The reproductive biology of Cyclops vicinus

Investigations of the reproductive biology of Cyclops vicinusrevealed that mated females oscillate between gravid and nongravidreproductive conditions. The gravid condition can be dividedin two recognizable phases: gravid/nonovigerous and gravid/ovigerous,the former phase being shortest. The maturation of new oocytestakes place when the old egg sacs are still being carried; thisensures a rapid clutch succession. Females which remain unmated,extrude few eggs, in no case complete egg sacs, and remain gravidthus conserving oocytes. Females which mate only once, showa similar reproductive pattern (clutch size and clutch succession)to those which remain combined with males, and thus have theopportunity to remate, but tend to produce fewer clutches. Malesare able to fertilize 3–4 females day^–1. Matingcapacity of males is possibly limited by the time needed tofill a new spermatophore. Short-term starvation (5 days) lengthenedclutch-to-clutch periods and diminished clutch size. When thestarvation period started in the gravid/ovigerous phase, a normalclutch was extruded but no new oocytes matured during starvation,indicating that the energy for egg maturations is provided inthe first part of the reproductive cycle.     

Fish impact on rotifer community structure

Larger species, e.g. Asplanchna priodonta and Conochilus unicornis, and grasping species, e.g. Gastropus stylifer and Ascomorpha spp., became more abundant, while smaller filter feeders, e.g. Keratella cochlearis, decreased after an experimental reduction of the fish population. This development is probably caused by changes in basic regulating factors. The change to invertebrate predator dominance may affect smaller species (e.g. Keratella cochlearis) more than others, the increase of net phytoplankton (e.g. peridineans) will favour grasping species, and the change in seasonal occurrence of certain crucial food species may affect the competitive balance between certain rotifers (e.g. Polyarthra spp.).     

Potential importance of algae in the diet of adult Cyclops vicinus

• 1 The potential importance of phytoplankton to the nutrition of adult Cyclops vicinus was studied.
• 2 The flagellate Chlamydomonas reinhardii was ingested and digested at a higher rate than the coccale green alga Monoraphidium minutum.
• 3 The predation rate on the rotifer Brachionus rubens decreased if C. reinhardii was also available as food. No significant reduction of predation was found when M. minutum was offered together with B. rubens.
• 4 The species of available phytoplankton influenced egg production. Females which were allowed to feed on B. rubens and C. reinhardii produced more eggs than females which fed on rotifers only or a diet containing rotifers and M. minutum. Egg production was also possible when rotifers were absent from the diet.
• 5 Production efficiency was higher when C. reinhardii was the only food resource than on a diet containing rotifers only.

     

Regulation of Rotifer Community by Predation of Cyclops vicinus (Copepoda) in the Římov Reservoir in Spring

The structuring role and predation impact of Cyclops vicinus on the rotifer community was studied using in situ enclosure experiments in Římov Reservoir during the spring of 2000. Seasonal changes in abundance and birth rates of the rotifer species Synchaeta lakowitziana , Polyarthra spp., Keratella cochlearis and Kellicottia longispina were related to predation pressure, i.e. selectivity and cropping rates of C. vicinus . All four rotifer species were found to be consumed by C. vicinus whose predation rates showed a marked succession through the spring period and corresponded to changes in the relative abundance of the pelagic species. The highest predation rates exhibited by C. vicinus were on Synchaeta lakowitziana and Polyarthra spp., being 11.3 and 6.4 ind Cyclops ^–1 day^–1 respectively. The activity of the predator switched among three types of preferred food during the spring period. The most preferred, Synchaeta, was replaced by Polyarthra after Synchaeta became extinct and these species were replaced by Keratella when both soft‐bodied forms were not available in sufficient quantities. Loricated species (K. cochlearis and K. longispina) were consumed at a slower rate. We calculated the proportion of rotifer production cropped day^–1 in order to estimate the predation impact of C. vicinus , which ranged from 11.6 to more than 100% over time and rotifer species. This shows that relative predation impact can be high not only on species most strongly selected, but also on species which are not selected. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Feeding of Cyclops vicinus (Uljanin) (Copepoda: Cyclopoida) in Lake Balaton on the basis of gut content analyses

Consumption of planktonic algae by Cyclops vicinus living in Lake Balaton were studied in eighteen feeding experiments during 1980–1981. Gut contents of 284 adult C. vicinus were analysed in comparison with the natural phytoplankton assemblage. Rates of algal cells elimination were also studied and compared to controles which did not contain animals. C. vicinus in Lake Balaton was found to be an omnivore.     

