resources, the comparison with G. sanguineum and some interesting taxonomic observations. The four flagellate taxa selected for this investigation were Gymnodinium uberrimum (Allman) Kofoid & Swezy, Dinobryon cf. sociale var. americana (Brunnthaler) Bachmann, Campylomonas sp. and Tetraselmis sp. Number of individuals and biovolume calculated for each taxon during the experiments were statistically related to NO3-N and TP concentrations, water temperature, pH and oxygen saturation. A prompt and positive response to P-enrichment was found in all experiments for both G. sanguineum and G. uberrimum. However, the first taxon showed a pronounced development only when nutrients were coupled with high light intensities, while the latter appeared to be a better competitor in low light intensities and low water temperature. The behaviour of Tetraselmis sp. was similar to that of G. sanguineum, while the development pattern of Campylomonas sp. was similar to that of G. uberrimum. D. sociale did not show a clear relationship either to nutrient enrichment or weather conditions.

Long-term phytoplankton responses in Lake Geneva to a decline in phosphorus (P) loading are examined in terms of summer (July–September) biomass and community structure. With the rapid development of human activity on its banks and within its catchment area in the 1960s, this large subalpine hydrosystem shifted from oligotrophy to eutrophy within approximately one decade. Measures to reduce P loading were initiated successfully in the mid-1970s, when total P concentrations in the winter overturn altered from 90 μg/L in 1980 to 40 μg/L in 1998. Until the 1990s, algal descriptors improved as expected (biomass decline, reappearance of diatom species, increased contribution of nanoplankton). Then, paradoxically, and in contrast to the reappearance of oligotrophic species, summer algal biomass began to increase. Pre-summer (period prior to the beginning of the clear water phase) dissolved inorganic phosphorus concentrations and summer phytoplankton composition presented similar interannual trends. However, the succession of phytoplankton structure during the reoligotrophication phase differed greatly from that during the eutrophication period, and a recent abnormal upward trend in algal densities is mainly the result of the development of large species that formerly were only common from late September until November. This community change, mainly triggered by filamentous (Mougeotia gracillima, Tribonema) or motile forms (Dinobryon sociale, Cryptophycea), seems to have been induced by the earlier and greater deepening of the P-depleted layer. In addition to milder summers, this massive development of larger forms seems to be favoured by four of their biological features: tolerance to warm temperatures, tolerance to low-light intensity (might exploit deeper layers where P is not yet limiting), shapes not only providing a large surface to volume ratio or motility (adaptation to low-nutrient concentrations), but increasing resistance to zooplankton grazing. This paradoxical trend, perhaps reinforced by the decline on roach Rutilus rutilus abundance (an opportunistic planktivore), is likely to remain until the P-depleted zone is extended below the layers that can be frequently resupplied in nutrients by hydrodynamic processes.

Vieux-Pre is an artificial reservoir in the north-east part of France (61 Mm3), created in 1986 for hydraulic management. The phytoplankton and several environmental parameters in the upper part of the lake were monitored at a mid-lake station, from 1988 to 1997. The specific composition of the community changed during this period, from a predominantly pennate-diatom phytoplankton (Asterionella formosa, Fragilaria crotonensis), the lake passed to dominance by a sparse, motile nanoplankton (Mallomonas akrokomos, M. caudata, Cryptomonas erosa, Chroomonas/Rhodomonas, a.o.) and then by large colonies of small-celled species (Uroglena americana, Dinobryon spp., Radiocystis geminata, Aphanothece clathrata, Coelosphaerium kuetzingianum a.o.). This paper describes the algal successions involved and shows the decisive effects of the decrease of trophic level from an eutrophic stage to an oligo-mesotrophic condition. In the beginning, externally imposed disturbances (flooding and dewatering) were frequent, while now the lake has stabilised as a deep, stratified pelagic system. Under these conditions, autogenic phytoplankton appear to dominate.

Introduction It is difficult to generalize about the ecological tolerances and distributions along environmental gradients of a group of organisms as large and diverse as the chrysophytes. Many excellent floristic papers lack quantitative ecological data, while others provide ecological data but lack critical microscopical detail. There are many more detailed studies pertaining to the scale-bearing forms than for non-scaled taxa. Thus, we know more about the forms with scales and have much to learn about the non-scaled species. In addition, many methodologies have been used by the different researchers to assemble their data. Despite the apparent obstacles, many generalizations have been made for the chrysophytes as a group as well as for specific and subspecific taxa. Although there is much scattered information concerning the ecology of the chrysophytes (Kristiansen 1986; Siver & Hamer 1989; Siver 1991), especially for individual taxa, there are few comprehensive studies (Kristiansen 1986; Hartmann & Steinberg 1989; Wee & Gabel 1989). Sandgren (1988) provided an excellent review of the ecology of the group as a whole. Siver (1991) and Eloranta (1989 b ) summarized ecological tolerances for many taxa of Mallomonas and Dinobryon , respectively; however, similar works are lacking for most other common genera. Kristiansen (1986) and Smol (1986, 1990, this volume) provide excellent starting points for the use of the chrysophytes as biological indicators and in paleolimnological work, respectively.

Introduction Consideration of the nutrition of chrysophytes from a biochemical or biophysical viewpoint in comparison with that of other algal taxa has become relatively more difficult over the years. This is not necessarily a function of laxness in using presumptive chrysophytes for such work, but rather that many of the more widely used genera are now classified in other major taxa. The most obvious examples are the separation of the class Prymnesiophyceae, with such nutritionally well investigated genera as Emiliania, Isochrysis and Pavlova , and the recognition that Olisthodiscus (Heterosigma) , a molecular-genetically and cell-biologically well understood organism, is probably a chloromonad (raphidophyte) (Heywood 1989; Patterson & van Valkenberg 1990). Even fewer data would be available if the chrysophytes sensu stricto were considered in the absence of the recently separated Synurophyceae. However, both of these classes (Chrysophyceae and Synurophyceae) are considered here, as are recently discovered marine picoplanktonic chrysophytes (Anderson 1987; Shapiro et al . 1989; Keller & Rice 1989), giving a range of organisms from marine picoplankton, through the more familiar freshwater unicells and colonies, to the large benthic freshwater Hydrurus . To be more positive, there is a substantial body of data on various aspects of nutrition in the chrysophytes. We start by considering the evidence as to the ratio of major nutrients found in chrysophytes growing at their maximum specific growth rates, their qualitative allocation to different molecular species, and the mechanism of synthesis of these molecular species from such common intracellular substrates as hexose, ammonium and phosphate.

