Pelagic rotifers of Lake Glubokoe from 1897 to 1984

After alteration in the pattern of drainage of run-off from the surrounding swamps and changes in the colour and transparency of the Lake Glubokoe water, the previously epilimnial Trichocerca similis, Conochilus unicornis and Keratella cochlearis showed a shift of their maximum numbers to deeper layers. Pompholyx sp. and Trichocerca capucina, which are regarded as indicators of eutrophic waters, have disappeared from the pelagic zone of the lake and Conochilus hippocrepis, Synchaeta pectinata, Gastropus stylifer, Asplanchna herricki, Ascomorpha ecaudis, Ascomorpha saltans, Euchlanis dilatata and Trichocerca porcellus have made their appearance. Most of the new species are considered to be indicators of oligotrophic conditions. However the total density of pelagic rotifers remained at the same level. Apparently the establishment of the new species of rotifers was possible due to some ‘rarefaction’ of the epilimnion, the disappearance of predaceous Mesocyclops leuckarti and the invasion of the pelagic zone by Peridinium cinctum.     

Biodiversity of Rotifera in some tropical floodplain lakes of the Brahmaputra river basin,Assam (N.E. India)

One hundred and sixteen species of Rotifera are recorded from seven floodplain lakes of the Brahmaputra basin (northeastern India), the highest rotifer biodiversity recorded from these biotopes in the Indian subcontinent to date. The Australasian Brachionus dichotomus reductus and Lecane batillifer; the Oriental Keratella edmondsoni, Lecane blachei and L. acanthinula; the Palaeotropical Lecane braumi, L. lateralis, L. unguitata, Trichocerca tropis, Testudinella greeni and T. brevicaudata; the Pantropical Brachionus donneri and a rather widely distributed Horaella brehmi represent taxa of biogeographical interest. Three species are new additions to the Indian rotifer fauna and eight are new to the N.E. region. Lecanidae > Brachionidae = Colurellidae > Trichocercidae > Testudinellidae comprise the largest fraction (68.0%) of the examined fauna. Comments are made on the general nature and composition of the rotifer taxocoenosis as well as on acidophilic elements, ecology of various taxa and on the species richness of different lakes.     

Dominant rotifers of Võrtsjärv (Estonia)

Rotifers form 71% of the zooplankton of the strongly eutrophic (total N 2 g m^–3, total P 53 mg m^–3) Võrtsjärv (Estonia). Altogether 150 taxa of rotifers occur. Species characteristic of oligo- and mesotrophic waters have totally disappeared during the last 30 years, or are disappearing now. Species whose numbers and biomass reached 20% or more of total zooplankton were considered dominants. These were Anuraeopsis fissa, Keratella cochlearis, K. quadrata frenzeli, Polyarthra dolichoptera, P. luminosa, Synchaeta verrucosa and Trichocerca rousseleti. The contribution of dominant rotifers to total zooplankton and its biomass is as follows: S. verrucosa 25% and 39%, P.dolichoptera 34% and 25%, K. cochlearis 25% and 7%, K. quadrata frenzeli 9% and 7%, A. fissa 28% and 0.4%, T. rousseleti 20% and 0.6%, respectively.     

The effect of fish on planktonic rotifers

The dynamics, community structure, and productivity of planktonic rotifers were studied during 3 years in two lakes near St. Petersburg (Russia). One lake was repeatedly stocked with larvae of the fish Coregonus peled; the other contained no fish. Fish addition led to a shift in plankton community structure. Population densities of some rotifer species (Keratella cochlearis, K. irregularis, Asplanchna priodonta) increased as a result of the elimination of large crustaceans by fishes during summer and autumn. An inverse relationship was found between the biomass of rotifers and Daphnia.     

Comparative analysis of rotifer community structure in five subtropical shallow lakes in East China: role of physical and chemical conditions

Worldwide, there have been few comparative studies on rotifer communities in subtropical lakes. We studied changes in rotifer community structure over 1 year and its relationship to several physicochemical variables in five subtropical shallow lakes in East China, covering a nutrient gradient from mesotrophy to moderate eutrophy. In these lakes, the genera Brachionus, Lecane, and Trichocerca dominated the rotifer species composition, and Polyarthra dolichoptera, Keratella cochlearis, Filinia longiseta, T. pusilla, and Anuraeopsis fissa were the dominant species. With increased nutrient loading, total rotifer abundance and species dominance increased, indicating that rotifer abundance might be a more sensitive indicator of trophic state than species composition. Comparative analyses of the six rotifer community indices calculated in this study and redundancy analysis (RDA) revealed that the two slightly eutrophic lakes and the other two moderately eutrophic lakes exhibited a high degree similarity in community structure. This suggests that the trophic state of a lake determines the rotifer community structure. In contrast, in the two moderately eutrophic lakes, the mass ratios of TN:TP and the contents of TP suggested N-limitation and cyanobacteria dominance in phytoplankton communities might be possible. In these lakes TN played a more important role in shaping the rotifer community according to stepwise multiple regression and RDA. RDA analysis also suggested that rotifer species distribution was strongly associated with trophic state and water temperature, with water temperature being the most important factor in determining seasonality.     

