Microcystis Colonies Research Articles

FATE OF THE TOXIC CYCLIC HEPTAPEPTIDES, THE MICROCYSTINS, FROM BLOOMS OF MICROCYSTIS (CYANOBACTERIA) IN A HYPERTROPHIC LAKE1

ABSTRACTThe in situ fate of the toxic cyclic heptapeptides, the microcystins, produced by blooms of Microcystis was examined at two stations in a hypertrophic Japanese lake. Microcystins were detected in all samples of Microcystis with quantities varying seasonally and spatially (230–950 μg · g dry wt−1 at St. 1 and 160–746 μg · g dry wt−1 at St. 2) and composed of microcystin‐LR, ‐RR, and‐YR. Microcystin‐RR was the dominant toxin in most samples. A large amount of microcystin (1.1 μg · L−1) was detected in only one sample of filtered lake water. Accumulation of microcystin in zooplankton was indirectly estimated from a newly developed equation model. Large amounts of microcystin (75–1387 μg · g dry wt−1) were accumulated in the zooplankton community, which consisted of two cladocerans, Bosmina fatalis Burckhardt and Diaphanosoma brachyurum Lieve, and a copepod, Cyclops vicinus Uljanin, that co‐occurred with the toxic Microcystis blooms. The maximum percent of microcystin content in zooplankton to that in Microcystis was 202%. Among the three species of zooplankton, only B. fatalis seemed to be responsible for accumulation of the microcystins because C. vicinus appeared to avoid contact with Microcystis cells and D. brachyurum did not consume colonies of Microcystis. Microcystins may be transferred to higher trophic levels through B. fatalis.

Microcystis changes its buoyancy in response to the average irradiance in the surface mixed layer

A population of buoyant colonies of Microcystis sp. dominated the phytoplankton of the small Vinkeveen Lake, in the Netherlands. The Microcystis colonies were circulated within the surface mixed layer whose depth (usually 2 to 4 m) usually exceeded the euphotic depth (usually less than 1.5 m) in this wind-exposed lake. Colonies held in bottles at the lake surface responded to the high irradiance by losing their buoyancy, while those kept at greater depths remained buoyant. For colonies circulating within the surface layer the degree of buoyancy loss that occurred during the day depended on the mean irradiance to which they were exposed, which could be determined from the average surface irradiance, the mixed depth and the vertical extinction coefficient. Buoyancy loss was also correlated, but less strongly, with the proportion of the daytime spent by colonies within the euphotic zone. Surface scums were usually prevented from forming by wind mixing.

Diurnal changes in buoyancy and vertical distribution in populations of Microcystisin two shallow lakes

Changes in the buoyancy of Microcystis populations were followed over 24 h periods in two shallow well-mixed lakes, Lake Vinkeveen (area 0.6 km2) and Lake IJsselmeer (1190 km-2), in the Netherlands. The Microcystis colonies collected from the surface layers in both lakes showed a buoyancy decrease during the day and an increase at night. The buoyant colonies, and especially the faster-moving large ones, became concentrated by flotation into the surface mixed layers. As a result the mean position of the cyanobacterial population became located nearer the surface than that of other non-buoyant phytoplankton, such as Scenedesmus. The cyanobacteria would, therefore, have received a higher average irradiance. The Microcystis in these shallow lakes had weaker gas vesicles than those found previously in deeper lakes but it was demonstrated that the loss of buoyancy, which occurred at high irradiances, resulted from an increase in carbohydrate ballast rather than through turgor-driven gas vesicle collapse.

