Vertical distribution of virus-like particles (VLP) and viruses infecting Micromonas pusilla during late summer in the southeastern Skagerrak, North Atlantic

Vertical profiles were made at one offshore station and onecoastal station, on 4-5 September 1996, in the south-easternSkagerrak. The surface water of the two stations differed significantlywith respect to both temperature and salinity, as the outerstation (A) was situated in high-saline water originating fromthe North Sea, while the low-saline surface water at the innerstation (B) was influenced by the Baltic current. Virus-likeparticle (VLP) abundance was 5 x 10⁹–25 x 10⁹1^–1H in the 0-50 m water column. Maximal VLP values were foundin the surface water, although a lower number was detected inthe low-saline surface water (0 m depth) at station B. Virusesinfective to Micromonas pusilla were estimated to     

Alcian Blue-stained particles in a eutrophic lake

We used a neutral solution of Alcian Blue to stain transparentparticles in eutrophic Lake Frederiksborg Slotss0, Denmark.Alcian Blue-stained particles (ABSP) appeared to be similarto the so-called transparent exopolymer particles (TEP) identifiedwith an acidic solution of Alcian Blue. Our results on the abundance,size distribution and bacterial colonization of ABSP thereforereflect general patterns of TEP. The abundance of ABSP in thesize range 3–162 µm and retained by 3mu;m pore sizefilters averaged 3.62.4910⁵ ml^–1 (SD), which is amongthe highest concentrations reported for comparable size spectraof TEP. On average, 35 % of ABSP (by number) were colonizedby bacteria and 8.610⁵ bacteria ml^–1 lake water wereattached to ABSP, which corresponds to 7% of the total bacterialabundance.     

Food size selectivity of Artemia franciscana at three developmental stages

Food size selectivity was examined in Artemia franciscana metanaupliiat three different developmental stages. Clearance rates weredetermined in short-term experiments either by measuring thedecrease in concentration of live particles and plastic beads,or by measuring the radioactivity accumulated in animals thatgrazed ¹⁴C-labelled live particles. The maximum clearance rateofA.franciscana metanauplii increased during development andwas measured at 50–63 µl ind.^–1 h^–1,254 µl ind.^–1 h^–1 and 1.48–2.10 ml ind.^–1h^–1 in 2-, 4- and 7-day-old metanauplii, respectively.A preference for particles with a diameter of 4–8 µmwas observed at all three developmental stages. The abilityof A.franciscana metanauplii to graze bacterial particles wasalso demonstrated, although the efficiency in grazing such smallparticles was low compared to microalgae (28, 20 and 9% of themaximum clearance rate in 2-, 4- and 7-day-old metanauplii,respectively). Electron microscopy showed that the inter-setulardistance in antennae and thoracopods was 0.20 ± 0.07,0.16 ± 0.05 and 0.18 ± 0.04 µm in 2-, 4-and 7-day-old metanauplii, respectively, and accordingly independentof stage.     

Size, composition and distribution of particles related to wind induced resuspension in a shallow tropical lagoon

The size, composition and distribution of particles in the watercolumn were surveyed in a shallow area (1 m depth) of a tropicallagoon (Cte d'Ivoire) during a sequence of wind-induced resuspension.Water samples were collected hourly near the surface duringone tidal cycle. Three characteristic periods were distinguished:a calm period with low wind speed (average 1.2 m s^–1 awindy period with wind speed >3 m^–1 s (range between4 and 6 m s^–1) inducing sediment resuspension and a relaxationperiod during the decrease of wind velocity. From the analysisof several parameters (particle size and volume, bacteria. pico-and nanophytoplankton, ciliates and detritus), sediment resuspensioncaused a regular injection of particles from the bed. The finestparticles (1.5–6 µm: chlorophytes such as Chiorellaspp., picocyanobacteria such as Synechococcus) were the firstto be affected by wind-induced turbulence, whereas large particles(6–12 µm: diatoms. cyanobacteria such as Lyngbiaspp.) were dispersed into the water column at the highest windspeed. The fate of the different seston components differedaccording to their size. Therefore, wind-induced resuspensioncould greatly influence the food web organization through thequantity, quality and size of edible particles available ata given time.     