Seasonal dynamics of rotifer and crustacean zooplankton populations in a eutrophic,monomictic lake with a note on rotifer sampling techniques

The abundances, biomass, and seasonal succession of rotifer and crustacean zooplankton were examined in a man-made, eutrophic lake, Lake Oglethorpe, over a 13 month period. There was an inverse correlation between the abundance of rotifers and crustaceans. Rotifers were most abundant and dominated (>69%) the rotifer-crustacean biomass during summer months (June–September) while crustacean zooplankton dominated during the remainder of the year (>89%). Peak biomasses of crustaceans were observed in the fall (151 µg dry wt l^–1 in October) and spring (89.66 µg dry wt l^–1 in May). Mean annual biomass levels were 46.99 µg dry wt l^–1 for crustaceans and 19.26 µg dry wt l^–1 for rotifers. Trichocerca rousseleti, Polyarthra sp., Keratella cochlearis and Kellicottia bostoniensis were the most abundant rotifers in the lake. Diaptomus siciloides and Daphnia parvula were the most abundant crustaceans. Lake Oglethorpe is distinct in having an unusually high abundance of rotifers (range 217–7980 l^–1). These high densities can be attributed not only to the eutrophic conditions of the lake but also to the detailed sampling methods employed in this study.The research was supported by National Science Foundation grants DEB 7725354 and DEB 8005582 to Dr. K. G. Porter. It is lake Oglethorpe Limnological Association Contribution No. 25 and Contribution No. 371 of the Harbor Branch Foundation, Inc.     

Changes in Rotifer Species Composition and Abundance along a Trophic Gradient in Loch Lomond,Scotland, UK

Loch Lomond is the second largest body of freshwater in Great Britain. It is a long, narrow lake (36.4 km long, 8.8 km wide). The northern basin is fjord-like and surrounded by a mountainous, base-poor, rocky catchment. In contrast, the southern basin is much broader and shallower with a mainly lowland, calcareous, agricultural catchment. This causes a trophic gradient along the length of the loch that runs from the oligotrophic northern basin to the more mesotrophic southern basin. Rotifer samples were collected at monthly intervals between May and October 2002 at three locations along the length of the loch. More than 12 species were found, the commonest of which were Keratella cochlearis (Gosse) and Trichocerca stylata (Gosse). Although the species composition of the rotifer community varied very little among the sites, rotifer abundance increased markedly from north to south, apparently reflecting the trophic gradient along the length of the loch. The results suggest that rotifer abundance may be a more sensitive indicator of trophic state, and changes in trophic state, than species composition.     

Eutrophication of Lakes Leman and Neuchâtel (Switzerland) indicated by oligochaete communities

In 1978–80, oligochaete communities of meso-eutrophic Lake Léman (Lake of Geneva) were compared to those of mesotrophic Lake Neuchâtel. Worm species were classified into three groups corresponding to their increasing tolerance to eutrophication: (1) oligotrophic species, mostly Peloscolex velutinus, Stylodrilus heringianus; (2) mesotrophic species, mostly Potamothrix vejdovskyi, P. bedoti; (3) eutrophic species, mostly Potamothrix hammoniensis, P. heuscheri, Tubifex tubifex. In both lakes, eutrophic species constituted the bulk of the communities in terms of absolute abundance. However, relative abundance of mesotrophic and eutrophic species was higher in Lake Léman; oligotrophic species were more important in Lake Neuchâtel. These data confirmed the trophic classification of lakes based on chemical parameters. The number of zero values, which perturbated statistical analysis, was reduced by using species groupings instead of isolated species. Thus, making the lakes more comparable even if different species were present in each one. Relative density values based on all samples were distributed among 4 density classes for the 3 species groupings. The 12 resulting frequencies described the community structure expressed in terms of eutrophication. Furthermore, these frequencies may be used for comparison of eutrophication levels in several lakes.     

