Ecological problems of Lake Ladoga: causes and solutions

We studied the outcome of competition between a large (Brachionus calyciflorus) and a small (Anuraeopsis fissa) rotifer species at five algal (Scenedesmus acutus) concentrations (0.5 × 10⁶ to 40.5 × 10⁶ cells ml^–1) and with varying initial densities in mixed populations (100 to 0% of B. calcyciflorus or A. fissa), the combined initial biomass being 0.2 µg ml^–1 in all test jars. Experiments were conducted at 28 ± 1 °C.Regardless of food concentration, B. calcyciflorus showed a greater increase in biomass than A. fissa, peak densities (mean ± standard error) at the lowest food concentration in the controls being 1.34 ± 0.31 µg dry weight ml^–1 and 0.82 ± 0.08 dry weight ml^–1, respectively. At the lower food concentrations, A. fissa displaced B. calyciflorus and vice versa at the higher food concentrations. At the intermediate food concentrations of 4.5 × 10⁶ cells ml^–1, B. calyciflorus outcompeted A. fissa only if its initial population density was three times higher. The rates of population growth in controls varied from 0.792 ± 0.06 d^–1 to 1.492 ± 0.13 d^–1 for B. calyciflorus and 0.445 ± 0.04 to 0.885 ± 0.01 for A. fissa depending on food level. When both species were introduced together, low food levels favoured higher abundance of A. fissa than B. calyciflorus, suggesting, in nature, it is likely that small Anuraeopsis colonize oligotrophic water bodies more successfully than larger Brachionus. The results also suggest that the outcome of competition depends not only on the size of the competing species and food availability but also on their colonizing density.     

Bacterial feeding by the rotifer Brachionus calyciflorus: Clearance and ingestion rates,behavior and population dynamics

Summary The rotifer Brachionus calyciflorus is capable of collecting and ingesting cells or short chains of a laboratory-grown bacterium Aerobacter aerogenes. Clearance rate, the volume of water effectively processed animal ^-1h^-1, does not vary systematically with bacterial density between 0.01 and 100 g dry weight ml^-1. Consequently, ingestion rates are strongly density-dependent, reaching maximal values at the highest food densities tested. Bacterial feeding rates are consistently lower than those determined with larger food types, except in very dense cell suspensions. A. aerogenes in high concentration (100 g ml^-1) induces Brachionus to orient their pseudotrochal cirri to form screens over the buccal funnel; this behavior is at least four times less frequently observed at low (10 g ml^-1) food density. Despite its occurrence, pseudotrochal screening appears ineffective in regulating bacterial ingestion rate. B. calyciflorus can be cultured xenically for greater than 40 generations fed A. aerogenes alone, with no diminution in net reproductive rate or intrinsic rate of natural increase, and no lengthening in cohort generation time.     

Rotifers as predators on small ciliates

Clearance rates of Synchaeta pectinata, Brachionus calyciflorus and Asplanchna girodi on Tetrahymena pyriformis (46 µm in length) at a density of 10 cells ml^–1, in the presence of algal food, were 2.5 to 6.1 ml rot.^–1 day^–1. Clearance rates of these rotifers were, respectively, about 2, 3, and 13 times lower on Strobilidium gyrans (58 µm in length) than on T. pyriformis, indicating that the saltations of S. gyrans are an effective escape response. Clearance rates of S. pectinata were considerably lower on Colpidium striatum (81 µm) than on S. gyrans, suggesting that S. pectinata may not be able to ingest ciliates of this size. S. pectinata had a clearance rate of 19 ml rot.^–1 day^–1 on S. gyrans at a density of 1.2 cells ml^–1, in the absence of edible algal food. Rotifers may prey extensively on ciliates in natural plankton communities, ingesting 25 to 50 individuals in the 45–60 µm size range day^–1.     

Brachionus calyciflorus Pallas as agent for the removal of E. coli in sewage ponds

Brachionus calyciflorus (Pallas) is a common brachionid in sewage oxidation ponds. The uptake and assimilation of E. coli was optimal at concentrations of 2.7–6.9 × 10⁸ cells ml^–1 while assimilation coefficient per body weight of B. calyciflorus was found to be 10% · Ind.^–1 d^–1. More than two eggs per individual were produced during 24 hours when brachionids were fed with a mixutre of E. coli (10⁹ cells · ml^–1) and Chlorella spp. (10⁶ cells · ml^–1). The nutritional value of the mixture of E. coli and Chlorella spp. was found to be higher than that of bacteria alone.     

