Alga consumption of four dominant planktonic crustaceans in Lake Balaton (Hungary)

Between 1981–83 the gut contents ofDaphnia galeata, D. cucullata, Eudiaptomus gracilis, andCyclops vicinus were examined with light and scanning electron microscope to obtain information on the feeding of these species in Lake Balaton. The twoDaphnia species feed mainly on abioseston, and it is assumed that their primary nutrient source was organic matter adsorbed onto the surfaces of the abioseston granules plus bacteria and detritus.E. gracilis feeds on algae, showing a preference for green algae and diatoms.C. vicinus is also a prodigious consumer of algae in Lake Balaton, utilizing the whole size spectrum of phytoplankton. Concerning the trophic relationships between phytoplankton and zooplankton in Lake Balaton, that between diatoms and bothE. gracilis andC. vicinus is the most conspicouos. Convincing evidence for an extensive utilization of blue-green algae was not found. Though there is no firm evidence yet, it is likely that theDaphnia are dependent on organic matter adsorbed on the abioseston.     

Variable life history of a cyclopoid copepod: the role of food availability

Populations of the copepod Cyclops vicinus in two Danish lakes differed in their life cycles. In Lake Væng C. vicinus was absent during summer, whereas in Lake Søbygård it continued producing distinct cohorts throughout summer. A comparison between the lakes showed that in the lake where C. vicinus was absent during summer, food limitation generally existed. In contrast, abundance of C. vicinus during summer in Lake Søbygård always coincided with available resources sufficient for the whole life cycle. Thus, summer diapause of C. vicinus is suggested to be a strategy to avoid food limitation. Avoidance of fish predation does not seem substantially to influence life cycles.     

Planktonic bloom of an introduced species of Polysiphonia (Ceramiales,Rhodophyta) along the coast of North Carolina,USA

Analysis was made of the species composition, egg number per female and the size-frequency of Amphipoda living on the dominating submerged macrophytes (Potamogeton perfoliatus and Myriophyllum spicatum) at 10 sampling stations of the northern and southern shoreline of Lake Balaton. The dominating Amphipoda at each sampling station was Corophium curvispinum (85.9–99.8%, mean: 96.6%). Besides this, two other species — Dikerogammarus haemobaphes and D. villosus — were also found in the samples. The two Dikerogammarus species were found in highest percentage near Keszthely (14.1 %); at the other places studied they were under 5%. The number of Amphipoda individuals per g macrophyte dry weight ranged from 5 to 574; the lowest value was found near Keszthely, the highest near B. Mária. The developmental stages of the C. curvispinum population differ in different parts of Lake Balaton: the adult (male and female) specimens occurred in highest percentage near Keszthely. The mean number of eggs per C. curvispinum female ranged from 2.4 to 6.3, showing differences at the different sampling stations. Regarding the two Dikerogammarus species, there were many more D. haemobaphes than D. villosus individuals at almost every station (mean: 75%). The mean number of eggs per egg-carrying female of D. haemobaphes was 11.7, being 19.1 for D. villosus.The total biomass of amphipods (in mg animal dry weight/g macrophyte dry weight) ranged from 1.2 to 59.8. The lowest value was observed near Keszthely (the most hypertrophic basin of Lake Balaton), the highest value near B. Maria     

Cyclops heberti n.sp. and Cyclops singularis n.sp., two new species within the genus Cyclops (‘strenuus-subgroup’) (Crust. Copepoda) from ephemeral ponds in southern Germany

Some of the species within the genus Cyclops O. F. Müller, 1785 can only be determined exactly by combining different methods and techniques. Based on the comprehensive analysis of morphometrical data, some populations in periodical ponds near Lake Constance were examined for their pattern of chromatin diminution and were compared by enzyme electrophoresis. These studies provided evidence of two new species. Together with C. furcifer Claus, 1857 and C. vicinus Uljanin, 1875 one of the ponds (‘Litzelsee’) was inhabited by four Cyclops species. In addition to morphological differences and distinct electrophoretic characteristics, C. furcifer and the new species differ in the timing of their chromatin diminution: C. singularis in the fourth, C. heberti in the fifth, and C. furcifer in the sixth cleavage. The qualitative course of chromatin diminution is rather similar in all three species. The same combination of three Cyclops species (without C. vicinus) was also found in an older sample (1990) from another ephemeral pond near Lake Constance. A close genetical relationship between the three species seems probable.     