Seasonal variations of bacterial abundance and biomass and their relation to phytoplankton in the hypertrophic tropical lagoon Cienaga Grande de Santa Marta, Colombia

The seasonal development of bacteria was studied in the hypertrophiccoastal lagoon Ciénaga Grande de Santa Marta (Caribbeancoast of Colombia). This large but only 1.5 m deep lagoon issubject to strong seasonal variations of salinity from almostfully marine (April/May) to brackish conditions in October/November.Chlorophyll ranged from 6 to 182 µg L^–1, and grossprimary production amounted to 1690 g C m^–2 per year.Total bacterial number (TBN) ranged from 6.5 to 90.5 x 10⁹ cellsL^–1 and bacterial biomass (BBM) from 77 to 1542 µgC L^–1, which are among the highest ever reported for naturalcoastal waters. Neither TBN nor BBM varied significantly withsalinity, phytoplankton or seston concentrations. Only the bacterialmean cell volume showed a significant relation to salinity,being highest (0.066 µm³) during the period of increasingand lowest (0.032 µm³) during decreasing salinity. Bacterialprotein accounted for 24% (19–26%) and phytoplankton proteinfor 57% (53–71%) of total seston protein. The ratio (annualmean) of bacterial carbon to phytoplankton carbon was 0.44 (range0.04–1.43). At low phytoplankton abundance [chlorophylla (Chl a) < 25 µg L^–1], bacterial carbon wasalmost equal to phytoplankton biomass (i.e. the mean ratio was1.04). In contrast, at Chl a > 100 µg L^–1, BBMwas low compared to phytoplankton biomass (the mean ratio was0.16). In general, BBM varied less than phytoplankton biomass.Most probably, the missing correlation between bacterial andphytoplankton variables was due to (i) organic material partlyderived from allochthonous sources serving as food resourcefor bacteria and (ii) a strong resuspension of bacteria fromthe sediment caused by frequent wind-induced mixing of the veryshallow lagoon.     

Phosphorus gain by bacterivory promotes the mixotrophic flagellate Dinobryon spp. during re-oligotrophication

Bacterivory by mixotrophic flagellates may contribute to theirnutrient supply, providing a competitive advantage in oligotrophicwaters. We hypothesized an increase in Dinobryon biomass duringthe re-oligotrophication process in the large and deep LakeConstance. To estimate whether bacterivory contributed substantiallyto the flagellates’ phosphorus supply, we determined ingestionrates. Dinobryon biomass increased with decreasing total phosphorusconcentrations in the lake over a period of 17 years (P = 0.0005).The promotion of Dinobryon biomass during re-oligotrophicationmay be explained by the increasing light availability due tothe decreasing biomass of other phytoplankton yielding a releasefrom competition. The date of the Dinobryon abundance maximumshifted to earlier time points in the year, probably becausea smaller phosphorus pool was depleted more quickly. Ingestionrates of Dinobryon ranged between 0.5 and 13 bacteria cell^–1h^–1 (0.2–5.4 fg C pg C^–1 h^–1), and clearancerates varied between 0.2 and 3.2 nL cell^–1 h^–1 (4–78pL pg C^–1 h^–1), leading to bacterial losses of upto 30% day^–1 of bacterial standing stock. The ingestionof bacteria covered 77% of the phosphorus need of the flagellateduring the period of maximum growth in 1996 (net growth rate0.34 day^–1), and it fully covered the need at all othertimes.     

