Coupling between benthic biomass of Microcystis and phosphorus release from the sediments of a highly eutrophic lake

Variations in microbial biomass and activity in the sediments of hypereutrophic Lake Vallentunasjön were followed during a period of 5 years. The data were compared to the calculated release of phosphorus from the sediments during the same period. A strong co-variation was found between biomass of Microcystis, heterotrophic bacterial activity in the sediments and internal phosphorus loading. These parameters exhibited mainly a declining trend during the investigation period. A pronounced stability of the sediment chemistry, including the fractional composition of the sediment phosphorus, during the studied period indicates that microbial activity affected the phosphorus release from the sediments. Calculations of the percentage of sediment bacteria that was associated to the mucilage of Microcystis colonies imply, together with the specific bacterial production, that Microcystis in the sediment stimulates bacterial production. In the highly phosphorus-saturated sediments of Lake Vallentunasjön this would ultimately lead to an increased release of phosphorus from the sediment. Lake Vallentunasjön does not follow the common pattern of recovery after reduction of external phosphorus loading. The large biomasses and long survival of Microcystis in the sediment are probably important reasons for the delayed recovery of the lake.     

Evaluation ofChaoborus predation on natural populations of herbivorous zooplankton in a eutrophic lake

Hydrobiologia - The effect ofChaoborus predation on natural zooplankton communities was tested in enclosure experiments during June, July and August in the eutrophic Frederiksborg Slotssø,...     

Effects of food limitation and temperature on cladocerans from a tropical Brazilian lake

Food limitation was tested in the laboratory by individual growth and reproduction of two cladoceran species, Ceriodaphnia richardi and Daphnia gessneri, from the shallow tropical Brazilian Lake Monte Alegre. The cladocerans were fed cultivated green alga Scenedesmus spinosus in concentrations of 0.20, 0.10, 0.05, and 0.025 mg C l⁻¹. Higher biomass and growth rates occurred in the two highest-food concentrations; the two lowest ones negatively affected clutch size and first reproduction. The threshold food concentration is lower than 0.025 mg C l⁻¹ and the incipient limiting level is a value between 0.10 and 0.20 mg C l⁻¹. The largest species, D. gessneri, was more sensitive to low food concentrations. The effects of low and high temperatures (19 and 27°C) were evaluated by life table experiments with three cladocerans from the lake—Daphnia ambigua, D. gessneri, and Moina micrura—with no food limitation (1 mg C l⁻¹ of S. spinosus). Higher population growth rates for the three species were found at 27°C; better performance in most life table parameters was observed for the former two species at the highest temperature, D. gessneri being the most sensitive to the lowest temperature. There are indications that temperature is an important abiotic factor that constrains populations of cladocerans for a short period in winter in the lake, when temperature decreases to 18–19°C. However, its influence cannot be separated from a biotic factor such as food, whose effect is stronger in the cool season, when concentrations are lower and contribution of inedible algae is relatively higher.     

The effect of temperature on growth characteristics and competitions of <Emphasis Type="Italic">Microcystis aeruginosa</Emphasis> and <Emphasis Type="Italic">Oscillatoria mougeotii</Emphasis> in a shallow,eutrophic lake simulator system

Blue-green algal blooms formed by Microcystis and Oscillatoria often occur in shallow eutrophic lakes, such as Lake Taihu (China) and Lake Kasumigaura (Japan). Growth characteristics and competitions between Microcystis aeruginosa and Oscillatoria mougeotii were investigated using lake simulator systems (microcosms) at various temperatures. Oscillatoria was the superior competitor, which suppressed Microcystis, when temperature was <20°C, whereas the opposite phenomenon occurred at 30°C. Oscillatoria had a long exponential phase (20 day) and a low growth rate of 0.22 day⁻¹ and 0.20 day⁻¹ at 15°C and 20°C, respectively, whereas Microcystis had a shorter exponential phase (2–3 days) at 30°C and a higher growth rate (0.86 day⁻¹). Interactions between the algae were stronger and more complex in the lake simulator system than flask systems. Algal growth in the lake simulator system was susceptible to light attenuation and pH change, and algae biomasses were lower than those in flasks. The outcome of competition between Microcystis and Oscillatoria at different temperatures agrees with field observations of algal communities in Lake Taihu, indicating that temperature is a significant factor affecting competition between Microcystis and Oscillatoria in shallow, eutrophic lakes.     