Utilization of cyanobacteria by Brachionus calyciflorus: Anabaena flos-aquae (NRC-44-1) as a sole or complementary food source

The rotifer Brachionus calyciflorus can utilize the cyanobacterium Anabaena flos-aquae as either a sole or supplementary food source in laboratory culture. Positive population growth rates accompany food densities of 10 or 100 µg dry weight ml^–1, but slightly negative rates are found at a lower density (1.0 µg ml^–1). These results are consistent for rotifers feeding on two strains of A. flos-aquae, UTEX-1444 and NRC-44-1, with slightly enhanced survivorship and reproduction with the latter food. A 1:1 mixture (by dry weight) of Euglena gracilis and A. flos-aquae (NRC-44-1) produces survivorship comparable to that of control rotifer cohorts fed E. gracilis alone, but elicits significantly greater fecundity and population growth rates than found with the control food suspension at the same biomass density.     

Respiration of different stages and energy budgets of juvenile brachionus calyciflorus

Respiration data for different stages of Brachionus calyciflorus, fed with three concentrations of Kirchneriella lunaris at 20°C, are presented. Increasing oxygen consumption from 4.1 to 4.6 .10^–3 µl/h × ind. with food decreasing from 5.10⁶ to 10⁶ and 4.10⁵ cells/ml has been fourid for adult females with one egg, but other age groups showed divergent results. Based on the respiration data for age groups o to 12 and 12 to 24 h old and some other results and calculations-e.g. dry weight and caloric content of eggs and females, ingestion rates/h for the different concentrations of food-energy budgets for juvenile, growing B. calyciflorus are presented.     

Clearance rates of bacteria by the rotifer Filinia longiseta (Ehrb.) measured using three tracers

The clearance rates (CRs) of bacteria by Filinia longiseta were measured at 19°C, both in situ in Lake Loosdrecht and in the laboratory during summer. The tracer particles used in the field were: (1) 0.51 µm fluorescent microspheres, and (2) fluorescently labelled bacteria (FLB). A third type of tracer particle, natural [methyl-³H]-thymidine-labelled bacteria (< 1.2 µm), were used as a radiotracer in a laboratory experiment. The uptake of the first two tracer-particle types was measured by microscopic examination of the rotifer guts. In the third case, the uptake of radioactivity was determined by liquid scintillation counting. The rate of uptake of the microspheres decreased 10 min after the start of the experiment, probably because the gut passage time was exceeded. Using a 5 min feeding time, the rate of uptake of microspheres was higher than that of the FLB, though the variation in the uptake in both cases was high. The ingestion rates and CRs of bacteria by F. longiseta based on the fluorescent tracers were: microspheres, 5115 bact.ind^–1 h^–1 and 0.368 µl ind^–1 h^–1; FLB, 2252 bact.ind^–1 h^–1 and 0.162 µl ind^–1 h^–1. The mean CR using the thymidine-labelled natural bacteria and a 10 min feeding time was 0.179 µl ind^–1 h^–1. Thus, the CR based on the microsphere method was twice as high as for the other two methods.     

Feeding in Euchlanis dilatata lucksiana Hauer on filamentous cyanobacteria and a prochlorophyte

Ingestion and assimilation rates of Euchlanis dilatata lucksiana Hauer, isolated from Lake Loosdrecht (The Netherlands) and cultured on lake water (seston < 33 µm), were measured in the laboratory using the ¹⁴C-tracer technique. The five taxa used as tracer foods, together with 6–7 mg C l^–1 of lake seston in each case, included four species of filamentous cyanobacteria (Oscillatoria redekei, O. limnetica, Aphanizomenon flos-aquae, Anabaena PCC 7120) and a prochlorophyte (Prochlorothrix hollandica). Except Anabaena, they are all commonly encountered in eutrophic Loosdrecht lakes, including Lake Loosdrecht, and their dimensions ranged between 150 and 250 µm in length and 2 and 3.5 µm in width. The small and large Euchlanis used as experimental animals had mean lengths of 217–223 µm and 276–305 µm, respectively. Euchlanis fed on all the taxa offered as food. Clearance rates ranged from 51 to 99 µl ind^–1 d^–1 for the large animals and from 22 to 41 µl ind^–1 d^–1 for the small animals. The highest ingestion rate observed, 1.7 µg ind^–1 d^–1, was for the large animals feeding on Aphanizomenon. The daily ration for both size classes far exceeded 100% of body weight, reaching up to 690% for the small animals feeding on Aphanizomenon. The small animals generally appeared to assimilate the ingested food more efficiently (assimilation efficiencies: 37–100%) than the large animals (34–77%). Compared with an earlier study in which only lake seston (<33 µm) was used as food, the specific clearance rates of Euchlanis on the cyanobacteria and Prochlorothrix were generally somewhat lower.     