The effect of detrital addition on the development of nanoflagellates and bacteria in Lake Kinneret

The effect of adding dissolved substrates derived from algalcells on the patterns of nutrient cycling and growth of bacteria,heterotrophic nanoflagellates (HNAN) and photoautotrophs wasdetermined in samples of near-surface waters from Lake Kinneret.Supplementation of substrates always resulted in an increasedpeak of HNAN numbers and had little effect on bacterial numbers.HNAN-mediated nutrient remineralization of nitrogen and phosphoruswas also stimulated. In light-incubated samples the remineralizednutrients were taken up by photoautotrophic cells. Maximum growthrates observed for HNAN ranged from 0.03 to 0.11 h^–1,clearance rates for bacteria 1.1–7.3 nl HNAN^–1 h^–1and remineralization rates 6.4–8.4 µg N mg dry wt^–1h^–1 and 0.37–0.99 µg P mg dry wt^–1 h^–1.     

Viral dynamics and patterns of lysogeny in saline Antarctic lakes

Antarctic lakes are extreme ecosystems with microbially dominated food webs, in which viruses may be important in controlling community dynamics. A year long investigation of two Antarctic saline lakes (Ace and Pendant Lakes) revealed high concentrations of virus like particles (VLP) (0.20–1.26 × 10⁸ ml⁻¹), high VLP: bacteria ratios (maximum 70.6) and a seasonal pattern of lysogeny differing from that seen at lower latitudes. Highest rates of lysogeny (up to 32% in Pendant Lake and 71% in Ace Lake) occurred in winter and spring, with low or no lysogeny in summer. Rates of virus production (range 0.176–0.823 × 10⁶ viruses ml⁻¹ h⁻¹) were comparable to lower latitude freshwater lakes. In Ace Lake VLP did not correlate with bacterial cell concentration or bacterial production but correlated positively with primary production, while in Pendant Lake VLP abundance correlated positively with both bacterial cell numbers and bacterial production but not with primary production. In terms of virus and bacterial dynamics the two saline Antarctic lakes studied appear distinct from other aquatic ecosystems investigated so far, in having very high viral to bacterial ratios (VBR) and a very high occurrence of lysogeny in winter.     

Abundance, size distribution and bacterial colonization of transparent exopolymeric particles (TEP) during spring in the Kattegat

The abundance, size distribution and bacterial colonizationof transparent exopolymeric particles (TEP) were monitored inthe Kattegat (Denmark) at weekly intervals throughout the spring(February-May) encompassing the spring diatom bloom. These recentlydiscovered particles are believed to be formed from colloidalorganic material exuded by phytoplankton and bacteria, and mayhave significant implications for pelagic flux processes. Duringthis study, the number concentration of TEP (>1 µm)ranged from 3 x 10³ to 6 x 10⁴ ml^–1 and the volume concentrationbetween 0.3 and 9.0 p.p.m.; they were most abundant in the surfacewaters subsequent to the spring phytoplankton bloom. The rangeof TEP (encased) volume concentration was similar to that ofthe phytoplankton, although at times TEP volume concentrationexceeded that of the phytoplankton by two orders of magnitude.The TEP size distribution followed a power law, with the abundanceof particles scaling with particle diameter^–(ß+1).The seasonal average estimate of ß (2.3) was not significantlydifferent from three, consistent with TEP being formed by shearcoagulation from smaller particles. However, date-specific estimatesof ß differed significantly from three, probably becauseTEP are fractal. All TEP were colonized by bacteria, and bacteriawere both attached to the surface of and embedded in TEP. Yetthe number of attached bacteria per TEP was related neitherto the surface area nor the volume, but rather scaled with TEPsize raised to an exponent of     

Characteristics of the Cl- Action Site in the O2 Evolving Reaction in PS II Particles: Electrostatic Interaction with Ions