The influence of several environmental factors (e.g., light intensity, temperature, nitrogen, and phosphorus) on population density and odor-compound production of two chrysophytes, Synura petersenii and Dinobryon cylindricum ; and two cyanobacteria, Anabaena laxa and Phormidium calcicola was investigated. The odors associated with each alga were evaluated by flavor profile analysis (FPA) at several intervals during their initial culturing in defined media. Algal cell and media extracts were analyzed individually by capillary gas chromatography-mass spectrometry (GC-MS). Both cyanobacteria produced geosmin (“earthy” and “corn” odors); however, the P. calcicola also produced relatively large amounts of MIB (“musty-earthy” odors). Both chrysophyte cultures contained 2t,4c,7c-decatrienal (“fishy” odor); and in addition, 2t,6c-nonadienal (“cucumber” odor) was isolated from the S. petersenii . Young cultures of Anabaena laxa (e.g., P. calcicola was detected in the media rather than in the cells. Synura petersenii ,produced more 2t,4c,7c-decatrienal than 2t,6c-nonadienal and retained nearly 90 percent of both compounds throughout the algal population growth. Dinobryon cylindricum produced 2t,4c,7c-decatrienal, and, like the S. petersenii , retained most of the compound. Greater production of the compounds by the two chrysophytes was apparently associated with log-phase growth rather than specific environmental conditions; extended log-phase growth (and prolonged production of compounds) was observed in the S. petersenii culture during the low-temperature treatment.

Mixotrophic algae are algae that combine photosynthesis with phagotrophy to satisfy nutritional requirements. Mixotrophic algae have been found to dominate the nanoplankton assemblage in some aquatic environments, and algal phagotrophy can account for a significant fraction of total bacterivory on occasion. The distribution and abundance of mixotrophic algae have not been widely characterized, however, and the factors that control their abundances and phagotrophic activity in aquatic environments are poorly understood. The vertical distribution and abundance of mixotrophic nanoplankton was therefore documented in a variety of aquatic environments including the oligotrophic open ocean (Sargasso Sea), nine freshwater seepage ponds (Adirondack Mountains, NY) and three coastal salt ponds (Falmouth, MA) using epifluorescence microscopy and fluorescently labeled prey to trace ingestion by algae. Field experiments designed to examine the influence of prey density, nutrient availability and light intensity on mixotrophic nanoplankton abundances and their phagotrophic activity were also carried out to examine the adaptive significance of phagotrophy for mixotrophic algae in surface waters of the Sargasso Sea and in the epilimnion of one freshwater seepage pond. Mixotrophic nanoplankton abundances in the Sargasso Sea ranged from less than a few cells mi-l to more than 140 cells mi-l, and they were more abundant in surface waters. On two occasions rnixotrophic algae comprised more than 50% of the total algal nanoplankton assemblage in surface waters. The results of field experiments indicate that phagotrophy may provide mixotrophic algae in surface waters of the Sargasso Sea with major nutrients and may enable them to compete with purely phototrophic algae during periods of low nutrient concentrations. Mixotrophic nanoplankton abundances comprised a small fraction of the total algal nanoplankton (

19 pages, 6 figures, 3 tables, The mixotrophic (bacterivorous), freshwater chrysophyte Dinobryon cylindricum was cultured under a variety of light regimes and in bacterized and axenic cultures to investigate the role of phototrophy and phagotrophy for the growth of this alga. D. cylindricum was found to be an obligate phototroph. The alga was unable to survive in continuous darkness even when cultures were supplemented with high concentrations of bacteria, and bacterivory ceased in cultures placed in the dark for a period longer than one day. Axenic growth of the alga was poor even in an optimal light regime. Live bacteria were required for sustained, vigorous growth of the alga in the light. Carbon (C), nitrogen (N), and phosphorus (P) budgets determined for the alga during growth in bacterized cultures indicated that bacterial biomass ingested by the alga may have contributed up to 25% of the organic carbon budget of the alga. Photosynthesis was the source of most (≥75%) of the organic carbon of the alga. D. cylindricum populations survived but did not grow when cultured in a continuous low light intensity (30 μE m-2 sec-1), or in a light intensity of 150 μE m-2 sec-1 for only two hours each day. Net efficiency of incorporation of bacterial C, N, and P into algal biomass under these two conditions was zero (i.e., no net algal population growth). We conclude that the primary function of bacterivorous behavior in D. cylindricum may be to provide essential growth factor(s) or major nutrients for photosynthetic growth, or to allow for the survival of individuals during periods of very low light intensity or short photoperiod. © 1993 Springer-Verlag New York Inc

Ochromonas sensu lato is the largest genus in the Chrysophyceae, containing over 100 names. Ochromonas species are biflagellate, naked, plastid-bearing single cells, distinguished from loricate, scaled, colonial and colorless genera. Most, if not all, species of Ochromonas are mixotrophic, i.e., they photosynthesize but they also engulf bacteria and other small prey. Preliminary evidence from SSU rRNA sequences show that Ochromonas is a polyphyletic genus. Ochromonas tuberculata is the most distinct from all other Ochromonas species. The other Ochromonas species (examined thus far) are scattered in three clades. For example, O. danica and O. sphaerocystis are sister to Poterioochromonas stipitata and P. malhamensis. Four additional species (identified by light microscopy as O. elegans Doflein, O. globosa Skuja, O. ovalis Dolfein, O. sociabilis Pringheim) have SSU rRNA sequences identical to P. malhamensis. Of these, only O. sociabilis has been transferred to Poterioochromonas. Thus, at least some species may be synonymous with others. Two clades of marine species are also known, one containing coastal species and the other containing open ocean species. A number of genera (some also polyphyletic) are interspersed amongst the Ochromonas species (e.g., Chrysolepidomonas, Chrysonephele, Chrysoxys, Cyclonexis, Dinobryon, Epipyxis, Uroglena, Uroglenopsis). The goal of this research (just beginning) is to establish a monophyletic Ochromonas, probably by assigning some species to other genera (existing or new). One major problem is that the type species, O. triangulata Vysotskii, hasn't been observed in over 100 years, and it is unclear which of several clades of Ochromonas contains the type. Results will be discussed.