Biogeochemical influence on carbon isotope signature in boreal lake sediments

The functional morphology of the feeding palps and prostomium of the spionid polychaetes Streblospio benedicti and S. shrubsolii was studied. Three functional groups of cilia of the feeding palps were found on both species – frontal cilia, latero-frontal cirri and lateral cilia. Frontal cilia line the food groove and transport food particles to the pharynx, and have been reported for all spionid polychaetes except species of the genus Scolelepis. Latero-frontal cirri deflect particles onto the frontal surface and have been observed in several spionid genera including Paraprionospio, Streblospio, Polydora and Dipolydora. Lateral cilia beat in continuous metachronal waves creating lateral vortices that potentially entrain suspended particles, and are known in Paraprionospio and Streblospio. The two species of Streblospio did differ in the distribution of prostomial papillae. These papillae are eversible and thought to function in particle selection as particles on the pharynx come in contact with the papillae. Prostomial papillae were restricted to the peripheral surface of S. benedicti and were widely scattered on all surfaces of the prostomium of S. shrubsolii. A conical tentaculate structure occurs between the branchiae of the first setiger of S. benedicti, but only a low raised elevation is present on S. shrubsolii.     

Relative importance of the trophic and direct pathways on PCB contamination in the rotifer species Brachionus calyciflorus (Pallas)

To determine the contribution of food ingestion (trophic pathway) to PCB contamination of zooplankton in the river Meuse (Belgium), we used ¹⁴C-labelled algae (Dictyosphaerium ehrenbergianum) to measure ingestion and assimilation rates in the rotifer species Brachionus calyciflorus. When the concentration of algae in the culture medium varied from 20 10³ to 200 10³ algal cells ml^–1 (0.12 to 1.18 mg Cl^–1), the Brachionus calyciflorus ingestion rate varied from 0.25 ± 0.12 to 1.52 ± 0.43 ng C ind^–1 h^–1 at 15 °C and from 0.74 ± 0.17 to 5.93 ± 0.61 ng C ind^–1 h^–1 at 20 °C. The assimilation efficiency (ratio of the assimilation rate to the ingestion rate) measured in a culture medium containing 200 10³ algal cells ml^–1 was 55.7 ± 5.8%. Since the PCB concentration measured in the phytoplankton of the river Meuse is about 3 µg PCBs g^–1 D.W., the estimated PCB contamination of zooplankton ascribable to the trophic pathway ranges from 0.22 ± 0.17 to 1.31 ± 0.77 µg PCBs g^–1 D.W. at 15 °C and from 0.64 ± 0.34 to 5.10 ± 2.10 µg PCBs g^–1 D.W. at 20°C. The lower figure based on measurements effected at 20 °C is comparable to the actual level measured in zooplankton samples collected in the river Meuse (0.69 ± 0.20 µg PCBs g^–1 D.W.). The applicability of the formula used in our estimate was checked in a 48-hour in vitro experiment in which the rotifers were fed contaminated algae. The PCB accumulation measured in the rotifers was found to coincide with the calculated PCB contamination. Additional experiments were carried out to determine the contribution of the direct pathway to PCB contamination of zooplankton living in the river Meuse (0.02 µg PCBs l^–1 of water; average dissolved organic matter: 3 mg C 1^–1). The PCB concentration in zooplankton resulting from direct uptake of PCBs from the water was estimated at 0.19 ± 0.05 µg PCBs g^–1 D.W. These results show that in zooplankton living in polluted ecosystems, PCBs are likely to accumulate via the trophic pathway to concentrations up to 30 times higher than by direct contamination. Furthermore, our estimates of PCB contamination via the trophic pathway coincide quite well with actual concentrations measured in situ.     