Morphological structure and functional patterns of Keratella cochlearis (Gosse) populations in stratified lakes

Vertical distribution of the rotifer Keratella cochlearis in stratified water columns of mesotrophic and eutrophic lakes during summer stagnation has been studied. Coexisting morphs K. cochlearis hispida (Lauterborn, 1898), K. c. tecta (Gosse, 1851) and K. c. cochlearis (Gosse, 1851) inhabit different layers in the water column and are vertically subdivided. The distribution of morph abundance and reproductive potential indicate that substitution of morphs within the vertical water column may be due to trophic conditions. The maximum population productivity is observed at the epi-metalimnion border. The maximum density zone lies below the zone of the highest productivity. The principle of sliced functioning is used to explain the adaptive significance of the morphological structure of populations under heterogeneous environmental conditions.     

Rotifer communities from some Araucanian lakes of southern Chile

During the last decade much information has been produced about the zooplankton communities in southern Chile; however, most of this is related to the crustacean assemblages. The present communication examines the spatial and temporal distribution of rotifer assemblages and their relation to the environmental variables during one-year period in four Araucanian lakes. A total of 19 species was found in these oligotrophic lakes. Keratella cochlearis, Synchaeta stylata, Trichocerca porcellus, Conochilus unicornis and Collotheca pelagica were widespread, and seven species exhibited a more restricted distribution among the lakes. Species richness varied from 6 to 12; similarly, one or two dominant species usually accounted for more than 80% of the total annual abundance. Similar dominant species occurred in two lakes, but their maximum peaks of abundance differed in time; in the remaining lakes the most important species were different. Calculated rotifer diversity showed a fluctuating pattern, with low values during the year in three lakes, and high ones in Lake Llanquihue. Species diversity was significantly related to species richness in all lakes. Discriminant analysis based on the occurrence and abundances of species throughout the year revealed that the rotifer assemblage in Lake Llanquihue was different from that in the rest of the Araucanian lakes. Furthermore, the same analysis using environmental variables showed that this lake is clearly discriminated from the others on the basis of the ionic composition of the water (i.e. Cl^–, Na⁺, Mg²⁺). Rotifer abundances in these lakes were significantly influenced by a number of abiotic variables, including those related to water ionic composition. These relationships may imply that the small differences in chemical characteristics of these lakes influence the structure of the rotifer community.     

Planktonic rotifer community structure in Adirondack,New York,U.S.A. lakes in relation to acidity,trophic status and related water quality characteristics

The structure of the mid-summer planktonic rotifer communities of 101 Adirondack lakes ranging in pH from 4.0 to 7.3 were characterized in relation to acidity and selected water quality parameters. More than 70 rotifer species were identified from collections in 1982 and 1984. None of the species collected could be considered acidobiontic or alkalibiontic. Keratella taurocephala was the most commonly collected rotifer, occurring in 94 of the study lakes. It was abundant throughout the range of pH investigated but was particularly dominant in acidic waters, averaging > 85 % of the rotifers collected from waters of pH < 5.0.Rotifer community structure can be related to three groups of water quality parameters. Community parameters (richness and diversity) are most highly correlated with parameters indicative of acidity status. Rotifer abundance correlates with trophic state indicators, i.e. chlorophyll a and total phosphorus, over the full range of pH investigated. However, in acidic lakes, rotifer abundance is related to true color and DOC, indicators of humic influences.The rotifer communities of the Adirondacks can be classified into four broad types: 1) A diverse, productive community of the more alkaline lakes, generally with 13 species, and dominated by Conochilus unicornis, Kellicottia bostoniensis, Kellicottia longispina, and Polyarthra major; 2) Relatively diverse communities of productive, highly colored acid lakes, with 8 species, and often with very large populations (> 200 · 1^–1) dominated by K. bostoniensis and K. taurocephala; 3) Depauperate (< 4 species) communities of clear water acid lakes with generally low density populations dominated by K. taurocephala (> 90 % of rotifers in each sample); and 4) Extremely depauperate (2–3 species) acid lake communities associated with small lakes with high flushing rates dominated by C. unicornis.     

