On nine Tropodiaptomus-species (Copepoda,Calanoida) from equatorial East Africa

Of the nine species of Tropodiaptomus occurring in Equatorial East Africa, seven are redescribed and figured in great detail. Their relationships are discussed. A primary homonym is eliminated, and types are indicated wherever possible.     

Morphology,physics, chemistry and biology of Lake Rara in West Nepal

A survey of oligotrophic Lake Rara, the biggest lake in Nepal, was carried out from 1982 till 1984. Mean depth is 100 m, and maximum depth is 167 m. The surface area covers 9.8 km², and the lake contains 0.98 km³ volume of water. Transparency was about 16 m, photoquantum yield decreased exponentially with depth below 5 m, and the extinction coefficient was 8.3 × 10⁻². The concentration of Chl.-a was in the range of 0.06–0.46 mg m⁻³, and total nitrogen was 18–30 μg 1⁻¹. The whole water column was well oxygenated. Primary productivity was extremely low. It has more than 30 inflowing brooks and one outlet. The water quality of the brooks changes drastically with their location. The pH, electrical conductivity, and EDTA hardness in the waters from a landslide area were high. In the waters from a rich pine forest they were extremely low. The zooplankton consisted of two species of protozoa, five species of rotifers, two species of Cladocera, and two species of Copepoda. The zooplankton density range was 6200–16200 individuals m⁻³. The minimum was on November 11th, 1983 and the maximum on August 19th, 1983.     

Vertical distributions of zooplankton and population dynamics of Daphnia in a meromictic lake

Vertical distributions of zooplankton were studied in relation to profiles of temperature, oxygen and chlorophyll a in Roi Lake, a small meromictic lake in central Alberta. Zooplankton were distributed fairly evenly through the oxygenated part of the water column in early summer, but a gradual descent of several species became evident in June. The vertical distribution of chlorophyll was dominated by a huge peak at the 8- to 9-m-deep chemocline. the location of a plate of photosynthetic sulfur bacteria. Ambient concentration of chlorophyll was a poor predictor of the numbers of zooplankton and the fecundity of Daphnia pulicaria at different depths, and per capita birth rates of Daphnia were usually highest in the surface waters. The reproductively disadvantageous restriction of daphnids to deep water by late summer and their catastrophic decline in the face of high ambient concentrations of chlorophyll suggest that factors other than temperature and food supply are important in influencing the dynamics and distribution of zooplankton in this lake.     

The impact of zooplankton size structure on phosphorus cycling in field enclosures

Plastic bag field enclosures (1570 1) were used to investigate the relationship between zooplankton size distributions and the turnover rate of pelagic phosphorus. Water within the enclosures was filtered to simulate either low (200 µm mesh net) or high (80 µm) planktivory. The bags were then spiked with radiolabelled phosphorus and sampled 7 times during the following 24 h period. Zooplankton communities dominated by smaller size classes cycled more phosphorus than those composed of larger species. These experiments reveal that higher trophic level interactions, such as size selective predation, may have a significant impact upon nutrient regeneration rates and, hence, primary production.     

Embryonic development times of entomostracan zooplankton from Lake le Roux (Orange River,South Africa), and their possible relationships to seasonal succession

Embryonic development times of the principal entomostracan zooplankton of Lake le Roux, Orange River, South Africa, are described. Durations decreased monotonically with temperature over the thermal tolerance range and are described using Blehrádek's equation. The present data are compared with other observations on rate-temperature responses of warm-water and temperate zooplankton. Small, but ecologically significant, differences are discerned. The possible significance of species-specific rate-temperature responses to the phenomenon of seasonal succession is explored.     

Some Crustacea Copepoda from Venezuela

The study of 38 samples of aquatic fauna from Venezuela increased the number of known species here from 28 to 66. Fifteen new species for science are described. A list of Copepoda known from the other regions of South America is presented. From this list, it can be said that only 50% of the inland water Copepoda living actually in Venezuela are known.     

The effect of Cyanophyta upon zooplankton in a eutrophic tropical lake (Lake Valencia,Venezuela)

The effect which Cyanophyta have upon the zooplankton varies according to the form of the alga (mucilaginous colonies or filaments) and its abundance. Periodical blooms of Microcystis aeruginosa were not detrimental for the zooplankton, in spite of the fact that copepods, cladocerans and rotifers consume small colonies. High concentrations of Lyngbya limnetica and Oscillatoria limnetica in Lake Valencia, Venezuela, proved to be inhibitory for cladocerans. A total absence of cladocerans was detected when filaments increased.     

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.     

Biomass and production of Argyrodiaptomus furcatus,a tropical calanoid copepod in Broa Reservoir,southern Brazil

The biomass and the production of Argyrodiaptomus furcatus (Sars), the most abundant copepod in Broa Reservoir (São Carlos, São Paulo State), were estimated, determining in the laboratory the development time and the quantity of organic carbon and establishing the relationship between these two parameters. The daily production was calculated from P = B(1- e^gt) and the annual production was obtained by integrating daily production against time. The maximum production of Argyrodiaptomus furcatus in the reservoir depends on the region considered and on the period of the year. The maximum production was 45.15 mg C m^–3d^–1 in March, 1976 at station II, region of macrophytes and 6.74 mg C m^–3d^–1 at station IV, near the dam. The mean production for the year is 6.26 mg C m^–3d^–1 at station II and 1.43 mg C m^–3d^–1 at station IV.     

Zooplankton-trophic state relationships in some north and central Florida lakes

In a survey of eight lake systems located in north-central Florida, total zooplankton abundance showed a strong positive correlation (r²=0.87, a=0.01) with trophic state. Zooplankton abundance averaged 1.0 × 10⁵ organisms · m^–2 in oligotrophic systems and up to 8.2 × 10⁵ organisms · m^–2 in the eutrophic systems. Seasonal variations in total abundance were greatest in the eutrophic lakes where rotifers dominated and periodically produced sharp population peaks (approaching 2.0 × 10⁶· m^–2). In contrast, the more oligotrophic systems had relatively stable levels of total abundance and were dominated by copepods. Diversities of the major taxa in the lakes were variable with one to three species of copepods, zero to four species of cladocera, and two to seven species of rotifers dominant at any one time. Planktonic cladoceran communities were often composed of only one or two species. Low cladocera diversity in these subtropical systems was suggestive of increased predation pressure on this group of crustaceans. A comparison of the total crustacean abundance in the Florida systems to those of some of the Great Lakes indicated that lower standing crops of crustacean zooplankton in the Florida lakes may be a response to both predation and temperature.Contribution Number 043, Marine Science Programs Laboratory, Dauphin Island, Alabama, U.S.A.Contribution Number 043, Marine Science Programs Laboratory, Dauphin Island, Alabama, U.S.A.