Competition between Brachionus calyciflorus Pallas and Brachionus patulus (Müller) (Rotifera) in relation to algal food concentration and initial population density

Competitive laboratory experiments between Brachionus calyciflorus and B. patulus were conducted at low (1×10⁶ cells ml^–1) and high (3×10⁶ cells ml^–1) densities of Chlorella vulgaris and four initial inoculation densities (numerically, 100% B. calyciflorus; 75% B. calyciflorus + 25% B. patulus; 50% each of the two species; 25% B. calyciflorus + 75% B. patulus and 100% B. patulus). Population densities were enumerated and the medium was changed daily for 20 days. B. patulus was a superior competitor in low food density regardless of inoculation density. At high food density, B. calyciflorus showed higher population growth in the first week but thereafter was outcompeted by B. patulus regardless of initial density. When grown alone, B. calyciflorus reached peak abundances (mean ± standard error) of 31±3 and 81±7 individuals ml^–1 at low and high food densities, respectively. The corresponding values for B. patulus were 130±2 and 306±13. The adverse effects of B. patulus on the peak abundances of B. calyciflorus were higher at low food concentration. Data on egg ratios (eggs female^–1) revealed an inverse relation with population abundance of both tested rotifer species. Our results indicated that the rate of population increase of a species was not a good indicator of its competitive ability. Instead, the ability to reproduce under continuously diminishing food resources (until a threshold level) was responsible for the competitive edge of B. patulus over B. calyciflorus. This was further influenced by the relative inoculation densities of the tested rotifer species and the offered food densities.     

Particle size dependent feeding by the rotifer Brachionus plicatilis

Size selective feeding by Brachionus plicatilis was investigated with algae and bacteria (0.3–3.5 µm) and mono-disperse latex beads (0.3–3.0 µm) in short term feeding experiments. B. plicatilis demonstrated maximum clearance rate of particles with diameter 2µm, but particles with diameter down to 0.3 µm were also ingested. The clearance rate of bacteria was 15–55% of that obtained for optimal sized particles (2 µm), and was related to particle size. The relative reduction in retention of particles with diameter < 2 µm was more pronounced for latex beads than for natural food particles, suggesting other mechanisms than size to be important for the particle retention by the rotifer. This is emphasized by the fact that the clearance rates were much lower for latex beads than for natural food particles of comparable size. Efficient retention of bacteria was observed for rotifers in poor physiological condition, i.e. rotifers with low maximum clearance rate. This may reflect a strategy to optimize energy utilization by reducing locomotion costs and increasing energy intake.The results indicate that B. plicatilis has a low to medium ability to feed on bacteria. In natural ecosystems, its importance as a bacterial grazer is of limited importance. At high population densities, such as in live feed cultures, the rotifer may, however, efficiently remove bacteria from the culture.     

Formation of Polar Bundles of Pili and the Behavior of Azospirillum brasilenseCells in a Semiliquid Agar

This paper describes the formation of single polar bundles of pili on Azospirillum brasilensecells, the twitching motility of cell aggregates, and a new type of social behavior—the dispersal of bacterial cells in semiliquid agar associated with the formation of granular inclusions (the so-called Gri⁺phenotype)—which is an alternative to swarming (the Swa phenotype). The wild-type A. brasilensecells occurring in a semiliquid agar may show either the Swa⁺Gri^–, or Swa^–Gri^–, or Swa^–Gri⁺phenotype. The formation of single polar flagella (Fla) or polar bundles of pili may reflect two alternative states of A. brasilensecells. The components of the Fla system may be involved in the regulation of the phenotypic variation of azospirilla.     

