Ostracods (Ostracoda,Crustacea) from two freshwater lakes near Maarssen,The Netherlands

Summary In Lake Maarsseveen I (with the lowest trophic level) 15 ostracod species were collected, whereas 9 species were found in Lake Maarsseveen II.Physocypria kliei Schäfer, 1934, andCypridopsis obesa Brady and Robertson, 1869, are new to the Dutch fauna.     

Occurrence,succession and distribution of chroöcoccal Cyanobacteria in Lake Maarsseveen I

Four species of chroöcoccal Cyanobacteria were dominant in Lake Maarsseveen I in 1987:Gomphosphaeria lacustris, Chroöcoccus sp.,Aphanocapsa sp. andMicrocystis aeruginosa. The first two were dominant in the water column, the latter two in the sediment. In the water columnAphanocapsa, Microcystis andGomphosphaeria appeared and showed highest abundance at the same time, whileChroöcoccus filled the gaps between the peaks of the others. The distribution in the sediment was related to its texture.     

Factors governing the spatial and temporal distribution of Chironomid larvae in the Maarsseveen lakes with special emphasis on the role of oxygen conditions

Distribution patterns of the larvae of Chironomidae are compared in three water systems in The Netherlands, which vary in trophic state and oxygen regimes. The life cycles and flying periods of some dominant chironomid species in two of the investigated lakes, Lakes Maarsseveen I and II, are determined by comparing data on the seasonal variations in larval densities with existing literature on Chironomidae in the Maarsseveen lakes. In the oligo-mesotrophic Lake Maarsseveen I (LM I), hypoxic or anoxic conditions in the hypolimnion are observed only at the end of the stratification period. A clear zonation of the chironomid fauna is present in this lake. The littoral zone is dominated byCladotanytarsus gr.mancus andStictochironomus sticticus, the littoriprofundal zone byTanytarsus bathophilus, and the profundal zone byChironomus anthracinus. In comparison with the other species in LM I,T. bathophilus larvae show the most variable distribution patterns over time. Larvae are found in all depths from July to September, but disappear from the hypolimnion as soon as oxygen conditions deteriorate. In the eutrophic Lake Maarsseveen II (LM II), oxygen depletion of the hypolimnion starts immediately after the onset of the thermal stratification in June, and continues until autumnal turnover in November. In this lake, the chironomid community consists primarily ofS. sticticus andCl. gr.mancus, and is confined to the narrow littoral zone. No chironomid larvae are found in the deeper parts of the lake. The eutrophic Lake Gijster in the Brabantse Biesbosch is a deep, man-made reservoir, that is artificially destratified during the summer. In this lakeTanytarsus bathophilus is found in the profundal sediments, whereas almost noChironomus is found in this zone. It is concluded that oxygen conditions existing in the deeper regions of the investigated lakes in large part determine the occurrence and distribution of chironomid species. The distribution ofT. bathophilus is limited by unfavorable oxygen conditions and not by the trophic state of the lake. These findings are part of a thesis (HEINIS, 1993).     

Diversity of desmids in three Thai peat swamps

Three peat swamps situated in the southern part of Thailand were investigated for their desmid flora in relation to a number of physical and chemical habitat parameters. Altogether, 99 species were encountered belonging to 22 genera. 30 species are new records for the Thai desmid flora. Laempagarung peat swamp showed the highest diversity (45 species), followed by Maikhao peat swamp (32 species) and Jud peat swamp (25 species). Despite its relatively low species richness, Jud swamp appeared to house a number of rare taxa, e.g., Micrasterias subdenticulata var. ornata, M. suboblonga var. tecta and M. tetraptera var. siamensis which can be considered Indo-Malaysian endemics. Differences in composition of the desmid flora between the three peat swamps are discussed in relation to environmental conditions. Presented at the International Symposium Biology and Taxonomy of Green Algae V, Smolenice, June 26–29, 2007, Slovakia.     

