Composition and abundance of zooplankton in the limnetic zone of seven reservoirs of the Paranapanema River, Brazil.
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The species composition and abundance of the zooplankton community of seven reservoirs of the Paranapanema River, located between 22 degrees 37'-23 degrees 11'S and 48 degrees 55'-50 degrees 32'W, were analysed over four periods, in the year of 1979. The zooplankton community was composed of 76 species of Rotifera, 26 species of Cladocera and 7 species of Copepoda. For a large part of the period under study the Rotifera were dominant, followed by Copepoda. The Piraju and Salto Grande reservoirs, which occupy intermediate positions in the cascade of reservoirs, were richest in species, most of them belonging to Rotifera and Cladocera. In the reservoirs Rio Pari and Rio Novo, lateral to the cascade of reservoirs, a lower species richness was observed, although higher densities of organisms were found than in the other reservoirs located in the main river body. Different rotifer species occurred in succession, being abundant in different periods, with no defined pattern. Among the copepods, Thermocyclops decipiens predominated in the majority of the reservoirs. Ceriodaphnia cornuta was the most abundant cladoceran in the intermediate reservoirs of the cascade, and Daphnia gessneri, Bosminopsis deitersi and Moina minuta, in the reservoirs lateral to the cascade. The most frequent zooplankton species were Notodiaptomus conifer, Thermocyclops decipiens, Ceriodaphnia cornuta cornuta and C. cornuta rigaudi, Daphnia gessneri, Bosmina hagmanni, Keratella cochlearis and Polyarthra vulgaris. Some relationships were found between the trophic state of the reservoirs and the zooplankton community. (+info)
High-speed video analysis of the escape responses of the copepod Acartia tonsa to shadows.
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The copepod Acartia tonsa exhibits a vigorous escape jump in response to rapid decreases in light intensity, such as those produced by the shadow of an object passing above it. In the laboratory, decreases in light intensity were produced using a fiber optic lamp and an electronic shutter to abruptly either nearly eliminate visible light or reduce light intensity to a constant proportion of its original intensity. The escape responses of A. tonsa to these rapid decreases in visible light were recorded on high-speed video using infrared illumination. The speed, acceleration, and direction of movement of the escape response were quantified from videotape by using automated motion analysis techniques. A. tonsa typically responds to decreases in light intensity with an escape jump comprising an initial reorientation followed by multiple power strokes of the swimming legs. These escape jumps can result in maximum speeds of over 800 mm s(-1) and maximum accelerations of over 200 m s(-2). In A. tonsa, photically stimulated escape responses differ from hydrodynamically stimulated responses mainly in the longer latencies of photically stimulated responses and in the increased number of power strokes, even when the stimulus is near threshold; these factors result in longer escape jumps covering greater distances. The latency of responses of A. tonsa to this photic stimulus ranged from a minimum of about 30 ms to a maximum of more than 150 ms, compared to about 4 ms for hydrodynamically stimulated escape jumps. Average response latency decreased with increasing light intensity or increasing proportion of light eliminated. Little change was observed in the vigor of the escape response to rapid decreases in visible light over a wide range of adaptation intensities. (+info)
Occurrence of Mesocyclops ogunnus Onabamiro, 1957 (Copepoda Cyclopoida) in water bodies of Sao Paulo State, identified as Mesocyclops kieferi Van de Velde, 1984.
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The aim of this work is clarify the identification of Mesocyclops ogunnus that occur in several reservoirs in the State of Sao Paulo and that was previously identified as Mesocyclops kieferi. These two species are closely related species with very similar characteristics. The differential characteristics are presented and the distribution of both species in the world is discussed. (+info)
Immunohistochemistry, ultrastructure and pathology of gills of Abramis brama from Lake Mondsee, Austria, infected with Ergasilus sieboldi (Copepoda).
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Immunohistochemical, ultrastructural and pathological studies were carried out on the gills of bream Abramis brama (L.) from Lake Mondsee, Austria, that were naturally infected with Ergasilus sieboldi Nordmann, 1832. Of a total of 14 specimens of bream examined, the gills of 7 (50%) were parasitized with this copepod and the intensity of infection ranged from 1 to 23 crustaceans per host. Histopathological investigations of infected gill showed extensive tissue damage due to attachment and feeding of the crustacean. Parasites attached close to the base of filaments near the gill arch. Pressure exerted by the ectoparasite attached to the lateral margin of the gill filaments induced atrophy of the secondary lamellae. Tissue reactions included hyperplasia and mucous cell proliferation of the respiratory epithelium. Mucous cells displayed an intense immunohistochemical reactivity with the anti-nitric oxide synthase antibody. In parasitized primary and secondary lamellae, a high number of eosinophilic granular cells and rodlet cells were noticed. Rodlet cells represent an inflammatory cell type closely linked to other piscine inflammatory cells. Presence of a high number of inflammatory cells at the site of E. sieboldi attachment is related to intense host cellular reaction. (+info)
A new species of Acantholochus (Copepoda: Bomolochidae) parasitic on Centropomus undecimalis (Osteichthyes: Centropomidae) from the coastal zone of the State of Rio de Janeiro, Brazil.