Morphology and infraciliature of Holosticha bradburyae nov. spec. (Ciliophora,Hypotrichida) from the Yellow Sea,China

The living morphology and infraciliature of a new marine hypotrichous ciliate, Holosticha bradburyae nov. spec., collected from the coastal water off Qingdao (Tsingtao), China, are investigated. This species is characterized by: body size 150–320 × 25–75 m with brownish to dark brown cell colour, ca. 53 adoral membranelles and 1 anteriorly positioned buccal cirrus; 3 frontal, 2 frontoterminal and 20–26 transverse cirri; midventral rows comprising 27-32 pairs of cirri; one conspicuous gap always present between anterior and posterior parts of AZM, and 2–5 distinctly elongated membranelles are always present at the posteriormost end; cortical granules conspicuous, round and flattened with central depression, arranged in about 10 lines on dorsal side; 28–33 irregularly arranged macronuclear nodules; 9–11 complete dorsal kineties; caudal cirri absent.     

Feeding rate inhibition in crowded Daphnia pulex

Feeding rates of Daphnia pulex fed a range of levels of the alga Chlamydomonas reinhardi of 15 °C are strongly density-dependent. At lower densities, Daphnia (30 1^–1) fed at higher rates than crowded (270 1^–1) Daphnia which manifest a relatively depressed saturation feeding response. At 30 individuals/liter, Daphnia consumed 8.5 – 15.7 × 10⁴ cells d^–1h^–1 (on a volume basis, 12.1 – 22.2 × 10⁶ m³), at 270 L^–1 3.7 – 3.9 × 10⁴ (5.2 – 5.5 = 10⁶ m³ cells d^–1h^–1 when feeding on algae at 80 000 cells ml^–1 (11.3 × 10⁶ m³ ml^–1). The feeding rate data best fit an Ivlev feeding function. An autoallelopath might be causing the repression. Water preconditioned with crowded Daphnia completely repressed feeding in uncrowded Daphnia after six hours.     

Optimum growth conditions and light utilization efficiency of Spirulina platensis (= Arthrospira fusiformis) (Cyanophyta) from Lake Chitu, Ethiopia

Spirulina platensis (= Arthrospira fusiformis) was isolated from Lake Chitu, a saline, alkaline lake in Ethiopia, where it forms an almost unialgal population. Optimum growth conditions were studied in a turbidostat. Cultures grown in modified Zarrouk's medium and exposed to a range of light intensities (20–500 µmol photons m^–2s^–1) showed a maximum specific growth rate (µ_max) of 1.78 d^–1. Quantum yield for growth (µ) was 3.8% at the optimum light for growth of 330 µmol photons m^–2s^–1, and ranged from 2.8 to 9.4%. With increase in irradiance, the chlorophyll a concentration decreased, and the carotenoids/chlorophyll a ratio increased by a factor of 2.4. The phosphorus to carbon ratio (P/C) showed some variation, while the nitrogen to carbon ratio (N/C) remained relatively constant, thus causing fluctuations in the N:P ratio (7–11) of cells. An optimum N:P ratio of about 7 was attained in cells growing at the optimum light for growth. Results from the continuous culture experiments agreed well with maximum values of photosynthetic efficiency given in the literature for natural populations of S. platensis in the soda lakes of East Africa, Lake Arenguade (Ethiopia), and Lake Simbi (Kenya).     

Extracellular DNA in aquatic ecosystems may in part be due to phycovirus activity

In a eutrophic lake, a crash of the algal population was followed by a significant increase in the number of virus-like particles (from ca. 1 10⁶ ml^–1 to ca. 26 10⁶ ml^–1), and soon thereafter by an increase of the amount of extracellular DNA (from ca. 20 µg l^–1 to ca. 40 µg l^–1). The same pattern of correlation between decrease of algae and increase of viruses and extracellular DNA could be demonstrated by an in vitro experiment with a Chlorella-virus-system. Lysis of algae by viruses increased both the number of viruses and the amount of DNA in the culture medium. Extracellular DNA mainly consisted of material with a molecular weight below 500 bp.The Chlorella-virus-system is discussed. It could be used as a model-system for studying the dynamics of interaction of viruses and algae in aquatic ecosystems.     