The effect of lake fertilisation on the rotifers of Seathwaite Tarn,an acidified lake in the English Lake District

Seathwaite Tarn, in the English Lake District, was used as an experimental site to test the feasibility of increasing the pH of an acidified waterbody by adding a phosphorus-based fertiliser solution. The impact of this experiment on the planktonic rotifer community was assessed by monitoring for two years before treatment (1990–1991), and for a further two years once treatment had begun (1992–1993). The pH of the water rose by 0.5 pH units over the period of fertilisation, and the lake became very eutrophic. This had little effect on the species composition of the rotifer assemblage, which continued to reflect the acid, oligotrophic nature of the untreated lake. However, there were marked changes in the levels of abundance of most planktonic species. Population densities of Keratella serrulata and Trichocerca longiseta increased in early spring, compared to pre-treatment levels, apparently due to the rises in chlorophyll-a concentrations. In contrast, Polyarthra dolichoptera became very scarce after fertilisation began. The treatment seemed to have little effect on the population dynamics of the dominant openwater rotifer, Polyarthra remata. In 1993, very high densities of Bosmina coregoni (up to 250 × 10³ ind M^–3 ) developed in response to the eutrophication programme. This seemed to suppress the rotifer community in the summer months.     

Preliminary remarks on the characteristics of the rotifer fauna of Australia (Notogaea)

Unusually large forms of Asplanchna sieboldi, Brachionus plicatilis, B. calycijlorus, Filinia pejleri, Trichocerca similis and Keratella slacki were collected from waters of south-eastern Australia. These giant forms are figured, and brief location and ecological data are given. Although the rotifer fauna of the Murray riversystem contains pan-tropical and pan-subtropical species, there exists a greater degree of endemicity than previously considered.     

THE INFLUENCE OF SUBMERGED MACROPHYTES ON SEDIMENTARY DIATOM ASSEMBLAGES1

Submerged macrophytes are a central component of lake ecosystems; however, little is known regarding their long‐term response to environmental change. We have examined the potential of diatoms as indicators of past macrophyte biomass. We first sampled periphyton to determine whether habitat was a predictor of diatom assemblage. We then sampled 41 lakes in Quebec, Canada, to evaluate whether whole‐lake submerged macrophyte biomass (BiomEpiV) influenced surface sediment diatom assemblages. A multivariate regression tree (MRT) was used to construct a semiquantitative model to reconstruct past macrophyte biomass. We determined that periphytic diatom assemblages on macrophytes were significantly different from those on wood and rocks (ANOSIM R = 0.63, P < 0.01). A redundancy analysis (RDA) of the 41‐lake data set identified BiomEpiV as a significant (P < 0.05) variable in structuring sedimentary diatom assemblages. The MRT analysis classified the lakes into three groups. These groups were (A) high‐macrophyte, nutrient‐limited lakes (BiomEpiV ≥525 μg · L^?1; total phosphorus [TP] <35 μg · L^?1; 23 lakes); (B) low‐macrophyte, nutrient‐limited lakes (BiomEpiV <525 μg · L^?1; TP <35 μg · L^?1; 12 lakes); and (C) eutrophic lakes (TP ≥35 μg · L^?1; six lakes). A semiquantitative model correctly predicted the MRT group of the lake 71% of the time (P < 0.001). These results suggest that submerged macrophytes have a significant influence on diatom community structure and that sedimentary diatom assemblages can be used to infer past macrophyte abundance.     

An Experimental Analysis of the Acid Sensitivity of the Common Planktonic Rotifer Keratella cochlearis

An in situ mesocosm experiment was performed at neutral pH Lake O'Woods, West Virginia, to assess the impacts of acidification on the common planktonic rotifer Keratella cochlearis. This rotifer is typically replaced by K. taurocephala during the acidification of North American lakes. Despite a rapid pH reduction in this experiment (from 7.0 to 4.8 in 14 days), the abundance, mean body length and egg ratio of K. cochlearis did not decline in the acid treatment as compared to the untreated control. These results support the hypothesis that K. cochlearis is acid-tolerant, and suggest that its disappearance from acid lakes is the result of biotic interactions within the plankton, rather than the result of toxic effects of altered water chemistry.     

Rotifer community structure in three shallow lakes: seasonal fluctuations and explanatory factors