Interactions between Chironomus plumosus (L.) and the microbial community in surficial sediments of a shallow, eutrophic lake

Feeding by Chironomus plumosus (L.) larvae on sedimentary microbiota was studied in eutrophic Vallentunasjön, where microbial biomass constitutes a large portion of sedimentary organic matter. The life history of C. plumosus consisted of two univoltine cohorts with an overall production of 1.4 g ash‐free dry wt m−2. Gut concentrations of bacteria, Microcystis, and Melosira were several times higher than sedimentary concentrations, indicating that the larvae are foraging selectively. Assimilation of bacteria and newly sedimented Melosira cells on average accounted for 11 and 49% of the estimated carbon requirement (production + respiration) of the larvae. Digestive efficiencies for bacteria and Melosira seasonally averaged 43 and 34%. “Overwintering” Microcystis colonies, which constitute the dominant proportion of microbial biomass in the sediments, were used to a small extent ifat all as a carbon source by the chironomids. Ifa decrease in autofluorescence intensity of cells during gut passage is indicative of partial digestion of the cells, Microcystis was used with a digestive efficiency of 9% and accounted for ~ 10% of the carbon requirements of the larvae. On the basis of ambient Chironomus densities, gut passage time, enrichment factor (gut vs. sedimentary density of bacteria), and digestive efficiency, chironomid grazing is not a dominant sink for sedimentary bacteria in Vallentunasjön. The feeding activity of Chironomus larvae decreased bacterial densities but increased the cell‐specific production in laboratory experiments. The decrease was not proportional to grazer density, indicating that indirect effects of the chironomids (on sedimentary structure and chemistry) also affect the abundance of bacteria.

Optical properties of Gas-vacuolate cells and colonies of Microcystis in relation to light Attenuation in a Turbid, Stratified Reservoir (Mount Bold Reservoir, South Australia)

Profiles of downwelling and upwelling irradiance were measured in a stratified, turbid reservoir, when Microcystis aeruginosa formed a significant proportion of the phytoplankton community. The attenuation coefficient (Kd) was c. 2.1 m-1 and the reflectance (R) c. 0.03. Application of Kirk's simulation model relating apparent and inherent optical properties enabled calculation of coefficients of absorption (a; 1.3-1.6 m-') and scattering (6; 5-7 m-1). The asymptotic diffuse backscattering coefficient (0.2 m-1) was derived from the relationship b′b = 3.6 RaKd, a slight modification of Kirk's original equation. Turbidity measurements supported the general rule that nephelometric turbidity was numerically equivalent to the scattering coefficient. There was good agreement between the measured light profile and one reconstructed from inherent optical properties using the relationship between Kd, a and b. The optical properties of cells and colonies of Microcystis were investigated before and after the collapse of gas vacuoles. The Chla-specific absorption coefficient for cells (0.0138 m2 mg,-1 Chla) was higher than for colonies (0.0106 m2 mg,-1 Chla) at a depth equivalent to 0.2 m. Both coefficients decreased with increasing depth as the spectral composition changed. The Chla-specific scattering coefficient for vacuolate cells (0.14 m2 mg,-1 Chla) was greater than for colonies (0.11 m2 mg,-1 Chla), and a similar correspondence occurred for non-vacuolate cells and colonies (0.029 and 0.020 m2 mg,-1 Chla respectively). These measurements illustrate the package effect and also that c. 80% of light scattering is due to gas vacuoles. The relationship between pressure-sensitive turbidity and gas-vacuole volume suggested that 1 gL mL-1 was equivalent to a turbidity of 2 NTU. These optical characteristics, combined with the buoyant nature of Microcystis, suggest that it is a canopy species.

Seasonal dynamics of a cyanobacteria-dominated microbial community in surface sediments of a shallow, eutrophic lake

The seasonal variation of microbial biomass and activity in the surface sediments (0–10 cm) of the shallow, eutrophic Lake Vallentunasjon was followed during one year. “Overwintering”Microcystis colonies dominated the microbial community during all seasons, constituting 60–90% of the total microbial biomass. Expressed on an areal basis, the benthic biomass was, throughout the year, larger than or similar to the planktonic biomass during the peak of the summer bloom, indicating an ability of the colonies to survive in the sediments for extended periods. Abundance of “other”, non-photosynthetic bacteria varied in the range 3.0–15.5 · 1010 cells g−1 d. w. over the year with minimum values in summer and maximum values in autumn in connection with the sedimentation of theMicrocystis bloom. A substantial part of the non-photosynthetic bacteria, up to circa 40%, was associated with the mucilage of healthyMicrocystis colonies. Bacterial production (3H-thymidine incorporation) appeared to be strongly temperature dependent and less influenced by the seasonal sedimentation pattern. Our data indicate an increasing proportion of non-growing cells in autumn and winter. Biomass-bound phosphorus constituted a significant portion, circa 10%, of the phosphorus content in Lake Vallentunasjon sediments. This pool has normally been overlooked in studies on phosphorus dynamics in lake sediments. Different mechanisms whereby organic phosphorus can be released from the sediments are discussed.