Predation by juvenile roach on the calanoid copepod Eudiaptomus gracilis and the cyclopoid copepod Cyclops vicinus: a laboratory investigation with mixed and single prey

We tested the outcome of predation by juvenile roach on the calanoid copepod Eudiaptomus gracilis and the similar sized cyclopoid copepod Cyclops vicinus in laboratory experiments with mixed and single-prey. When ovigerous females and adult non-ovigerous females of the calanoid copepod and the cyclopoid copepod were offered in equal numbers to the fish in the mixed-prey experiments, the cyclopoid copepods were significantly more heavily preyed upon than the calanoids. Between 14 and 16 females of the cyclopoid copepod and only between 2 and 4 calanoids had been consumed after the observation period of two hours. The single-prey experiments revealed that the conspicuousness of the calanoid vs the cyclopoid depended on sex and gravidity. Ovigerous females of the cyclopoid copepod were slightly earlier detected by the fish than ovigerous females of the calanoid, probably a result of the highly visible egg-sacs carried by the cyclopoid females. Females without eggs and males of the cyclopoid copepod were recognized later by the predator than females without eggs or males of the calanoid, probably a result of the different behaviours of the different copepod taxa. Cyclopoids frequently congregated near the aquarium bottom while calanoids were closer to the water surface where they were better visible. The calanoid copepod could better escape the fish's attacks than the cyclopoid copepod. Egg-bearing females of both the calanoid and the cyclopoid copepod could significantly better escape than non-ovigerous females or males. Probably ovigerous females react very early to water disturbances caused by the predator. Activity measurements showed that the cyclopoid copepod displayed 2 to 4 times more hops per time unit than the calanoid. Probably the high number of jerky movements displayed by the cyclopoid attracted attention of the predator and contributed to its greater vulnerability.     

Predation by invertebrate predators on the colonial rotifer Sinantherina socialis

Abstract. Colonies of the freshwater colonial rotifer Sinantherina socialis (Monogononta, Flosculariidae) have been shown to be unpalatable to a variety of small-mouthed, zooplanktivorous fishes. To test whether invertebrate predators ingest the rotifer S. socialis , we conducted two types of experiments: (1) Microcosm experiments—in separate experiments, four invertebrate predators (i.e., dragonfly nymphs, damselfly nymphs, notonectids, and Hydra ) were offered prey either singly or in combination. Prey were comprised of S. socialis; Epiphanes senta , a solitary, free-swimming rotifer; and Daphnia magna , a microcrustacean. In each experiment, the percent of prey surviving after 12, 18, and 24 h was recorded. (2) Paired-feeding experiments—in separate experiments, predators were offered prey in a pairwise fashion, in which members of D. magna were alternated with a rotifer, either S. socialis or E. senta. The results of the microcosm experiments showed that, after 24 h, 60–100% prey items of S. socialis survived the predators, but significantly fewer individuals of E. senta (6–89%) and D. magna (<25%) survived. When offered rotifers and individuals of D. magna simultaneously, predators tested consistently consumed more specimens of Daphnia. However, predators significantly reduced percent survival in E. senta but not in S. socialis. Predators, given a choice between the two rotifer species, all consumed significantly more specimens of E. senta than S. socialis after 24 h. In the paired-feeding experiments, three of the four predators captured members of S. socialis , but these colonies were frequently released rather than ingested, although in some cases colony structure was seriously disrupted. Our results suggest that the unpalatable nature of members of S. socialis to certain fishes extends to several invertebrate predators, but the nature of the putative factor(s) responsible for this remains unknown.     

Effects of water-depth and water-level fluctuations on the macroinvertebrate community structure in the littoral zone of Lake Constance

This article presents an evaluation of two sampling methods for assessing the biodiversity of heavily vegetated wetlands. The aim was to establish an effective sampling regime to maximise total taxon richness and minimise sampling effort. Three Integrated Constructed Wetland (ICW) systems in Annetown Valley, Co. Waterford, SE of the Republic of Ireland, were sampled during spring and summer 2005. The two methods that were evaluated were pond netting and two types of horizontal activity traps, namely “horizontal activity traps” (HATs) and modified “horizontal activity traps” (modified HATs). The activity traps provided a one-way funnel system and were constructed from 2 l plastic bottles, allowing for the passive collection of taxa. HATs were designed to capture macroinvertebrates in open water and modified HATs, which were designed specifically for this study, were used to sample within stands of dense emergent vegetation. Results show that a combination of pond netting and activity traps will yield a more complete estimate of taxon richness. The performance of Modified HATs was not significantly different from that of the HATs in dense vegetation. Tests on the sampling effort required for each method are also discussed. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Guest editors: R. Céréghino, J. Biggs, B. Oertli and S. Declerck The ecology of European ponds: defining the characteristics of a neglected freshwater habitat     