Use of15N/14N rations to evaluate the food source of the mysid,Neomysis intermedia Czerniawsky,in a eutrophic lake in Japan

The stable isotope ratios of nitrogen were measured in the mysid,Neomysis intermedia, together with various biogenic materials in a eutrophic lake, Lake Kasumigaura, in Japan throughout a year of 1984/85. The mysid, particulate organic matter (POM, mostly phytoplankton), and zooplankton showed a clear seasonal change in ¹⁵N with high values in spring and fall, but the surface bottom mud did not. A year to year variation as well as seasonal change in ¹⁵N was found in the mysid. The annual averages of ¹⁵N of each material collected in 1984/85 are as follows: surface bottom mud, 6.3 (range: 5.7–6.9); POM, 7.9 (5.8–11.8); large sized mysid, 11.6 (7.7–14.3); zooplankton, 12.5 (10.0–16.4); prawn, 13.2 (9.9–15.4); goby, 15.1 (13.8–16.7). The degree of¹⁵N enrichment by the mysid was determined as 3.2 by the laboratory rearing experiments. The apparent parallel relationship between the POM and the mysid in the temporal patterns of ¹⁵N with about 3 difference suggests the POM (mostly phytoplankton) as a possible food source ofN. intermedia in this lake through the year.     

Chaoborus predation and zooplankton community structure in a rotifer-dominated lake

During summer, Chaoborus punctipennis larval densities in the water column of fishless, eutrophic Triangle Lake become very high, and coincidently, the spined loricate rotifer Kelfcottia bostoniensis becomes the dominant zooplankter. Research was done to test the hypothesis that selective predation by Chaoborus on soft-bodied rotifers controls species dominance in the mid-summer zooplankton of this lake. In situ predation experiments showed positive selection by Chaoborus for the soft-bodied Synchaeta oblonga, negative selection for K. bostoniensis, and intermediate selection for Polyarthra vulgaris, a species with rapid escape tactics. However, during a 21 day in situ mesocosm experiment, zooplankton dominance and succession in Chaoborus-free enclosures was identical to that in enclosures with Chaoborus at lake density. Despite the selective predation, Chaoborus larvae may not exert significant top-down control on rotifers, whose intense reproductive output during mid-summer in temperate eutrophic lakes results in new individuals at rates that exceed predatory losses.     

Human urine is an excellent liquid waste for the culture of fish food organism, Moina micrura

With a view to converting human urine into bio-wealth in the form of zooplankton, the nutrient potentials of liquid wastes (0.11 mL L⁻¹)—(i) human urine (♂), (ii) cow urine, (iii) human–cow mixed urine or some solid wastes (0.11 g L⁻¹): (iv) vermi-compost, (v) cow dung, (vi) poultry droppings and (vii) mixed wastes (vermi-cow-poultry)—were evaluated for the mass culture of zooplankton Moina micrura in 24 outdoor tanks (4500 L) in triplicate treatments using life table as indicator during the period of October–December, 2005. Neonates of Moina micrura held in the treatment with human urine started reproduction at least 4 days earlier than other solid wastes tested. Total number of Moina micrura enumerated in the culture tank, related with offspring production per life span, was maximum in case of human urine treatment, followed by human–cow mixed urine, cow urine, vermin-compost, poultry droppings, mixed wastes (vermin–cow–poultry), cow dung and control treatments. The relationship between the total offspring production per female per life span and the nitrogen content of water in different treatments implied that human urine was an excellent liquid waste that can be used for the mass production of zooplankton Moina micrura required for larval and post larval rearing of commercial fishes.     

Impact of whitefish on an enclosure ecosystem in a shallow eutrophic lake: selective feeding of fish and predation effects on the zooplankton communities

Bag-type enclosures (75 m³) with bottom sheets and tube-type enclosures (105 m³) open to the bottom sediment were stocked with exotic whitefish (Coregonus lavaretus maraena) to study their predation effects on the plankton community. The fish fed mainly on adult chironomids during the period of their emergence (earlier part of the experimental period). Thereafter, the food preference was shifted to larvae of chironomids and crustacean zooplankters. The predation effects on the plankton community were not evident in the bag-type enclosures where zooplankton densities were consistently low. The fish reduced the crustacean populations composed ofBosmina fatalis, B. longirostris andCyclops vicinus in the tube-type enclosures where the prey density was high (above ca. 50 individuals 1⁻¹). The results suggested that the intensity of predation depended on the prey density. Rotifers increased in the fish enclosure, probably becauseCoregonus reduced the predation pressure byCyclops vicinus on rotifers and allowed the latter to increase. In the fish enclosures, no marked changes in species composition were observed. Zooplankton predated by the fish seemed to be distributed near the walls of the enclosures. Problems of enclosure experiments for examining the effects of fish predation on pelagic zooplankton communities are discussed.     