Use of desmids to assess the natural conservation value of a Hungarian oxbow (Malom-Tisza,NE-Hungary)

A method recently proposed by Coesel that uses the desmid flora to assess the conservation value of aquatic habitats was applied to an alkaline and hypertrophic oxbow of the Upper Tisza river (NE Hungary). According to the macrophyte community the oxbow contains two distinct habitats, both of which provide suitable conditions for the development of a rich desmid flora. High temporal and spatial differences in the algal flora were observed in periphyton and plankton samples taken in June and August 2004. The sample of Utricularia vulgaris periphyton collected in August was characterised by the most species-rich desmid flora. The conservation value of this sample was the maximum according to Coesel’s method. The latter also proved to be useful for the assessment of the conservation value of plankton net samples taken from among the macrophytes. The use of modified rarity value calculations as recently proposed by Fehér did not significantly affect the conservation value, but different enumeration methods to quantify the floristic diversity did result in different conservation values. We found that Coesel’s desmid based method is a useful tool for assessing the conservation value of the studied oxbow. Based our results the Coesel method’s applicability and usefulness depended on (i) the sampling location (open water or macrophytic region) samples were taken from open water or from macrophytic region; and (ii) species enumeration procedures (up to 400 specimens counted, or whole droplets counted). Presented at the International Symposium Biology and Taxonomy of Green Algae V, Smolenice, June 26–29, 2007, Slovakia.     

The cladocerans of the littoral zone of Lake Maarsseveen I

The littoral cladocerans of aPhragmites australis vegetation, and incidentally, the benthic chydorids on a sandy flat were studied from March through September in Lake Maarsseveen I (The Netherlands). A total of 31 species was found. Comparing the species list with data of Lake Constance before and after eutrophication, it can be concluded that Lake Maarsseveen I is still in an oligo-mesotrophic state. The littoral cladocerans peaked in the beginning of June and on the end of July. The species involved differed between the leeward SW and the windward NE sides. A larger number of chydorid species were found on the leeward shore. In the reed vegetation, the benthic chydorid densities showed a high degree of heterogeneity. A range of 23,000–406,000 specimens per m² was observed. The pattern sampler described by WHITESIDE and WILLIAMS (1975) gave no reliable results for the truly benthic chydorids. They will not swim up into the tubed bottles of this apparatus.     

Density fluctuations in populations (1982–1986) and biological observations ofPotamopyrgus Jenkinsi in two trophically differing lakes

The hydrobiid snailPotamopyrgus jenkinsi (E.A. Smith), characterized by parthenogenesis and ovovivipary, was quantitatively sampled monthly between June, 1982, and December, 1986, on sandy bottoms in the shallow zones of the meso-oligotrophic Lake Maarsseveen I and the eutrophic Lake Maarsseveen II. The snail demonstrated a very clumped distribution in both lakes. The mean numbers of juveniles and adults taken together fluctuated strongly. Organisms in Lake I showed relatively high densities (up to 25,000 per m²) in 1982, followed by a sudden drop to values approaching zero in December, 1982, with a subsequent rapid increase in densities, fluctuating between 2,000 and 200 per m². In Lake II, densities of snails fluctuated between 13,000 and 300 per m² with decreases in the spring of 1985 and 1986. The various types of decreases in the lakes are extensively discussed, but no explanation is presently available. The reduction in Lake I was of catastrophic proportions, but the speed of recovery of the population was remarkable.Floating was observed only in Lake I, and only during the occurrence of the highest densities on the sediment. Burrowing behaviour was very common, but strongly suppressed under an uninterrupted dark regime. A shift of temperature from 15 to 22°C had the same effect. A number of submerged macrophyte species from Lake I proved to attractP. jenkinsi in the absence of sandy substrate, though these plants were only covered by the snail during the period of the highest densities in 1982. Temperatures of 20°C or lower were well tolerated, unlike temperatures of 25 and 30°C. Growth was distinct at 10, 15 and 20°C. Keeled individuals were encountered in much higher numbers in Lake I than in Lake II.     