The seasonal cycle of Thermocyclops crassus (Fischer, 1853) (Copepoda: Cyclopoida) in a shallow,eutrophic lake

The seasonal cycle of Thermocyclops crassus was studied from 1985 to 1987, in the Gronne, a shallow, productive lake. T. crassus was present from late April to early October, while water temperature was above 10 °C. It produced three generations per year. Population peak was usually reached by the second generation, in August. Abundance was positively correlated with water temperature. Females carried 18.3 to 32.3 eggs on average. Reproduction rates were highest in July and August. Sex ratio was low, as females generally outnumbered males. Between October and April copepodites 4 went in diapause, predominantly in the deepest part of the lake and 0–4 cm deep in the bottom mud. Variations in body size were low across the year. T. crassus coexisted with the cyclopids, Cyclops vicinus and Mesocyclops leuckarti. In 1985 and 1986, abundances of M. leuckarti were low, while those of T. crassus and C. vicinus were high. In 1987 lower water temperatures, caused by cold weather, resulted in a marked decrease of the population density of T. crassus, while the abundance of M. leuckarti increased, and density of C. vicinus remained high. Comparison of the egg duration times of T. crassus, C. vicinus and M. leuckarti showed that at 15 °C and below T. crassus may be outcompeted by its comparatively longer egg development times. However, experiments in limnocorrals showed that T. crassus has an advantage over C. vicinus when fish predation is high.Department of Biology III, University of Ulm     

Paleolimnological reconstruction of the trophic state in Lake Balaton (Hungary) using Cladocera remains

The sediment of Lake Balaton (Hungary) provides important information about the lake’s history, particularly with regard to eutrophication. In this study, we used fossil pigment analysis and subfossil Cladocera remains preserved in a dated sediment core to identify trophic stages from ~250 bc to present. Dates of the most recent eutrophic events are in good agreement with previously published data. In general, the abundance and diversity of the Cladocera community increased with eutrophication and decreased with oligotrophication. The sediments of Lake Balaton were characterised by Chydoridae remains, of which Alona species were the most abundant. Of these, Alona quadrangularis and Alona affinis accounted for 40 and 20% of the total Cladocera remains, respectively. The trophic state of Lake Balaton varied between mesotrophic and eutrophic regimes. Seven different trophic periods were identified in Lake Balaton on the basis of Sedimentary Pigment Degradation Unit (SPDU) content of the sediment. Eutrophic states were (1) from ~250 to ~30 bc, (3) between ~300 and ~590 ad, (5) between 1834 and 1944 and (7) from the 1960s until present. Mesotrophic states were (2) ~30 bc to ~300 ad, (4) 590–1834, (6) 1944–1960s. Discriminant analysis of the cladoceran data confirmed these historic events, except for the short mesotrophic episode between 1944 and 1960. The first stage of eutrophication of Lake Balaton (~250 to ~30 bc) was characterised by extensive macrophyte vegetation, as indicated by the increasing abundance of vegetation-associated Cladocera species (Eurycercus lamellatus, Sida crystallina, Pleuroxus sp.). Intensification of eutrophication was identified since the 1980s, reflected by a high abundance of Bosmina species. The most significant planktivorous fish of Lake Balaton was the Sabre carp (Pelecus cultratus), and when its number decreased, the abundance of Bosmina species increased. This study shows that Cladocera are responsive to trophic state changes, underlining their importance as a tool for the assessment of lake eutrophication.     