The development of phytoplankton assemblages in the two main basins of the deep (Zmax=350 m) and large (49 km3) subalpine Lake Garda (Northern Italy) was investigated through monthly samplings from 1998 to 2000. The algal development was strongly typified by the alternation, from spring to autumn, of Fragilaria crotonensis and Mougeotia sp. and by the increasing importance of filaments of the complex Planktothrix rubescens/agardhii in summer and autumn. These three “master species” are characterised by higher biovolumes and/or more regular and wide annual development in comparison to the other dominant taxa. The simultaneous application of ordination (NMDS-Non metric Multi Dimensional Scaling) and cluster analysis techniques revealed an ordered and coherent temporal succession of phytoplankton assemblages in the two main basins of the lake. These temporal and spatial regularities arise from the high inertia and resilience against perturbations that characterise the deep and large lakes, and contrast sharply with the less ordered or chaotic and unpredictable seasonal assemblages that may be found in small and shallow lakes. It is stressed that, owing to the use of different methodologies, the modifications of the phytoplankton assemblages in the last fifty years must be interpreted with particular caution. The only demonstrable differences seem to indicate that, with the speeding up of eutrophication processes in the 1960s and 1970s, detectable populations of Planktothrix and irregular increases of Conjugatophyceae (Mougeotia sp., Closterium aciculare) were established. During and after the 1980s, the increase of phosphorus concentrations in the lake and the progression towards more mesotrophic conditions was accompanied by the appearance of further substantial populations of cyanobacteria (Planktolyngbya limnetica, Anabaena lemmermannii). In contrast with these signs of alteration, Fragilaria crotonensis, Asterionella formosa, Ceratium hirundinella and Dinobryon spp. were among the most abundant taxa from the 1950s to the present time. These modifications are largely consistent with the changes observed during the 1990s in consequence of the different extent of the deep vertical mixing. During complete overturn, with the maximum spring replenishment of nutrients in the euphotic layers, a greater development of Mougeotia sp. and Oscillatoriales was observed. The historical trend and the ecological results allowed elucidation of the trophic characteristics of many important species developing in Lake Garda and, in general, in the deep subalpine lakes.

Unusually large virus-hke particles (VLPs) with tails were found in water samples from Norwegian and Danish coastal waters. Size of the VLP heads were 340 to 400 nm and the tails were 2.2 to 2.8 vm long. The VLPs occurred at a maximum concentration of about 104 ml-'. The possible hosts are unknown. Most viruses measure between 20 and 350 nm (Bitton 1980). The largest are found among the animal viruses and the smallest among the plant viruses and the bacteriophages. Filamentous viruses may be as long as 1000 nm or longer, but the diameter of these viruses is 10 nm or less (Bradley 1967, Laskin & Lechevalier 1973). The viral population of natural marine waters is dominated by forms with heads < 60 nm in diameter (Bergh et al. 1989). Most of these small viruses are thought to be bacteriophages (Bratbak et a1 1990). Viruses in the size range of 100 to 150 nm usually make up < 1 to 10 % of marine viral communities. Water samples in w h c h we observed unusually large virus-like particles (VLPs) were collected at 0.2 m depth in Raunefjorden, western Norway in April 1991 (Bratbak et al. 1990) and during a mesocosm experiment in Knebelvig, Denmark in July 1991 (Nybroe et al. 1992). The mesocosm experiment was set up in the beginning of July and sampled every 2 or 3 d for 3 wk. Samples preserved with 1 O/O glutaraldehyde were harvested by centrifugation onto electron microscope grids, stained with 2 % uranyl-acetate, and inspected in a JEOL100CX transmission electron microscope as previously described (B~rsheim et al. 1990, Bratbak et al. 1990). The VLPs (Fig. l a ) we observed in the mesocosm experiment were found in 2 of the 4 enclosures investigated. A maximum concentration of ca 104 ml-' was observed on Day 5 of the experiment. The particles were also found in the sample taken 3 d later, but not in earlier or later samples. The head structure of the particles appears to have an octahedral form and the size of the head, as it appears on the electron micrographs, was 370 nm (SD = 17) X 340 nm (SD = 12). The tail structure was ca 2.2 pm (SD = 0.3) long and 80 to 85 nm wide. The VLP found in the free water masses of Raunefjorden was similar in morphology to the VLP found in the enclosure study (Fig. lA , B) but the head structure was slightly larger (400 X 370 nm) and the tail structure was about 2.8 pm long and 55 to 60 nm wide. The only comparable VLP we know of has a head diameter of 390 nm and a tail of about 1 pm and has been found in cultures of the filamentous green algae Uronema gigas (Dodds & Cole 1980). Fig. 1. Transmission electron micrograph of the unusually large virus-like particles. (A) Sample from mesocosm experiment in Denmark; (B) sample from Raunefjorden, Norway. Arrow: virus-like particles of a more typical size (< 100 nm); b: bacterium O Inter-Research 1992 0171-8630/92/0085/0201/$ 03.00 202 Mar. Ecol. Prog. Ser. 85: 201-202, 1992 Compared to microorganisms such as bacteria and flagellates, viruses will generally appear as electrondense structures after positive staining with uranylacetate due to their high nucleic acid content. As shown in Fig. 1A. B the large VLPs have a high electron density in the head structure. We do not know of any biological or non-biological structure that gives a similar appearance after this preparation and we therefore assume that these particles are indeed viruses. The host of the viruses found in the enclosure study must be a planktonic organism because they were produced within the enclosures where only planktonic organisms were present. The size of these large viruses limits the number of possible host organisms. The viruses we observed resemble tailed bacteriophages but the size of the bacteria (Fig. 1) found together with the viruses makes them unlikely hosts. The eucaryotic community found together with the virus in the enclosure study was numerically dominated by unidentified autotrophic and heterotrophic forms that were 1 to 5 pm in diameter. The most abundant larger phytoplankton forms included the diatoms Rhizosolenia fragilissima and Probiscia alata; some unidentified cryptophyceans; some dinophyceans (including Gymnodim.um sp. and Scripsiella sp.); and the chrysophyceans Dinobryon balticum and D. petiiolatum. The most abundant protozoans included colorless flagellates, and the ciliates Urotricha sp., Strombidium spp., and Mesodinium rubrum. The roles of viruses in natural waters have just begun to be revealed and we are still groping to find our way with new methods and approaches. Our observation of the large VLP is mainly qualitative and its host is unknown. The finding does emphasize that the choice of method for detecting and counting viruses may be crucial. Large viruses such as those described here would probably have been lost if any prefiltration had been applied (Cottrell & Suttle 1991, Paul et al. 1991) and they would probably have been considered small bacteria if they had been observed in the epifluorescence microscope after staining with DAPI (Hara et al. 1991). This note was submitted to the editor Acknowledgements. This study was supported by the EEC MAST program, contract no. 0020, the Danish Natural Research Council, Danish Technical Research Council (J.-nos. 11-8630 and 16-4806), National Agency of Environmental Protection in Denmark (HAV9O Marine Research Programme in Denmark contract no. 1.23), the Royal Norwegian Council for Scientific and Industrial Research (contract 27744), the Norwegian Council for Fisheries Research, and the Norwegian Council for Science and the Humanities. The electron microscope work was done at the Laboratory for Electron ~Microscopy, Science Faculty, Univ. of Bergen.