The role of Cl^– in the reactivation of O₂ evolution inphotosystem II (PS II) particles derived from spinach chloroplastswas studied in the presence of various salts. Multivalent ion(especially anion) salts were found to strongly suppress thereactivation of O₂ evolution by Cl^– in the Cl^–-depletedPS II particles in a competitive manner. The effectiveness ofanions in the suppression of Cl^–-supported O₂ evolutionwas in the order of trivalent>divalent>monovalent ones.Multivalent anions similarly suppressed O₂ evolution in theuntreated PS II particles under low and moderate Cl^– concentrations.pH dependence of the Cl^–-affinity (K_m) value for Cl^–)was also studied. Within the pH range 5.5 to 8 the K_m valuebecame higher as the pH of the medium increased. These resultssuggest that the membrane surface in the vicinity of the Cl^–action site is net positively charged and attracts Cl^–electrostatically, and that the site is almost freely accessibleto various anions. The origin and role of the local net positivedomain and the role of peripheral proteins are discussed. (Received May 27, 1985; Accepted October 8, 1985)     

Diurnal variations in the contributions of autotrophic picoalgae and heterotrophic bacteria to planktonic production in an upland lake

An investigation of the diurnal variation in contributions toproduction of the autotrophic and heterotrophic components ofthe picoplankton community was carried out during August andSeptember in Llyn Padarn, a mesotrophic upland lake in NorthWales. The picoplankton was separated using 1 µm pore-sizedfilters into the smaller cell sized fraction (<1 µm),the majority of the bacteria and the larger cell sized picoalgae(<3>1 µm), together with some bacteria. The distributionof bacterial heterotrophic activity between these two fractionsof picoplankton was assessed by uptake of [¹⁴C]glucose and differentialfiltration. Thus, the absolute autotrophic production by picoalgaeand the heterotrophic contribution by bacteria to picoplanktoncommunity production via uptake of extracellular organic carbon(EOC) were determined. Rates of picoplankton community productionexhibited diurnal variation with maximum rates of 19.1 mg Cm^–3 h^–1 recorded at 18.00 h at 4 m depth in September.The bacterial contribution to picoplankton community productionincreased markedly between 15.00 and 18.00 h. Rates of absoluteautotrophic production varied less over 24 h than rates of accumulationin bacteria of ¹⁴C-labelled EOC released from the entire phytoplanktoncommunity. Bacteria contributed up to 86–98% of the neworganic carbon within the picoplankton community at the endof the day. The maximum rate of absolute autotrophic productionin the picoplankton was 1.6 mg C m^–3 h^–1 at 18.00h at 1 m in August, and the maximum rate of bacterial accumulationof new organic carbon was 18.5 mg C m^–3 h^–1 at 18.00h in September at 4 m depth. The diurnal pattern of picoplanktoncommunity production involved increasing rates during the daywith a maximum at 18.00 h. Autotrophic processes were dominantin the first 3–6 h of the light cycle and heterotrophicuptake of ¹⁴C-labelled EOC was the major component from 15.00h onwards. Bacterial uptake of newly released EOC by phytoplanktonwas rapid, comprised the majority of picoplankton production,particularly later in the day, and contributed a maximum of60% of the total pariculate primary production in plankton between15.00 and 18.00 h at 4 m in September with a mean contributionof between 6 and 26% over 24 h in these investigations. Theimportance of autotrophic processes in picoplankton communityproduction has been overestimated in previous investigations.Bacteria play a major role in transferring newly produced EOCrapidly from phytoplankton to the picoplankton community. Atthe end of the day, the majority of newly produced organic carbonis in bacterial cells and this production is significant inthe dynamics of carbon production within the entire planktoniccommunity.     