Cladoceran filtration rate-body length relations: model improvements developed for a Microcystis-dominated hypertrophic reservoir

Filtering rates were measured for zooplankton species in Situ on single-celled Chlorella and on four Microcystis colony size fractions (5–20, 20–40, 40–60 and 60–100 μm) in a hypertrophic reservoir. Natural-log-transformed filtration rates of five cladoceran species, one copepod and one rotifer were included in an all-food-particle, all-species multiple regression model which explained 43% of the variance in filtration rate as a function of animal body length. An additional 14% and 7.6% of the variance was attributable to food type and zooplankton species respectively, with temperature accounting for <4% of the variance. Restricting the filtration rate model to cladocerans alone explained 51% of the variance as a function of animal length, 16% as a function of food type, 7.5% as a function of species and only 0.2% as a function of temperature. In linear filtration rate models for each food type, cladoceran body length explained 70% of the variance when feeding on Chlorella and between 57 and 67% of the variance on the four Microcystis colony fractions. Models describing cladoceran filtration rates on Chlorella and the 5–20 μm Microcystis colony fraction were significantly different from the three models on larger colonies due to cladoceran responses to increasing food particle size. Accordingly, a combined model for Microcystis colonies >20 μm was developed. Inclusion of food quality factors such as cyanophyte colony size seems justified in models aimed at estimating clearance rates, resource utilization and phytoplankton grazing losses in plankton or ecosystem studies when applied to eutrophic or hypertrophic lakes where large cyanophyte particles are abundant.

Insights into zooplankton‐cyanobacteria interactions derived from enclosure studies

Abstract Few workers have used enclosures specifically to study interactions between zoo‐plankton and cyanobacteria. Differences among studies in enclosure size, nutrient level, plankton abundance and species composition, presence or absence of fish, and length of experiments make generalisations difficult. Zooplankton had no direct effect on the growth of ungrazed cyanobacteria (Anabaena flos‐aquae, Aphanizomenon flos‐aquae, large Microcystis colonies) in short‐term ( 1 month) enclosure studies. When large cyanobacteria were abundant, some Daphnia spp. snowed reduced reproduction and development. When large grazers were abundant they suppressed the growth of edible, colonial cyanobacteria (Aphanizomenon elenkinii, small Microcystis colonies). By altering the ambient light and nutrient environment, large zooplankton may suppress cyanobacteria; evidence for the importance of grazers in promoting cyanobacterial dominance by removing competing phytoplankton species is equivocal. Zoop...

Laboratory studies on zooplankton‐cyanobacteria interactions

Abstract Laboratory studies on cyanobacteria‐zooplankton interactions have largely focused on the inadequacy of cyanobacteria as a food source. Some features of cyanobacteria can be regarded as anti‐herbivore defences. Large colonies of Aphanizomenon, Anabaena and Microcystis cannot be handled by zooplankton, but do not interfere seriously with the filtering process. Small colonies and filaments, however, may cause severe inhibition of the feeding process by mechanical interference. This reduces zooplankton growth, reproduction, and survival. Copepods, rotifers, and Bosmina are less affected by mechanical disturbance than cladocerans. If ingested, some cyanobacteria may be poorly digested or may not provide essential nutrients. Some cyanobacteria are reported to be toxic to zooplankton. Several strains of Microcystis produce an endotoxin, but the amount of toxin produced differs among strains and with the condition of Microcystis. Zooplankton encountering toxic cells cease feeding. Some evidence of an ext...