Investigations into the Food Selectivity of the Planktic Crustaceans Daphnia hyalina,Eudiaptomus gracilis and Cyclops vicinus

The food selectivity of Daphnia hyalina, Eudiaptomus gracilis and Cyclops vicinus was investigated in laboratory experiments using algae of different sizes and at different concentrations as food sources. Vanderploeg and Scavia's (1979a, b) coefficient, which is most suitable for characterising selectivity, was selected from the literature and used to analyze the results. None of the three species was found to feed selectivity, however. The results show, on the other hand, that the leaky-sieve model can be used to describe the feeding patterns of these species. There were clear differences between the particle size ranges consumed by our experimental species, and these showed that, during the experiments, Daphnia hyalina acted as a microfilter-feeder, whereas Eudiaptomus gracilis and Cyclops vicinus acted as macrofilter-feeders.     

Life cycle of Cyclops vicinus in relation to food availability, predation, diapause and temperature

The seasonal cycle of Cyclops vicinus was studied during a 5year period in the shallow and hypertrophic Lake Søbygård.The annual number of generations varied between three and sixand sometimes included midsummer generations. Naupliar and copepoditedensity was extremely high, the maximum recorded being 1313and 745 1^–1 respectively. The seasonal fluctuation inthe abundance of C.vicinus was related to the concentrationof edible phytoplankton (EDP): when diatoms and cryptomonadswere abundant, nauplii and copepodites were also abundant, whereaswhen greens such as Scenedesmus spp. were dominant, no cohortswere observed. The maximum density of copepodites in the separatecohorts and the amount of EDP, expressed as carbon content,were found to be significantly correlated. The development ofthe second cohort also seemed to depend on the occurrence ofa peak in rotifer density. High number of eggs per female generallycoincided with high biovolume of EDP, suggesting that algaeconstituted a major part of the diet of adult C. vicinus. Theduration of the naupliar stage was inversely related to temperatureand is one of the shortest times that have been recorded inthe literature. The short duration is probably attributableto the abundance of food. Fish composition and the calculatedsex ratio of C.vicinus indicate low predation pressure fromplanktivorous fish. The high density of C.vicinus during thesummer, when the whole population would be expected to haveentered diapause, is probably attributable to the concurrenceof low predation and the abundance of food.     

Dynamics of autotrophic picoplankton in Lake Constance

The vertical distribution, biomass concentrations and growthrates of autotrophic picoplankton (APP) were investigated duringthe growing season (March-October) in Lake Constance in differentdepths. Cell numbers determined by epifluorescence microscopyvaried between 1.0 x 10³ and 1.6 times; 10⁵ cells ml^–1depending on season and water depth. Highest concentrationswere recorded above the thermodine in late summer. Numerically,APP consisted almost exclusively of chroococcoid cyanobactena.During lake stratification several peaks of biomass concentrationsoccurred in epilimsietic waters at intervals of 6–8 weeks.In-situ experiments using a dilution technique and dialysisbags revealed that during summer APP population dynamics wereprimarily driven by combined changes of their growth and grazingrates, whereas temperature was less important. Gross growthrates varied between 0.006 and 0.051 h^–1, grazing ratesbetween 0.002 and 0.053 h^–1. On average APP productionwas completely removed by grazing within the microbial community.Ciliates, heterotrophic nanoflagellates and rotifers have beenidentified as the major consumers of APP cells. APP biomassis small compared to larger phytoplankton, ranging from ito5% of total phytoplankton biovolume. Due to its high gross growthrates, which are on the same level as those of free-living pelagicbacteria, APP contributes slightly more to overall primary productionwith maximum percentages of {small tilde}15% in late summer.     

Internal solitary waves in Upper Lake Constance

Estimation of microbial biomass depends on cell shape and size determinations, and thus, there is a wide biovolume variability among morphotypes. Nevertheless, data on morphology and morphometry of prokaryotic cells under different trophic status are seldom published, due to the methodological difficulties of cell measurements. The main question addressed in this paper concerns the suitability of prokaryotic size and shape for environmental characterization. Microbial biovolumes were compared among different ecosystems, located in temperate and tropical regions. Samples were taken from fresh, brackish, mixohaline, and estuarine waters that were classified as oligo-, meso-, eu-, and hypertrophic by comparing synoptically different trophic indices. Prokaryotic cell abundance and volume were quantified by Image Analysis, used to calculate biomass, and correlated to environmental variables. Some samples were analyzed by flow cytometry also, and data from sub-populations with a different apparent DNA content were available. Prokaryotic abundances generally increased from oligo- to hypertrophic waters while cell volumes increased from oligotrophic to eutrophic waters. Although significant correlations between cell volumes and environmental variables were detected (positive with salinity and negative with Chlorophyll-a), different morphotypes dominated each studied regions. Our results sustain the hypothesis that prokaryotic cell size and shape could be useful to ecosystem characterization.     