Temporal and spatial patterns of water mites in Lake Maarsseveen I

The paper analyses the distribution and seasonal changes in numbers of the water mite fauna of Lake Maarsseveen I. Water mites were collected from 1977 until 1986 by dipnet, underwater light trap, hydraulic lift sampler and by frame net. Fifty-two species belonging to the Hydrachnellae and one to the Halacaridae were sampled. The faunal picture obtained is characteristic of mesotrophic to eutrophic lakes.Arrenurus nobilis. Piona paucipora andP. imminuta can be characterised as lake species. The dominant species in the littoral sand flat areHygrobates nigromaculatus andH. trigonicus, at a depth of 0.5–1 m, andMideopsis orbicularis at depths of 2–7 m.Limnesia maculata is also very common on depths between 2 and 7 m. In early summer, however, they prefer shallow water up to 1 m depth. Some species likeHygrobates nigromaculatus andH. trigonicus were not captured by the underwater light trap. The hydraulic lift sampler gave underestimations of the densisty of certain speciese.g. Hygrobates spp. andLimnesia maculata. Unionicola spp. even can avoid this sampler. Sampling by frame net gave the most realistic data. The highest number of water mites was observed in the littoral sand flat, generally up to 1000 ind. m⁻². The genusHygrobates was represented with an average of 800 adult ind. m⁻² throughout the year, and appeared to be the main invertebrate predator in this habitat.     

Desmids in mountain lakes of the subpolar Urals

The species composition of desmids was studied in eight mountain lakes of the Kozhim and Malyi Patok River basins in the “Yugyd Va” National Park (subpolar Urals, Russia). A total of 98 desmid taxa representing 13 genera belonging to 4 families were identified. Geographical and ecological analyses showed that the desmid flora is typical, with a predominance of cosmopolitan species, planktic-benthic forms, acidophilic and pH indifferent species, and halophobic to salinity indifferent species. The investigated lakes can be classified as pristine and in good ecological condition on the basis of their hydrochemical and algal biodiversity characteristics. Presented at the International Symposium Biology and Taxonomy of Green Algae V, Smolenice, June 26–29, 2007, Slovakia.     

Desmids (Chlorophyta,Zygnematophyceae) from the Girutiskis mire complex reserve (East Lithuania)

The desmid flora of the Girutiskis mire complex reserve in Lithuania, a Natura 2000 territory and a potential Ramsar site, was investigated for the first time. Despite being a relatively small area with homogenous ecological conditions and a narrow range of pH-values, some pattern in the distribution of desmid species was observed. The lowest number of species was observed in the highly acidic lakes that were surrounded by sub-shrub bogs, and the highest number in less acidic lakes that were surrounded by trembling bogs. A total of 78 desmid taxa were found of which 16 were first records for Lithuania. Almost half of the taxa were uniquely found at one site, and only 10% were classified as frequent. Presented at the International Symposium Biology and Taxonomy of Green Algae V, Smolenice, June 26–29, 2007, Slovakia.     

GENETIC VARIATION IN ASTERIONELLA FORMOSA (BACILLARIOPHYCEAE): IS IT LINKED TO FREQUENT EPIDEMICS OF HOST‐SPECIFIC PARASITIC FUNGI?1

Understanding of the genetic basis for susceptibility and resistance is still lacking for most aquatic host–parasite systems, for instance, for phytoplankton and their fungal parasites. Fungal parasites can have significant effects on phytoplankton populations, mainly through their ability to decimate algal host populations during epidemics. We used random amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP) analysis to study levels of genetic variation within a population of the freshwater diatom Asterionella formosa Hassall in relation to parasitism by the obligate, host‐specific, fungal parasite Zygorhizidium planktonicum Canter. The level of genetic variation within the A. formosa population in Lake Maarsseveen, The Netherlands was found to be high despite the presumed absence or very low frequency of sexual reproduction in this species, the limited gene flow, and the severity of parasite attack that would purge the population from susceptible genotypes. RAPD analysis revealed four distinct banding patterns, with 3 of 21 markers (14%) being polymorphic. In AFLP analysis, every single isolate of A. formosa showed a unique banding pattern, and 120 of the 210 AFLP markers (57%) were found to be polymorphic. Furthermore, character compatibility analysis revealed that sexual reproduction may be one of the mechanisms that generates and maintains genetic variation in the A. formosa population in Lake Maarsseveen. The presence of genetic variation in A. formosa was reflected in infection experiments, which showed that genetically different A. formosa strains differed in their susceptibility to various Z. planktonicum strains and that parasite strains differed in their ability to infect particular host strains.     