Preparation and Characterization of Heat-Stable and Very Active Oxygen-Evolving Photosystem II Particles from the Thermophilic Cyanobacterium, Synechococcus elongatu

Very active and heat-stable oxygen-evolving photosystem II particleswere isolated from the thermophilic cyanobacterium Synechococcuselongatus by treatment of thylakoid membranes with a non-ionicdetergent, sucrose monolaurate (SML). The particles were analyzedin a comparison with photosystem II particles prepared withß-octylglucoside (OG). The two preparations had similarpolypeptide compositions, which were caracterized by high levelsof polypeptides from phycobilisomes. The ratio of chlorophylla to QA was 45 and there were four Mn atoms and one tightlybound Ca²⁺ ion per QA in the particles prepared with SML. Thepreparations were thermophilic, showing substantial rates ofoxygen evolution at temperatures up to 60°C. The maximumrates attained at 45°C were as high as 6.0 mmoles O₂ mg^–1Chl h^–1. PS II particles prepared with OG were similarlythermostable but were less active in oxygen evolution at alltemperatures examined. Kinetic analysis of flash-induced absorptiontransients revealed that about 22% and 28% of photosystem IIreaction centers were not associated with the functional QBsite in the SML- and OG-particles, respectively. When correctedfor the inactive reaction centers, the maximum rates of oxygenevolution by SML- and OG-particles were 7.7 and 7.0 mmoles O₂mg^–1 Chl h^–1, which correspond to half times of1.9 and 2.1 ms for the first-order electron transfer, respectively.Comparison of these half times with those of the S-state transitionand the release of oxygen indicates that the overall photosystemII electron transport is limited by the reduction of added electronacceptors and not by release of oxygen. ³On leave from National Chemical Laboratory for Industry, Higashi1-1, Tsukuba, Ibaraki 305     

Bacterioplankton growth, grazing mortality and quantitative relationship to primary production in a humic and a clearwater lake

Bacterial growth and grazing mortality were estimated from Mayto October in two south Swedish oligotrophic lakes, one beinga clearwater lake (water colour 5–10 mg Pt l^–1 DOC2.9–3.4 mg l^–1, Secchi disk depth 5.0–9.4m) and the other a humic, brownwater lake (water colour 105–165mg Pt l^–1, DOC 13.7–22.7mg l^–1, Secchi diskdepth 1.3–2.1 m). Specific rates of growth and grazingmortality were generally similar for both lakes. However, theabundance of bacteria was consistently 2–3 times higherin the water of the humic lake, suggesting that the total productionand consumption of bacterial cells were also higher than inthe dearwater lake. The ratio of bacterial secondary productionto primary production was higher in the humic lake than in theclearwater lake, indicating that the bacterioplankton of thehumic lake utilize allochthonous substrates, in addition tosubstrates originating from autochthonous primary production.Most of the bacterial loss in both lakes could be attributedto small protozoan grazers. This implies that allochthonousand autochthonous organic carbon fixed by bacterioplankton isless important in terms of carbon flow to higher trophic levelsthan would be expected if macrozooplankton were the dominantbacterivores, providing a more direct and efficient transferof carbon to larger organisms.     

Conspicuous Peak of Oligotrichous Ciliates Following Winter Stratification in a Bog Lake

We analysed early spring protozooplankton peaks following winterstratification in two different basins (northeast, NE; southwest,SW) of an artificially-divided bog lake Große Fuchskuhle(Brandenburg,Germany). The maximum ciliate biomass and numbers (660 and 990µg l^–1 of organic carbon, and 290 and 260 cellsml^–1 in NE and SW, respectively) were reached in the surfacelayer during the ice melting and then continuously decreased.The surface layers were numerically dominated by species ofthe genus Urotricha, while in the ciliate biomass during thefirst part of the study, a mixotrophic oligotrich, Pelagostrombidiummirabile prevailed (C_org up to 940 µg l^–1). We observeda conspicuous ciliate peak that could not be related to thefeeding activity of the dominant ciliate species upon picoplankton.Seemingly, the peak was related to the specific conditions resultingfrom the ice melting where these ciliates could be concentrated.Additionally, the mixotrophy of oligo-trichous species allowedthem to penetrate below the oxycline, although feeding on nanoplanktonsuch as flagellates was also very likely. Our direct measurementsof uptake rates of bacteria showed that the abundant strombidiidswere not nutritionally dependent on bacterivory. However, theciliate uptake rate (up to 670 bacteria ciliate^–1 h^–1)contributed significantly to the overall bacteria mortalityrate. The maximum (community average) cell-specific ciliatefeeding rate of over 200 bacteria ciliates^–1 h^–1was reached, along with an increasing contribution of scuticociliates,paralleled by a drop in large oligotrichs.     

