University, Diss., 2002--Kiel.

University, Diss., 2003--Bremen.

Since the beginning of the Industrial Revolution, carbon dioxide (CO2) has been emitted into the atmosphere at rates unprecedented to Earth’s history. Nearly 30% of the anthropogenic CO2 in the atmosphere has been absorbed in surface waters of the ocean, pushing carbonate chemistry towards increased bicarbonate ions and hydrogen protons and decreased carbonate ions. Consequently, seawater pH has decreased from pre-Industrial Revolution levels of 8.2 to current levels of 8.1, and it is expected to continue to drop to 7.8 by the year 2100 if carbon emissions continue as predicted. The combination of these effects is referred to as ocean acidification. It is at the forefront of marine research as it poses a serious threat to several marine organisms and ecosystems. Ocean acidification has the most notable direct effect on calcifying organisms with calcium carbonate skeletons and shells, because fewer carbonate ions in the water column result in reduced calcification. Coral reefs are especially vulnerable to ocean acidification since reefs are composed of complex carbonate structures. Coral reefs have a high biodiversity; thus, not only will the corals themselves be affected by ocean acidification, but so will many of the animals that dwell in them. The primary objective of this thesis was to examine the effects of ocean acidification on demersal zooplankton that reside in coral reefs. Ocean acidification research on zooplankton has primarily been single- species experiments on calcifying species or generalist copepod species. Scaling-up to experiments examining ocean acidification effects on entire zooplankton communities is logistically difficult, thus the ability to predict community changes in zooplankton due to ocean acidification has been rather limited. However, a few locations around the world have submarine volcanic CO2 seeps that can be used as natural laboratories to study ecosystem effects of ocean acidification. Two CO2 seeps located in coral reefs in Papua New Guinea were used as windows into the future to examine the effects of ocean acidification on entire zooplankton communities while they live naturally in their environment. Over three expeditions to two CO2 seeps, nocturnal plankton were sampled with horizontal net tows and emergence traps. Additional experiments were also conducted, and collectively this work is summarized in chapters 2-5 as outlined below. Chapter 2 reports on the observed changes in zooplankton abundance and community composition between control and high-CO2 sites. Consistent results between seep sites and expeditions showed that zooplankton abundances were reduced three-fold under high-CO2 conditions. The abundance loss was partially attributed to habitat change within the coral reef, from more structurally complex corals in the control sites to a replacement of massive bouldering corals in the high-CO2 sites. The loss of structural complexity in the reef meant there were fewer hiding spaces for the zooplankton to seek refuge in during the day. All zooplankton taxa were reduced under high-CO2 conditions but to varying levels, suggesting that each taxon reacts differently to ocean acidification. Since each taxonomic group within the zooplankton communities was reduced to varying levels under ocean acidification, the copepod genus with the largest reduction in abundance was investigated in more detail. Labidocera spp. are pontellid copepods that are generally considered surface-dwellers and are not known to inhabit coral reefs. Therefore, as a preface to the ocean acidification study, the new discovery of these copepods living in coral reefs is first described (Chapter 3). Not only were they found to be residential to the reef, but Labidocera spp. living at the control reefs preferred to reside in coral rubble, macroalgae, and turf algae. Labidocera spp. were one of the most sensitive copepods to high-CO2 conditions and were reduced by nearly 70% in abundance, prompting a more detailed investigation about the effect of ocean acidification on their physiology and habitat preference (Chapter 4). Physiological parameters, e.g. size, feeding, and oocyte development, were unaffected by