Temperature tolerance and biogeography of seaweeds: The marine algal flora of Helgoland (North Sea) as an example

Temperature tolerance (1 week exposure time) was determined at intervals during two successive years in 54 dominant marine benthic algae growing near Helgoland (North Sea). Seawater temperatures near Helgoland seasonally range between 3°C (in some years 0°) and 18°C. All algae survived 0°C, and none 33°C. Among the brown algae,Chorda tomentosa was the most sensitive species surviving only 18°C, followed by theLaminaria spp. surviving 20°, however not 23°C.Fucus spp. andCladostephus spongiosus were the most heat-tolerant brown algae, surviving 28°C. Among the red algae, species of the Delesseriaceae(Phycodrys rubens, Membranoptera alata) ranged on the lower end with a maximum survival temperature of 20°C, whereas the representatives of the Phyllophoraceae(Ahnfelitia plicata, Phyllophora truncata, P. pseudoceranoides) exhibited the maximum heat tolerance of the Helgoland marine algal flora with survival at 30°C. The latter value was also achieved byCodium fragile, Bryopsis hypnoides andEnteromorpha prolifera among the green algae, whereas theAcrosiphonia spp. survived only 20°C, andMonostroma undulatum only 10°C, not 15°C. Seasonal shifts of heat tolerance of up to 5°C were detected, especially inLaminaria spp. andDesmarestia aculeata. The majority of the dominant marine algal species of the Helgoland flora occurs in the Arctic, and it is hypothesized that also there the upper lethal limits of these species may hardly have changed even today. The data presented should provide a base for further analysis of the causes of geographical distribution of the North Atlantic algal species, but have still to be supplemented with similar investigations on other coasts, and supplemented with determinations of temperature requirements throughout the life cycle.Paper presented at the Seaweed Biogeography Workshop of the International Working Group on Seaweed Biogeography, held from 3–7 April 1984 at the Department of Marine Biology, University of Groningen (The Netherlands). Convenor: C. van den Hoek     

Microbial colonization of soil aggregates as affected by temperature

Summary Sucrose-amended soil aggregates incubated at 15, 25 and 35°C exhibited quantitative and qualitative differences in microbial ecology. Numbers of bacteria and fungi showed a faster increase to the maximum level and a faster decrease with prolonged incubation the higher the temperature. Soil yeasts developed rapidly and extensively in aggregates incubated at 15 and 25 but not at 35°C.The fungal flora that developed on the aggregates varied with temperature: (a)M. silvaticus and anAlternaria species were the predominant primary flora at 15 and 25°C; (b)Sclerotium andPseudogymnoascus species developed in abundance in the later stages of incubation at 15 but were rare at 25°C; and (c)R. rhizopodiformis andA. fumigatus were virtually the only fungi observed on aggregates incubated at 35°C.Direct microscopic examination provided an estimate of the extent and type of fungal development that occurred on the aggregates. In general, dilution plate counts reflected accurately the growth and sporulation of the primary fungal flora of high sporulating capacity. But because spores of the primary flora remained viable in the soil and dominated the dilution plates long after the mycelia of these fungi had apparently decomposed, the plate counts provided little direct information regarding the development of the secondary fungal flora on the aggregates.     

