Comunidade planctônica como indicadora do estado trófico em um viveiro de piscicultura
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Data
2020-02-17
Autores
Silva, Juliane dos Santos Alves da
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Universidade Estadual Paulista (Unesp)
Resumo
Todas as mudanças temporais que ocorrem nos ecossistemas são complexas e podem ser responsáveis pelos padrões cíclicos de variações. Se o tempo de vida de um organismo é curto em relação às mudanças ambientais são esperadas oscilações ou flutuações da densidade populacional. Os sistemas artificiais rasos, como viveiros e tanques de piscicultura, são dinâmicos, apresentando manejo intensivo, com uso de ração para alimentação e frequente adição de fertilizantes, onde qualquer alteração, pode acarretar condições adversas ao meio, como por exemplo, a eutrofização. O presente estudo analisou as condições bióticas (plâncton) e abióticas (variáveis ambientais) de um viveiro de piscicultura, comparou as concentrações de nutrientes com a presença das espécies planctônicas indicadoras de estado trófico e avaliou a aplicação de índices de estado trófico em um viveiro de piscicultura. Amostras de água e plâncton em diferentes profundidades (superfície e fundo) e sedimento foram coletadas durante cinco dias consecutivos em cada mês, durante seis meses (julho-dezembro) em um ponto de amostragem localizado no centro do viveiro, nas estações de seca e chuva. As diferenças significativas entre as amostras foram avaliadas através de uma ANOVA one-way. Todas variáveis da água apresentaram diferenças (p<0,05) entre os períodos de seca e chuva. No entanto, em relação à superfície e fundo somente fósforo total e sólidos totais solúveis diferiram (p<0,05) no período de seca e coliformes termotolerantes, pH e sólidos totais solúveis no período de chuva. Elevada densidade da comunidade zooplanctônica e fitoplanctônica tanto na superfície quanto no fundo do viveiro foram observados no período de chuva. Dentre as espécies zooplanctônicas, somente náuplios de Copepoda Argyrodiatomus furcatus foi abundante na superfície e fundo em todos os meses. Entretanto, para a comunidade do fitoplâncton, Euglena sp. foi a única espécie dominante ao longo do período de amostragem. A densidade de Cyanobacteria foi extremamente baixa, menor que 0,41% do total da comunidade fitoplanctônica e ausente na estação chuvosa. O índice de estado trófico modificado por Lamparelli foi o melhor índice para classificar sistemas artificiais rasos. No entanto, a avaliação baseada em espécies planctônicas deve ser reconsiderada, uma vez que espécies que indicam tanto o estado oligotrófico quanto o eutrófico ocorreram simultaneamente. A presente pesquisa indica que o fluxo contínuo de água de outros viveiros de peixes e a adição freqüente de nutrientes, juntamente com as condições climáticas, podem interferir na qualidade da água e promover o domínio de espécies comuns aos ambientes eutróficos.
The temporal changes that may occur in the ecosystems are complex and may be responsible for the cyclic pattern of the variations. If the life spam of certain organism is too short compared with the environmental changes, fluctuations on population density are expected. Shallow artificial systems, such as constructed fishponds, are employed for intensive management. This practice demands intense artificial fish feed and fertilization, which may lead to eutrophication. The present study analyzed the biotic (plankton) and abiotic (environmental variables) conditions of a constructed fishpond and compared the nutrients concentration in the presence of plankton species which are indicators of trophic state. Water, plankton (surface and bottom) and sediment samples were collected along five consecutive days, for six months (July-December). The sampling point was in the center of the pond. The experiment period comprised a dry and a wet season. The significant differences between samples was assessed through a one-way ANOVA. All water variables displayed significant differences (p < 0.05) between the dry and wet season. However, when surface and bottom are compared, only total phosphorus and total soluble solids displayed significant differences (p < 0.05) in the dry season and thermotolerant coliforms, pH and total soluble solids in the wet season. Zooplanktonic and phytoplanktonic communities presented high density both in the surface and bottom, in the wet season. Among zooplankton species, only the Copepods nauplius Argyrodiatomus furcatus was abundant both in the surface and bottom, along the entire experimental period. The only dominant phytoplankton species in both seasons was Euglena sp. The Cyanobacteria density was lower than 0.41% of the plankton community and was absent in the wet season. The trophic state index modified by Lamparelli displayed a better index to classify shallow artificial systems. However, the assessment based on planktonic species must be reconsidered, since species that indicate both oligotrophic and eutrophic state occurred simultaneously. The present research indicates that continuous flow of water from other fishponds and the frequent addition of nutrients, together with weather condition, may interfere on water quality and promote the dominance of species common to eutrophic environments.
The temporal changes that may occur in the ecosystems are complex and may be responsible for the cyclic pattern of the variations. If the life spam of certain organism is too short compared with the environmental changes, fluctuations on population density are expected. Shallow artificial systems, such as constructed fishponds, are employed for intensive management. This practice demands intense artificial fish feed and fertilization, which may lead to eutrophication. The present study analyzed the biotic (plankton) and abiotic (environmental variables) conditions of a constructed fishpond and compared the nutrients concentration in the presence of plankton species which are indicators of trophic state. Water, plankton (surface and bottom) and sediment samples were collected along five consecutive days, for six months (July-December). The sampling point was in the center of the pond. The experiment period comprised a dry and a wet season. The significant differences between samples was assessed through a one-way ANOVA. All water variables displayed significant differences (p < 0.05) between the dry and wet season. However, when surface and bottom are compared, only total phosphorus and total soluble solids displayed significant differences (p < 0.05) in the dry season and thermotolerant coliforms, pH and total soluble solids in the wet season. Zooplanktonic and phytoplanktonic communities presented high density both in the surface and bottom, in the wet season. Among zooplankton species, only the Copepods nauplius Argyrodiatomus furcatus was abundant both in the surface and bottom, along the entire experimental period. The only dominant phytoplankton species in both seasons was Euglena sp. The Cyanobacteria density was lower than 0.41% of the plankton community and was absent in the wet season. The trophic state index modified by Lamparelli displayed a better index to classify shallow artificial systems. However, the assessment based on planktonic species must be reconsidered, since species that indicate both oligotrophic and eutrophic state occurred simultaneously. The present research indicates that continuous flow of water from other fishponds and the frequent addition of nutrients, together with weather condition, may interfere on water quality and promote the dominance of species common to eutrophic environments.
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Palavras-chave
Zooplâncton, Fitoplâncton, Parâmetros bióticos e abióticos, Zooplankton, Phytoplankton, Biotic and abiotic factors