Influence of net-cage fish farming on zooplankton biomass in the It芍 reservoir, SC, Brazil Influ那ncia da piscicultura em tanque-rede sobre a biomassa do zooplancton no reservat車rio de It芍, SC, Brasil

作者：Bruna Roque Loureiro; Christina Wyss Castelo Branco; Evoy Zaniboni Filho

来源：Acta Limnologica Brasiliensia, 2011.

• Zooplancton
• peso seco
• tanque-rede
• reservatorio
• Zooplankton
• dry weight
• net cage
• reservoir

OBJECTIVES: This study aimed to verify the influence of net-cage fish farming on zooplankton biomass in the It芍 reservoir (Uruguay River, Brazil). METHODS: Samples were collected monthly from October/2009 to May/2010 at the surface and at the bottom in two sampling stations, the net-cage area and in a control area using a Van Dorn bottle and a plankton net (68 米m). RESULTS: The Cladocera and Copepoda biomass was estimated by dry weight using a micro-analytical balance, and the Rotifera biomass by Biovolume. Total zooplankton biomass varied between 6.47 and 131.56 mgDW.m-3 Calanoida copepod presented the highest value of biomass (127.56 mgDW.m-3) and rotifers, despite having an important contribution to total density, showed a maximum biomass of 2.01 mgDW.m-3. Zooplankton biomass at the net-cage area surface was higher when compared with the control area during the months of October to January. However, the zooplankton biomass was similar at the bottom of the two areas throughout the studied period. From February until May, zooplankton biomass decreased in both sampling stations, a fact probably associated with the flushing of the reservoir, followed by an increase in water transparency and a decrease in chlorophyll-a concentration in the following months (February to May). CONCLUSIONS: The influence of fish farming on zooplankton biomass was detected at the surface of the net-cage area only from October to January. From February to May this influence was not found, probably by the influence of the flushing of the reservoir. OBJETIVO: Este estudo teve o objetivo de verificar a influencia da piscicultura em tanque-rede sobre a biomassa da comunidade zooplanct nica no reservat車rio de It芍 (Rio Uruguai, Brasil). METODOLOGIA: Foram realizadas coletas mensais de outubro/2009 a maio/2010 na superf赤cie e no fundo em dois pontos amostrais, ponto tanque-rede e em uma 芍rea controle, com o aux赤lio da garrafa Van Dorn e rede de plancton (68 米m). RESULTADOS: A biomassa dos rot赤feros foi obtida atrav谷s do c芍lculo do biovolume e a dos clad車ceros e cop谷podos por peso seco, a partir da pesagem em balan a micro-anal赤tica. Os valores de biomassa total zooplanct nica variaram entre 6,47 e 131,56 mgDW.m-3. Os cop谷podos Calanoida apresentaram os maiores valores de biomassa (127,56 mgDW.m-3) e os rot赤feros, apesar de importantes em termos de densidade, apresentaram uma biomassa m芍xima de 2,01 mgDW.m-3, contribuindo pouco para biomassa total. A 芍rea de cultivo apresentou maiores valores de biomassa zooplanct nica na superf赤cie quando comparada com a 芍rea controle, durante os mes