Lipid content and utilization of lipids in planktonic copepods in Lake Pääjärvi,southern Finland

The variation of the lipid content of a planktonic copepod species, Eudiaptomus gracilis G. O. Sars, was studied in an oligotrophic lake, Pääjärvi, southern Finland, during 1982. The variation was caused by changes in the food resources and by the use of lipids for reproduction. The lipids are partly present in the form of droplets, which provide an energy reserve for some of food shortage, or may be used in reproduction. The utilization of lipid droplets for nutrition was studied by culturing specimens of two species, Eudiaptomus gracilis and Thermocyclops oithonoides G. O. Sars, in the absence of food. It was found that about half of the energy required for the 30-hour experimental period was obtained from the lipid droplets. However, not all the animal groups could use their lipid droplets and they had to use other reserves to satisfy their energy requirement. Lipid droplets seemed to have only a minor effect on the sinking rate of Eudiaptomus gracilis.     

Egg predation by copepods in Daphnia brood cavities

Both field observations and enclosure experiments show that juvenile copepods enter Daphnia brood cavities to feed on Daphnia eggs and embryos. The ability to perform such in vivo exploitation is reported for both cyclopoid and calanoid copepods. Copepodites of Acanthocyclops robustus (G.O. Sars) were found to eat eggs in brood cavities of D. magna, D. pulex and D. pulicaria in experimental enclosures rich in algae. Copepodites of Eudiaptomus gracilus (G.O. Sars) were found in brood cavities of D. hyalina in a mesotrophic lake. The copepods' intrusions into brood cavities caused dramatic declines in the clutch size of infested Daphnia, and this predation effect could easily be confused with the effect of severe food limitation.     

Causes of Technogenic Changes in a Freshwater Zooplanktonic Community

The situation in water bodies of northwestern Karelia in 1992–2001 was analyzed. As a result of waste discharge from the mining and ore-processing works, weakly mineralized hydrocarbonate-calcium waters changed into highly mineralized waters with the prevalence of potassium ions and sulfates. The total abundance and biomass of zooplanktonic communities decreased. Using the methods of principal components and partial correlations, differences in the responses of zooplankters to mineral pollution were revealed. Typical inhabitants of northern water bodies decreased in numbers, and the species Eudiaptomus gracilis Sars and Heterocope appendiculata Sars (Calanoida) disappeared. On the other hand, eurybiontic species prevailing in water bodies with higher mineralization manifested a positive reaction to the increase in the contents of dissolved mineral compounds. Toxicological experiments made it possible to estimate the survival threshold for E. gracilis and H. appendiculata: the populations of these crustaceans in the polluted water body perished when potassium concentration in water exceeded 50 mg/l.     

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

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

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.     

Embryonic and naupliar development of Eudiaptomus gracilis and Eudiaptomus graciloides at different temperatures: comments on individual variability

Eudiaptomus gracilis and Eudiaptomus graciloides are amongstthe most common calanoid copepods in Europe and co-occur inmany lakes. To understand their ecological dynamics, it is essentialto know their responses to environmental variation. The findingthat E. graciloides exhibits diapause in winter, whereas E.gracilis reproduces throughout the year indicates that the twospecies might differ in their temperature responses. We measuredembryonic and naupliar development times, clutch size (numberof eggs per sac), hatching percentage and body length of thefirst copepodid stage (CI) of both species under non-limitingfood conditions at different temperatures. Special attentionwas given to individual variability on development times andto the use of the gamma density function (GDF) for fitting theprobability of moulting. Results show that E. gracilis exhibitsjust slightly faster development times, lower individual variability,higher hatching percentage and larger clutches than E. graciloidesand that extreme temperatures affected E. gracilis less intenselythan E. graciloides. GDF was a good tool for estimating individualvariability in the different experiments.     

Results Regarding the Food of the Planktic Crustaceans Daphnia hyalina and Eudiaptomus gracilis

The graph of maximum filtering and grazing rates versus particle size shows that Daphnia hyalina is a microfiltrator and Eudiaptomus gracilis is a macrofiltrator. In contrast to Eudiaptomus gracilis, Daphnia hyalina is also able to utilize larger bacteria (c. 1 μm³) as a food source.     