Buoyancy regulation byMicrocystisin Lake Okaro

In Lake Okaro (see Vincent et al.: p. 509 this issue) for site description), a species of Microcystis produced large spherical colonies which floated rapidly when buoyant and sank rapidly when not. This organism exhibited a very clear-cut buoyancy change in response to light intensity, which would provide it with the ability to make vertical migrations over considerable depths, even when some degree of mixing occurs. The buoyancy and distribution of Microcystis colonies were investigated at Lake Okaro on 2627 February and 7-10 March 1987. Surface concentrations were estimated by counting the colonies in seven 3-litre dip samples (Walsby et al. 1983) at up to 14 stations over the lake. Individual colonies, of average diameter 3 mm, were collected one by one with a 5.5 mm ID glass tube fitted with a rubber teat. For in situ incubation experiments, 50 to 60 colonies were suspended in 2 litres of tissue-filtered lake water in a clear polycarbonate bottle closed with a screw cap and suspended at the lake surface in the south-west corner of the lake. Sinking velocities of the colonies were measured in a 100 ml graduated measuring cylinder filled to the top, about 60 mm above the top graduation mark. The cylinder was placed in a jar of water and the jar was stood in a tray of ice; this gave a temperature gradient in the jar and cylinder, which minimised convective mixing. The colony was released at the water surface and the times were recorded as the colony passed the 100, 70, 40, and 10 ml graduation marks, which were each 47 mm apart. Floating colonies were timed as they rose

Zooplankton feeding on size fractionated Microcystis colonies and Chlorella in a hypertrophic lake (Hartbeespoort Dam, South Africa): implications to resource utilization and zooplankton succession

Experiments measuring zooplankton filtration rates on radiolabelled Chlorella and on Microcystis colonies were carried out in situ during both the annual spring Daphnia phase and following the shift to the summer Ceriodaphnia phase in Hartbeespoort Dam. Cladoceran filtration rates on natural Microcystis of discrete colony size-classes (5–20, 20–40, 40–60 and 60–100 μm) were compared with rates measured on cultured Chlorella (∼ 8.5 μm cell diameter). The small bodied cladoceran species Ceriodaphnia reticulata, Moina micrura and Diaphanosoma exasum filtered Microcystis colonies at very low rates compared to Chlorella . Only the largest herbivore Daphnia pulex fed significantly on Microcystis colonies of up to 60–100 μm. Colonies of 100–150 μm were not ingested by any zooplankter tested. Both particle size limitation and low filtration rates on small Microcystis colonies and unicells led to low Daphnia filtration efficiencies and reduced grazing pressure on Microcystis . Suppression of Daphnia filtration rates in situ on Chlorella was evident during the mid-summer increase in Microcystis abundance. Daphnia filtration rates during this period when inedible phytoplankton were abundant were only 25–36% of the maximum filtration, rates measured during the spring clear water phase when the phytoplankton was largely composed of edible species. The aforementioned small cladoceran species exhibited high filtration rates on Chlorella when Microcystis was abundant, suggesting that filtration efficiency of the summer cladoceran community was not reduced by interference from Microcystis colonies. However, their low filtration rate on Microcystis suggests that this is not an important food resource. Concomitant reductions in bacterial numbers and edible phytoplankton food resources available in summer imply that the small body-sized cladoceran community rather relies on the smallest size fraction of the summer food resource.

DEVELOPMENT AND USE OF ZOOPLANKTON LENGTH - FILTRATION RATE RELATIONSHIPS FOR ESTIMATING PHYTOPLANKTON GRAZING LOSSES

SUMMARY Water quality is impaired by high chlorophyll concentrations. Limitation of algal stocks by high zooplankton grazing is an important component in many lake ecosystems and models. Measurement of grazing rates is labour intensive, expensive and requires specialized skills. This paper examines relationships that allow use of easy-to-obtain data on zooplankton to calculate clearance rates and thus estimate phytoplank-ton grazing losses in eutrophic and hypertrophic lakes dominated by blue-green algae. A positive correlation exists between zooplankton body-length and filtration rate regardless of species. Pooled data from in situ experiments on five species of cladocerans fed Chlorella shows that 70% of variance in filtration rate is explained by body-length. Temperature has little influence. Feeding rates on Microcystis colonies can also be predicted from zooplankton body-length; decreasing intercept with increasing slope showing marked size limitation to colony ingestion by small cladocerans as colon...