Location-dependent infection of fish parasites in Lake Constance

Perch Perca fluviatilis and roach Rutilus rutilus were caught at various locations around Lake Constance (Bodensee). Infection of perch and roach with the eyeflukes Diplostomum spathaceum and Tylodelphis clavata was greatest in the western location (Bottighofen). The varied occurrence of parasite species at different locations indicated that maximum interchange between fish populations was slight. Whitefish Coregonus lavaretus migrating up the River Rhine were less infected with both the tapeworm Proteocephalus exiguus and the copepod Ergasilus sieboldi than whitefish from the middle of the lake. Some of the parasites had already left their hosts. Newly established infections were not found in migrating whitefish.     

Sedimentation of principal phytoplankton species in Lake Constance

Sedimentation of nine phytoplankton species was studied in LakeConstance with the aid of sedimentation traps exposed at sixdifferent depths from 20 to 120 m. The study examines sedimentaryfluxes at all depths, temporal variation of sinking velocitiesinto the uppermost trap, annual averages of the sinking velocitiesat all depths and survival of algae during the sedimentationprocess. In spite of high intraspecific temporal variabilityof the sinking velocity there is a clear hierarchy from thepennate and the filamentous centric diatoms sinking the fastestto the Cryptomonads, nearly not at all affected by sedimentarylosses. Temporal variability of the sinking velocity withinspecies seems to be related to the ‘physiological state’,the highest velocities always occurring during stationary ordecline phases of the population development. An analysis ofthe role of sedimentary losses in the population dynamics ofAsterionella formosa, Fragilaria crotonensis, Stephanodiscusbinderaniss, Melosira granulata reveals positive correlationsbetween the sedimentation rate and cell mortality.     

The first decade of oligotrophication in Lake Constance

Phytoplankton biomass and species composition were measured with a relatively high temporal resolution (once or twice a week during the growing season) from 1979 to 1989 in Lake Constance/Überlingersee. Over this period soluble reactive phosphorus (SRP) concentrations during winter mixing were reduced by ca. 50% from 104 to 47 g 1^–1, which caused a prolongation and amplification of the epilimnetic P depletion during the growth period. Seasonal dynamics of phytoplankton reacted to the decrease of SRP in the following ways: (1) Algal biomass decreased at least proportionally to the winter SRP concentrations in summer, but not in spring and autumn when biomass fluctuated irregularly. (2) The peak of biomass concentration changed from summer to spring. (3) The earlier onset of epilimnetic P depletion during the season in recent years promoted a stronger growth of some pennate diatoms in spring. It caused an amplification of the silicon depletion in summer, which may cause still greater reduction of diatoms and total algal biomass in summer. (4) Reduction of algal biomass during the clear-water phase proper became shorter and less pronounced. (5) The temporal variability of algal biomass decreased in summer and autumn but not in spring. (6) Average cell sizes remained unchanged in summer and autumn but increased in spring during the beginning of oligotrophication. These results are largely in agreement with other studies on lake restoration and expectations derived from the PEG (Plankton Ecology Group) model (Sommer et al. 1986). They show that a 50% reduction of SRP concentrations during homothermy may have pronounced effects on seasonal dynamics of algal biomass in a large and deep lake. The algal response to the external change of SRP concentrations can be described by the Le Chatelier principle, implying that the internal structure of the system (e.g. species composition) changes in order to minimize the effect of the external pressure (e.g. reduction of total biomass). Suggestions are made as to how this system behaviour may emerge from local interactions.     