The importance of phytoflagellate, heterotrophic flagellate and ciliate grazing on bacteria and picophytoplankton sized prey in a coastal marine environment

The uptake of bacteria and picoplankton sized fluorescentlylabelled beads was measured off the west coast of the SouthIsland of New Zealand in winter. Phytoflagellates and heterotrophicflagellates showed similar grazing rates on 0.49 µm beads,with mean clearance rates of 1.1 and 1.8 nl ind.^–1 h^–1,respectively. Clearance rates for 1.09 µm beads were 0.9nl ind.^–1 h^–1 for heterotrophic flagellates and0.5 nl ind.^–1 h^–1 for phytoflagellates. Non-loricateciliates had clearance rates of 1.5 µl ind.^–1 h^–1for the picoplankton sized particles. The heterotrophic flagellatesshowed no significant difference between clearance rates of0.49 and 1.09 µm particles. Phytoflagellates, however,showed an apparent preference for the smaller particles. Themeasurement of significant grazing by phytoflagellate populationsin the marine environment is important and indicates that weneed to reassess our concepts of food web structure.     

The fate of discarded appendicularian houses: degradation by the copepod, Microsetella norvegica, and other agents

Despite the potential importance of zooplankton in degradationof marine snow, the association of colonising zooplankton withdiscarded appendicularian houses has not been investigated innorthern areas. We sampled the vertical distributions of appendicularians,houses and potential zooplankton colonisers at two stationsin the central North Sea during late summer. In addition, grazingexperiments were performed with the copepod Microsetella norvegica,which was assumed to be the main contributor to house degradation.The results were used in (i) inverse modelling, to estimatethe factors which were significant in shaping the vertical distributionof houses and (ii) calculations to estimate potential housedegradation rates. M. Norvegica was able to feed on appendicularianhouses, with feeding rates up to 0.42 g C (g C)^–1 day^–1(0.14 µg C ind.^–1 day^–1). The model resultssuggested that the vertical distribution of houses was shapedby sinking of houses, bacterial degradation and feeding of M.norvegica and invertebrate larvae. The estimated community degradationrate by M. norvegica was low, whereas invertebrate larvae haddegradation rates close to bacterial degradation. We concludethat at the typical concentrations of M. norvegica in the NorthSea (10⁴ ind. m^–2), its role in marine snow degradationis likely to be small. Degradation by other zooplankton groups,such as invertebrate larvae, can, however, be substantial.     

Microbial ammonium cycling in the Mississippi River plume during the drought spring of 2000

Microbial potential uptake and regeneration rates of ammonium(NH₄⁺) were studied along a salinity gradient (salinities 0.2–34.4)in the Mississippi River plume during an extreme drought inspring 2000. Chlorophyll concentrations up to 30 µg L^–1were highest in the low- and mid-salinity regions (salinities8.5–28.2) and comparable to records of other years butextended over smaller areas than during periods of normal riverflow. Bacterial biomass (5.1–28.3 µg C L^–1)was at the low end of the range observed in normal flow years,decreased with distance from the river mouth and did not peakwith chlorophyll. Heterotrophic nanoflagellate abundance (1.4–4.0µg C L^–1) did not reflect phytoplankton and bacterialspatial distribution but peaked at 9.2 µg C L^–1at salinity 8.5. Microbial NH₄⁺ regeneration rates were estimatedby ¹⁵NH₄⁺ isotope dilution experiments for the whole microbialcommunity, under light and dark conditions, and for the <2µm bacterium-dominated size fraction. Microbial NH₄⁺ regenerationrates (0.018–0.124 µmol N L^–1 h^–1) werelow relative to previous reports and peaked at salinity 28.Total NH₄⁺ regeneration rates were higher than those in the<2 µm size fraction at only four stations, suggestingthat bacterial mineralization was a significant component ofNH₄⁺ recycling in some parts of the river plume. Higher NH₄⁺regeneration in whole-water samples versus <2 µm fractionsprovided evidence for microbial grazing in regions where chlorophylland regeneration rates peaked and at two full-salinity stations.     