APPARENT PREDATION OFMICROCYSTIS AERUGINOSAKüTZ. EMEND ELENKIN BY ASAPROSPIRA-LIKE BACTERIUM IN A HYPERTROPHIC LAKE (HARTBEESPOORT DAM, SOUTH AFRICA)

SUMMARY The cyanobacterium Microcystis aeruginosa is the dominant autotroph in hypertrophic Hartbeespoort Dam, South Africa. Tn early summer (November) of 1983 and 1984 Microcystis colonies were heavily colonized by a gram-negative, spiral-shaped organism whose filaments appeared as si.ngle cells under both the light and scanning electron microscope. DNA staining with 4'6 diamidino-2-phenylindole (DAPI) revealed that each filament consisted of a number of bow-shaped cells. The organism has been tentatively identified as a bacterium, Saprospira albida, on the basis of it morphology. The Microcystis cells at the site of colonization were apochlorotic suggesting lysis by Saprospira.

Hypothesized resource relationships among African planktonic diatoms

Several hypotheses are advanced for resource relationships among planktonic diatoms in African freshwater lakes that are consistent with the light and nutrient conditions of the lakes and the extant and fossil distributions of the diatom species in them. The hypotheses are all testable and are potentially powerful tools for interpreting past climatic conditions. A ranking is proposed along a Si: P gradient: at the high end are the planktonic Synedra spp. with the highest Si requirements and lowest P requirements (high Si : P), the planktonic Nitzschia spp. are intermediate, and the Stephanodiscus spp. are at the low end with the lowest Si requirements and highest P requirements (low Si : P). Melosira species may be ranked along a light: P gradient. We suggest that Melosira distans and Melosira ambigua grow under high light and have low P requirements, Melosira agassizii and Melosira granulata are intermediate, and Melosira nyassensis has the lowest light and highest P requirements. There also appears to be a relationship between pore size and the light regime for growth among the Melosira species; thus, M. distans and M. ambigua have the smallest pores and highest light requirements, M. nyassensis has the largest pores and lowest light requirements. Melosira granulata is intermediate and seems to be very variable in pore size, depending on the light environment. One diatom, Nitzschia fonticola, lives in and on colonies of Microcystis and is considered to be an obligate nitrogen heterotroph.

The Effect of Temperature on Recovery of Buoyancy by Microcystis

Summary: Colonies of Microcystis in Abbots Pool, Avon, UK, were found to regulate their buoyancy according to light (photon flux density). The autumnal decline of the population was associated with an increase in the proportion of colonies that were non-buoyant, and with declining temperatures in the pond. Non-buoyant colonies taken from the pond regained buoyancy in the dark rapidly at 20°C but only slowly at 12°C and below. A laboratory strain of Microcystis behaved in a similar manner. Comparisons of the behaviour of this organism placed at 8°C and 20°C were made; in high photon flux density buoyancy was lost at both temperatures due to accumulation of dense carbohydrate. When transferred to the dark cells at 20°C became buoyant again as carbohydrate was utilized and more gas vesicles were made; at 8°C much less carbohydrate was used and no increase in gas-vacuolation occurred. The failure to regain buoyancy in the dark at low temperatures accounts for the loss of buoyancy and sedimentation of the Microcystis in Abbots Pool.

Simulation of water-bloom in a eutrophic lake—IV Modeling the vertical migration in a population of Microcystis aeruginosa

Simulation of the water-bloom dominated by Microcystis (blue-green algae) was carried out by modifying the mathematical model presented previously on the rising and sinking of the algal colonies through a still water-column. In contrast to the earlier work on the simulation of single colonies, an overall behavior of many algal colonies, having not only the size distribution but also having distribution initially throughout the water-column was simulated. The points of the model modified are: (i) the specific growth rate was shown by a quadratic function of light intensity that takes the inhibitory effect into account and (ii) the extinction coefficient incorporated the light-shielding effect by the algal cells existent depthwise in the water-column rather than a linear function of the concentration of suspended materials in the water. The numerical solutions of the model (280 dimensions) were in agreement qualitatively with the observations ever reported on Microcystis behavior in eutrophic lakes. Factors relevant to the extinction coefficient underwater, i.e. the concentrations of either Microcystis colonies or other suspended materials were significant from the viewpoint to control the algal growth as a whole, assuming that no nutrients were limiting. The vertical mixing of lake waters was effective for decreasing the average value of the specific growth rate expecially when the concentrations of colonies or other materials were large. Consequently, an artificial aeration was suggested to be a commendable means to ward off the water-bloom.