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)     

Changes in the abundance and composition of cyclopoid copepods following fish manipulation in eutrophic Lake Væng, Denmark

1. The seasonal cycle of cyclopoid copepods during and following an approximately 50% reduction in planktivorous fish biomass was studied in shallow, eutrophic Lake Vaeng, Denmark, from 1986 to 1990. 2. The dominant cyclopoid copepods changed from Cyclops vicinus and Mesacyclops leuckarti during 1986–1989 to M. leuckarti and Megacyclops viridis in 1990. The abundance of cyclopoid copepods gradually increased from 1986 to 1988–89, decreased in autumn 1989 and markedly decreased in 1990. 3. The increase in the abundance of cyclopoid copepods from 1986 to 1988 is attributed mainly to the reduction in fish predation pressure, there being no concomitant increase in edible phytoplankton. The appearance of M. viridis in 1990, and the general decrease in cyclopoid copepod density in autumn 1989 and in 1990, are attributed to the appearance of submerged macrophytes. 4. Temperature, predation and availability of edible phytoplankton appear to determine whether C. vicinus or M. leuckarti dominates the cyclopoid copepod population of eutrophic Lake Væng.     

Ingestion Rates of Some Daphnia Species in a Shallow Lake (Lake Balaton,Hungary)

Filtering rates of three species of Daphnia were studied in situ by the ¹⁴C technique during the summer in a lake with a water temperature of 20-25°C (Lake Balaton, Hungary). The renewal time of gut contents proved to be 3-5 min in each of the three species whether fed on natural or artificial food. From May to September, filtering rates of D. cucullata, D. hyalina and D. galeata averaged 7.8, 10.3 and 9.2 ml ind.⁻¹ day⁻¹, respectively. Identically long individuals of all three species had almost the same filtering rates in spring, whereas in summer animals of identical weights had similar filtering rates regardless of species because of the length variability of the helmets. The grazing rate of adult filter-feeding crustaceans is suggested to be approximately 7 % per day.     

Post-embryonic development of cyclopoid copepods in various seasons at Lake Balaton (Hungary)

The development, generation number and diapausing state of threeCyclops species dominant in the open water of Lake Balaton werestudied by means of vials placed back into the lake, in naturalfeeding conditions. The males of all three species turned intoadults earlier than the females. The copepodite V stage wasof the longest duration. Three generations of Cyclops vicinusdeveloped yearly; in spring, autumn and winter. About 50% ofthe copepodite stage IV of the spring generation entered activediapause at the end of May, beginning of June, then entereddormancy between the middle of June and middle of July. Consideringthe literary data as well, it seems that the generation numberof the species is the function of temperature and of the water'strophic state. The Acanthocydops robustus f. limnetica is fondof warm water (> 14°C). Seven generations of this speciesdeveloped completely yearly, during an average of 2-week intervalsbetween May and September. The eightli generation died in thenaupliar stage. The generation number of A. robustus f. limneticadepends on the average temperature of the lake. Inactive diapausecould not be observed for this species. Only one generationof Mesocyclops latckarti developed in autumn. The copepoditeV of the winter generation entered active diapause below a watertemperature of 10°C, and inactive diapause from the endof January, which state ended in March.     

Seasonal Dynamics of Picocyanobacteria and Picoeukaryotes in a Large Shallow Lake (Lake Balaton,Hungary)

The abundance and composition of autotrophic picoplankton (APP) were studied between February 2003 and March 2004 in Lake Balaton. Water samples were taken fortnightly in the eutrophic western basin and mesotrophic eastern basin. Our study, which took more than one year, revealed pronounced seasonal pattern of the picoplankton abundance and composition. According to our results there were three types of picoplankton in Lake Balaton: 1. Phycoerythrin‐rich coccoid cyanobacteria (PE), dominant summer picoplankters in the mesotrophic lake area; 2. Phycocyanin‐rich cyanobacteria (PC), the most abundant summer picoplankters in the eutrophic lake area; 3. Picoeukaryotes, dominant winter picoplankters in the whole lake. The observed abundance of picoeukaryotes (3 × 10⁵ cells ml^–1) was one of the highest ever found. Our study confirms that in Lake Balaton the colonial autotrophic picoplankton (colonial APP) become dominant in summer in the nutrient limited period. We have found strong negative relationship between the concentrations of available nitrogen forms (NH₄–N, NO₃–N, urea‐N) and the colonial APP abundance. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The life cycle of Cyclops vicinus in Lake Søbygård: new aspects derived from sediment analyses

Cyclops vicinus is the only copepod species in the pelagic zone of Lake Søbygård and can be found there all year round. We studied the population dynamics of this copepod over a one-year period. In contrast to earlier studies we included the copepods in the pelagic zone as well as the copepods resting in the sediment. Cyclops vicinuswas found not only in the open water, but also in the sediment throughout the year. From the fluctuations of the abundances in both habitats we suggest that the life cycle is more complex than known so far: different diapause pattern appear within the population and the induction of diapause is different than in other populations. We assume that these features contribute to the predominance of C. vicinusin Lake Søbygård.     