Identification and characterization of 10 microsatellite primers for the calanoid freshwater copepods Eudiaptomus gracilis and E. graciloides using enriched genomic libraries

The calanoid copepods Eudiaptomus gracilis and Eudiaptomus graciloides are widespread among European lakes. We constructed enriched genomic libraries for both species in order to isolate and characterise microsatellite markers. The obtained 7 polymorphic microsatellite‐loci for E. gracilis and 3 for E. graciloides are the first for any freshwater copepod. They display an expected heterozygosity ranging from 0.60 to 0.96 and 0.63 to 0.94 and observed heterozygosity ranging from 0.53 to 0.87 and 0.57 to 0.87, respectively. We were not able to cross‐amplify the isolated loci across species, indicating long divergence among both congeneric species despite morphological similarity.     

Lipid profiles of Nematocarcinus gracilis a deep-sea shrimp from below the Arabian Sea oxygen minimum zone

Specimens of the deep-sea benthic shrimp Nematocarcinus gracilis were collected from 900 m to 1000 m in the Arabian Sea, close to where the permanent oxygen minimum zone meets the sea floor. Lipid profiles, encompassing total lipid, lipid class and fatty acid composition, were compared with previously reported crustacean lipid assays and provided an insight into the life history of the species. The major storage lipid in N. gracilis was triglyceride, supporting the supposition that this species exists in benthic regions. Neutral lipid levels were commensurate with N. gracilis being an opportunistic feeder. Fatty acid composition was typical of an organism with a diet based on an ultimately photosynthetic source of organic carbon, but also reflected the reduction in the availability of labile organic carbon (in the case of lipid, highly unsaturated fatty acids) in the deep sea.     

Top-down effects of crustacean zooplankton on pelagic microorganisms in a mesotrophic lake

A series of single-factor in situ experiments was conductedin a mesotrophic lake in Brandenburg, North Germany, to studythe predatory impact of Eudiaptomus graciloides (adults, copepodites,nauplii), cyclopoid copepods (adult Diacyclops bicuspidatus,Thermocyclops oithonoides) and daphnids (adult Daphnia hyalina,Daphnia cucullata) on the microbial community (bacteria, autotrophicpicoplankton, flagellates, ciliates). All zooplankton speciestested reduced the ciliate community significantly and ingestionrates were always higher for ciliates in the 20–55 µmsize category as compared to smaller ciliates (10–20 µm).Adult E.graciloides, which exhibited the highest predatory impacton ciliates, differed from cyclopoids and daphnids by theirability to decimate ciliates to very low abundances. Ingestionrates of ciliates by the crustacean zooplankton followed thesequence E.graciloides > daphnids = cyclopoids = copepodites.While top-down control was evident for ciliates, top-down effectsdown to the autotrophic picoplankton and flagellates were mostlyrestricted to Daphnia-dominated treatments. Top-down effectswere never strong enough to produce negative bacterial growthrates. For all zooplankton tested, clearance rates for ciliatesexceeded those for phytoplankton. Besides the potential of thecrustacean zooplankton to influence the structure of ciliatecommunities, ciliates may contribute to the energy demands ofcopepods and daphnids, especially when phytoplankton resourcesare limited.     

A description of pelagic zooplankton in the large lakes of the Todzha Depression (Bolshoi Yenisey River basin, Tuva)

The zooplankton structure of large lakes (Noyon-Khol’, Shuram-Khol’, Borzu-Khol’, Many-Khol’, Kadysh, and Todzha) of the Todzha Depression has been studied. A comparison of the species composition, abundance, and biomass of zooplankton in the lakes was made. Rotifers have the largest species diversity: from 10 to 16 species, with Conochilus sp., Collotheca sp., Kellicottia longispina (Kellicott), and Asplanchna priodonta Gosse being the most abundant. Copepods are represented mostly by Arctodiaptomus paulseni (Sars), Eudiaptomus graciloides (Lilljeborg), Cyclops scutifer Sars, and Mesocyclops leuckarti Claus. Daphnia galeata Sars and Bosmina longispina Leydig are the dominant cladoceran species. It is shown that the zooplankton communities of the lakes in the Todzha Depression are characterized by a high degree of species composition similarity. Factors forming the taxonomic structure of pelagic zooplankton in the system of these lakes are displayed.     