Jöri Lake III (2512 m a.s.l., zm = 22 m, A = 57.81 ´ 103 m2, V = 601.1 ´ 103 m3) is situated in the Vereina region in the eastern part of the Swiss Alps. We studied microbial grazing on bacteria and bacterial productivity during the ice-free period. The lake normally gets thermally stratified for two months between July and September. In 1996, chlorophyll-a concentrations varied from 0.5 to 2.0 μg l-1 with maximum values just below the thermocline (6 m depth), in 1997, they were between 0.6 and 5.0 μg l-1 with maximum values at 10 m depth – several meters below the thermocline. Bacterial densities varied between 0.7 and 1.7 ´ 106 ml-1 with maxima in the thermocline, one to two meters above the chlorophyll maximum. The areal bacterial biomass (volume beneath 1 m2 to a depth of 8 m) was 10 μg C l-1 which remained more or less constant for the periods investigated. In 1997, bacterial growth rate and production rates were determined using [3H]-thymidine incorporation. The rates were as low as 0.002 to 0.006 h-1 and 0.01 to 0.03 μg C l-1 h-1, respectively. We found a carbon ratio of bacteria, phytoplankton, and autotrophic picoplancton (APP) of 1.5:1.1:1 which shows a rather high abundance of bacteria and autotrophic picoplankton (APP) compared to larger phytoplankton. Bacterial growth followed a temperature dependence similar to the one observed for bacteria from Lake Zürich, a prealpine and mesotrophic lake which was studied for comparison. Microbial food web in Jöri Lake III was not top down controlled during the periods of our study and mixotrophic algae like Dinobryon cylindricum var. alpinum and autotrophic nanoflagellates (ANF) were the dominant bacterial grazers observed.

Myvatn, Iceland, is the only lake in the world where diatomite is dredged commercially. Although we anticipated an enormous production ofplanktonic diatoms at the peak of the summer production cycle in mid-July, upon analysis of our samples, we realized that less than 5% of the phytoplankton standing crop was composed of diatoms. Benthic, rather than planktonic diatom species, appeared to be the key primary producers in the lake. The phytoplankton assemblage was dominated by Chlorophyta (green algae), Cyanophyta (blue-green algae), and Chrysophyta (yellow-green algae). The relative absence of planktonic diatoms in this shallow lake (mean depth less than 2.5 m) was associated with the presence of dense stands of macrophytes, which appeared to limit local turbulence. The spatial heterogeneity in phytoplankton abundance and species composition was correlated with the spatial distribution of nutrients in this volcanic spring-fed lake. Phytoplankton abundance was highest where warm spring waters from the north basin flowed into the eastern channel and mixed with the cold spring nutrient-rich waters coming from the southeastern corner of the lake. Intermediate nutrient levels were found in the center of the lake where relatively high phytoplankton standing crops of chrysophytes (Chrysochromulina and Dinobryon), cyanophytes (Anabaena and Gloeocystis), and colonial chlorophytes (Sphaeorocystis, Oocystis, and Pediastrum) developed during the annual phytoplankton production peak. During this midsummer peak in primary production, nitrogen, rather than phosphorus appeared to be the "limiting" nutrient.

In ice-free seasons, phytoplankton production in subalpine Eastern Brook Lake, Sierra Nevada, California, ranged from 11.9 to 61.4 tig C L-1 d-1. Integrated production ranged from 40 to 235 mg C m-2 d-1 and yearly values would be 23.8 gC m-2 yr-1 (1986) and 22.4 gC m-2 yr-1 (1987). These values were in the middle ranges of those for other north-temperate, high-elevation lakes. Photosynthetic efficiencies were 0.016 to 0.103% and were similar to those in other subalpine lakes. Near-surface chlorophyll (ice-free season) ranged from 1.46 to 2.62 A~g L-1 but approached 25 tAg L-1 under the ice (winter 1987). Ice-free season chlorophyll values in Eastern Brook Lake were similar to those for other Sierra Nevada lakes except Lake Tahoe (lower values), but were generally higher than estimated values for other lakes. Dominant genera (ice-free season) were Chlorella or Disphora. Other genera were dominant in other lakes. Under the ice (1987) a massive bloom of the Chrysophyte Dinobryon occurred; a similar winter bloom was reported for a Colorado lake. Bacterial production ranged from 3 to 19 tug C L-1 d-~ and was similar to that in Austrian alpine lakes, but greater than that for a Norwegian mountain lake. Bacterial numbers ranged from 0.1 to 5.5 x 109 cells L-' and were similar to those in other mountain lakes. In contrast with other mountain lakes, nutrients were rarely detectable in Eastern Brook Lake and the biota must depend on regeneration. We conclude that Eastern Brook Lake is oligotrophic, not ultraoligotrophic.

Summary During and after the period of icebreaking 1982 20 ponds in the Waldviertel have been explored, as it was done since some years (1977–1981).This time mostly in the northern (Herren-and Kufsteinteich) and northeastern part (Brunn-Teiche).The temperatures of the water oscillated between 2 and 15 °C, the pH-values between 5.1 and 9.5, the alcalinity between 0.10 and 1.20 mval/1 · 1−1. The aspekts of the plankton were dominated by Chrysophytes (55 %), by Cryptomonades (20 %), in some ponds also by Diatomes (15 %).Chlorophyceae (10 %) were coming up. Interesting observationes: various phaenomens of reproduction, isogamous hologamy, zygotes.Cystes in Dinobryon sertularia.Development of Sphaerellopsis lefevrei has been studied. New for the Waldviertel: Pediastrum duplex var.coaherens, Fragilaria feneslrata var.asterionelloides, Katodinium edax, K.musei, Phacus minutus. New for the science: Chloromonas gelatinosa n.sp.and Sphaerellopsis gleocystiformis forma ferruginosa n.f.will be described and discussed.