The present work aimed at studying the rotifer communities of three shallow eutrophic lakes in Portugal (lakes Mira, Vela and Linhos). At the time of the study, Mira and Vela faced large inputs of allochthonous nutrients, while Linhos was facing terrestrialisation, with cycles of dominance-senescence of macrophytes. The three lakes differed in terms of their abiotic features, with Linhos presenting very high nutrient levels and low pH, while Vela and Mira shared most of the characteristics. The rotifer communities of these two lakes were poorly diversified but highly abundant (max. > 2000 ind l⁻¹), with a clear dominance of eurytopic euplanktonic species (mainly Keratella cochlearis). On the other hand, Linhos presented lower abundances (<1000 ind l⁻¹) but higher species richness, mainly due to macrophyte-associated taxa, such as the littoral genera Lepadella, Testudinella and Squatinella. In all lakes, summertime represented a peak in terms of abundance and diversity. Canonical correspondence analysis (CCA) identified two main environmental gradients that shape up the rotifer assemblages: a temporal gradient, mainly related to temperature, and a eutrophy gradient, associated with nitrogenous nutrients. The latter gradient is clearly dependent on between-lake variation, due to the high nutrient levels observed in lake Linhos. Variance partitioning using CCA revealed that the largest portion (27.5%) of the total variation explained (52.1%) was attributed to the interaction between lake and environmental variables.     

Community structure and bottom-up regulation of heterotrophic microplankton in arctic LTER lakes

Microplankton community structures and abundance was assessed in lakes at the Toolik Lake LTER site in northern Alaska during the summers of 1989 and 1990. The microplankton community included oligotrich ciliates, but rotifers and zooplankton nauplii comprised greater than 90% of total estimated heterotrophic microplankton biomass. Dominant rotifer taxa included Keratella cochlearis, Kellicottia longispina, Polyarthra vulgaris, Conochilus unicornis and a Synchaeta sp. Microplankton biomass was lowest in highly oligotrophic Toolik Lake (< 5 μgCl⁻¹ at the surface) and highest (up to 55 μCl⁻¹) in the most eutrophic lakes, experimentally fertilized lakes, and fertilized limnocorrals, consistent with bottom-up regulation of microplankton abundance.     

Indicative profundal oligochaete assemblages in selected small Swedish lakes

Fifty-seven small- to middle-size lakes of Sweden (size-range from <0.1 to about 200 km²) representing different regions and lake-types were selected for the purpose of demonstrating the indicative value of profundal oligochaete communities also of relatively small lakes. It is well known since previously that profundal oligochaete assemblages of large lakes in Europe may be particularly indicative of the current trophic situation, but little has been known about smaller lakes in this respect. Characterizations based on oligochaete community structure in these lakes could be summarized in eight different groups: Characteristic oligochaete communities in oligotrophic lakes of relatively small size are Spirosperma ferox, Stylodrilus heringianus and Tubifex tubifex. Oligochaete species richness is low (1–3 species) and so is species abundance (<300 specimens m^–2). Very eutrophic lakes of the same size-range are largely dominated by the tubificids Limnodrilus hoffmeisteri and/or Potamothrix hammoniensis. Substitute or complementary species may be T. tubifex. Species richness is usually low (1–3 species), but abundance is high to very high (>5000 specimens m^–2). Mesotrophic to moderately eutrophic lakes of the same size categories contain more species than the above extremes, most of them being fairly tolerant to oxygene deficiency such as Tubifex ignotus, a number of species of the genera Aulodrilus and Limnodrilus and a variety of so-called Ponto-Caspian Potamothrix species, most of them having recently invaded south-eastern Sweden. Species richness is moderate to high (4–8 species), while abundance may vary considerably (range from about 300 to about 5000 specimens m^–2). In this respect, small- to middle-size lakes do not differ much from larger lakes. For the trophic characterization of lake water the mean concentrations of total-phosphorus (in g l^–1) is generally regarded to be the most appropriate measure. The match between characterizations based upon oligochaete community structure and total-phosphorus concentrations is generally very good for large lakes. The present study shows that this applies fairly well also to the majority of the small- to middle-size lakes selected for this study. This has not been shown before. Obvious deviations from this rule could be caused by a scarcity of reliable chemical data, or considerable seasonal shifts in the chemical composition ot the water, which in its turn may be caused by short water residence time. Littoral elements in the fauna, which are generally less indicative, or effects of local inflows may also be more frequent here than in lakes of larger size.     

Zooplankton biomass dynamics in oligotrophic versus eutrophic conditions: a test of the PEG model

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Taxonomic problems with the species Keratella hiemalis

Keratella hiemalis was described by Carlin (1943) from Motalaström in southern Sweden. It was distinguished from K. quadrata by its low morphological variability and its occurrence at only low temperatures. Morphological characteristics are: straight lateral borders of carapace and spines, caudal spines of medium length, and triangular, first median facet. The species has been found by many authors in the hypolimnion of oligotrophic lakes. Some workers have applied the name Hiemalis to a similarly-sized species, K. testudo. This species occurs in high mountain and arctic pools and displays substantial morphological variability.Deceased.