Methane production in littoral sediment of Lake Constance

Maximum rates of CH₄ production in the littoral sediment were observed in 2–5 cm depth. The CH₄ production rates increased during the year from about 5 mmol m⁻²d⁻¹ in December to a maximum of about 95 mmol m⁻²d⁻¹ in September. CH₄ production rates showed a temperature optimum at 30°C and an apparent activation energy of 76 kJ mol⁻¹. A large part of the seasonality of CH₄ production could be ascribed to the change of the sediment temperature. Most of the produced CH₄ was lost by ebullition. Gas bubbles contained about 60–70% CH₄ with an average δ¹³C of −56.2% and δD of −354%, and 2% CO₂ with an average δ¹³C of −14.1% indicating that CH₄ was produced from methyl carbon, i.e. mainly using acetate as methanogenic substrate. This result was confirmed by inhibition of methanogenesis with chloroform which resulted in an accumulation rate of acetate equivalent to 81% of the rate of CH₄ production. Most probable numbers of methanogenic bacteria were in the order of 10⁴ bacteria g⁻¹d.w. sediment for acetate-, methanol- or formate-utilizing, and of 10⁵ for H₂-utilizing methanogens. The turnover times of acetate were in the order of 2.3–4.8 h which, with in situ acetate concentrations of about 25–50 μM, resulted in rates of acetate turnover which were comparable to the rates of CH₄ production. The respiratory index (RI) showed that [2−¹⁴C]acetate was mainly used by methanogenesis rather than by respiratory processes, although the zone of CH₄ production in the sediment overlapped with the zone of sulfate reduction.     

太湖水体中微型原生动物对细菌的捕食作用

运用稀释法研究了太湖中不同粒径的微型原生动物对细菌的捕食压力,探讨了捕食作用对细菌生长及温度对捕食作用的影响.结果表明:太湖水体中32μm以下的微型原生动物对细菌的捕食率为5.07d-1,其中大部分捕食压力来自小于16μm的超微型原生动物,占总捕食率的90.7%;小于16μm的超微型原生动物的捕食作用明显抑制了细菌的生长;温度对捕食作用有明显影响,随着温度的升高,超微型原生动物的捕食率和细菌的生长率均明显升高.     

Sulfate-reducing bacteria in littoral sediment of Lake Constance

Abstract The viable population of sulfate-reducing bacteria (SRB) in littoral sediments of Lake Constance was investigated using enrichment and enumeration techniques. Enrichment studies established that most types of SRB grew best in media with low salt concentrations (max. 0.4 g Cl⁻/1), consistent with the low salinity of the freshwater habitat. Enumerations were based on an adequate medium with the following electron donors: H₂, lactate, acetate, propionate, butyrate, caprylate, succinate, benzoate, or S₂O₃²⁻ for thiosulfate-disproportionating bacteria. Cultures were incubated for 6 weeks to obtain maximum counts. A maximum cell density of 6.3 × 10⁶ cells per ml sediment was estimated, which is the highest number of SRB ever reported for anoxic sediments. A comparison with measured sulfate reduction rates showed that the enumeration techniques were about 10–100-fold more efficient than those previously used. The population of SRB had a characteristic structure consisting of 87.7% H₂-utilizing SRB (physiologically resembling the classical Desulfovibrio species); 12.0% propionate utilizers (tentatively identified as Desulfobulbus species); 0.3% long chain fatty acid-oxidizing Desulfovibrio sapovorans species. Acetate-utilizing SRB ( Desulfotomaculum acetoxidans ) constituted ≤ 0.05% of the total estimated population. Moreover, the latter species was only present as inactive spores. Benzoate-degrading SRB were not detected.     

Life cycles of two limnetic cyclopoid copepods, Cyclops vicinus and Thermocyclops crassus, in two different habitats

The life cycles of Cyclops vicinus and Thermocyclops crassusin two shallow eutrophic habitats, Junsainuma and Naganuma Ponds,Hokkaido, Japan, were investigated. Both ponds exhibited similarseasonal patterns of temperature, oxygen levels and pH duringice-free periods; however, oxygen levels were extremely lowerunder the ice in Naganuma Pond. Cyclops vicinus showed differentlife cycles in the two ponds; in Junsainuma Pond, it reproducedin winter and spring (January-May) and entered diapause duringsummer and autumn (June-October) as copepodite IV stage, whileit reproduced in autumn (October-November) and spring (April-May),and entered diapause in summer (June-September) and winter (Januaryand February) as copepodite V stage in Naganuma Pond. Thermocyclopscrassus entered diapause during winter (December-April) as copepoditeIV and V stages in both ponds, and egg-bearing females appearedonly during the warmseason, from early May to late October,when water temperatures were >10°C. Summer diapause inC.vicinus was suggested to be an adaptation against fish predation,whereas C.vicinus entered winter diapause in Naganuma Pond probablyto avoid low oxygen levels. Thermocyclops crassus entered diapausein both ponds to avoid low water temperature. These resultssuggest that biotic and abiotic factors are important for leadingto specific life cycles of cyclopoid copepods in small waterbodies.