Population dynamics and production of cladoceran zooplankton in the highly eutrophic Lake Kasumigaura

The growth rate, birth rate, death rate and production of the cladocera of Lake Kasumigaura were studied. Standing crop of zooplankton seemed to be governed by predation rather than food. Maximum productivity of cladocerans was observed in late August and early September. There were differences in production between sampling stations. The highest production was recorded in the most eutrophic basin, where heavy water blooms of Microcystis aeruginosa occurred. Maximum secondary production coincided with maximum primary production, which was mainly due to M. aeruginosa. Cladocerans probably utilize decomposed or decomposing Microcystis cells and bacteria in summer. Estimates of annual production of cladocerans varied from 4.2 to 13.1 g dry wt · m^–3, and annual P:B ratios ranged from 36 to 108. The production of cladocerans in Takahamairi Bay was 2.7% of gross primary production.     

Generation time of Acanthocyclops robustus in relation to food availability and temperature in a shallow eutrophic lake

The generation time of the predatory cyclopoid copepod Acanthocyclops robustus was estimated on 11 occasions during the years 1980 to 1982 in Alderfen Broad. In a multiple regression model, generation time was found to be uncorrelated with temperature, positively correlated (p < 0.05) with the densities of Bosmina longirostris and rotifers, and negatively correlated (p < 0.001) with the density of nauplii of the calanoid copepod Eudiaptomus gracilis. It is suggested that generation time was determined largely by the availability of calanoid nauplii as prey, even though these constituted only 2% of zooplankton standing biomass.     

Role of bacteria as food for zooplankton in a eutrophic tropical pond (Ivory Coast)

The aim of the study was to determine whether bacteria could be a substantial source of carbon for zooplankton and whether the grazing pressure of these metazoan filter-feeders could influence the fate of bacterial production. Eight grazing experiments using natural bacteria labelled with³H thymidine were conducted in a tropical pond (Ivory Coast) during various phases of biological colonization (rotifer-dominated and copepod-dominated phases of the colonization). Higher grazing and clearance rates were observed with rotifers (Brachionus plicatilis andHexarthra intermedia), while very low values were obtained when the cyclopoid copepodApocyclops panamensis was dominant. Less than 1% of the bacterial production was harvested when copepods were dominant, whileB. plicatilis consumed up to 36% of this production. However, this consumption of bacteria appeared to contribute only to an insignificant proportion of the daily carbon intake (e.g. 0.9 to 7.1% of body carbon for rotifers). The low contribution of bacteria in the nutrition of zooplankton is discussed in terms of their cell size and their relative abundance in the total amount of seston available.     

Elemental composition of <Emphasis Type="Italic">Microcystis aeruginosa</Emphasis> under conditions of lake nutrient depletion

Electron probe X-ray microanalysis (XRMA) was used to determine the elemental composition of the blue-green alga, Microcystis aeruginosa, in a stratified freshwater lake during the late summer. Colonies of this alga were initially observed in mid-July, at a time when phosphorus concentration in the lake water had decreased to minimal levels (total P 0.04 mg l⁻¹). The P quota of these cells was high (mean concentration 132 mmol kg⁻¹ dry weight) with a cell P to lake water P concentration ratio of 10⁵. The elemental concentrations of Microcystis remained relatively stable throughout the sampling period (July–September), with mean cell concentrations of Mg, P, S and Ca showing no significant changes. Mean elemental ratios and the ratio of monovalent/divalent cations were also relatively constant (SE <10% mean). The pattern of cell elemental associations, determined by Factor and Pearson correlation analysis, was consistent throughout – with Mg, P, K and S forming a core tetrad of inter-correlated elements. The relative constancy of cell composition seen in Microcystis would be expected of an alga with a K-selection strategy. The continued high P quota over a period of nutrient depletion in lake water is consistent with the ability of this alga to sink to nutrient-rich lower regions of the water column.     

