Cladoceran Densities Research Articles

Fish predation on epiphytic microcrustacea in Tivoli South Bay, a Hudson River tidal freshwater wetland

The littoral microcrustacean fauna of Tivoli South Bay was studied from July to September, 1989. The effects of fish predation on microcrustacean densities were tested in a short-term predator exclusion experiment. Fish were excluded from water chestnut (Trapa natans) plots in four screened exclosures. An equal number of open cages allowed foraging. Fish predation did not have a significant effect on densities of ostracods or other microcrustaceans. Ostracod densities increased in cages throughout the experimental period, whereas cladoceran and copepod densities decreased in both treatments. Gut contents analysis of banded killifish (Fundulus diaphanus) revealed that ostracods and other microcrustaceans were commonly ingested by larval, juvenile, and adult killifish utilizing T. natans as habitat. These results suggest that ostracods and other microcrustacean epifauna associated with T. natans may represent an important trophic link in the tidal freshwater wetlands of the Hudson River Estuary.

Limnological Factors Influencing Growth of Cage-Cultured Bighead Carp ♀ x Silver Carp ♂ Hybrids

Four 2-m3 cages each stocked with 120 bighead carp ♀ X silver carp ♂ hybrids were placed in each of four ponds varying in trophic status from mesotrophic to hypereutrophic. Fish were cultured, without feeding, from 13 March to 1 October, 1987. All fish survived but lost weight (-0.37 g/fish/day) in the mesotrophic pond. Maximum fish growth rate occured in the two eutrophic ponds (6.61 and 7.04 g/fish/day). Fish growth in the hypereutrophic pond was about one-half (3.64 g/fish/day) that in the two eutrophic ponds until a sudden thermal destratification and dissolved oxygen depletion killed all the fish. Multiple linear regression analysis revealed that gross phytoplankton primary productivity accounted for 68% of the variation in fish weight gain (R2 = 0.68; P < 0.0001) in all ponds. When eliminating primary productivity data from the statistical model, number of algal taxa comprising phytoplankton communities explained 49% of the variation in fish growth (R2 = 0.49; P < 0.0001). Conditions of hypereutrophy believed to be detrimental to fish growth were: a decline in cladoceran density; a preponderance of blue-green algae, especially colonial forms with mucilaginous sheaths; a shift from numerous, relatively small plankton algal taxa to fewer but larger forms; degraded water quality.

Long‐term Annual and Seasonal Changes of Meta‐ and Protozooplankton in Lake Müggelsee (Berlin): Effects of Eutrophication, Grazing Activities, and the Impact of Predation

AbstractAnnual changes of rotifers, copepods, cladocerans, the ciliate Epistylis rotans, and larvae of Dreissena polymorpha were analysed for the period 1908–1990. Though food resources increased 6–10 fold in the course of eutrophication, only rotifers and Epistylis increased accordingly. Probably as a result of increased predation pressure crustaceans increased only twice.The seasonal pattern of metazoans and protozoans (flagellates, sarcodines, ciliates) were analysed for 12 and 3 years, resp. During winter and spring, large heterotrophic flagellates and ciliates dominated the zooplankton and were responsible for a pronounced ‐ formerly underestimated ‐ grazing pressure on phytoplankton. In early summer, metazoan filter‐feeders were often able to cause a significant reduction of phyto‐ and protozooplankton. However, during some years, phytoplankton declined in the absence of a pronounced grazing pressure. Field data and experiments revealed that predators were able to regulate the density of cladocerans in early summer (mainly cyclopoids) and summer (mainly Leptodora, smelt and fish juveniles).

Alterations in zooplankton community structure after selenium-induced replacement of a fish community: a natural whole-lake experiment

Most of the fish species in Belews Lake, a cooling reservoir in the Piedmont area of North Carolina (USA), were eliminated in 1976–77 because of selenium poisoning. Zooplankton samples collected in 1974–75, prior to the fish kill, when the lake's fauna included a regionally-typical assemblage of piscivores and planktivores at a density of 14000 ha−1, were compared to those collected in 1984–86, when the piscine community was dominated by three planktivorous fish (Notropis lutrensis, Pimephales promelas and Gambusia affinis) at a density of 28000 ha−1. Zooplankton diversity was similar in 1984–86 compared to that in 1974–75. However, densities of the predominant cladocerans (Bosmina longirostris, Pseudosida bidentata, Ceriodaphnia pulchella, Holopedium amazonicum, Daphnia parvula, D. ambigua) and copepods (Diacyclops thomasi, Mesocyclops edax, Tropocyclops prasinus, Skistodiaptomus pallidus, S. reighardi) declined, though the magnitude of the reduction was greatest for the cladocerans and S. reighardi. Densities of copepod nauplii and rotifers also decreased markedly. No colonizations or extinctions of crustacean species occurred between 1975 and 1986. Thus, while crustacean species richness (n = 18 species) remained the same, the relative proportions of individual species changed dramatically, most notably among the Cladocera. The observed changes in crustacean species densities and dominance are attributed to the replacement of the regionally-typical fish fauna by one consisting primarily of planktivores.

