Evaluation of the environmental impact resulting from the cultivation of Rachycentron canadum in net tanks installed on the northeast coast of Brazil
The cultivation of marine organisms in net tanks has been showing high growth rates, however, they generate considerable inputs of nutrients and organic matter to the surrounding environment. Monitoring measures allow to maintain adequate levels to the requirements of the cultivated species, as well as to evaluate the effects of the cultivation on the water quality. This study aimed to evaluate the possible environmental impacts resulting from an experimental cultivation of Rachycentron canadum off the coast of the State of Pernambuco. To this end, collections of water and sediment were carried out every two months, in the region surrounding the crop. Dissolved oxygen, temperature, salinity, pH and water transparency (Secchi) were monitored, in addition to the concentrations of compounds such as NH4 +, NO2, N (t), P (t) and TOC in the water and the amount of carbon in the sediment.Phytoplankton biomass was also monitored, using chlorophyll a. Temperature and salinity varied according to seasonality and rainfall, but remained within the optimal ranges for the species. The dissolved oxygen values were always above 5 mg/L and the pH varied between 8.5 and 9.5. The water transparency values varied according to the concentrations of chlorophyll a, which ranged from 0 to 1.02 μg/L, with most samples being less than 0.45 μg/L, typical of an oligotrophic region. As for the nutrients in the water, phosphorus was not detected, and ammonium and nitrite were very low. However, the mean values of total nitrogen (6.66 mg/L) and total organic carbon (94.01 mg/L) were higher, including the control points,which can be explained by the proximity of the cultivation to the mouth of the Capibaribe River, very rich in organic matter. The carbon values in the sediment varied between 8.7% and 10.69%, including at the control point, and the values can be explained by the abundance of benthic organisms in the region. Apparently, the cultivation did not negatively impact the adjacent area. The low biomass of fish produced and the great dynamics of the environment, which presented high current speeds (average of 0.26 m/s), are related to the results. It is believed that the environment has great support capacity, however, it is necessary to monitor new cultivation cycles to confirm the results found.