Zooplankton abundance, hydrilla biomass, and physicochemical parameters were sampled for one year in a small central Florida lake. Annually, rotifers comprised most of the species collected and were the most abundant zooplankton group. Hydrilla biomass was lowest during winter and spring while orthophosphate and phtoplankton concentrations were highest. Zooplankton densities were highest when hydrilla biomass was low. Small-bodied limnetic herbivores comprised most of the zooplankton during the spring. Zooplanton abundances were lowest during summer and fall and may have been either directly or indirectly related to the hydrilla growth. Factors, such as lower phytoplankton and dissolved oxygen concentrations, possible increased predation by fish, and substances that may have been secreted by the hydrilla may have had a negative effect on the lake's zooplankton density. Littoral zooplankton species were frequently collected from the lake when hydrilla biomass was high. Species diversity (─æ) was lowest during winter and spring and ranged from 1.69 to 2.11; species diversity peaked during the summer reaching 3.04.

No description available.

No description available.

Anglers unlawfully introduced gizzard shad Dorosoma cepedianum into Claytor Lake, Virginia in the late 1980s, apparently with the intention of improving the sportfishery by adding an additional clupeid prey resource. This study examined the trophic interactions between larval shad and resident zooplanktivorous fishes, in an attempt to discover the potential for trophic competition and negative impacts to these fish species. Ichthyoplankton sampling in 1997 and 1998 showed that peak abundances of larval shad overlapped temporally and spatially with both larval Lepomis spp. and larval alewife Alosa pseudoharengus. Peak larval shad density (0.04-0.06 fish/m3) was two to three orders of magnitude less than that reported from other reservoir systems, slightly less than that of larval alewife in Claytor Lake (0.05-0.07 fish/m3), and significantly less than that of larval Lepomis spp. in Claytor Lake (0.28-0.51 fish/m3). Diet overlap values indicated potential resource overlap among all three larval taxa. Diet of larval shad did not overlap with that of either age-0 Micropterus spp. or adult alewife. All species of limnetic larvae examined showed feeding preferences for Diaphanosoma and copepod nauplii. Crustacean zooplankton densities did not respond negatively to peak larval fish abundances, and never dropped below 250-400 organisms/L. In Claytor Lake, the impact of trophic competition with larval gizzard shad on other zooplanktivores currently appears to be minimized by low densities of larval shad and abundant crustacean zooplankton. / Master of Science

Twenty-eight species of zooplankton were identified from Lake Texoma. Seasonal density of the overall microcrustacean community and seasonal cycles of individual species were compared with northern populations and any available literature from the Southwest. Cycles of occurrence and abundance were similar to those observed in northern populations but tended to occur earlier in the year due to higher temperatures. Spatial distributions within the reservoir were heavily influenced by nutrient and salt input from the Red River, which resulted in dense populations in the Red River Arm. In addition, during the summer, the microcrustacean community was restricted to the epilimnion due to anoxic conditions in the hypolimnion of the reservoir.

Seventy-one aquatic species including the copepodids and nauplii were identified from Lake Texoma from August 1996 to September 1997. Zooplankton community structure, abundance and spatial and temporal distributions were compared among five lake zones delineated a priori based on chloride concentration. The zones, in order of decreasing chloride concentration, are the Red River zone (RRZ), Red river Transition zone (RRTZ), Main Lake zone (MLZ), Washita River Transition zone (WRTZ) and Washita River zone (WRZ). Bray Curtis Similarity Index showed community structure was most similar in the two Red River arm zones, the two Washita River arm zones and the MLZ. Zooplankton abundance was greatest in the Red River arm (312 org/L), intermediate in the Washita River arm (217 org/L) and least in the Main Lake body (103 org/L). A significant increase in the abundance of a deformed rotifer, Keratella cochlearis, was observed mainly in the Red River arm during a second study from March 1999 to June 1999. Seasonal dynamics, rather than spatial dynamics, were more important in structuring the zooplankton community, especially in the two river arms. Spatial variance was solely attributed to station and zone effects independent of time for a few crustacean species and many of the water quality parameters supporting the presence of longitudinal gradients of differing water quality. Three independent models (Red River arm, Washita River arm, Main Lake body) rather than a single model for the entire reservoir, best describe patterns in the zooplankton community and its relationship to seasonal, physical and chemical factors. Statistical power, sample size and taxonomic resolution were examined. When monitoring seasonal and annuals trends in abundance, the greatest statistical power was achieved by analyzing count data at taxonomic levels above genus. Taxonomic sufficiency was assessed to determine if costs could be reduced for zooplankton identifications. For water quality monitoring purposes only, it is recommended that genus identifications are sufficient if supplemented with quarterly species identifications.