Copepod communities in karstic mediterranean lakes along the eastern Adriatic coast

The copepod communities of karstic lakes along the eastern Adriatic coast were studied. Lakes were divided in several groups according to their morphology (deep, shallow, barrage and reservoirs), production (oligotrophic, mesotophic and eutrophic), and salinity of water: freshwater and brackish. Copidodiaptomus steueri, Eucyclops serrulatusand Macrocyclops albidus belong to the group that inhabited most of the lakes under the study, regardless of lake type. The shallow karstic lakes are usually inhabited by Thermocyclops dybowskii, T. oithonoides, Cyclops vicinus and Eudiaptomus padanus etruscus in freshwater biotopes, and Calanipedia aquaedulcis and Copidodiaptomus steueri in brackish biotopes. The last two species can also be found in deep karstic lakes with brackish water (Bacina lakes in the Neretva River delta). Species like Cyclops abyssorumcan be found in most deep freshwater lakes. Some Calanoida were recorded in only one lake, like Eudiaptomus transsylvanicusin the deep Lake Vrana on the island of Cres, or Eudiaptomus hadzici in the barrage Lake Visovac. Production of the lakes, expressed as copepod biomass, depends on lake trophy, and in some lakes also on hydrology and salinity. Most of the meso-eutrophic lakes in the study area had Calanoida dominating, while Cyclopoida dominated in some oligotrophic and eutrophic lakes as well.     

Zooplankton in a Danube River Arm near Rusovce (Slovakia)

Poor quantity of zooplankton was recorded in a Danube arm situated on the right side of the Danube River in Slovakia (river km 1857) in 2002 and 2003. All over the year the arm is significantly influenced by groundwater by reason of seepage. Because of low mean water temperature (12°C) and poorly developed macrovegetation in particular, the arm reminds gravel pit-like. The annual average of zooplankton biomass was low and ranged from 0.35 g m⁻³ (2002) to 1.28 g m⁻³ (2003), because of low crustacean abundance. Total cladoceran abundance was excessively low in both years and ranged from 3.5 N L⁻¹ (2002) to 16.6 N L⁻¹ (2003). Small species, Bosmina longirostris and Chydorus sphaericus were dominant. Only four adult Copepoda — Cyclops vicinus, Thermocyclops crassus, Eurytemora velox and Eudiaptomus gracilis — were recorded in quantitative samples of both years. In the zooplankton assemblage dominated rotifers (Synchaeta pectinata, Synchaeta oblonga, Polyarthra dolichoptera and Keratella cochlearis) which represented 78% and 67% of total abundance respectively. The total of 19 species of rotifers, 34 Cladocera species and 16 taxa of Copepoda were found.     

Field experiments on the optical orientation of pelagic rotifers

Avoidance of shore by pelagic rotifers is considered to be the result of an optical orientation. Field experiments show that the spatial light distribution in the shore region determines the preferred direction of migration. The behaviour of Eudiaptomus gracilis was tested in comparison to that of rotifers.This publication is dedicated to Pater Dr. Josef Donner on the occasion of his 70th birthday     

Diapause in the calanoid freshwater copepod Eudiaptomus graciloides

The seasonal appearance and the intensity of diapausing-eggproduction in Eudiaptomus graciloides in five lakes of differentsize and trophic level were studied. In all lakes, diapausingeggs were produced in autumn. In the large mesotrophic lakeSelenter See, the population’s shift to the productionof diapausing eggs was more complete than in other lakes. Weexamined day length, temperature and food as proximate factorsfor the production of diapausing eggs with laboratory experiments.Eudiaptomus graciloides produced diapausing eggs in all treatments,but a significantly higher percentage of diapausing eggs wasfound under short day conditions except when algal food wasabundant and temperature was high. To investigate the adaptivesignificance of diapause in E. graciloides, we compared thesurvival of adult and juvenile at different temperatures forE. graciloides with Eudiaptomus gracilis, a sympatric speciesthat does not exhibit diapause. At 8°C, adult E. graciloidessurvived better than adult E. gracilis and exhibited reducedgut contents and accumulation of storage lipids, traits characteristicof adult diapause. Eudiaptomus graciloides nauplii did not reachthe copepodid stage at 6°C, but E. gracilis nauplii exhibitedhigh mortality and developed very slowly. We hypothesize thatadult diapause and production of diapausing eggs facilitatethe survival of E. graciloides during cold periods and enhancecoexistence with its congener, E. gracilis, in temperate zones.     