Contrasting zooplankton assemblages consistently produced different compositional shifts in a phytoplankton community. Two experiments in 120-liter enclosures were used to assess the responses of the algae to two different-sized zooplankton communities. Grazing by a mixture of small copepods, Bosmina longirostris, and rotifers led to increased growth of phytoplankters with greatest axial linear dimensions < 25 pm and ratios of surface area to volume ~2.6, such as Chlamydomonas and Chlorococcales. Larger phytoplankton taxa such as Asterionellafirmosa, Closteriopsis Iongissimus, and Synedra sp. declined in the presence of small zooplankters. In contrast, a mixture of large zooplankters dominated by Daphnia pulex and Diaptomus oregonensis caused declines in phytoplankters with greatest axial linear dimensions ~60 pm and ratios of surface area to volume ~2.75, while larger algae such as Aphanocapsa and Dinobryon increased. Discriminant analyses showed that volume and surface area were the most effective characters for determining the response of algae to grazers. Zooplankton community structure was important in determining the responses of algal assemblages to-grazing.

Simultaneous measurements of inorganic carbon fixation and phagotrophic particle uptake by Dinobryon in a metalimnetic algal abundance peak showed that this alga depended more strongly on ingested bacteria for nutrition than on photosynthesis. Measurements of the grazing rate at different depths in Lac Gilbert, Quebec, showed that the particle ingestion rate depends on water temperature rather than light availability. Phagocytosis of bacteria proceeded at a similar rate both day and night in most lakes where Dinobryon was found. Since other chrysomonad genera (Chlsophaerella, Uroglena, Catenochrysis, Ochromonas, Chromulina, and Chrysococcus) were also found to ingest particles, it will not be possible to estimate grazing on bacteria by counting nonpigmented cells and ignoring those containing chlorophyll. In oligotrophic Lac Bowker, 30% of the phytoplankton cells were actively ingesting small particles, and it was these phytoplankton and not the less numerous zooplankton that were responsible for most bacterial grazing in the lake. Phagotrophy by algae appears to be an important but unexpected pathway for energy flow in lakes. The flagellated Chrysophyceae, or chrysomonads, bear affinities to both plants and animals and have been claimed for study by zoologists as well as by botanists (Allen 1969). Coexistence of autoand heterotrophy in the chrysomonads and the widespread tendency toward complete loss of chlorophyll have fostered the suggestion that these algae may model progenitors of the Metazoa (Provasoli and Pintner 1953). The diversity and versatility of the group are strongly expressed in the genus Uchromonas, which is capable of phagotrophy, heterotrophy, photoheterotrophy, and photoautotrophy (Pringsheim 19 5 5; Aaronson and Baker 1959). However, Ochromonas is ’ This work was supported by a Natural Sciences and Engineering Research Council of Canada operating grant to J. Kalff and an NSERC postgraduate scholarship to D. Bird. A contribution to the McGill Limnology Research Centre, Lake Memphremagog Project. one of only a few chrysomonads to have been studied extensively in the laboratory, and the nutritional capabilities of other chrysomonads are virtually unknown, especially in their natural setting. Pascher (1943) observed under the microscope that the colonial chrysophycean alga Dinobryon could capture and digest small particles, and thus concluded that at least some part of this alga’s nutrition was heterotrophic. This unusual phagotrophic ability was not studied further until the recent discovery that several Dinobryon spp. are not only phagotrophic in nature, but can be major grazers of bacteria in lakes (Bird and Kalff 1986). Here we present further work on four different aspects of the capabilities of this alga: first, the relative importance of bacterivory and photosynthetic carbon fixation to Dinobryon’s nutrition; second, a comparison of day and night grazing rates; third, the relationship of grazing

A new species of Dinobryon is described from Australian freshwaters. It is characterized by distinctive, anteriorly-tapered unguentariform loricae grouped in compact colonies, and by the external attachment of daughter loricae.

The seasonal cycles of abundance of the phytoplankton and zooplankton in Lake Ototoa, Northland, at 36° 31 S, 174° 14 E, are described. Concentrations of chlorophyll a were low (range 0.04–4.61 mg.m‐3; mean 0.97 mg.m‐3), and highest values were in winter. Phytoplankton densities were also low; an oligo‐trophic diatom‐desmid assemblage associated with Botryococcus, Dinobryon, and Svhaerocyslis was found. The zooplankton was dominated by the calanoid copepod Calamoecia lucasi whose numbers remained fairly constant throughout the year, and the only other copepod found was the cyclopoid Mesocyclops leuckarti which was present in very low numbers. Bosmina meridionalis was the only limnetic cladoceran and was most abundant during autumn and spring. A number of rotifer species were also common.

SUMMARY. 1. Differential use of food resources by instars I-1V of Chaoborus punctipennis was examined in a mesotrophic New Hampshire lake during midsummer when all instars coexisted. Diet composition and prey preference were quantified first, at night when all instars were feeding at the same depth, and second, during the day when the early instars (I-II) and instar III were segregated by depth. Relative abundance, per cent biomass, and per cent frequency of occurrence of soft and hard-bodied rotifers, flagellated phytoplankton, protozoans, and crustaceans in C. punctipennis diets were quantified using crop content analyses. 2. All four instars ingested large, flagellated phytoplankton (mainly Dinobryon and Ceratium). This unexpected result suggests that the effects of phytoplankton on Chaoborus growth and survival should be investigated. All instars also consumed rotifers (mainly Kellicottia, Gastropus, Polyarthra), but only instars III and IV fed upon crustaceans (mainly Daphnia, Bosmina and Diaphanosoma). Small rotifers (Gastropus spp., Keratella cochlearis, Trichocerca similis) occurred more frequently and were more abundant in early instar diets than late instar (III and IV) diets, whereas large rotifers (Asplanchna priodonta and Keratella crassa) were eaten only by instars III and IV. Zooplankton with gelatinous sheaths (e.g. Ascomorpha, Collotheca and Holopedium) were rarely ingested. 3. Developmental increase in gape diameter of C. punctipennis seemed to be the major proximate mechanism causing dietary differences among instars. Body widths of hard-bodied prey in C. punctipennis crops were always less than gape diameter. The relationship between prey body width and Chaoborus gape diameter, coupled with knowledge of prey escape behaviour, should be useful for predicting the presence of hard-bodied prey taxa in diets of other Chaoborus species. 4. All four instars of C. punctipennis selected soft-bodied, or weakly loricate, rotifer prey over crustaceans and phytoplankton. Early instars preferred the small rotifer T. similis and the protozoan Difflugia sp. to other rotifers and phytoplankton when feeding in the epilimnion or thermocline during the day or night. Late instars positively selected the rotifer, Asplanchna. Prey value (prey weight ingested per unit handling