ocean acidification. Unlike the zooplankton community as a whole, the main cause for the abundance loss of Labidocera spp. was not a shift in the habitat because their preferred substrata were of equal percent coverage across high-CO2 and control sites. Instead, Labidocera spp. were no longer associated with any substrata type. Multiple direct and indirect effects of ocean acidification will act on each zooplankton taxa separately, and their collective response will contribute to the community response. The effects of ocean acidification on zooplankton communities were then scaled up to potential impacts on entire ecosystems. Zooplankton are the primary food source for corals, fish, and other zooplanktivores. The impacts of ocean acidification on zooplankton communities will have cascade effects on the food chain via the pathway of zooplanktivorous organisms. A case study on the stony coral Galaxea fascicularis explored the effects of ocean acidification on the ability of corals, which had lived their entire lives under high-CO2 conditions, to feed on zooplankton (Chapter 5). Under anthropogenic changes, whether it is from bleaching, high turbidity, or ocean acidification, some corals rely more on heterotrophy and consume more zooplankton. Contrary to expectation, this study showed that when given equal quantities of food particles these corals consumed less zooplankton under ocean acidification. Corals rely on heterotrophy for essential nutrients, like nitrogen and phosphorus, which they cannot otherwise obtain from autotrophy and their symbiotic zooxanthellae. In conclusion, my thesis shows that not only is there fewer zooplankton available to consume, but the existing zooplankton is consumed with lower capture rates under high CO2 conditions. Coral reefs in future oceans will likely have reduced zooplankton abundances as an indirect effect of ocean acidification, partially caused by a change in habitat from branching corals to more massive bouldering corals. Zooplankton abundances were reduced yet the community composition was unaffected by ocean acidification. All zooplankton taxa were reduced yet present under high-CO2 conditions suggesting that the zooplankton are at least able to survive under ocean acidification. Fewer zooplankton will be available to zooplanktivores, but the fatty acid content and nutritional value of the zooplankton as a food source is expected to be similar to current food. Together this is expected to negatively impact the entire coral reef ecosystem, with some coral species unable to consume zooplankton at normal rates. In an ecosystem already highly vulnerable to ocean acidification, coral reefs may be even more threatened if the very basis of their food webs is reduced.

The observation was carried out in twenty fishponds in the surrounding of Vodňany and seven fisponds in the surrounding of Třeboň. The aim of the work was to evaluete the quality and quantity of the zooplankton depending on fish production. The samples were obtained and the observations were realized during the 4 years in Vodňany fishponds area and during the 2 years in Třeboň fishponds area. At first the samples were collected and data about the observed localities were organized. These data should explain changes in the aquatic ecosystems of these fishponds areas during the last decades.

The aim of the diploma thesis was a seven month research at the valley waterworks reservoir called Opatovice by Vyškov na Moravě. Taking of the water samples was carried out once a month from two sampling places, which were located on the leeward and windward sides. On the same day these water samples were analyzed at the Fishery and Hydrobiology Department of the Mendel Univerzity in Brno, where there were determined physical and chemical parameters of water, quantitative and qualitative content of the plankton associations. The results were compared with my bachelor thesis: The Development of the Quality of Water in the waterworks reservoir Opatovice, with the results from the previous years, which were provided by the Water Supply and Sewerage company, plc in Vyškov, with the valid legislation of the Czech Republic and with selected waterworks reservoirs situated in the south Moravian region.