Regions containing gradients of vertical flow are often associated with sharp changes in hydrographic and biochemical water properties in coastal marine ecosystems. Often these are sites of dense plankton aggregations of critical ecological importance. In this study, a recirculating flume apparatus with a laminar, planar free jet (the Bickley jet) was used to create finescale gradients of fluid velocity (shear) in both upwelling and downwelling configurations for zooplankton behavioral assays. Particle image velocimetry (PIV) was used to fully resolve the velocity fields allowing us to fine-tune experimental parameters to match fluid mechanical conditions commonly measured in the field. Zooplankton behavioral assays with two tropical calanoid copepods, Acartia negligens and Clausocalanus furcatus, an estuarine mysid, Neomysis americana, and the larvae of an estuarine mud crab, Panopeus herbstii, were conducted in control (stagnant), upwelling, and downwelling flow configurations. Statistical analyses (ANOVA) of individual zooplankton trajectories revealed the potential for individual behavioral responses to persistent finescale vertical shear layers to produce population scale aggregations, which is proposed here as a mechanism of patchiness in coastal marine ecosystems. Results from behavioral analyses reveal species-specific threshold shear strain rates that trigger individual behavioral responses. Furthermore, results show statistically significant changes in behavior (relative swimming speed, turn frequency, heading) for all species tested in response to a coherent shear structure in the form of finescale upwelling and downwelling jets. The results show that changes in individual behavior can increase Proportional Residence Time (PRT = percent time spent in the jet structure). On a population scale, the increase in PRT can lead to dense aggregations around persistent flow features, which is consistent with numerous field studies. These dense, patchy aggregations of zooplankton have profound trickle-up ecological consequences in coastal marine ecosystems.

