Effects of food concentration on the life table demography and morphology of three Keratella quadrata morphotypes

Keratella quadrata with two (2PS), one (1PS) and none posteolateral (0PS) spines were cultured under four food levels (0.75 × 106, 1.5 × 106, 3.0 × 106 and 6.0 × 106 cells·mL−1 of Scenedesmus obliquus) to test the differences in the life table demography and the morphological characteristics among these three morphotypes. The results showed that each K. quadrata morphotype could produce 2PS, 1PS and 0PS offsprings. The frequencies of 0PS were extremely low (<5%) and could be considered as a small probability event, suggesting that the 0PS morphotype might be an abnormal status. The following life table demographic tests suggested that 0PS morphotype had a relatively lower intrinsic rate of population growth at high food concentrations and a relatively lower average lifespan, in comparison to 2PS rotifers. These results further supported that the 0PS K. quadrata might be an abnormal development. Along with the elevating food concentration, 1PS morphotype reproduced more 2PS offsprings, suggesting that high energy input might be helpful to grow more posterolateral spines. However, in response to the increasing food concentration, 0PS rotifers produced more 1PS offsprings. The underlying mechanisms required further investigations. The posterolateral spine length of offsprings of 0PS K. quadrata was significantly longer than those of 2PS and 1PS rotifer parents at the four food concentrations, which probably help the offsprings of 0PS rotifer parents to survive in natural environments, since long and more posterolateral spines offer rotifers high ability to compete with other rotifers and cladocerans for food or to resist predators.

ECOLOGICAL EVALUATION OF ZOOPLANKTON GROUPS IN LAKE GERANIMOVAS-ILZAS AND LAKE GARAIS

Lake Garais is the second deepest lake in Latvia. Its maximum depth is 56.0 meters, but its average depth is 16.5 meters. Lake Geranimovas-Ilzas is the fifth deepest lake in Latvia. Its maximum depth is 46.0 meters, but its average depth is 9.8 meters [13]. During the research of Lake Gernimovas-Ilzas and Lake Garais three zooplankton groups have been found, i.e. Rotatoria, Cladocera and Copepoda. Having analysed the quality composition of species the authors have concluded that the pollution level of these lakes is low, because there are such olygosoprobic zooplankton species as Keratella cochlearis, Keratella quadrata, Filinia longiseta, that die from lack of oxygen in few hours.

Evidences of zooplankton vertical migration in stocked and never-stocked alpine lakes in Gran Paradiso National Park (Italy)

Zooplankton vertical migration was described in four high altitude lakes in Gran Paradiso National Park (Northern Italy) during 2008 summertime. The authors succeeded in describing the vertical distribution of 6 species: diel vertical migrations were observed in the case of adult crustacean species (Cyclops gr. abyssorum, Arctodiaptomus alpinus and Daphnia gr. longispina), whereas the remaining rotifer species (Keratella quadrata, Polyarthra gr. dolichoptera and Synchaeta gr. stylata-pectinata) and naupliar stages of copepods did not undergo migrations. Migratory behavior of Daphnia gr. longispina and Cyclops gr. abyssorum was influenced by the size of individuals, especially larger individuals use to migrate deeper during the day compared to the smaller conspecific. This study provides new evidences of zooplankton vertical migration in never-stocked lakes and highlights the need to consider the zooplankton migration as result of multiple causal factors.