Bacterial growth and losses due to bacterivory in a mesotrophic lake

Bacterial secondary production and rates of bacterivory weredetermined from samples collected from mesotrophic Lake Arlington.Bacterial production and losses were determined by comparingthe growth of natural bacterial assemblages in the presenceof predators (unfiltered samples) to growth in the absence ofpredators (water filtered through 1.0 (im porosity filters).Growth rates of heterotrophic nanoflagellates (HNF) were estimatedfrom growth in the absence of predators (water filtered through5.0 µm porojity filters). Bacterial growth rates rangedbetween 0.002 and 0.069 h^–1 and averaged 0.026 h^–1.HNF grew at rates ranging between 0.003 and 0.107 h^–1and averaged 0.028 h^– Grazing rates ranged between 0.002and 0.043 h^–1, and averaged 0.018 h. The annual averagerate of bacterial biomass synthesis was 3.2 –g Cl^–h^–1 and {small tilde}69% of this production was grazed.Temporal changes in growth and grazing rates suggest a tightlycoupled predator-prey linkage in this lake. ¹Present address: Hydrobiological Institute, Czech Academy ofSciences, Na sddkach 7, 370 05 teski Budjovice, Czech Republic     

Primary and bacterial production compared to growth and food requirements of Daphnia longispina in Lake Kvernavatnet, west Norway

Primary production, and bacterial production as measured byincorporation of [³H-methyl]thymidineinto ice cold TCA insolublematerial were investigated during 1984 in Lake Kvernavatnet,west Norway. Primary production averaged 222 mg C m^–2day^–1 and bacterial production averaged 163 mg C m^–2day^–1. The bacterial production in the euphotic pelagiczonecontributed -60% of the total pelagic bacterial production.The zooplankton was dominated byDaphnia longispina. From growthexperiments with animals fed only natural food in coarse filteredlake water, the population daily growth increments were calculated.The average production of D.longispina was 151 mg C m^–2day^–1 during the period investigated. The estimated primaryproduction was too low to sustain both the bacterial productionand the zooplankton food requirements. These results imply thatthe carbon cycle of the lake is dependent on the supply of allochtonousmaterial, or that the current methods for measuring productionrates in aquatic environments are systematical erratic.     

Feeding of nauplius stages of Eudiaptomus gracilis on mixed plastic beads

Eudiaptomus gracilis makes up 30–40 and 80–90% ofthe zooplankton in Lake Balaton during the summer and the winterrespectively. More than half of the species population consistsof nauplii We studied feeding and size selectivity of naupliiin suspensions which contained polystyrol latex beads in a concentrationdose to the natural seston. Guts of NI nauplii were free ofboth beads and remnants of natural food Of NII–NVI nauplii,67–87% took in beads. Older animals consumed more andlarger particles. The maximum diameter of ingested beads reached29 µm On an average, NII nauplii took in 128 µm³of beads in 10 min, whereas older animals consumed 615–900µm³. The clearance rate remained below 0 01 µl h^–1NII nauplii strongly preferred 1 2 µm particles Oldernauplii did not show any preference or selected only slightlyfor the smallest particles. Nauplii rejected 4–11 µmbeads. In some cases a weak positive selection could be observedtoward 12 µm or larger beads.