Made available in DSpace on 2016-06-02T19:32:05Z (GMT). No. of bitstreams: 1 4768.pdf: 6398545 bytes, checksum: da59eeea98c77e3bb13845ab8f838873 (MD5) Previous issue date: 2012-09-06 / Financiadora de Estudos e Projetos / The planet Earth is facing a serious crisis of the biodiversity loss. Often, human activities are responsible for biological invasions that alter significantly the various ecosystems and could lead to the extinction of native species. Dendrocephalus brasiliensis ( branconeta ) is a native freshwater Anostraca species, which has been studied and used in aquaculture to replace the brine shrimp originating from saline environments. Its occurrence in natural environments was recorded in Brazilian southeast and northeast regions, from the city of Urucuia-MG to Piauí State. However, there are records of its accidental introduction into fish ponds in São Paulo state, cities of Tabatinga and Arealva. The goal of this work is the study of the interactions of competition and predation / herbivory between D. brasiliensis and other planktonic species native of São Paulo in order to assess the possible impacts of a possible introduction of this species in natural environments where it does not occur originally. This study was conducted in an experimental system (10.000L tank) in Aquaculture Station of Department of Hydrobiology (EA-DHb), Federal University of São Carlos (UFSCar), São Carlos, SP, Brazil. Initially, the experimental tank was inoculated with the green algae Pseudokirchneriella subcapitata grown in laboratory. After the establishment of phytoplankton, zooplankton species were collected in limnic ecosystems of São Paulo state, in particular near São Carlos (June and July/2011), for the establishment of a zooplankton community in the experimental tank. Zooplankton succession in the tank was monitored for 133days before the introduction of branconeta. To evaluate the interaction of D. brasiliensis with other zooplankton species, the experimental tank was divided in two equal compartments that do not communicate to each other: one of them was kept with the original composition of the zooplankton, while in the other, cysts of the anostracean were introduced. In both experimental compartments samples were collected daily during 39 days, for quantitative and qualitative analyzes of zooplankton community, besides chlorophyll a, physical and chemical variables. The environmental variables were correlated to zooplankton groups using the statistical method of Canonical Correspondence Analysis (CCA). Numerical densities of Cladocera and Copepoda groups decreased in the presence of D. brasiliensis. We can conclude that the presence of D. brasiliensis does not exclude but significantly alters the composition and density of the plankton community. / O planeta Terra vem enfrentando a grave crise da perda da biodiversidade. Muitas vezes, as atividades humanas são responsáveis pelas invasões biológicas que alteram significativamente os vários ecossistemas, podendo levar à extinção espécies nativas. Dendrocephalus brasiliensis (branconeta) é uma espécie nativa de anostráceo dulcícola, que vem sendo estudada e utilizada na aquicultura, em substituição às artêmias originárias de ambientes salinos. Sua ocorrência em ambientes naturais foi registrada nas regiões sudeste e nordeste brasileira, a partir do município de Urucuia-MG até o Piauí. Entretanto, há registros de sua introdução acidental em pisciculturas localizadas no estado de São Paulo, municípios de Tabatinga e Arealva. O objetivo do presente trabalho é o estudo das interações de competição e de predação/herbivoria entre D. brasiliensis e outras espécies planctônicas nativas do estado de São Paulo, a fim de avaliar os possíveis impactos de uma eventual introdução dessa espécie em ambientes naturais onde a mesma não ocorra originalmente. Este estudo foi realizado em um sistema experimental (tanque de 10.000L) na Estação de Aquicultura do Departamento de Hidrobiologia (EA-DHb) da Universidade Federal de São Carlos (UFSCar), São Carlos, SP, Brasil. Inicialmente, o tanque experimental foi inoculado com a clorofícea Pseudokirchneriella subcapitata cultivada em laboratório. Logo após o estabelecimento do fitoplâncton, foram coletadas espécies de zooplâncton em ecossistemas límnicos do estado de São Paulo, em especial na região de São Carlos (junho e julho/2011) para o estabelecimento de uma comunidade zooplanctônica no tanque experimental. A sucessão zooplanctônica no tanque foi acompanhada por 133 dias antes da introdução da branconeta. Para a avaliação da interação de D. brasiliensis com outras espécies zooplanctônicas, o tanque experimental foi dividido em dois compartimentos iguais sem comunicação entre eles: em um deles foi mantida a composição zooplanctônica original, enquanto no outro foram introduzidos cistos do anostráceo. Em ambos os compartimentos experimentais foram recolhidas amostras diárias durante 39 dias, para análises quantitativas e qualitativas da comunidade zooplanctônica, além de variáveis físicas, químicas e clorofila a. As variáveis ambientais foram correlacionadas aos grupos zooplanctônicos através do método estatístico da Análise de Correspondência Canônica (CCA). As densidades numéricas dos grupos Cladocera e Copepoda diminuíram na presença de D. brasiliensis. Podemos concluir que a presença de D. brasiliensis não exclui, mas altera significativamente a composição e densidade da comunidade planctônica.