Zooplankton-based assessment of the trophic state of a tropical forest river in Nigeria

In this study, we explore the usefulness of zooplankton as a tool for assessing the trophic status of a Nigerian forest river. The river was sampled monthly and investigated for water physico-chemistry and zooplankton community structure using basic statistical measurement of diversity indices to characterize the zooplankton fauna. The trophic sta?tus of the river evaluated from its physico-chemical parameters indicates that the river is oligotrophic. The zooplankton composition was typical of a tropical freshwater river, with a total of 40 species, made up of 16 rotifers, 12 cladocerans, and 12 copepods and their developing stages in the following order of dominance: Rotifera > Cladocera > Cyclopoida > Calanoida. There were strong correlations between the lake's trophic status and its zooplankton communities. The zoo?plankton community was dominated by numerous species of rotifers and crustaceans, which are typical of oligotrophic to mesotrophic systems, such species including Conochilus dossuarius and Synchaeta longipes. However, the most dominant zooplankton species in West African freshwater ecosystems, viz., Keratella tropica, Keratella quadrata, Brachionus angularis, Trichocerca pusilla, Filinia longiseta, Pompholyx sulcata, and Proales sp., and others that are indicator species of high trophic levels, were not recorded in the river. The river is very clear and can be used for all manner of recreational activities.

Regulation of Rotifers by Predatory Calanoid Copepods (Subgenus Hesperodiaptomus) in Lakes of the Canadian Rocky Mountains

The abundance of planktonic rotifers in alpine lakes is regulated by predation from Diaptomus (subgenus Hesperodiaptomus) arcticus (a large calanoid copepod) regardless of nutrient conditions. We manipulated both predators and nutrient levels in large in situ enclosure experiments (2250 L). Hesperodiaptomus arcticus suppressed densities of the soft-bodied rotifer Polyarthra dolichoptera significantly (two to three orders of magnitude) and the loricate rotifer Keratella quadrata less so (up to one order of magnitude) relative to populations in predator-free enclosures. Keratella quadrata's armoured lorica may limit predation by Hesperodiaptomus. Nutrient addition resulted in higher phytoplankton standing crops and rotifer densities but did not permit rotifers to exceed predator consumption. In 69 lakes from the Canadian Rocky Mountains, the presence of Keratella or Polyarthra was negatively correlated with Hesperodiaptomus density. A maximum-likelihood logistic regression model predicts that as Hesperodiaptomus densities increase the probability of occurrence for both rotifer genera decreases, with Polyarthra declining more rapidly than Keratella.

Seasonal Development of Zooplankton in the Lower River Rhine during the Period 1987–1991

This paper presents some results of a five year monitoring programme on Zooplankton in the River Rhine at the Dutch sampling stations Lobith (German/Dutch border) and Maassluis (at the discharge of the river into the North Sea). During the entire period the Zooplankton composition showed an apparent seasonal pattern at both stations. This pattern was characterized by low densities during the winter and higher densities during the summer with an obvious spring peak. Zooplankton was dominated by rotifers with Brachionus angularis, B. calyciflorus, Keratella quadrata and K. cochlearis as dominant species. The possible role of environmental factors (flow rate and chlorophyll-a content) as controlling factors for Zooplankton dynamics is indicated.

Complex Interactions of Multiple Aquatic Consumers: An Experimental Mesocosm Manipulation

In 7-m3 outdoor tanks filled with lake water, the presence/absence of omnivorous young-of-the-year Micropterus salmoides, zooplanktivorous Menidia beryllina, and herbivorous larval Hyla chrysocelis was experimentally manipulated. A cross-classified design was used to assess the interactive effects of these vertebrate consumers on the experimental food webs. Large zooplankters and large, actively swimming macroinvertebrates (Ceriodaphnia, Simocephalus, Corixidae, Notonectidae, and Dytiscidae) were particularly susceptible to depletion by both fish species. Micropterus tanks contained greater numbers of Keratella quadrata and Hebridae but fewer benthic cyclopoid copepods. Menidia tanks contained more Synedra and algal filaments. Hyla exerted only minor direct effects on the tank communities. When both fish species were in the same tank, both had elevated mortality. Micropterus, in tanks with Menidia and Hyla, were larger and in better condition than in tanks without Hyla. The primary effects of the experimental manipulations on food web components were two- and three-way interactions in which the effect of a given treatment was dependent on the presence of another treatment. Results suggest that the addition or removal of consumers may not cause linear, additive changes in food webs.