Zooplankton composition and abundance in two impoundments in Zimbabwe

The composition and abundance of the main zooplankton groups in Cleveland dam (less eutrophic) and Lake Chivero (more eutrophic) were studied. Samples were taken at two-month intervals. Rotifers were the most diverse zooplankton group in both reservoirs. Together with the copepods they formed the bulk of the zooplankton during summer. Cladocerans were particularly present in winter although still at relatively low densities.     

Zooplankton associations in some Ethiopian crater lakes

SUMMARY. 1. The zoopiankton associations in five crater lakes in Ethiopia were examined in April 1984. The two least alkaline lakes had the most diverse zoopiankton.
2. The large diaptomid copepod Lovenula africana was present in the lakes with alkalinities between 10 and 63 meq l⁻¹, but was absent from Lake Chitu (239 meq l⁻¹).
3. The contribution of the zoopiankton to the nocturnal deoxygenation of Lake Aranguadi is negligible.     

Zooplankton associations in the swamps of southern Sudan

Samples from the main Nile channel yield a poor zooplankton, deficient in species and heavily laden with organic debris. Samples from side arms and floodplain lakes yield a richer zooplankton, often containing 15–20 species of rotifers and ten or more species of Crustacea. When the floodplain lakes are heavily vegetated the number of species increases. For the Crustacea the index of diversity () normally varies between 0.6 and 2.4, but in a side arm of the Bahr el Zeraf it reaches 6.1 and in Lake Ambadi on the Bahr el Ghazal it reaches 8.4. The diversity of the rotifers is somewhat higher, normally ranging between 2 and 4.5, but reaching 23 in Lake Ambadi. The zooplankton of Lake Ambadi is the most distinctive and contains several species not found at other stations. The reasons for the peculiar zooplankton of Lake Ambadi are discussed.     

Zooplankton associations in East African lakes spanning a wide salinity range

Abstract The zooplankton of 38 East African lakes has been analysed in terms of species richness and dominance. The conductivities of the lakes range from 48 to 72 500 µS cm^–1 20 °C. The lakes generally contain more species of rotifers than either Copepoda or Cladocera. The number of species of rotifers begins to decline at a conductivity below 1000 µS cm^–1, and falls to 2 or 3 species above 3000 µS cm^–1. Similar reductions occur in the Copepoda and Cladocera.Many species can be dominant at conductivities below 1000 µS cm^–1, but the range is restricted progressively with increasing salinity. The dominant species of Rotifera, Copepoda and Cladocera change independently along the salinity gradient, but there are indications of interactions and modifications of community structure by predation and competition.     

Zooplankton associations and environmental factors in Ogunpa and Ona rivers, Nigeria

Zooplankton abundance, composition and environmental parameters were monitored in two tropical rivers over a twenty month period. The data was subjected to cluster, factor and correlation analysis to determine the grouping pattern of zooplankton and their relationship to environmental parameters. Environmental factors in Ogunpa and Ona rivers--included buffering capacity, trace metal ions, pH-temperature/transparency--were primarily influenced by rainfall. The dominance of the Rotifera in both rivers was attributed to their short developmental rate and fish predation on larger zooplankton. Two groups of associations were identified in each river--a commonly occurring species group exhibiting strong homogenous correlation with environmental factors and a predominant group exhibiting weak correlation with environmental factors and whose abundance/composition may be defined by biotic factors.     

Zooplankton in the Vychegda River

The species composition of plankton invertebrates was studied in the middle Vychegda River (the main tributary of the Northern Dvina River) in 2003–2005. A list of planktonic rotifers and lower crustaceans was made. The dominating complexes of zooplankton organisms were found. The quantitative characteristics of plankton communities in the river were described.     

Biogas development in Zimbabwe

Summary Two main biogas prorammes have been developed in Zimbabwe, one for the development of biogas at the individual household level (40 digesters) and the other for institutional users like schools and rural community centres (10 digesters). The funding of these digesters is provided by the users themselves and the Government provides the technical advice. In the future four projects are considered: (1) a biogas promoter will work in rural areas from village to village to inform leaders and teach the people; (2) rural resettlement schemes based on dairy farming are planned to integrate biogas production; (3) commercial farmers will get technical advices to build digesters for their workers; finally (4) two industries have been identified as candidates for biomethanation projects: a food-processing industry and a brewery.