Vertical distributions of zooplankton and population dynamics of Daphnia in a meromictic lake

Vertical distributions of zooplankton were studied in relation to profiles of temperature, oxygen and chlorophyll a in Roi Lake, a small meromictic lake in central Alberta. Zooplankton were distributed fairly evenly through the oxygenated part of the water column in early summer, but a gradual descent of several species became evident in June. The vertical distribution of chlorophyll was dominated by a huge peak at the 8- to 9-m-deep chemocline. the location of a plate of photosynthetic sulfur bacteria. Ambient concentration of chlorophyll was a poor predictor of the numbers of zooplankton and the fecundity of Daphnia pulicaria at different depths, and per capita birth rates of Daphnia were usually highest in the surface waters. The reproductively disadvantageous restriction of daphnids to deep water by late summer and their catastrophic decline in the face of high ambient concentrations of chlorophyll suggest that factors other than temperature and food supply are important in influencing the dynamics and distribution of zooplankton in this lake.     

Long-term changes in crustacean zooplankton and water quality in a shallow, eutrophic Chinese lake densely stocked with fish

From surveys made in 1962–1963, 1973–1974, 1979–1996 at two Stations in Lake Donghu, a shallow eutrophic water body near Wuhan, P. R. China, the authors, derive long-term changes in species composition, standing crop and body-size of planktonic crustaceans. The species number decreased from the 1960s to the 1990s. The cladocerans dropped from 46 (1960s) to 26 (1980s) to 13 (1990s); the copepods decreased from 14 (1960s) to 10 (1980s) to 7 (1990s). From the mid-1980s on, the dominant crustaceans also changed: Daphnia hyalina and D. carinata ssp. were replaced by Moina micrura and Diaphanosoma brachyurum at Stations 1 and 2, respectively; Cyclops vicinus replaced Mesocyclops leuckarti.Densities and biomass of Cladocera decreased markedly after 1987. Annual average densities and biomass of cladocerans were statistically differences between 1962–1986 and 1987–1996 (P > 0.01). Annual average densities of Daphnia (Station 1 + Station 2) were negatively correlated with fish yield .Since the 1980s, annual average body length of Cladocera and Calanoida decreased, while annual average body length of Cyclopoida increased. In the same years, average body length of copepods was lower during May–October than during January–April and November–December.A 12-yr data analysis showed annual average concentration of chlorophyll^-a (Chl^-a) to be negatively correlated with annual average density of Daphnia, whilst lake transparency was positively correlated with annual average densities of Daphnia. The results imply that, since Daphnia feeds efficiently on phytoplankton, it could decrease concentration of Chl^-a, and enhance water transparency.     

Food and feeding behaviour of a planktivorous cyprinid, Pelecus cultratus (L.), in a shallow eutrophic lake, Neusiedler See (Austria)

Pelecus cultratus (razor fish), a cyprinid fish, has become a dominant species in Neusiedler See. Gut content analyses of 400 specimens collected in 1989 and 1990 showed that Pelecus fed mainly on large zooplankton (Diaphanosoma, Leptodora and Arctodiaptomus), although their diet also included Insecta (larvae, pupae and adults) and Arachnida (spiders), occasionally small fishes. Comparison of the relative abundance of the zooplankton species in the stomach to the lake indicated that Pelecus strongly selected cladocerans over copepods, and fed mostly on large-sized individuals of Diaphanosoma, Leptodora and Arctodiaptomus. The fish showed a significant positive selectivity only for individuals of Diaphanosoma > 1.0 mm and Leptodora > 4.0 mm. In contrast, selectivity increased continuously in relation to the diameter of the compound eye of both prey species. This suggested that prey visibility was a key factor in determining the prey selectivity by Pelecus. It also seems likely that the persistence of the Leptodora population in Neusiedler See can be attributed to negligible predation pressure on the smaller sized individuals of this species.     

Vertical and seasonal distributions of micro-organisms,zooplankton and phytoplankton in a eutrophic lake

The vertical distributions of bacteria, picoalgae,protozoan and metazoan zooplankton, and phytoplanktonin the highly eutrophic Lake Köyliönjärvi(SW Finland) were studied monthly during the period ofice-cover in January-April 1996. For comparison, wealso provide some data on the distributions of theplankton during the summer. The whole watercolumn remained oxic during the ice-covered period,although the near-bottom oxygen concentrations werealways very low. The heterotrophic nanoflagellateswere more abundant in winter than in summer, butciliates, picoalgae and bacteria were more numerous insummer. In general both zooplankton and phytoplanktonhad low biomass during the ice-covered period.However, the biomass of the diatom Aulacoseiraislandica ssp. islandica was high under the icein April. The calanoid copepod Eudiaptomusgraciloides was the dominant zooplankton species fromJanuary to March, but had almost disappeared by thebeginning of April and did not increase again until inJune. The dominant rotifer species in winterwere Keratella cochlearis, Filinia terminalis,and Filinia longiseta in the surface water andRotaria neptunia near the bottom.     

