Effects of nutrients increase on the copepod community of a reservoir using cages

Abstract

Aim: This study investigated changes in copepod abundance and the influence of environmental variables in a reservoir with fish farming using cages, on temporal and spatial scales. We hypothesised that the copepod abundance will increase when influenced by changes in environmental variables due the increase of nutrients originating from fish farming. Methods A 120-day sampling of copepods and environmental variables was carried out in a subtropical reservoir of the Paraná River basin (Rosana reservoir), upstream and downstream of three sets of cages with different fish stocking densities. A Principal Component Analysis was conducted to characterise sampling periods and points through environmental variables. The differences between copepod abundance according to sampling periods and points were tested by ANOVA. Results We observed higher maximum values for most nutrient concentrations and dissolved oxygen in the final stage of the experiment and in the location of cages installation. The copepod abundance increased sharply during the first days of the experiment and then decreased during the following periods with a tendency towards returning to the initial conditions at the final stage of the experiment. A significant difference in copepod abundance between the location of cages installation and downstream was showed. In addition, turbidity, chlorophyll-a, and nitrate significantly predicted copepod abundance. Conclusion The results suggested that the changes in copepod abundance over time are influenced by environmental variables, evidenced by the increase in nutrient concentration after the cage installation, related to the increase in the practice of fish farming. The environmental variables related to system productivity were linked to the availability of food resources. Thus, our hypothesis that copepod abundance is increased due the alterations in environmental variables caused by the increase in the practice of fish farming using cages was corroborated.

Influence of inlet water on the biotic and abiotic variables in a fish pond

“…The water flow brings allochthonuous material (anthropic activities) resulting in an eutrophication process. According Tibúrcio et al (2015) abundance of the community of Copepoda increases due to alterations in environmental variables caused by the increase in the practice of fish farming. Themocyclops decipiens and A. furcatus adults were frequently abundant and shared habits in oligo-mesotrophic environments (Sipaúba-Tavares et al, 2011;Tibúrcio et al, 2015).…”

Macrophyte - environment relationships during a monospecific and a multispecific massive invasion in a fishpond

“…The abundance of the mesotrophic-eutrophic environments copepod bio-indicator Thermocyclops decipiens (Tibúrcio et al 2015) and the large amounts of Rotifera observed in both studied periods respond to the high nutrient and organic loadings always entering the pond. The differences in zooplankton species composition observed in both invasion periods seem not to be largely related to season, since 38 out of the 40 taxa in table 2 have been recorded during the rainy summer and during the dry winter either in this or in previous macrophyte studies conducted in this farm (Travaini-Lima et al 2016, Sipaúba-Tavares et al 2017.…”

Influence of the chlorophyll-a gradient on the community structure of plankton microcrustaceans (Cladocera and Copepoda) in a Neotropical reservoir

“…Net cage fi sh farming in reservoirs is considered as a promising alternative to meet the increasing need for food of the world population (Alves & Baccarin 2005, Dias et al 2011, Tiburcio et al 2015. The increase of this activity is related to the exploitation of available reservoirs and lakes, high effi ciency in management, readiness of fi sh removal and continuous water fl ow that would theoretically improve the water quality inside the cages and reduce the production costs (Cyrino & Kubtiza 1996, Furlaneto et al 2006, Halwart et al 2007.…”