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Resumen En Zimbabwe se han desarrollado dos programas principales en relación con el biogas. Uno para el desarrollo de sistemas de biogas a nivel doméstico (40 digestores) y el otro para su utilización en instituciones tales como escuelas y centros de cominidades rurales (10 digestores). Estoa digestores han sido costeados por sus usuarios mientras que el gobierno ha proporcionado la asistencia técnica. Para el futuro se han tomado en consideración 4 proyectos: (1) La divulgación de información y la enseñanza por parte de unpromotor de biogas que visitara pueblo a pueblo las areas rurales. (2) replanificación de asentamientos rurales basados en la elaboración de productos lacteos integrando la producción de biogas. (3) asistencia técnica a ganaderias comerciales para construir digestores para sus trabajadores y finalmente (4) se han identificado dos industrias candidatas para proyectos de biometanación: una industria transformadora de alimentos y una fábrica de cerveza.

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Résumé Deux programmes de biométhanisation ont été développés au Zimbabwe. Le premier pour le développement de la production de biogaz au niveau des ménages (4) digesteurs) et l'autre pour le développement de cette production au niveau d'utilisateurs tels que les écoles et les centres ruraux (10 digesteurs). Le financement de ces digesteurs est assuré par les utilisateurs euxmêmes tandis que le gouvernement en assure le suivi technique. Actuellement quatre nouveaux projets sont considérés: (1) l'envoi de village en village d'un promoteur du biogaz pour informer les dirigeants et former la population; (2) l'intégration de la production de biogaz dans le schéma de sédentarisation de la population rurale dans les fermes laitières; (3) la distribution d'informations aux agriculteurs commerciaux afin qu'ils construisent des installations pour leurs ouvriers; et (4) l'identification d'industries candidates pour le développement d'un projet de biométhanisation.

     

Zooplankton research in the North Sea

Summary Water types of the North Sea with different plankton are the thermally stratified northern and central regions with a relatively nutrient rich inflow of Atlantic water, a mixed region in the southern North Sea with a poor inflow of Channel water, and turbid narrow coastal zones with inflow of nutrient rich river water. Plankton studies reveal that the primary production starts early, in February, in the southern region, but is delayed in the coastal zones by turbidity. In stratified areas the algal spring bloom is delayed by mixing towards the greater depth and usually starts with the onset of thermal stratification. The spring bloom soon declines and the algae remain on a low density level in summer, presumably due to depletion of nutrients in the euphotic zone. The coastal zones and the frontal zones between mixed and stratified water have a relatively high summer primary production.The herbivores (mainly planktonic copepodes and the tunicateOikopleura dioica) grow and increase in number when the temperature rises and food is available. There is a considerable mismatch with the algal spring bloom, which comes too early and is too short in most regions. The best coincidence occurs in the coastal zones and maybe the frontal zones. Carnivores build high biomasses in late summer and fall in the coastal regions and compete with fish larvae for food and also kill many fish larvae. The large scyphomedusae are most important in this respect.The overall yearly primary production of the North Sea is estimated to be about 100 mg C.m^–2. The estimates for herbivores and fish are 20 and 1 mg C.m^–2. Considering a growth efficiency of 20%, the herbivores must consume all algae produced. The indication of a low consumption due to bad phenological coincidence in most regions leads to the assumption, that either primary production is underestimated or there is a considerable influx of organic matter from the Atlantic Ocean. During June–July 1979 the carnivore consumption was estimated in the coastal zone of the Southern Bight to be 39 mg C.m^–2.d^–1 at a copepod production of 20 mg C.m^–2.d^–1. Consumption by fish larvae and large jellyfish (Cyanea lamarckii) was 15% and 74%, respectively.It seems clear that the productivity of the North Sea depends highly on coastal and frontal zones, where herbivores find sufficient food at optimal growth conditions. Most organic matter will at the end be consumed by invertebrate carnivores, which urge fish populations to reproduce early in spring or to recruit at remote places.     

江苏常熟尚湖浮游动物种群初步研究

2003年3～5月对尚湖浮游动物种群结构特征和生物多样性进行了初步研究。观察到尚湖浮游动物93种,其中原生动物38种,轮虫27种,枝角类18种,桡足类10种。采用Shannon-Wiener多样性指数公式,对浮游动物的物种多样性指数、密度多样性指数和生物量多样性指数进行了分析。     

Zooplankton in high-mountain lakes of Altai

In July to August 1999–2001, 53 zooplankton species were recorded in high-mountain lakes of Altai (1800–2400 m above sea level). The abundance of zooplankton varies considerably, but the average values of abundance and biomass are low. According to zooplankton characteristics, the high-mountain lakes are oligotrophic and oligosaprobic. The species composition of the zooplankton community depends on the area and depth of the lakes, and the quantitative indices, particularly in the littoral zone, are determined by water temperature.     

Selective Predation in Freshwater Zooplankton Communities

The impact of selective predation in freshwater zooplankton communities is examined with special emphasis on the ecological and evolutionary consequences for the prey. The behavioral interactions between predators and prey are reviewed, and the general patterns in age- and size-selective predation are derived in a semi-quantitative model. The final section explores the life history adaptations that zooplankton have evolved in response to these different patterns of selective predation.     