Limnological Changes in a Large Reservoir Following Vegetation Removal by Grass Carp

ABSTRACT Grass carp (Ctenopharygodon idella) reduced the areal coverage of submersed macrophytes from 44% to 0% in a 8,100-hectare reservoir. This resulted in increased nutrient concentrations and abundance of all major phytoplankton divisions. During this seven-year study, conducted between 1979 and 1987, average annual chlorophyll a levels increased from 12–13 mg/m3 to 19–22 mg/m3. Water clarity declined, and this was attributable to higher algal biomass and not to increases in abiotic turbidity. Summer blue-green algal density and relative abundance to the phytoplankton increased over time coincident with macrophyte elimination. Densities of rotifers, cladocerans, and total zooplankton decreased approximately 1.5 years after macrophyte removal. This decline was likely due to increased abundance of planktivorous fishes.

Interdependence of phosphorus, fish, and site effects on phytoplankton biomass and zooplankton

We conducted an outdoor tank experiment of factorial design with three levels of phosphorus addition cross‐classified with two levels of mosquitofish (Gambusia affinis) at two lake sites, allowing us to examine both main effects and interaction effects of phosphorus, fish, and site on phytoplankton biomass and zooplankton. Phosphorus addition significantly increased total phosphorus concentration and chlorophyll and decreased Secchi depth. Fish significantly decreased cladoceran densities and Secchi depth and increased chlorophyll and turbidity. Most phosphorus and fish effects were independent of each other except for a significant phosphorus × fish interaction on rotifers. The two sites had significant differences in total phosphorus concentration, turbidity, Secchi depth, chlorophyll, and densities of cladocerans, copepods, and rotifers. The only significant site ×phosphorus interaction was for total phosphorus. Significant site x fish interactions were detected for turbidity, Secchi depth, chlorophyll, and densities of cladocerans and rotifers. Fish effects were independent of phosphorus addition but dependent on site‐specific plankton community composition.

Correlations between Physico ‐ chemical factors and population density of cladocerans in the Tigris and Diyala rivers at Baghdad ‐ Iraq

Abstract Seasonal variation of some environmental factors such as water temperature, dissolved oxygen, hydrogen ion concentration, transparency, electrical conductivity, velocity of water flow and chlorophyll a were studied for one year in two rivers, Tigris and Diyala at Baghdad. Seasonal qualitative and quantitative studies of the cladocerans of the two rivers are reported. Eight species comprise the cladoceran fauna of Diyala River, Bosnina longirostris, Moina affinis, Ceriodarhnia cornuta, Simocephalus vetulus. Daphnia lumholtzi, Chydorus sphaericus, Macrothrix laticomis, Diaphanosoma brachyurum, whereas at Tigris River five species comprise the cladocerans fauna B. longirostris, M. affinis, C. cornuta, S. vetulus, S.vetulus and D. brachyurum. Population density of these cladocerans was studied in relation to some physico‐chemical factors as mentioned previously and found there is a positive relationship between population density and dissolved oxygen concentration, velocity of water current, and transparency for both rivers and negative relationship with surface water temperature and chlorophyll a.

Atlantic salmon start-feeding with live zooplankton: Pressure shock treatment to increase prey availability

The experiment was carried out in 1984 in a coastal lake near Bergen, Norway. A total of four (later eight) groups of Atlantic salmon ( Salmo salar) fry were start-fed with live zooplankton delivered by a pump. Small fine-meshed net pens were used. Supplemental feed promoted additional growth after the start-feeding phase. The fish in zooplankton-fed groups increased their average length by 0·15 mm/day during the first 30 days compared with 0·08 mm/day in fish given both zooplankton and dry feed. Initial food lack (low density of cladocerans) is the main explanation for the low growth rates. Food selection and pump-increased zooplankton capture probabilities are also discussed. An unexpected avoidance of calanoid copepods, even when debilitated, was observed at the end of the experiment when other potential prey species were scarce. Even Daphnia were not preferred as expected. Live zooplankton is recommended for initial start-feeding, but dry food should be available to salmon when the yolksac has been absorbed.

Importance of Food Supply to Nutritional State of Larval Striped Bass in the Potomac River Estuary

Abstract Surveys of larval striped bass Morone saxatilis and zooplankton in the Potomac River upper estuary were made in 1981. In addition to distribution and abundance, nutritional state of larvae was assessed by morphometric, histologic, and two biochemical techniques: RNA:DNA ratio and fatty acid composition and concentration. All four techniques gave evidence of poor nutritional state early in the season but not later. Analyses of distribution indicated a significant correlation among nutritional indices and copepod and cladoceran densities.