Amphipoda (Crustacea) in the Littoral Zone of Lake Balaton (Hungary). Qualitative and Quantitative Studies

Species composition, size distribution, egg number and biomass of different amphipod species on littoral submerged aquatic vegetation (Myriophyllum, spicatum and Potamogeton perfoliatus stands) and on the stony shores of Lake Balaton at Tihany were estimated in August 1983 and 1985. Three species occurred in the material: Corophium curvispinum, Dikerogammarus haemobaphes and Dikerogammarus villosus. The bulk was formed by C. curvispinum. The mean number of eggs per female of the three investigated species showed differences at the different sampling stations and ranged between the following values: C. curvispinum from 3.3 to 8.8, D. haemobaphes from 16.4 to 22.8 and D. villosus from 8.0 to 17.5. The total biomass of amphipods was 1.8 and 3.5 mg dry weight/g fresh weight of macrophytes in 1983 and 1985 respectively, and 4.7 mg animal per dm² stone surface in the stony littoral zone in 1983.     

Spatial distribution of resting stages,rate of emergence from diapause and times to adulthood and to the appearance of the first clutch in 3 species of cyclopoid copepods

The spatial distribution of dormant copepodids of 3 species of cyclopoid copepods — Cyclops vicinus, Mesocyclops leuckarti and Thermocyclops crassus — was studied in 4 small lakes in South Germany. The rate of emergence from diapause and times from the resting stage to adulthood and from adulthood to the appearance of the first clutch was studied at 4 constant temperatures (5, 10, 15, 20 °C) in the laboratory. Resting stages of C. vicinus were always concentrated in the deepest parts of the lakes and were found relatively deep in the mud. M. leuckarti- and T. crassus-copepodids preferred shallow areas in deep lakes but were concentrated in the deep areas in shallow lakes. Copepodids of both species were always concentrated in the uppermost mud layers.Rate of emergence from diapause was strongly temperature-dependent. At high temperatures (20 °C) copepodids of all species under study emerged within 2 weeks. At lower temperatures C. vicinus copepodids showed the highest rate of emergence. At 5 to 10 °C only few M. leuckarti- and T. crassus-copepodids had emerged after the investigation period (7 weeks). Both C. vicinus and T. crassus showed the highest rate of emergence at the natural end of diapause but even at that time only few T. crassus-copepodids emerged at 5 °C. Times to adulthood at 5 °C were shortest in C. vicinus. At higher temperatures this species was passed by M. leuckarti. Times from adulthood to the appearance of the first clutch at 5–15 °C were shortest in C. vicinus. T. crassus produced no clutch at 5 and 10 °C.     

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 the Pikeperch,Stizostedion lucioperca (L.), in Lake Balaton

The pikeperch populations inhabiting three distinct water areas of Lake Balaton differ in regard of growth. Due to stock depletion, pikeperch in the NE-basin of the lake grew considerably faster than ten years ago. The annual rate of growth in length (von Bertalanffy's K) varied between 0.09 and 0.19. The specific rate of growth in length (G_L) ranged from 0.16 to 0.23 and that of growth in weight (G_W) from 0.52 to 0.69. Length and age-structures of the stocks differed significantly between different areas and years, but the overwhelming majority of the stocks consisted of age-groups IV–V (98.2–99.3%). From NE to SW, the rates of survival were 34, 29 and 70%, respectively. These differences, and the differences in growth resulted in changes in the productive capacity of the stocks. The ratios of production and biomass were 59% (NE-basin), 63% (central basin) and 39% (SW-basin), respectively. The magnitudes of production varied inversely. The 50% retention lengths of the seine nets used in Lake Balaton were 35.0, 35.7 and 42.5 cm with weights of 572, 655 and 1019 g, respectively.     