Submitted by BRUNO PAES DE CARLI null (bpdecarli@yahoo.com.br) on 2016-03-31T11:10:32Z No. of bitstreams: 1 defesa.pdf: 1334483 bytes, checksum: e1779a60c5cd2e5c364fc4e3cdf58b34 (MD5) / Approved for entry into archive by Ana Paula Grisoto (grisotoana@reitoria.unesp.br) on 2016-03-31T13:14:27Z (GMT) No. of bitstreams: 1 decarli_bp_me_soro.pdf: 1334483 bytes, checksum: e1779a60c5cd2e5c364fc4e3cdf58b34 (MD5) / Made available in DSpace on 2016-03-31T13:14:27Z (GMT). No. of bitstreams: 1 decarli_bp_me_soro.pdf: 1334483 bytes, checksum: e1779a60c5cd2e5c364fc4e3cdf58b34 (MD5) Previous issue date: 2016-02-12 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / O Sistema Cantareira compreende uma série de cinco barragens localizadas em bacias hidrográficas distintas, sendo o principal responsável pelo abastecimento de água na Região Metropolitana de São Paulo. Devido à crise de água na área, é necessário desenvolver estudos que descrevem as condições ambientais e possíveis interferências. Neste sentido, a comunidade de zooplâncton pode ser usada como importante ferramenta de biomonitoramento. Além disso, o zooplâncton é considerado um componente importante do fluxo de energia no ecossistema. Portanto, este estudo teve como objetivo caracterizar a comunidade zooplanctônica em cinco reservatórios do Sistema Cantareira (Jaguari, Jacareí cachoeira Atibainha e Paiva Castro) e relacionou os dados biológicos com as variáveis limnológicas, a fim de diagnosticar as mudanças nas condições ambientais. As amostras foram coletadas durante a estação seca (maio e junho) e chuvosa (novembro e dezembro) de 2013 em 19 pontos de amostragem. A temperatura, condutividade eléctrica, pH e o oxigênio dissolvido foram medidos in situ com sonda multi-parâmetrica. Nutrientes, material em suspensão e os pigmentos foram determinados no laboratório. Amostras do zooplâncton foram coletadas na zona fótica através de arrasto vertical com rede de 68 µm. Os resultados mostraram eutrofização no reservatório Jaguari e algumas variáveis físico-químicas não atenderam o limite estabelecido por lei. Embora o Sistema Cantareira possa ser classificado como multi-sistema, um padrão semelhante à de cascata de reservatórios foi observado. Em relação ao zooplâncton, o grupo dos rotíferos demonstrou maior riqueza de espécies, porém pouco representativo em biomassa. Ciclopóides foram mais abundantes na estação seca, enquanto os Cladocera superaram os outros grupos no período de chuva. Uma tendência positiva para a densidade de Cyclopoida foi evidenciada. A ocorrência de um rotífero invasor Kellicotia Bostoniensis e da alga exótica Ceratium furcoides (Levander) Langhans 1925 foram registrados. Juvenis de copépodes e Bosmina freyi foram mais abundantes na pesquisa realizada. Crustáceos Calanoida apresentaram os maiores valores de biomassa em relação aos outros grupos. Com base nas análises, a heterogeneidade espacial e temporal foi evidenciada. A maioria dos pontos de amostragem demonstraram impactos moderados e com qualidade da água variando de regular a ruim. Neste sentido, características como o tempo de residência da água e morfometria do reservatório, estado trófico e as interações ecológicas são os principais fatores que podem implicar em alterações na composição do zooplâncton. / The Cantareira System comprises a series of five dams located in distinct watershed, mainly responsible for water supply in the Metropolitan Region of Sao Paulo state. Due to water crisis in the area, its necessary to develop studies that describe environmental conditions and possible interference. In this sense, the zooplankton community is being used such as biomonitoring tool. However, the zooplankton is considered an important component of the energy flow in ecosystem. Therefore, this study aimed to characterize the zooplankton community in five reservoirs of the Cantareira System (Jaguari, Jacarei waterfall Atibainha and Paiva Castro) and associate biological data with the limnological variables in order to diagnose changes in environmental conditions. Samples were collected during the dry (May and June) and rainy season (November and December) of 2013 in 19 sampling points. Temperature, electrical conductivity, pH and dissolved oxygen were measured in situ with multi-parameter probe. Nutrients, suspended matter and the pigments were determined in the laboratory. Zooplankton samples were collected in the photic zone through vertical hauling with 68 µm net. Results showed eutrophication in Jaguari reservoir and some physico-chemical variables not agreement the limit established by law. Although the Cantareira System classified as multi-system, a pattern similar to the cascade of reservoirs was observed. Regarding the zooplankton, the rotifer group demonstrate higher species richness, however scarcely representative in biomass. Cyclopoids were more abundant in the dry season, while the Cladocera exceeded the other groups during the rainy. An positive trend for Cyclopoida density and trophic status were associated. The occurrence of invasive rotifer Kellicotia Bostoniensis and exotic algae Ceratium furcoides (Levander) Langhans 1925 were registred. Juveniles of copepods and Bosmina freyi were more abundant in the survey conducted. Crustaceans Calanoida showed the highest biomass values than the other groups. Based on the analysis, the spatial and temporal distribution were demonstrated. Most sampling points demonstrate moderate impact and water quality ranging from regular and poor. In this case, features such as water residence time and the morphometry, trophic status, ecological interactions are the main factors that could imply in changes in zooplankton composition. / FAPESP: 2014/04471-0