Competition among Cladocera

In situ enclosure experiments were used to assess the importance of competition to the population dynamics of three cladocerans (Daphnia pulex, Moina affinis, and Ceriodaphnia sp.) in a small pond. Competitive effects were nonlinear functions of cladoceran density, and both intra- and interspecific competition were important determinants of the dynamics of the pond populations. The data suggested that the degree of competition was dependent on resource levels and the age of competitors. The major pond predator, Chaoborus, was able to control prey populations only when the densities of prey and phytoplankton were low.

Competition Among Cladocera

In situ enclosure experiments were used to asses the importance of competition to the population dynamics of three cladocerans (Daphnia pulex, Moina affinis, and Ceriodaphnia sp.) in a small pond. Competitive effects were nonlinear functions of cladoceran density, and both intra and interspecific competition were important determinants of the dynamics of the pond populations. The data suggested that the degree of competition was dependent on resource levels and the age of competitors. The major pond predator, Chaoborus, was able to control prey populations only when the densities of prey and phytoplankton were low.

ZOOPLANKTON COMMUNITIES OF A NEW PUMPED STORAGE RESERVOIR1

ABSTRACT: Zooplankton colonization was followed for 16 months in Lake Oconee, Georgia, a new pumped storage reservoir. Data were interpreted to identify differences among stations and seasons, as a function of the reservoir's early stage of development and of pumped storage operations. Colonization was rapid, and the zooplankton community was characterized by a high species diversity; approximately 40 rotifer species and 14 cladoceran genera were recorded. Zooplankton density varied along an environmental gradient from riverine to lentic conditions. Rotifer abundance varied from 104‐106 individuals/m3, with maxima in the summers Copepod and cladoceran densities ranged from 103 to nearly 105 individuals/m3; maxima for stations other than the dam were observed in the summer and early fall, but high values at the dam station occurred throughout winter 1980. When pumped storage operations began in December 1979, zooplankton densities increased at the dam station. Pumpback decreased the intensity of the environmental gradient from riverine to lentic conditions, and led to a more similar zooplankton community structure throughout the reservoir.

SPATIAL VARIATIONS IN ABUNDANCE OF PHYTOPLANKTON, ZOOPLANKTON, AND LARVAL FISHES IN CENTER HILL RESERVOIR

Densities of phytoplankton, zooplankton, and larval fishes in Center Hill Reservoir, Tennessee, USA, were determined to evaluate differences in abundance between embayments and mainstream areas and to assess longitudinal gradients in the reservoir. Plankton were collected monthly from May 1978 through June 1979 and larval fishes were collected biweekly from May through August 1978 at five mainstream and five embayment sites established along the reservoir.Statistical analyses for the majority of plankton and larval fishes indicated that spatial variations in abundance were primarily related to localized environmental conditions rather than the hydraulic gradient of the reservoir. Most taxa were more abundant in embayments than in nearby mainstream sites, and although abundance usually varied significantly among the five mainstream stations, densities showed no consistent gradient in the up stream-downstream dimension of the reservoir. Abundance of phytoplankton and rotifers was more uniform at the mainstream stations during periods of low inflow and high water temperature. Copepod and cladoceran densities, however, were more uniform during periods of high inflow. The existence of spatial variations in biological communities should be recognized when assessing trophic status or developing predictive models of reservoir systems.

THE EFFECTS OF DIPOTASSIUM ENDOTHALL ON THE ZOOPLANKTON AND WATER QUALITY OF A SMALL POND1

ABSTRACT: Zooplankton samples and dissolved oxygen‐temperature readings and water samples were taken from a treatment and control pond on 41 and 42 separate occasions, respectively, both before and after the application of 5.0 mg/l (a.i.) dipotassium endothall to the 0.31 ha treatment pond on May 31, 1973. Seasonal fluctuations in the density of Cladocera and Copepoda coincided quite closely in both ponds and were similar to the fluctuations reported in the literature to be typical of temperate region ponds and lakes. An apparent seasonal shift in generic composition from .Daphnia spp. in May to Ceriodaphnia spp. in June to Chydorus spp. from July/early September occurred in both ponds and is thought to be at least partially due to fish predation. No apparent changes in species composition or generic densities of Cladocerans was noted in the treatment pond that did not also occur in the control pond. There were no noticeable effects of the dipotassium endothall on either the Calanoida or Cyclopoida suborders of Copepoda. A later pulse of Ostracoda in the treatment pond, when compared to the control, may have been due to the dipotassium endothall or to a combination of the effects of the herbicide on the macrophytes and the method of sampling. A decrease in dissolved oxygen below saturation, occurring in the treated pond from 3–21 days after treatment, was attributed to an increase in biological oxygen demand associated with weed‐kill. There was no noticeable increase in plant nutrients (N and P) in the treated pond following herbicide application, nor were there any apparent changes in the other chemical parameters studied.