Temporal variability of plankton and nutrients in shrimp culture ponds vs. adjacent estuarine water

• Autor(a) principal: Cardozo, Alessandro Pereira
• Data de Publicação: 2011
• Outros Autores: Britto, Vanessa Oliveira, Odebrecht, Clarisse
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: Repositório Institucional da FURG (RI FURG)
• Texto Completo: http://repositorio.furg.br/handle/1/2227
• topic: Phytoplankton; Chlorophyll; Zooplankton; Nutrients; Shrimps; Estuary; Fitoplâncton; Clorofila; Zooplâncton; Nutrientes; Camarões; Estuário

Water quality, phytoplankton and zooplankton were evaluated in a shrimp pond (Litopenaeus vannamei) and the adjacent Patos Lagoon estuary in summer from November/2007 to February/2008. Every two weeks, temperature, salinity, dissolved inorganic nutrients, total chlorophyll a and size fractions (>20μm; 1-20μm; <1μm) and phytoplankton and zooplankton densities were analyzed. Excepting temperature, significant differences were observed between both environments. In the estuary, salinity variations (1-21) were related with water exchange while, in the pond, increased salinity (7-20) probably resulted from evaporation. Silicate (51.08-100.73μM) was always higher in the estuary, while the levels of ammonium (0.71-5.37μM), phosphate (0.24-2.43μM) and suspended matter (10.57-78.63mg.L-1) were higher in the pond. High nitrate/nitrite (18.67μM) levels correlated with inorganic fertilization in the pond. In November/2007, the level of chlorophyll a in the pond was lower (5.7-16.4μg.L-1) than in the estuary (20.0-32.9μg.L-1) where diatoms always prevailed. In the pond, flagellates and cyanobacteria <1μm were the main organisms responsible for the chlorophyll a increase (30.6μg.L-1) in January/2008. Zooplankton, mainly the copepod Acartia tonsa, presented higher concentrations in the pond during the first month (238 org.L-1) and probably exerted important grazing pressure reducing chlorophyll a. After that, zooplankton decreased significantly releasing the grazing pressure on phytoplankton and indicating the importance of top-down control. In conclusion, changes in chlorophyll a levels were mainly related with water exchange in the estuary while the nutrient availability and top-down control in the pond, influenced significantly the size structure and composition of phytoplankton.