The factors influencing the seasonal distribution of phytoplankton were determined between July 1975 and December 1977 in Yellowknife Bay, Great Slave Lake. The initiation of the spring bloom occurred during April of each year in response to changing light conditions and despite the 0 °C water temperatures. Although the plankton showed some fluctuations in density (100–400 mg/m3) during the summer, there was no vernal decrease in the size of the populations. The end of the growing season was characterized by a sharp drop in numbers near the end of October. Multiple regression analysis indicated that changes in the standing crop of the plankton during the summer were primarily related to temperature (r = 0.60) and the concentrations of NO3–N (r=–0.74) and SiO2 (r=–0.82). Changing light conditions probably had little effect on the population during the growing season. Chlamydomonas lapponica was dominant during April of each year. While the growth of this species caused a reduction in the concentrations of total phosphorus and NO3–N, the level of SiO2 remained constant and consequently diatoms (Asterionella formosa, Stephanodiscus astraea, Diatoma tenue var. elongatum and Melosira islandica) waxed rapidly during May. By the first of June, nutrient concentrations were low, thereby permitting the development of Dinobryon bavaricum and Dinobryon cylindricum. The extremely rapid decrease in the densities of common species during the fall was probably due to the rapid decline in temperature and light levels and the formation of ice on the bay.

The ultrastructure of the stigma and associated flagellar-microtubular systems in Dinobryon cylindricum var. alpinum is described in detail and compared with observations on comparable photo-kinetic systems in other chrysophycean organisms. The chloroplastidic stigma of D. cylindricum var. alpinum is shown to lie in a particular positional relationship to the flagellar swelling in the anterior furrow and to several other organelles, to consist of a monolayer of c. 40 pigmented granules, each c. 250–500 nm diameter, arranged in a definite pattern, and to be overlain by several membrane systems. Other cytoplasmic pigmented bodies with dense crystalline contents surrounded by a single “unit membrane” aggregate near the anterior furrow on the side opposite the stigma. The swelling on the proximal portion of the smooth flagellum is separated from the plasmalemma of the anterior furrow by a nearly constant distance of 75–100 nm, has a multilamellate substructure that is linked by fine radiating interconnections...

Evidence is provided for the importance of phagocytosis to mixotrophic chrysophycean algae and to the phytoplankton community as a whole. First, we confirmed the major assumption of past work that the constituents of ingested particles are incorporated efficiently into algal tissue. Cells of the phagotrophic chrysomonad Dinobryon sertularia collected from Lac Gilbert, Quebec, incorporated carbon from radiolabeled bacterial prey with 54% efficiency (95% C.L. = 40-79%) over a 5-h period. When removed from labeled bacteria, the loss of previously incorporated label from Dinobryon was undetectable over a 4-h period. We conclude that this alga’s quantitative utilization of prey tissue is indistinguishable from that of purely heterotrophic organisms. Second, simultaneous measurements were made of phagotrophic feeding and photosynthesis within a highly concentrated layer of chrysomonads (Dinobryon and Ochromonas) in the metalimnion of Lac Gilbert on 3-4 July 1986. Chrysomonad abundance ranged from 300 cells ml-’ at 6 m, to 9,000 at 7 m, and back to < 100 at 9 m. At the 7-m peak, phagotrophy accounted for 79% of algal community carbon assimilation on this overcast day.

In a flooded Fenland brickpit 3 metres deep a 24-hr study (supplemented by other observations in the field and in the laboratory) revealed marked changes with depth and time in oxygen concentration, pH, total carbon dioxide, ammonium, oxidised nitrogen, phosphate and silica; as well as changes in the rate of cell-division and the vertical distribution of phytoplankton (Dinobryon and Peridinium), and the feeding and vertical movement of zooplankton (copepods, Bosmina, Ceriodaphnia, Polyarthra and Keratella). Directional trapping of zooplankton revealed relationships between population density and the intensity of locomotory activity (a relationship subsequently supported by laboratory experiments), and between the rate of change of light intensity and the direction of swimming. Significant temporal segregation of the occupancy of a given level by zooplankters implies interspecific competition. Transient peaks in the concentrations of some nutrients near the surface are tentatively attributed to nutrient release by zooplankters that have fed at depth. Small-scale temporal and spatial heterogeneity of the type described here may help to explain the ‘paradox of the plankton’.

The diet of the freshwater calanoid copepod Epischura lacustris from C2 to adult stage was examined with predation experiments, grazing experiments, and stomach content analyses. There was a transition from an exclusively herbivorous diet in early copepodid stages to an omnivorous diet in adults. Laboratory predation experiments revealed that C2 and C3 were incapable of ingesting Bosmina (0.25–0.35 mm), but from C4 to C6, ingestion rate of Bosmina increased with developmental stage. The order or prey selection for adult Epischura was Bosmina over Diaptomus and Cyclops. Grazing rate on small algae (

Major pelagic carbon pathways, including primary production, release of extracellular products (EOC), bacterial production and zooplankton grazing were measured in oligotrophic Lake Almind (Denmark) and in enclosures (7 m3) subjected to artificial eutrophication. Simultaneous measurements at three days interval of carbon exchange rates and pools allowed the construction of carbon flow scenarios over a nineteen day experimental period. The flow of organic carbon was dominated by phytoplankton EOC release, which amounted from 44 to 58% of the net fixation of inorganic carbon. Gross bacterial production accounted for 33 to 75% of the primary production. The lower values of EOC release (44%) and bacterial production (33%) were found in the enclosures with added nutrients. The release of recently fixed photosynthetic products was the most important source of organic carbon to the bacterioplankton. Uptake of dissolved free amino acids was responsible for 52 to 62% of the gross bacterial production. Thus, amino acids constituted a significant proportion of the EOC. Zooplankton (< 50 µm) grazing on algae and bacteria accounted only for a minor proportion of the particulate production in May. Circumstantial evidence is presented that suggests the chrysophycean alga Dinobryon was the most important bacterial remover. The results clearly demonstrated EOC release and bacterial metabolism to be key processes in pelagic carbon cycling in this oligotrophic lake.