Remarkable desmids (Desmidiaceae, Charophyta) from Sardinia, Italy

A number of benthic microfauna samples collected in Sardinia in the 1970s, and screened for the occurrence of microalgae in the 1990s, revealed some remarkable desmid species. Most of these species could not be found in a series of samples collected in 2006. Eleven desmid taxa are discussed in detail, two of which are described as new to science; Cosmarium majaeforme sp. nov. and Xanthidium sardiniense sp. nov. The specific composition of the Sardinian desmid flora is discussed both in relation to the prevailing environmental conditions and to its geographic position close to the African continent.     

Phytoplankton dynamics in a shallow,hypertrophic reservoir (Lake Arancio,Sicily)

Phytoplankton abundance and composition in the hypertrophic man-made Lake Arancio was analyzed, based on a programme of weekly sampling from May 1990 to November 1991 and supported by measurements of limnological parameters. The highest value of phytoplankton biomass (78 mg l^–1) was observed in October 1990, during a bloom of the desmid Closterium limneticum var. fallax, while the lowest (0.15 mg l^–1) was measured in April 1991. During spring, autumn and winter 1990, species of the genus Closterium dominated the community, in the sequence: C. aciculare, C. limneticum var. fallax, C. limneticum. The summer community was more diverse with the predominance of organisms belonging to Chlorophyceae (Chlamydomonas, Eudorina, Coelastrum) and Cyanophyceae (Microcystis, Anabaena). In spring 1991, there was a long clear-water phase during which small green algae (Ankyra, Oocystis) and cryptomonads dominated. Subsequently, the summer season was characterized by a clear sequence of dominants, drawn, in turns, from species belonging to: Bacillariophyceae, Dinophyceae, Cyanophyceae, Euglenophyceae. The physics of the reservoir and its depth, owing to filling/draining constraints in a summer-arid climate, appeared to play a key role in the dynamics of phytoplankton community.     

POLYMORPHISM IN THE DESMID XANTHIDIUM REGULARE AND ITS TAXONOMIC IMPLICATIONS

This paper refers to a case of polymorphism in the desmid genus Xanthidium Ehr. It is based on material from Lake Dais Irmaios, the main body of water in the Zoological and Botanical Garden in Recife, Pernambuco, northeastern Brazil, collected at 4 different times of the year during 1967 and 1968. A detailed examination of almost 1300 specimens showed an enormous variety in form of Xanthidium regulare Nordst., X. fragile Borge, and X. pseudoregulare Borge, thus allowing the authors to draw the following conclusions: (1) the name X. regulare Nordst. should be retained until further and more detailed studies on form variation within the species are available; (2) the names X. regulare Nordst. var. asteptum Nordst. in Borge, X. regulare Nordst. var. sexangulare Grönbl., X. regulare Nordst. var. sexangulare Grönbl. f. robustior Grönbl., X. fragile Borge, X. fragile Borge forma, and X. fragile Borge var. depauperatum Borge should be considered synonymous, all referring to a single variety of X. regulare Nordst., var. asteptum Nordst. in Borge emend. C. Bic. & L. M. Carv.; (3) X. pseudoregulare Borge must be treated as a variety of X. regulare Nordst. and must be called X. regulare Nordst. var. pseudoregulare (Barge) C. Bic. & L. M. Carv. Finally, a key is given to the 3 varieties of X. regulare Nordst. proposed in the present paper.     