In der Studie wurde die Ernährung und die Verteilung von larvalen und juvenilen Stadien von Plötze (Rutilus rutilus (L.)) und Barsch (Perca fluviatilis L.) untersucht. Untersuchungsgewässer war der Feldberger Haussee, ein geschichteter eutropher Hardwassersee, der seit über 15 Jahren biomanipuliert wurde. Der Bestand an Barschen war in diesem Gewässer im gesamten Biomanipulationszeitraum sehr gering (< 1% der Gesamtfischbiomasse). Längerfristig stabilisiert, aus wissenschafticher Sicht, eine hoher Bestand an piscivoren Barschen die Effekte der Biomanipulation. Ziel der Untersuchung war daher die Überprüfung der Hypothese, dass das Vorhandensein von Konkurrenz um die Ressource Zooplankton zwischen den juvenilen Barsch und Plötzen für den geringen Barschbestand verantwortlich ist (PERSSON & GREENBERG 1990, PERSSON et al. 1991). Die Ergebnisse der Untersuchungen ließen sich in folgenden Punkten zusammenfassen: i) Der juvenile Barsch segregierte in der Hochsommer- bis Herbstperiode in eine spezielle Nahrungsnische. Die beiden Fischarten unterschieden sich deutlich bezogen auf die Art der bevorzugten Zooplankter (0+-Barsch vorwiegend Eudiaptomus, Diaphanosoma, Leptodora; 1+/2+-Plötzen fraßen Cladocerennahrung Bosmina und in hohen Anteilen auch Daphnia). Separation und Aufteilung der Zooplanktonresourcen konnte auch für die bevorzugte Größe der Zooplankter beobachtet werden. Die hohen Wachstumsraten und der gute Konditionszustand des juvenilen Barsches sowie das Fehlen von Wintermortalität ließen konkurrenzinduzierte Mortalität als Begründung für den geringen Bestand nicht glaubhaft erscheinen. ii) Die räuberbedingte saisonale Mortalität der juvenilen Barsche in der Hochsommer- bis Herbstperiode ließ sich bei den 0+-Barschen und 1+-Barschen jeweils auf bis zu 90% einschätzen. Dadurch wurde auch ein starker Jahrgang (wie 1997) innerhalb der ersten zwei Lebensjahre auf bis zu 99% reduziert. iii) Als Alternativhypothese wurde aus den Ergebnissen der Studie und den Bedingungen am Feldberger Haussee gefolgert, dass eine Kombination von langer zooplanktivorer Phase und einem hohen Bestand an effektiven pelagischen Piscivoren (wie Sander lucioperca L.) für den geringen Barschbestand verantwortlich ist. / In the study the feeding behaviour and distribution of larval and juvenile stages of roach (Rutilus rutilus (L.)) and perch (Perca fluviatilis L.) was examined. The object of the study was the Lake Haussee, an stratified eutrophic hardwater lake that was biomanipulated for more than fifteen years. Over the whole period of biomanipulation the portion of perch population did not reach the level of one percent of the total fish biomass. From the scientific point of the view, a high biomass of piscivorous perch may stabilize the effects of biomanipulation in the long run. The aim of the study was to evaluate the hypothesis of strong competitive interaction between juvenile roach and perch for zooplankton, which could be responsible for the minor population of perch in lakes (PERSSON & GREENBERG 1990, PERSSON et al. 1991). The results of the study can be summarised as follows: i) In the period of midsummer to autumn juvenile perch segregated to a special food niche. In comparison to 1+/2+-roach, which fed on cladocerans (e.g. Bosmina and a high portion of Daphnia), 0+-perch preferred Eudiaptomus, Diaphanosoma and Leptodora. Thus, partitioning and separation were also observed for size-selectivity. Furthermore, the high growth rates and the good state of condition of the young perch as well as the lack of winter mortality did not indicate a competitive-induced mortality in the Lake Haussee. ii) In the period of midsummer to autumn the predator-induced seasonal mortality of juvenile perch (groups like 0+/1+) was estimated nearly up to 90 percent. Thereby, also a strong age group (like 1997) of juvenile perch was reduced up to 99 percent within the first two years of life. iii) The results of this study supported an alternative hypothesis: the morphological conditions of Lake Haussee, a prolonged zooplanktivore period of juvenile perch in combination with a strong stock of an effective pelagic piscivore predator (like Sander lucioperca L.) are responsible for the low perch stock.