The population structure and feeding dynamics of the hyperiid amphipod, Themisto gaudichaudii, was investigated during two cruises of the South African National Antarctic Programme conducted in the Indian sector of the Polar Frontal Zone during austral autumn (April) 2004 and 2005. During the 2004 cruise the frontal features that delimit the PFZ converged to form a single distinctive feature. In 2005, the research cruise was conducted in the vicinity of a cold-core eddy which was spawned from the Antarctic Polar Front. Total mesozooplankton abundance and biomass during the 2004 study ranged from 55.19 to 860.57 ind. m⁻³, and from 2.60 to 38.42 mg dwt m⁻³, respectively. In 2005 the abundance and biomass ranged from 23.1 to 2160.64 ind. m⁻³, and from 0.76 to 35.16 mg dwt m⁻³, respectively. The mesozooplankton community was numerically dominated by copepods, pteropods, and ostracods during both surveys. The abundance and biomass of Themisto gaudichaudii in the region of investigation was < 0.2 ind. m⁻³ (range 0.01 to 0.15 ind. m⁻³) and < 0.06 mg dwt m⁻³ (range 0.02 to 0.06 mg dwt m⁻³) during 2004, while in 2005 the abundance and biomass of the amphipod ranged from < 0.01 to 0.2 ind. m⁻³ and < 0.01 to 0.04 mg dwt m⁻³, respectively. These values correspond to < 1% of the total mesozooplankton abundance and biomass during both surveys. T. gaudichaudii exhibited no significant spatial patterns in abundance, biomass and total length during both 2004 and 2005 (p > 0.05 in all cases). A key feature of the two investigations was the virtual absence of juveniles (total length < 15 mm) among the amphipod population, supporting the suggestion that they exhibit strong seasonal patterns in reproduction. Gut content analysis during both years indicated that for both the male and female amphipods’, copepods were the most prevalent prey species found in stomachs, followed by chaetognaths and pteropods. Results of electivity studies indicate that T. gaudichaudii is an opportunistic predator, generally feeding on the most abundant mesozooplankton prey. Results of in vitro incubations indicated that the total daily feeding rate of T. gaudichaudii during 2004 ranged from 11.45 to 20.90 ind. m⁻³ d⁻¹, which corresponds to between 0.12 and 1.64% of the total mesozooplankton standing stock. In 2005, the feeding rate ranged between 0.1 and 1.73% of the total mesozooplankton standing stock. The low predation impact of T. gaudichaudii during this study can be related to their low abundances and high interannual variability throughout the region of investigation.

Orientador: Marcos Gomes Nogueira / Banca: Odete Rocha / Banca: Evaldo Luiz Gaeta Espindola / Resumo: O Brasil possui uma imensa rede de reservatórios artificiais que são utilizados para múltiplas finalidades, entre elas a piscicultura em tanques-rede. A implantação de sistemas de cultivo em tanques-rede está se desenvolvendo em larga escala, inclusive com incentivos governamentais. É importante lembrar que este tipo de cultivo emprega um volume considerável de insumos para sua produção, gerando uma grande quantidade de resíduos orgânicos e inorgânicos que podem levar a eutrofização das áreas aqüícolas e mudanças nas comunidades aquáticas. Os organismos zooplanctônicos são tidos como elos estruturadores das cadeias alimentares aquáticas, podendo inclusive ter um papel complementar na tilapicultura em tanques redes. Podem ainda ser considerados como indicadores da qualidade de água. O presente trabalho tem por objetivo analisar a composição, riqueza, abundância e diversidade das assembléias zooplanctônicas (Rotifera, Cladocera e Copepoda), e sua relação com mudanças potenciais do grau de trofia relacionadas à implantação de tanques-rede. Os trabalhos de campo foram conduzidos durante um ciclo sazonal completo (novembro de 2006 a novembro de 2007) nas zonas de transição rio-reservatório (Fartura, SP) e na barragem (Chavantes, SP) do reservatório de Chavantes, Rio Paranapanema. São Paulo. As amostragens foram realizadas em áreas com a presença de tanques-rede, bem como em áreas controle, sem efeito da tilapicultura. Além do zooplâncton também foram considerados as variáveis limnológicas (coluna d'água) temperatura, pH, oxigênio dissolvido, condutividade elétrica, transparência, turbidez, clorofila, nitrogênio orgânico total e fósforo total. As influências dos sistemas de cultivo em tanques-rede nas regiões de Chavantes e Fartura, reservatório de