Impacto da carcinicultura na estrutura do plâncton em estuários rasos e de baixo aporte fluvial

Abstract

Shrimp farming has been growing worldwide, which came along with an increased concern about its environmental impacts on coastal ecosystems. The objective of this work was to test the hypothesis that shrimp farming modifies the structure of planktonic communities in shallow tropical estuaries with low fluvial input. For this, we evaluated and compared the composition, richness and density of phytoplankton and zooplankton between different seasonal periods and between the water catchment points from estuaries to the farming and the effluent discharge point to estuaries in shrimp farms. Samples were collected during the rainy and dry periods of 2014 in farms located in two estuaries on the semiarid coast of Brazil. Regarding phytoplankton and zooplankton density, no significant seasonal (dry and rainy) differences were observed (p> 0.05) in both estuaries. This result could be related to prolonged drought and riverdams that would homogenize dry and rainy seasons and lead to seasonal similarity in the planktonic community densities. Between the catchment and drainage points, there was a significant difference in density only for the phytoplankton community of Jaguaribe farms, which suggests lower carrying capacity and / or greater anthropic impact in this region. This difference was mainly due to the increase of cyanobacterial cells at the drainage point. Cyanobacteria and Protozoa were more closely related to drainage points than to uptake points. Regarding phytoplankton and zooplankton composition, significant differences (p <0.05) were observed between uptake and drainage in Aracati farms and between locations (Aracati x Jaguaribe). This difference observed between the capture and drainage points in Aracati may be related to the trophic state of the environment, which may increase in drainage in relation to the capture point. The difference between the locations may be related to the distance between each farm and the mouth of the rivers, which vary between the farms located in Aracati and Jaguaribe. There were no significant differences (p> 0.05) in the number of taxa between seasonal periods and between uptake and drainage points. Thus, it is concluded that the use of estuary water in shrimp farming can alter plankton composition and density in shallow estuaries as suggested by the increase in the densities of few indicator groups of lower water quality. However, this change appears to be variable depending on the geographical location, ecosystem carrying capacity and cumulative impacts of farms along the estuary.