Die Gattung Daphnia nimmt eine zentrale Position im pelagischen Nahrungsnetz vieler Standgewässern (Seen, Talsperren) ein. Aufgrund hoher Filtrierleistungen sind Daphnien für das integrierte Gewässermanagement, z.B. im Rahmen einer Nahrungskettenmanipulation (Biomanipulation), von großem Interesse. Ihre relativ einfache Kultivierbarkeit machte sie außerdem zu einen weit verbreiteten Modellorganismus limnologischer Grundlagenforschung. Das Ziel dieser Arbeit besteht darin, ein umfassendes Modellsystem für die Gattung Daphnia zu entwickeln, das wesentliche Kenntnisse der Ökologie von Daphnia miteinander verknüpft, um eine Vernetzung des Wissens zu realisieren. Bestehende Modellansätze konnten diese Aufgabe nur unzureichend erfüllen, weil sie in der Regel einem "Problem-orientierten Ansatz" folgen und somit sehr unterschiedliche inhaltliche Ausrichtungen und verschiedene Modellstrukturen aufweisen. Eine Kopplung bzw. ein direkter Vergleich dieser Modelle ist deshalb in der Regel schwierig. Dieses Modellsystem wurde entwickelt, um ein Instrument zur Synthese des vorhandenen Prozesswissens bereitzustellen, und nicht, um ein spezifisches, abgegrenztes Problem zu bearbeiten; es steht somit diametral zu existierenden Ansätzen. Aus diesem Grunde wird der gewählte Ansatz als ein "Spezies-orientierter Ansatz" bezeichnet. Drei Eigenschaften charakterisieren diesen Ansatz. (i) Das Modellsystem umfasst mehrere hierarchische Ebenen biologischer Organisation, wobei der Schwerpunkt auf den Ebenen des Individuums und der Population liegt. Interaktionen zwischen diesen Organisationsebenen sind ausgeprägt und in Feld- und Laborstudien gut belegt, in existierenden Modellen aber noch unzureichend miteinander verknüpft. (ii) Da eine quantitative Interpretation der Ergebnisse beabsichtigt ist, wurden die Modellausgaben einer umfangreichen Validation an unabhängigen und bereits publizierten Daten unterzogen. (iii) Das Modellsystem zeichnet sich durch einen geschachtelten Aufbau aus (nested design), wodurch eine einfache Erweiterbarkeit des Modells oder auch die separate Anwendung bestimmter Modellkomponenten gewährleistet ist. / The scope of this thesis was to develop a comprehensive model system of the genus Daphnia, a key organism in the pelagic food web of lakes and reservoirs and a widely used model organism in experimental and theoretical ecology. Although its central role in applied and basic research in aquatic ecology is obvious, there are still fundamental problems in modelling the observed dynamics of Daphnia (for details see chapter 2). Therefore, a basic motivation of this work was to use scientific results obtained in independently conducted research for developing a model that brings these results into context. Instead of following a "problem-oriented" paradigm applicable to a single, well defined problem or scientific hypothesis, the underlying concept of the emerging model system was considered to be "species-oriented". Thus, various relevant processes are included into the framework in order to simulate the dynamics of daphnids displayed on different levels of biological organization. To facilitate its application to various problems in ecological research on the genus Daphnia, the model system fulfills the following three important properties: (1) model outputs are thoroughly validated on experimental data in order to guarantee sound quantitative outputs of the model system (2) the system spans over different levels of biological organization with special emphasis laid upon the individual level and the population level (3) the model´s architecture follows a nested design with a defined individual level model that is integrated into a population level model The whole model system is able to describe an individual´s development over time on basis of physiological properties of the organism and, furthermore, how these individual level processes interact with the dynamics on the population level. Due to its nested design, applications of separate submodels (e.g. the individual-level model) are possible.