Response of ciliates and Cryptomonas to the spring cohort of a cyclopoid copepod in a shallow hypereutrophic lake

The impact of a cyclopoid copepod population on the protozoacommunity (two ciliate categories and Cryptomonas) was assessedweekly during the spring cohort of Cyclops vicinus (one monthduration) in hypereutrophic Lake Søbygård by insitu gradient experiments with manipulation of ambient zooplanktonabundance. As C.vicinus always made up >92% of the zooplanktonbiomass, the response of protozoa is assumed to be a resultof predation by the copepod. Significant effects of copepodbiomass on protozoa net population growth rates were obtainedin the four experiments. Copepod clearance rates were significantlyhigher on oligotrichs than on prostomatids and Cryptomonas butdeclined for all three protozoa categories during the firstthree weeks of the copepod cohort, probably because of the changein developmental instar composition of the copepod population.Grazing impact on protozoa at ambient copepod abundance wasconsiderable (range, 0.05–0.87 day^–1) and could,together with the estimated reproductive potential of protozoans(range, –0.20–0.87 day^–1), account for thedecline in abundance and biomass of protozoa during the cohortdevelopment. Carbon flow from the protozoa to C.vicinus (range,2.8–23.5 µg C l^–1 day^–1) documents thepresence of a trophic link between protozoa and the spring cohortof C.vicinus in Lake Søbygård.     

Calculation of Fluctuating Asymmetry of the biggest Caspian whipsnake population in Hungary compared to a common snake species

The Fluctuating Asymmetry (FA) is a special type of asymmetry in the populations of bilaterally symmetrical creatures. The FA gives us numerical data on the developmental instability of the populations and refers to potential genetical and environmental stressors affecting the populations. Here we give the first data on the FA of the protected Caspian whipsnake (Hierophis caspius) from Hungary. The FA indices of the biggest population from Villány Mts were compared to the FA indices of two differently stressed Dice snake (Natrix tessellata) populations [stressed (Mád) and seminatural (Lake Balaton)]. Based on the values of the multiple and the simple indices derived from sublabial scales, we can say that the status quo of the highly protected Caspian whipsnake population does not represent significant deviation from the near-natural dice snake population from the Lake Balaton.     

The Availability of Condensed Phosphates for the Algal Strain Scenedesmus obtusiusculus Chodat,with Special Regard to Conditions Characteristic in Lake Balaton

The limiting factor in the water of Lake Balaton was calculated by means of Verduin's equation. If only the orthophosphate-phosphorus concentration is inserted into the equation, phosphorus is the primary limiting factor. If, however, total phosphorus is considered, the factor intensity of nitrogen will be the least, i. e. nitrogen will be the primary limiting-factor of plant growth. According to measurements during 1976, average values for the total dissolved phosphorus and orthophosphate-phosphorus content of Balaton Lake water were 15,66 mg/m³ and 7.66 mg/m³, respectively. Experiments with the algal strain Scenedesmus obtusiusculus Chod. (Chlorophyceae, Chlorococcales). were designed to test the availability of the condensed phosphorus form for the algae. The experiments were performed partly with synthetic polyphosphates, partly, with polyphosphates isolated from Balaton Lake water. The results showed, contrary to our expectations, that phosphates present in the condensed form (irrespective of their structure and degree of condensation). were not utilized by the algae under sterile conditions, i. e. in the absence of bacterial activity. In the light of the above it is recommended to consider only orthophosphate-phosphorus when calculating the limiting factor.     

Food consumption and utilization in two freshwater cyclopoid copepods (mesocyclops edax and cyclops vicinus)

The predatory feeding of Mesocyclops edax and Cyclops vicinus was studied using the ¹⁴C-labelled Ceriodaphnia and some other kinds of the crustacean zooplankters. When given a choice, both species exhibited clear selection of smaller specimens of prey. The feeding rates depend on the kind of prey. The daily ration for the prey readily accepted by Mesocyclops was roughly equal to the predator's biomass, while it was only one half or one third of the body biomass in Cyclops vicinus. Only about one third of the killed biomass was actually ingested and 21–32% was assimilated when the copepods preyed upon the cladocerans or the copepodid larvae. When fed with naupliar larvae the cyclopoid copepods assimilated over 70% of the killed biomass. Almost one half of the freshly assimilated carbon passes through the short term cycle and is quickly respired and excreted.