Chavantes, rio Paranapanema (SP/PR) puderam ser observadas no presente estudo... (resumo completo, clicar acesso eletrônico abaixo) / Abstract: Brazil has a complex network of artificial reservoirs that are used for multiple purposes, including fish farming in cage aquaculture systems. The introduction of cultivation systems in net cages has been is a large-scale development process, which receives governmental incentives. This kind of zootechnical production requires a considerable amount of ration and sanitary products, generating a large quantity of organic and inorganic wastes that can lead to eutrophication of the aquaculture areas. As a consequence it is expected a decrease in the water quality and modifications in the aquatic community. The zooplankton organisms are considered as basic links in the aquatic food webs, and may also have a complementary role in the net cage tilapiculture. The assemblages structure can also be considered as indicators of water quality. This work aimed to analyze the composition, richness, abundance and diversity of the zooplankton assemblages (Rotifera, Cladocera and Copepoda), and its relation to the potential changes of the trophic level related to the introduction of net cages farms. The field work was conducted during a complete seasonal cycle (November 2006 to November 2007) in the river-reservoir transition zone (Fartura, São Paulo State) and in the dam zone (Chavantes, São Paulo State) of Chavantes Reservoir (Paranapanema River, São Paulo/Paraná States). Samplings were taken monthly in areas with the presence of net cages, as well as in control areas (without the tilapiculture effects). Besides the zooplankton the limnological variables (water column) temperature, pH, dissolved oxygen, electrical conductivity, transparency, turbidity, chlorophyll, total organic nitrogen and total phosphorus were also analyzed. The influence of the fish cultivation systems in the regions could be observed. Due to the eutrophication process, changes in physical and chemical water characteristic... (Complete abstract click electronic access below) / Mestre

O zooplâncton possui grande sensibilidade ambiental e responde rapidamente a alterações ambientais com alterações na abundância e riqueza de organismos. Ainda se conhece muito pouco sobre os organismos aquáticos do Cerrado, assim como há poucos estudos sobre o zooplâncton de ambientes lóticos no Brasil. Esse trabalho teve como objetivo caracterizar dois córregos da bacia do Rio Preto, médio São Francisco, pela avaliação de comunidades zooplanctônicas e suas relações com características físicas, químicas e biológicas da água, comparando córregos em áreas de vegetação nativa conservada e sob influência de áreas agrícolas. Foram amostradas duas sub-bacias do Rio Preto, localizadas em área de Cerrado (DF e GO) durante quatro semanas nos períodos seco e chuvoso. Em dois pontos de amostragem por córrego, foram coletadas amostras de zooplâncton e de água. Variáveis físicas e químicas da água e a concentração de a clorofila a foram determinadas. Os dois córregos apresentaram tendência de aumento de íons no período chuvoso. O córrego Estanislau (em área agrícola) apresentou maiores concentrações de nitrato, sódio, cloreto e clorofila a em relação ao córrego Pindaíba (em área de vegetação nativa). O zooplâncton se caracterizou por densidades muito baixas e alta riqueza de espécies, com 63 táxons registrados ao todo. A riqueza de espécies e a densidade de organismos do zooplâncton foram maiores no córrego Pindaíba. O córrego Estanislau possui indícios de estar sofrendo impactos negativos do uso rural de sua bacia. / The zooplankton community has high environmental sensitivity and quickly responds to changes in the environment with changes in its abundance and diversity. Yet, little is known about the aquatic organisms of the Cerrado, as well there had been few investigations on the zooplankton of Brazilian lotic environments. This work had the aims to characterize two streams of Rio Preto watershed, part of the Rio São Francisco watershed; to assess their zooplankton communities and the relationships between chlorophyll a and physical and chemical characteristics of water; and to contrast forested and agricultural streams. Two streams, located in the Cerrado Biome (Federal District and the state of Goiás), were sampled for four weeks in dry and rainy seasons. Zooplankton and water samples were taken in two sampling points per stream. Physical and chemical characteristics of water and chlorophyll a concentration were determined. Ionic concentration was higher on rainy season in both streams. The agricultural stream (Estanislau) had higher concentrations of nitrate, sodium, chloride, and chlorophyll a than the forested stream (Pindaiba). Zooplankton was characterized by very low densities and high species richness, with a total of 63 taxa recorded on both streams. Zooplankton density and species richness were higher in Pindaiba stream. Estanislau stream has signs to be suffering negative impacts from the agricultural land use of its watershed.