The diatom flora and limnology of lakes in the Amery Oasis,East Antarctica

The diatom flora of three lakes in the ice-free Amery Oasis, East Antarctica, was studied. Two of the lakes are meltwater reservoirs, Terrasovoje Lake (31 m depth) and Radok Lake (362 m depth), while Beaver Lake (>435 m depth) is an epishelf lake. The lakes can be characterized as cold, ultra-oligotrophic and alkaline, displaying moderate (Radok and Terrasovoje lakes) to high (Beaver Lake) conductivities. There was no diatom phytoplankton present in any of the three lakes. While 34 benthic diatom taxa were identified from modern and Holocene sediments of Terrasovoje and Radok lakes, a 30-cm long sediment core recovered in Beaver Lake was barren. Five species (Luticola muticopsis, Muelleria peraustralis, Pinnularia cymatopleura, Psammothidium metakryophilum, P. stauroneioides) are endemic to the Antarctic region. All identified taxa are photographically documented and brief notes on their taxonomy, biogeography and ecology are provided. The most abundant diatom taxa are Amphora veneta, Craticula cf. molesta, Diadesmis spp, M. peraustralis and Stauroneis anceps. This is the first report on the diatom flora in lakes of the Amery Oasis.This revised version was published online in May 2004 with corrections to Figure 1.     

Population dynamic aspects of chironomid larvae of the littoral zone of Lake Maarsseveen I

Population dynamics of chironomid larvae in the littoral zone of Lake Maarsseveen I were investigated to a depth of 6 m. No essential differences in the composition and density between various sampling stations in the shallow sand flats were found. Two species,Cladotanytarsus mancus andStictochironomus sticticus, were found to be the main components of the chironomid population to a depth of 4 m. The density ofCladotanytarsus, which occurred predominantly to a depth of 1 m, increased from June to a maximum in December. In May and June, the entireCladotanytarsus population emerged.Stictochironomus had its peak of abundance in June. From this cohort, a part, differing in size for each of the various years, emerged in August. The remainder of this population, together with the offspring of the August adults, emerged in May. The size of the August midges, and the number of its eggs was smaller than that of the May midges. At depths greater than 4 m,Tanytarsus bathophillus was found to be the dominant chironomid.In summer the abundance of the small (second and third instars)Stictochironomus was primarily affected by water mite predation. In autumn and winter,Cladotanytarsus was the main food source for water mites. In autumn, whenStictochironomus larvae have molted into the fourth instar, predation by bream decreased the density of these larvae. In winter, the impact of this fish is negligible.     

A characterization and description of the Maarsseveen Lake system

The Maarsseveen Lakes system, located near the City of Utrecht, The Netherlands, consists of two major bodies of water, a larger lake (Maarsseveen I) and a smaller lake (Maarsseveen II), interconnected by a maze of channels known as a ‘petgaten’ area. The hydrodynamics of the lake region coupled with this ‘petgaten’ area are responsible for the maintenance of the relatively oligomesotrophic character of Lake Maarsseveen I, as compared with the more eutrophic lake maarsseveen II. Both lakes are plagued by problems of summer anoxia, although this phenomenon is far more pronounced in the more eutrophic small lake. Atmospheric deposition is responsible for contributions of significant quantities of trace metals to both lakes, and the River Vecht acts as an additional source for Lake Maarsseveen II.     

Wisconsin desmids. III. Desmid community composition and distribution in relation to lake type and water chemistry

This investigation summarizes quantitative data on the generic composition of the euplankton and aufwuchs desmid communities of 61 Wisconsin lakes, and analyzes the information with respect to 1) the role of the various genera in terms of frequency, density, and relative importance, 2) the suitability of various lake types for harboring desmid communities, and 3) the relationships between chemical parameters and desmid distribution. The generaStaurastrum, Cosmarium, andClosterium are of wide occurrence, appear to play major roles in the communities of all lake types, and are the most tolerant of varying chemical conditions. Most euplankton genera are of importance only in acid bogs, but aufwuchs genera generally are more widely distributed. Both the euplankton and the aufwuchs communities appear to be composed of 1–4 desmid assemblages, each with a differing range of importance values. Based on biological criteria, acid bogs appear to be the most suitable lake type for harboring desmid communities and calcareous spring ponds the least suitable type. High generic diversity of desmids appears to be correlated with low conductivity, calcium and alkalinity levels, pH values of 5.1–7.0, and the presence of free CO₂. The evidence attending various hypotheses concerning water chemistry and desmid distribution appears contradictory, and further studies are needed to help clarify the situation.