Stomach content analysis of a neustonic marine juvenile white hake (Urophycis tenuis (Mitchill)), revealed the presence of a unusual 0.70 mm bolus, consisting of a freshwater rotifer, Keratella cochlearis, and several species of freshwater phytoplankton: Asterionella formosa, Melosira granulata, Dinobryon bavaricum and Dinobryon cylindricum. Other gut items were typical for the predator during the August period, consisting of various stages of marine calanoid copepods and cladocerans; average prey length was 0.74 mm. The possibility of bolus introduction as a secondary diet component was eliminated; evidence indicated that the particle was ingested in toto. Consideration of a number of alternative mechanisms for bolus acquisition led to the conclusion that the bolus was disseminated via the ballast tank or contaminated freshwater holding tank of a ship. Urophycis tenuis appears to feed selectively on the basis of particle size. Consequently, this type of neustonic predator may be particularly vulnerable to man-made pollution and oil spills.

Summary A sexual reproduction in Dinobryon suecicum var. longispinum in the Wolfsegg-pond, Waldviertel, Lower Austria, is described and studies in Mallomonas reginae, Cryptomonas cylindracea and Dictyosphaerium elegans are discussed.

Six species of Chrysophyceae not previously reported from North America have been found in Ontario lakes: Chrysolykos angulatus (Willen) Nauwerck, Dinobryon tubaeforme Nygaard, Bitrichia ollula (Fott) Bourrelly, Paraphysomonas foraminifera Lucas, P. imperforata Lucas, and P. bandaiensis Tak. The taxonomy of these and related species is discussed relative to observed variations in morphology. It is suggested that they are probably of much wider worldwide distribution, but have been overlooked because of their fragility or their small size.

Factors influencing the consumption of algae and the rate of feeding by the larvae of Heterotrissocladius changi Saether and Polypedilum nebeculosum (Meigen) (Chironomidae: Diptera) were determined from collections made between July 1975 and May 1977 in Yellowknife Bay, situated in the Canadian subarctic. Although both species fed heavily on algae during the summer, few cells were ingested in the winter, coincident with an overall reduction in feeding intensity. H. changi fed primarily on benthic species (Achnanthes minutissima, Achnanthes pinnata, Fragilaria pinnata, Fragilaria vaucheriae, Navicula spp., Scenedesmus spp.) Whereas P. nebeculosum was restricted to planktonic forms (Dinobryon spp., Scenedesmus spp.). The consumption of algae by H. changi depended largely on the density of the microflora in the environment. This factor had little influence on P. nebeculosum and was replaced by size selection, which prevented the ingestion of many planktonic algal species. The importance of algae to both chironomids also depended on the susceptability of certain algal forms to digestion. Temperature generally regulated the intensity of feeding of both H. changi and P. nebeculosum. However, changing day-length initiated heavy feeding during April and May, despite low water temperatures. The depth of water and the organic content of the substrate had no detectable effect on the amount of material in the guts.

Based on 500 quantitative algal analyses from 1971–1980 the seasonal variations of phytoplankton biomass and species diversity have been evaluated in one natural and three fertilized subarctic lakes. Enrichment with P alone did not cause any biomass increase and inhibited dinoflagellates and Dinobryon. Enrichment with N alone stimulated Uroglena and Gymnodinium and the biomass increased. No species were inhibited. Enrichment with both N and P made the biomass increase 50–60 times and the stimulated genera were: Chlorella, Choricystis, Chromulina, Chrysochromulina, Gymnodinium, Monoraphidium, Ochromonas, Spiniferomonas, Rhodomonas and Uroglena. In all fertilized lakes monocultures of chlorococcal green algae finally developed.

Although field studies show inverse correlations between concentrations of dissolved phosphate and abundances of Dinobryon, phosphorus is not toxic even at high concentrations. Species abundance in water of low phosphate concentration may be traced instead to effective mechanisms for phosphate uptake which allow the cells to thrive at low ambient levels of PO.+-P. Half-saturation constants of less than 0.5 ,LLM P04-I? can be demonstratcd both in laboratory cultures and in situ in lakes. Ambient concentrations of potassium ion can be toxic to a variety of species of Dinobrzpn and thus can limit both their geographical and seasonal occurrcncc. Ammonium serves as a better nitrogen source than does nitrate, an observation supported by both field and laboratory data. At least one species, Dinobqon sertularia, is physiologically limited to water temperatures below 20°C.

Summary: An oligotrophic pond and a eutrophic pond of Bhagalpur, India, were studied for phytoplankton distribution and to establish the relationship between this distribution and the physico-chemical properties of the water. Altogether, 114 algal taxa were identified. In Rekabganj pond, diatoms constituted 54.4 % of the algal species followed by green algae (29.4 %), blue greens (11.7 %) and euglenoids (2.9 %). In Ramna pond, blue greens were the most dominant comprising 35.7 % of algal species followed by green algae (32.8 %), diatoms (18.5 %) and euglenoids (8.5 %). The members of Dinophyceae, Chrysophyceae and Xanthophyceae were poorly represented in both the water-bodies. Aphanizomenon flos-aquae, Microcystis aeruginosa, Chlorella vulgaris, Cladophora crispata, Volvox aureus and Euglena spp. were recorded only in Ramna pond, indicating its higher nutrient status. Dinobryon calciformis, many pennate diatoms and desmids, indicators of oligotrophy, were observed in Rekabganj pond only. Measurements of water properties in the two ponds showed that transparency, dissolved oxygen and silicate were higher in Rekabganj pond than in Ramna pond, while total alkalinity, hardness, total dissolved solids, dissolved organic matter, different cations, phosphate, nitrate and chloride were lower in Rekabganj pond than in Ramna pond.