Tema importante no estudo da ecologia, a competição inter-específica é a demanda ativa por indivíduos de duas ou mais espécies de mesmo nível trófico por um recurso comum que é potencialmente limitante. Esse estudo teve como objetivo avaliar a ocorrência de competição entre espécies de microcrustáceos cladóceros e seu papel na estruturação da comunidade zooplanctônica. Este elo é o que faltava para completar o modelo conceitual sobre interações no Lago Monte Alegre. Foram selecionadas duas espécies de microcrustáceos cladóceros coexistentes e abundantes no lago, Ceriodaphnia richardi e Daphnia gessneri. Dois experimentos de competição foram realizados, sendo utilizadas concentrações diferentes de alimento (0,70 mgC.L-1, 0,25 mgC.L-1 da clorofícea cultivada, Scenedesmus spinosus) para alimentar os cladóceros. Os tratamentos foram (3 réplicas cada): a. controle com Ceriodaphnia richardi em frascos individuais; b. controle com Daphnia gessneri em frascos individuais; c. duas espécies colocadas no mesmo frasco. Todos os experimentos foram conduzidos sob temperatura controlada de 23ºC, que representa a temperatura média anual no lago. A taxa de crescimento (r) por dia foi calculada pela equação exponencial: r = (ln Nt - ln No)/t, onde No e Nt são as densidades inicial e final, respectivamente, e t é o tempo em dias. A maior concentração de alimento favoreceu o crescimento populacional das duas populações estudadas. C. richardi não teve seu crescimento influenciado pela presença de D. gessneri, superando-a em termos de densidade e taxas de crescimento. Já D. gessneri teve sua taxa de crescimento populacional influenciado pela presença de C. richardi, na menor concentração de alimento. Para melhor compreender as razões da superioridade competitiva de C. richardi e o papel da predação com relação a essa espécie, foram feitos experimentos adicionais. Um deles testou a hipótese de que essa espécie pode alimentar-se de outros recursos além de algas, com os tratamentos (3 réplicas): a. água filtrada do lago e b. água filtrada, com adição da alga S. spinosus. Os resultados deram suporte à hipótese. O experimento de predação, com 5 cladóceros e 2 larvas IV de Chaoborus por réplica, mostrou que essa espécie é predada por elas. Flutuações das populações de microcrustáceos zooplanctônicos e dos predadores invertebrados (larvas de Chaoborus brasiliensis e o ácaro aquático Krendowskia sp.) foram acompanhadas semanalmente no lago, durante um ano, entre maio de 2011 e abril de 2012, bem como fatores físicos, químicos e biológicos, como temperatura, oxigênio dissolvido, condutividade elétrica, pH, transparência na coluna dágua e clorofila-a, na tentativa de estabelecer conexão entre os resultados de laboratório e campo. Os resultados mostraram que um período de estratificação térmica mais nítida ocorreu no lago entre outubro e abril (estação quente-chuvosa), sendo mais acentuada a partir de dezembro, enquanto circulação freqüente da coluna dágua foi registrada nos meses mais frios do ano, de maio a setembro (estação fria-seca). A distribuição vertical de outras variáveis ambientais mostrou relação com o padrão de circulação do lago, refletindo na dinâmica populacional das populações zooplanctônicas. Cladóceros foram mais abundantes na estação fria-seca, enquanto copépodos aumentaram no início da estação quente-chuvosa. Porém, ambos os grupos apresentaram as menores densidades entre os meses de fevereiro e abril de 2012. O aumento das larvas de caoborídeos e dos ácaros aquáticos na estação quente-chuvosa parece ser a principal causa do declínio de cladóceros neste período, devido à predação. Já o alimento e temperatura parecem ter maior influência sobre as populações na estação fria-seca. Além da predação, temperatura e alimento, os resultados de competição inter-específica também mostraram ser esse um dos fatores potencialmente controladores da dinâmica populacional do