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A new species of Acantholochus Cressey, 1984 (Copepoda: Bomolochidae) parasitic on the gills of common snook, Centropomus undecimalis, from the coastal zone of the State of Rio de Janeiro, Brazil, is described and illustrated. The new species differs from all other species of Acantholochus by the presence of only one inner seta on middle segment of the second and third endopods. (+info)
Zooplankton structure and potential food web interactions in the plankton of a subtropical chain-of-lakes.
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This study evaluates the taxonomic and size structure of macro-zooplankton and its potential role in controlling phytoplankton in the Kissimmee Chain-of-Lakes, six shallow interconnected lakes in Florida, U.S. Macro-zooplankton species biomass and standard limnological attributes (temperature, pH, total phosphorus [TP], chlorophyll a [Chl a], and Secchi transparency) were quantified on a bimonthly basis from April 1997 to February 1999. Concentrations of TP ranged from below 50 to over 150 microg l(-1). Peak concentrations of particulate P coincided with maximal Chl a, and in one instance a high concentration of soluble reactive P followed. The cladoceran zooplankton was dominated by small species, including Eubosmina tubicen, Ceriodaphnia rigaudi, and Daphnia ambigua. The exotic daphnid, D. lumholtzii, periodically was abundant. The copepods were strongly dominated by Diaptomus dorsalis, a species previously shown to be highly resistant to fish predation. These results, and findings of controlled experiments on a nearby lake with a nearly identical zooplankton species complement, suggest that fish predation may be a major factor structuring the macro-zooplankton assemblage. Zooplankton biomass, on the other hand, may be affected by resource availability. There was a significant positive relationship between average biomass of macro-zooplankton and the average concentration of TP among the six lakes. No such relationship existed between zooplankton biomass and Chl a, suggesting that the predominant food web in these systems may be based on bacteria-plankton, as has been documented in nearby Lake Okeechobee. All of the zooplankton taxa encountered in the Kissimmee Chain-of-Lakes (except Mesocyclops edax) are known bacteria grazers in Florida lakes. Phytoplankton biomass, measured as Chl a, was strongly associated with TP, both within and across lakes. Phytoplankton biomass was not associated with the biomass of zooplankton. These results, when considered in the context of nutrient-addition, zooplankton-exclosure studies on Lake Okeechobee, support the hypothesis that phytoplankton biomass in subtropical lakes is regulated by "bottom-up," rather than "top-down" forces. (+info)
A marine diatom-derived aldehyde induces apoptosis in copepod and sea urchin embryos.
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The diatom-derived aldehyde 2-trans-4-trans-decadienal (DD) was tested as an apoptogenic inducer in both copepod and sea urchin embryos, using terminal-deoxynucleotidyl-transferase-mediated dUTP nick-end labelling (TUNEL), DNA fragmentation profiling (laddering) and an assay for caspase-3 activity. DD induced TUNEL positivity and DNA laddering, but not caspase-like activation, in copepod embryos spawned by females fed for 10-15 days the diatom diet Thalassiosira rotula Meunier (in vivo), or when newly spawned eggs were exposed for 1 h to 5 micro g ml(-1) DD (in vitro). To our knowledge, this is the first time that evidence for an apoptotic process in copepods has been obtained by cytochemical (TUNEL) and biochemical (DNA fragmentation) approaches. The absence of caspase-like activity in copepod embryos suggests that caspase-independent programmed cell death occurs in these organisms. In sea urchin embryos, DD induced apoptosis and also activated a caspase-3-like protease. The saturated aldehyde decanal induced apoptosis at higher concentrations and after a longer incubation period than DD, indicating that alpha,beta-unsaturation of the molecule, coupled with the aldehyde group, is responsible for the greater biological activity of DD. Since diatoms are an important food source for marine herbivores such as copepods and sea urchins, these findings may help explain why unsaturated aldehydes often induce reproductive failure, with important ecological consequences at the population level. (+info)
The three-dimensional flow field generated by a feeding calanoid copepod measured using digital holography.
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Digital in-line holography is used for measuring the three-dimensional (3-D) trajectory of a free-swimming freshwater copepod Diaptomus minutus, and simultaneously the instantaneous 3-D velocity field around this copepod. The optical setup consists of a collimated He-Ne laser illuminating a sample volume seeded with particles and containing several feeding copepods. A time series of holograms is recorded at 15 Hz using a lensless 2Kx2K digital camera. Inclined mirrors on the walls of the sample volume enable simultaneous recording of two perpendicular views on the same frame. Numerical reconstruction and matching of views determine the 3-D trajectories of a copepod and the tracer particles to within pixel accuracy (7.4 microm). The velocity field and trajectories of particles entrained by the copepod have a recirculating pattern in the copepod's frame of reference. This pattern is caused by the copepod sinking at a rate that is lower than its terminal sinking speed, due to the propulsive force generated by its feeding current. Consequently, the copepod sees the same fluid, requiring it to hop periodically to scan different fluid for food. Using Stokeslets to model the velocity field induced by a point force, the measured velocity distributions enable us to estimate the excess weight of the copepod (7.2x10(-9) N), its excess density (6.7 kg m(-3)) and the propulsive force generated by its feeding appendages (1.8x10(-8) N). (+info)