Interrelations between Microcystis and Cladocera in the highly Eutrophic Lake Kasumigaura,Japan

The zooplankton community in the highly eutrophic Lake Kasumigaura was investigated and its relation to a bloom of Microcystis was analyzed. The zooplankton community was dominated by small cladocerans, whose biomass and production became highest in summer, when Microcystis bloomed. The high cladoceran production is considered to depend on the production of colonial Microcystis, because the production of nannoplankton was apparently too low to ensure the cladoceran production. Microcystis cells were unsuitable as food for the cladocerans inhabiting Lake Kasumigaura, but became utilizable when decomposed. Decomposed Microcystis may be the main food for Cladocera in the lake in summer. High water temperatures occurring in summer probably promoted decomposition of the Microcystis, leading to increased production of the small cladocerans.     

The effects of CO2 on sestonic stoichiometry and community structure of crustacean zooplankton in a eutrophic lake: Increased competitive ability of Bosmina

To explore the effects of CO₂ concentration on the sestonic stoichiometric values and the community structure of crustacean zooplankton in a eutrophic lake, in situ microcosm experiments were conducted at the Lake Taihu Ecosystem Station in spring and summer of 2012. The experimental treatments were three concentrations of CO₂, 270, 380 and 750 ppm, which represented preindustrial and present levels and the level predicted for the end of this century, respectively. The elevated atmospheric CO₂ concentration increased the sestonic C:P ratio, particularly in the spring when the C:P ratio was two-fold greater at the high level of CO₂ than at the low level of CO₂. As a result, the contribution of Bosmina to total crustacean zooplankton abundance increased, most likely because of the low phosphorus content and high adaptability to foods with large elemental ratio variation. The other dominant crustacean zooplankton genera, including Daphnia, Ceriodaphnia, Diaphanosoma and Sinocalanus, had no response to the change in pCO₂ during the microcosm experiments. The shift in crustacean zooplankton community structure between two seasons was primarily due to the transition of the phytoplankton community.     

Availability of suitable phytoplanktonic food for zooplankton in an ice-covered lake

Edible phytoplankters were found throughout the winter in a shallow ice-covered lake in Pennsylvania, U.S.A., in conjunction with a diverse population of zooplankton. Environmental conditions during the winter seemed to eliminate large and non-motile types of algae in favor of the smaller motile forms which may be the best foods for zooplankters. The phytoplankton were classified for study both by systematic position and by size group. The total volume of phytoplankton comprising the group Chrysophyta and algae 80 µ declined rapidly during the period of ice-cover, while algae 15 µ and Chlorophyta maintained more stable volumes. During the latter weeks of ice-cover phytoplankton densities were low (50–200/ml), and bacteria, detritus, or µ-algae (2 µ) not detected by the counting methods used, may have been important foods for the zooplankters. The lack of suitable phytoplanktonic foods may have contributed to the decline of calonoid copepods during the late winter.Based on a thesis submitted to the Department of Biology, East Stroudsburg State College, as a partial requirement for the degree of M.S. in Biology.     

Acute inhibition of protease and suppression of growth in zooplankter,Moina macrocopa,by Microcystis blooms collected in Central India

Cyanobacterial blooms consisting of Microcystis spp., collected from 14 water-bodies in Central India, and an adapted culture, were studied for likely impact on zooplankton community. When fed with single cells of Microcystis from several locations, in mixtures with Chlorella, population growth of the cladoceran Moina macrocopa was suppressed. Microcystis alone was unsuitable as food. In three cases, bloom extracts enhanced mortality of starved zooplankton. Extracts from several sources inhibited protease activity when trypsin or a crude extract from zooplankton served as enzyme source. Upon fractionation by solid-phase extraction, the C-18 passed extract contained the anti-protease and toxic substances for zooplankton, whereas a methanol eluted fraction retained the trypsin inhibitory substance. The study suggests that production of protease inhibitors by cyanobacteria is a factor responsible for feeding inhibition and mortality in zooplankton, which in turn could regulate the community structure of grazers.