zooplâncton no Lago Monte Alegre, particularmente no período frio, quando o alimento é mais escasso. / Competitive interactions are an important topic in the study of ecology. The interspecific competition is the demand for active individuals of two or more species of the same trophic level for a common resource that is potentially limiting. This study aimed to evaluate the occurrence of competition between species of cladocerans and their role in structuring the zooplankton community. This is the missing link to complete the conceptual model on interactions in the Lake Monte Alegre. Two species of abundant cladocerans that coexist in the lake were selected, Ceriodaphnia richardi and Daphnia gessneri. Two competition experiments were carried out, using different concentrations (0.70 mgC.L-1 and 0.25 mgC.L-1) of the cultivated chlorophycean Scenedesmus spinosus. The treatments were (with 3 replicates each): a. control with Ceriodaphnia richardi in individual bottles; b. control with Daphnia gessneri in individual bottles; c. the two species placed in the same bootle. All experiments were conducted under controlled temperature of 23 ºC, which represents the average annual temperature in the lake. The growth rate (r) per day was calculated by the exponential equation: r = (ln Nt - ln No)/t, where No and Nt are the initial and final densities, respectively, and t is time in days. Increased population growth of the two populations occurred in the highest concentration of food. The growth of C. richardi was not influenced by the presence of D. gessneri, exceeding it in terms of density and growth rates. The population growth of D. gessneri was also influenced by the presence of C. richardi in the lowest concentration of food. For a better understanding of the reasons for the competitive superiority of C. richardi and the role of predation related to this species, two additional experiments were made. For testing the hypothesis that the species exploits other food resources, the treatments were (3 replicates): a. with lake filtered water and b. with filtered water + alga S. spinosus. The results supported the hypothesis. The predation experiment with 5 cladocerans and 2 larva IV of Chaoborus per replicate showed that the species is preyed on by the larvae. The fluctuations of zooplanktonic microcrustaceans and invertebrate predators (Chaoborus brasiliensis larvae and aquatic mite Krendowskia sp.) were monitored weekly in the lake during one year, from May 2011 to April 2012. Physical, chemical and biological factors, such as temperature, dissolved oxygen, electrical conductivity, pH, transparency in the water column and chlorophyll-a were monitored in an attempt to establish a link between the results of laboratory and field. The results showed that the period of more stable thermal stratification in the lake occurred between October and April (warm-wet season). A more stable stratification started in December, while more frequent circulation of the water column was recorded during the coldest months of the year, from May to September (cold- dry season). The vertical distribution of other environmental variables are a consequence of the lake circulation pattern. Cladocerans were more abundant in the cold-dry season, while copepods increased in early warm-wet season. However, both groups had the lowest densities between February and April 2012. Increased densities of chaoborid larvae and water mites in the warm-wet season seem to be the main cause of the decline of cladocerans in this period due to predation. Food and temperature can exert greater influence on populations in the cold-dry season. In addition to predation, temperature, and food, the results of interspecific competition indicated that it may be one of the factors controlling the population dynamics of zooplankton in the Lake Monte Alegre in periods of food shortage, particularly in the cool period.