Of 10 lakes and a reservoir in the Churchill Falls region of western Labrador studied in 1970–71, nine lakes were 12 m or less deep, humic, thermally unstratified, and had Secchi disc transparencies between 3.5 and 8.25 m. Maximum surface temperatures of 16–17 C in the nine lakes were generally reached by mid-August. Michikamau Lake (area 1980 km2, depth 84 m) rarely exceeded 12 C and had a Secchi disc transparency of 13 m. Conductivities and alkalinities (as CaCO3) ranged from about 13 μmho/cm and less than 6.5 mg/liter, for lakes draining granite, gneiss, or quartz bedrock, to about 30 and 15, for those draining gabbro or slate. Maximum live phytoplankton biomasses in 1970 ranged from 70 mg/m3, in Michikamau Lake, to 739 mg/m3, in Ossokmanuan Reservoir, and, in general, there was a positive correlation with conductivity. Diatoms were the most abundant group, in particular Asterionella formosa, Tabellaria fenestrata, and Rhizosolenia eriensis; however, flagellated Chrysophyta, mainly species of Dinobryon, were more abundant in the reservoir than in the natural lakes. Predominant zooplankters included Diaptomus minutus, Cyclops scutifer, Holopedium gibberum, Daphnia longiremis, D. galeata mendotae, and Bosmina coregoni. Maximum seasonal standing crops ranged from 1600 to 8910 individuals/m3, with the highest densities being found in the reservoir. The chemical and biological data suggested that the reservoir 8 yr after filling, showed little evidence of trophic upsurge and was possibly entering a period of trophic depression.

In situ enclosure experiments were performed in a highly humic lake to examine the effects of acidification on phyto-, bacterio- and zooplankton. The acidity of three enclosures was adjusted with H2SO4 to pH 3.5, 4 and 5 and one enclosure and the lake served as controls. The diversity of plankton as well as the mean concentration of chlorophyll α, primary production and respiration of plankton decreased with increasing acidity. Bacterial density was slightly lower in the pH 3.5 enclosure than in the other enclosures and in the lake, but there were no differences in the morphological type or mean volume of the cells between different treatments. In the acidified enclosures Cryptomonas ovata and Chlamydomonas spp. were the dominant phytoplankters, while Dinobryon and Mallomonas species seemed to be most sensitive to acidity. Keratella cochlearis, Kellicottia longispina and Bosmina longispina were the most tolerant zooplankton to acidity.

Summary The presence of very fine microfibrils in the lorica of species of Dinobryon has been revealed by electron-microscope examination of shadowed material. No indication of scales or annular components in the lorica, such as have been recorded by earlier workers using the light microscope, can be detected.

On August 25, 1925, Jerome Park reservoir was treated with copper sulphate for Asterionella, 1500 units, dosage 0.18 p.p.m. Contrary to usual practice the reservoir was not turned into service again until September 8, two weeks later. Within a few hours some three hundred complaints were received over the telephone of foultasting water. The reservoir was immediately shut off again. Samples examined from top, middle and bottom depths indicated that the decaying organisms had concentrated in the bottom water, and as draft was from the bottom the full effect of the treatment was experienced. Usually taste and odor from treatment disappear in two to three days and experience like the above has not been noted. The complaints were well justified judging from certain of the samples received. Meantime a secondary growth of Dinobryon occurred, 1550 units, the protozoa probably feeding on the decaying Asterionella or on the bacteria which rapidly increase following the killing of microscopic organisms, since the Dinobryon predominated at the bottom. A second treatment was given on September 14 of the same dosage and it is interesting to note that, although, as usual, the surface water was treated, the organisms which were at the bottom were entirely destroyed. The depth of the reservoir is about 25 feet. Great care was exercised in turning the water on again. Samples from top, middle and bottom were again examined and the reservoir turned into service gradually from mid-depth, beginning on the 19th. By the 24th it was about one-half in service

The small daphnid inhabiting the two alpine lakes, Mikuri-ga-ike and Midoriga-ike, which lie at an elevation of 2405m. and 2430m. respectively on Mt. Tateyama, is identical with Daphnia ambigua SCOURFIELD, by the characteristics of the post-abdominal claws and the male antennules as well as in having a short shellspine. When the writers visited those lakes on October 6th, 1960, both the populations of that species yielded a great number of the males and the females carrying ephippial eggs. In Mikuri-ga-ike, the deeper one of the two lakes and having 14.5m. in greatest depth, most individuals were seen at the layer 4m. deep, where the temperature of water was 10.3°C. Dinobryon was found in the digestive truct of Daphnia in both the lakes, although it was uncertain whether Daphnia was able to use this alga as food or not. It is noticeable that both the populations of Daphnia were markedly red-coloured, probably due to the increase of haemoglobin. Red colour was remarkable in the population of Lake Midori-ga-ike, a. shallow body of humose water east of Lake Mikuri-ga-ike. Some limnological characteristics of these two alpine lakes are discussed in showing the nature of the habitats of Daphnia ambigua.

In New York City's supplies, despite the diversity of its sources, the only organisms which have given offense from taste or odors have been Asterionella, Tabellaria, Anabaena, Aphanizomenon (with admixtures of Coelosphaerium, Microcystis and Clathrocystis), Uroglena, Synura, Dinobryon and Peridinium. Asterionella produces a slightly aromatic odor when present in 500 to 1000 standard units per cubic centimeter. At 1000 units, and rarely less, the odor is distinctly similar to that of the geranium. The intensity of odor increases with increasing numbers until a fishy odor is produced by several thousand. The fishy odor may also be produced when smaller quantities die or are destroyed. Tabellaria, and similarly Asterionella, may produce an earthy odor when present in very small amounts (produced also by large amounts of Synedra). The odor passes through the aromatic, geranium and fishy stages with about the same relative quantities of organisms as Asterionella. At times the odor of Tabellaria has suggested illuminating gas, no other organism being present. Anabaena and Aphanizomenon, when present in 500 to 1000 units, produce a faintly grassy odor, like freshly-cut grass. With larger numbers the odor increases until it becomes pungent like nasturtium, or even onions. Upon decay the odor is of vile, pig-pen character. Uroglena produces an oily fishy taste and odor, first noticeable in probably 500 to 1000 units. In larger quantities it is very disagreeable, the flavor being that of cod-liver oil. Synura may cause trouble apparently in any amount judging from our recent experience, at least as little as 50 units. This organism is by far the most persistent and disagreeable of them all. The taste is variously described as cucumber, muskmellon, fishy, etc. It leaves a bitter after-taste when the undestroyed organisms are in the