Nutritional suitability of the dinoflagellate Ceratium furcoides for four copepod species

The nutritional suitability of Ceratium furcoides for Eudiaplomusgracilis, Mesocyclops leuckarti, Thermocyclops oithonoides andCyclops abyssorum was studied by observing ingestion and assimilation.The dinoflagellate was ingested by female adults of all species.The calanoid copepod E.gracilis could not utilize Ceratium;mortality was high and no egg production was observed when Ceratiumwas the only food source. Mortality was low for the adult cyclopoidson this food and reproduction indicated that Ceratium was assimilated.The first two copepodite instars of M.leuckarti were not ableto handle Ceratium, while older stages preyed on them. The dinoflagellatewas not ingested by female M.leuckarti when its densities werelow. Advanced copepodite stages of C.abyssorum developed intoadults on a diet of Ceratium only. Mesocyclops leuckarti femalesingested Ceratium when offered a mixed food source of Ceratiumand the rotifer Brachionus rubens, but the rotifer was positivelyselected, even if its density was low. The results show thatCeratium provides a suitable food source for advanced copepoditeinstars and adult cyclopoid copepods, although it is not a preferredfood source.     

SINGLE LOCUS MICROSATELLITES IN GRACILARIALES (RHODOPHYTA): HIGH LEVEL OF GENETIC VARIABILITY WITHIN GRACILARIA GRACILIS AND CONSERVATION IN RELATED SPECIES1

Four single locus microsatellites identified in the red alga Gracilaria gracilis (Stackhouse) Steentoft, Irvine, et Farnham (Rhodophyta) were examined for allelic diversity at different spatial and taxonomic levels. First, because simple morphological diagnostic characters are often missing within the Gracilariaceae, we developed a simple and rapid method based on rDNA ITS size variation in order to verify the taxonomic status of the samples used in this study. All European (including Mediterranean samples), Argentinian, and Namibian samples used in our study were confirmed to be a homogenous G. gracilis group. By contrast, our results on rDNA ITS sizes showed that Gracilaria from Japan, initially identified as G. gracilis, was different from the rest of the G. gracilis group. Secondly, microsatellite polymorphism and conservation at the species level was tested on the worldwide collection of G. gracilis and within a single population. The loci Gv1AAG and Gv1AAC showed no allelic variation, whereas two others, Gv1CT and Gv2CT, were highly polymorphic. All microsatellite loci were conserved within G. gracilis, except in the sample from Japan. The taxonomic status of G. gracilis from Japan is thus questionable. This study revealed a high level of within-population polymorphism (52 alleles for Gv1CT and 12 for Gv2CT). Moreover, the combination of these two loci was shown to be very powerful for identifying individuals within a population, that is, 93% of the individuals were characterized by a unique genotype. Finally, conservation of the four loci was tested in taxonomically related species of Gracilaria (G. chilensis, G. pacifica, and G. tikvahiae) and two Gracilariopsis species (Gs. sp. and Gs. longissima). The results suggest that the polymorphic locus Gv2CT may provide a valuable genetic marker within the different species of the Gracilariaceae.     

Daily changes in population structure and production of Eudiapomus gracilis (G.O. Sars) (Copepoda, Calanoida) during summer in a shallow lake (Balaton, Hungary)

Population structure and production of Eudiaptomus gracilis(G.O. Sars) have been calculated from daily measurements inLake Balaton for one month during each summer in 1975 and 1977.Fecundity was different in the two years 6.98 ? 1.16 and 10.68? 1.42 in 1975 and 1977, respectively. A total of 80% and 64%of the population were made up of larvae in 1975 and 1977, respectively.The ratio of males to females was 1:1.63 and 1:1.1, respectively.In 1975 it was possible to follow the development of cohorts,19 –20 days in the former year, 17 –20 days in thelatter. In both years of examination 80 – 83% of naupliiand 12–15% of copepodites were eliminated. Daily net biomassproduction was 6.88 mg (dry wt.)/m³ in 1975 and 1.94 mg (drywt.)/m³ in 1977. Ratios of eggs, nauplii and copepodites indaily production was 1:2.4:1.4 in 1975 and 1:1.0:1.0 in 1977.The daily potential biomass production were 34.40 mg (dry wt.)/m³ and 10.28 mg (dry wt.)/m³ and the elimination were 80 and81 wt.%, respectively. P/B ratio — allowing for net productionvalues — was nearly the same in both periods of investigation(0.12 and 0.099 respectively).     

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.