Statistical Mechanics of Zooplankton

Statistical mechanics provides the link between microscopic properties of many-particle systems and macroscopic properties such as pressure and temperature. Observations of similar “microscopic” quantities exist for the motion of zooplankton, as well as many species of other social animals. Herein, we propose to take average squared velocities as the definition of the “ecological temperature” of a population under different conditions on nutrients, light, oxygen and others. We test the usefulness of this definition on observations of the crustacean zooplankton Daphnia pulicaria. In one set of experiments, D. pulicaria is infested with the pathogen Vibrio cholerae, the causative agent of cholera. We find that infested D. pulicaria under light exposure have a significantly greater ecological temperature, which puts them at a greater risk of detection by visual predators. In a second set of experiments, we observe D. pulicaria in cold and warm water, and in darkness and under light exposure. Overall, our ecological temperature is a good discriminator of the crustacean’s swimming behavior.     

Zooplankton characteristics in monitoring of Lake Ladoga

Water lettuce (Pistia stratiotes L. (Araceae)) is alien to Africa and a declared weed in South Africa. In large perennial rivers it is effectively controlled by its biological control agent, Neohydronomus affinis (Coleoptera: Curculionidae). On those shallow isolated water bodies which are regularly subjected to alternate wet and dry regimes that become infested with water lettuce, chemical control is necessary to prevent further spread of the weed and to facilitate access to water. This paper discusses the short-term chemical control and the long-term biological control of water lettuce. The need for further research is outlined.     

Zooplankton densities in a Hydrilla infested lake

The number of individuals and species of zooplankton were sampled concurrently with Hydrilla biomass and water quality for one year in a small, eutrophic central Florida lake. Throughout the study, rotifer species and individuals dominated the zooplankton. The abundance of the zooplankton tended to remain high when Hydrilla biomass was at its seasonal low during late winter and early spring. When hydrilla growth increased in the late spring and summer months causing a decrease in total alkalinity, specific conductivity, water color, turbidity, orthophosphate and chlorophyll a concentrations; the abundance of the zooplankton declined. During this time, there was a shift from limnetic to littoral species, principally rotifers. Hydrilla growth did not affect the mean number of cladoceran or copepod species, but may have led to an increase in rotifer species.     

Zooplankton biomass in tropical reservoirs in southern Brazil

In order to test the hypothesis that zooplankton biomass distribution (total and taxonomic groups) was influenced by the nutrient concentration and primary productivity distribution in three tropical reservoirs, subsurface samples were taken in the fluvial, transitional and lacustrine regions of three reservoirs (oligotrophic, mesotrophic and eutrophic) in southern Brazil (Paraná State) in March and September 2002. Zooplankton biomass ranged from 0.04 to 264.47 mg DW m⁻³. Higher biomass values were observed for cladocerans (73.60%; 0.01–259.86 mg DW m⁻³), followed by copepods (22.05%; 0.01–69.69 mg DW m⁻³) and rotifers (4.35%; 0.01–11.52 mg DW m⁻³). In general, the total zooplankton, rotifer, cladoceran and copepod biomass, and chlorophyll-a and total nutrient concentrations showed a similar longitudinal distribution within the reservoirs. Total zooplankton, rotifer and cladoceran biomass were related to the chlorophyll-a concentration, and zooplankton biomass was related to the total phosphorus distribution. This may have been due to the significant multicolinearity between the chlorophyll-a and total phosphorus concentrations. Cyanobacteria influenced the taxonomic group biomass results by interfering with the filter feeding in larger zooplankton species, which favoured the dominance of smaller species. As regards the longitudinal distribution of copepod biomass, cyanobacteria biomass determined the displacement of the microcrustaceans to the fluvial region of Iraí Reservoir. Our results supported the hypothesis formulated and the primary productivity was the major predictor of the zooplankton biomass distribution in the reservoirs. Handling editor: S. Dodson     

Food of the nightjars in Zimbabwe

Jackson, H.D. 2000. Food of the nightjars in Zimbabwe. Ostrich 71 (3&4): 404-407. Analysis of the stomach contents of 282 nightjars (Caprimulgidae) collected in Zimbabwe showed that the seven species concerned feed almost exclusively on nocturnal flying insects, predominantly on beetles (Caleoptera, 52.7%). especially lamellicom beetles (Scarabaeidae, 67.5% of all beetles), and to a lesser extent on moths (Lepidoptera, 12.7%), grasshoppers (Orthoptem, 7.2%). bugs (Hemiptera, 3.5%) and, when available, termites (Isoptera, 20.4%). There is some seasonal variation in diet, and prey selection varies between species. Deliberate ingestion of grit to aid digestion is unlikely.