Selective inhabitation of parasitic Cyanophyte Pseudanabaena in water-bloom Microcystis colonies

Selective inhabitation of parasitic Cyanophyte Pseudanabaena in water-bloom Microcystis colonies

The sedimentation of buoyantMicrocystiscolonies caused by precipitation with an iron-containing colloid

Colonies ofMicrocystis aeruginosahave dominated the phytoplankton in Lund tube C, a limnetic enclosure in Blelham Tarn, English Lake District, during the summer and autumn in recent years. Following holomixis in autumn the previously buoyant colonies sedimented from the water column onto the bottom mud. In all samples gas vesicles, which provided the colonies with buoyancy, were present in sufficient volume to negate the combined ballast provided by protein, carbohydrate, lipid and phosphate, the major cell components. The gas vesicles, which accounted for about 10% of the cell protein, were too strong to be collapsed or regulated by cell turgor pressure. Consequently, the loss of buoyancy could not be explained by an increase in cell ballast or by disappearance of gas vesicles. Colonies collected in sediment traps were found to be buoyant after they had been agitated and diluted with lake water, which removed a colloidal precipitate from them. Similarly, 66% of the sinking fraction of a net tow sample was found to be buoyant after it had been treated in the same way. Previously buoyant colonies could be made to sink on mixing with the colloidal precipitate. This demonstrated the ability of the precipitate to trap colonies and to cause their sedimentation. The colloid comprised approximately equal amounts of organic and inorganic matter and was rich in iron. Colloids of this type form when the dissolved iron in the anoxic water of the hypolimnion becomes oxidized on mixing with the aerated water of the epilimnion.

Difference in bacterial floras among different size fractions of suspended particles in a hypertrophic pond.

The bacterial floras in four size fractions (>35 m, 35-5 m, 5-1 m, and 35 m fraction (bacteria associated mainly with the mucilage of Microcystis colonies) showed a simple generic composition during the Micro-cystis bloom, and was almost dominated by the bacteria tentatively identified as Pseudomonas-like, which were Gram-negative, strictly aerobic, catalase weakly positive, oxidase negative, colorless or pinkish pigmented, and slightly irregular rods with a single polar flagellum. In the 35-5 m and 5-1 m fractions (bacteria associated with various kinds of phytoplankton, detritus, and clay particles), bacterial populations showed a more diversified bacterial flora than that in the >35 m fraction. The bacterial flora in the <1 m fraction (free-living bacteria) was dominated by one or two genera such as Pseudomonas, Flavobacterium, Moraxella, Caulobacter, and Acinetobacter at each sampling time. These results suggest the existence of different bacterial floras among different size fractions of suspended particles in the pond water.

Diurnal changes in the vertical distribution of phytoplankton in hypertrophic Lake Kasumigaura, Japan

The daily vertical migration of five species;Microcystis aeruginosa (Kutz.) Trevis,Anabaena spiroides Klebahn f.crassa (L.) Elenkin,Aphanizomenon flos-aquae (L.) Ralfs,Melosira granulata (E). Ralfs, andCoscinodiscus lacustris Grun. was studied using a close-interval water sampler on a calm summer day in Lake Kasumigaura. Many colonies ofMicrocystis were observed at the middle of the water column (approx. 1.5 m depth) in the afternoon, and at the surface in the early morning.Anabaena occurred mostly in the upper layer whileAphanizomenon tended to be uniformly distributed. The difference in migration patterns suggests thatMicrocystis is superior toAnabaena andAphanizomenon in obtaining both light and nutrients from this lake. Among diatoms,Melosira remained at the bottom of the water column throughout day and night, but Coscinodiscus was uniformly distributed.