Predation on Ceriodaphnia cornuta and Brachionus calyciflorus by two Mesocyclops species coexisting in Barra Bonita reservoir (SP,Brazil)

Feeding experiments with two species of carnivorous copepod, Mesocyclops longisetus (Thiebaud) and Mesocyclops kieferi Van de Velde from Barra Bonita, a eutrophic reservoir in São Paulo, Brasil, were performed using two common types of prey: Ceriodaphnia cornuta, a cladoceran, with a mean body length of 464 µm (including spines) or 393 µm (without spines), and Brachionus calyciflorus, a rotifer with a mean body length of 350 µm (including spines) or 279 µm (without spines).Both species showed higher consumption rates on Brachionus than on Ceriodaphnia. For Mesocyclops longisetus, the average rates were: 2.19 prey ind^–1 h^–1 (Brachionus), and 1.30 prey ind^–1 h^–1 (Ceriodaphnia). For Mesocyclops kieferi, the rates were 1.85 prey ind^–1 h^–1 (Brachionus) and 0.60 prey ind^–1 h^–1 (Ceriodaphnia). These experimental data are discussed with reference to the dynamics of the predator and prey populations in the reservoir.Laboratorio de Limnologia, Departamento de Ciencias Biologicas, Universidade Federal de São CarlosCentro de Recursos Hidricos e Ecologia Aplicada Lab. de Limnologia, Departamento de Hidraulica e Saneamento, Escola de Engenharia de São Carlos, Universidade de São Paulo     

Impact of in vitro Cultivation Conditions on Stress Responses and on Changes in Thylakoid Membrane Proteins and Pigments of Tobacco during ex vitro Acclimation

Four physiologically and phenotypically diversified tobacco (Nicotiana tabacum L. cv. Samsun) plantlet variants had been generated by cultivation on media either lacking or containing sucrose (0 and 3 %, m/v) under two different photon flux densities (PFD), 50 µmol m^–2 s^–1 (LL) and 200 µmol m^–2 s^–1 (HL). Plantlets were transferred into soil without any pre-acclimation and grown either under PFD of 200 µmol m^–2 s^–1 or 700 µmol m^–2 s^–1. Sucrose feeding in vitro resulted in reduced degree and duration of wilting after transfer. The highest readiness for ex vitro acclimation was found in 3 % HL plants, in which changes of photosynthetic apparatus and stress responses were the smallest. On the contrary, the steepest decline of Fv/Fm ratio on the first day after transplantation, doubled chlorophyll content and almost tripled D1/LHC 2 ratio after 7 d of ex vitro growth under 700 µmol m^–2 s^–1 characterized 0 % HL plants, which had suffered chronic photoinhibition in vitro. Remarkably high abscisic acid content at the end of in vitro cultivation and during acclimation as well as increased synthesis of both D1 and LHC 2 proteins even at the end of analyzed acclimation period were found only in 0 % LL plants. Increase of D1/LHC 2 ratio and chlorophyll contents demonstrate that in vitro developed leaves of all plant variants are able to acclimate to new environment. The most surprising result in the whole study is the drop of D1 protein synthesis in all plants on the 3^rd day. Five times decline of photoprotection level of xanthophylls in plants after ex vitro transfer into the same PFD showed stress character of in vitro cultures.     

A redescription of the marine hypotrichous ciliate, Nothoholosticha fasciola (Kahl, 1932) nov. gen., nov. comb. (Ciliophora: Urostylida) with brief notes on its cellular reorganization and SS rRNA gene sequence

The morphology and infraciliature of the marine hypotrichous ciliate Nothoholosticha fasciola (Kahl, 1932) nov. gen., nov. comb., isolated from mariculture waters near Qingdao, China, are redescribed based on live and protargol-impregnated specimens. Features reported for the first time include the possession of more than 50 macronuclear nodules and details of the infraciliature, i.e. 50–60 adoral membranelles, shortened paroral and endoral membranes, six frontal, one buccal and two to seven transverse cirri, ca. 40 pairs of midventral cirri, ca. 60–120 left and 70–120 right marginal cirri, three dorsal kineties, caudal and frontoterminal cirri absent. In addition, brief details of two stages of cellular reorganization in N. fasciola are supplied and comparisons with some related urostylids based on SS rRNA gene sequence data are reported. The new genus Nothoholosticha is established based primarily on the absence of frontoterminal cirri, which distinctly separates it from similar urostylid genera. Anteholosticha longissima is transferred to Nothoholosticha as N. longissima (Dragesco and Dragesco-Kernéis, 1986) nov. comb. and Holosticha antarctica is transferred to Pseudokeronopsis as P. antarctica (Wilbert and Song, 2008) nov. comb.