Comunidade fitoplanctônica e qualidade de água em cultivo de camarão em sistema convencional e com bioflocos: interfaces da pesquisa e ensino para aquicultura sustentável

Abstract

The present work aims to characterize and evaluate the phytoplankton community and water quality in cultivation of conventional marine shrimp and with biofloc, and to promote an educational action to form a critical socio-environmental vision of sustainable aquaculture. The study was carried out in a farm of marine shrimp cultivation of the species Litopenaeus vannamei (BOONE, 1931) and in Lagoa de Guaraíras, an environment for capturing water and receiving effluents from cultivation, located in the municipality of Nísia Floresta, on the southern coast of the state Rio Grande do Norte, northeastern Brazil, from April to July 2018. Physico-chemical parameters of the water and phytoplankton community were analyzed during the final growth phase until shrimp harvesting. An analysis of the students' perception about aspects of sustainable aquaculture and an interactive exhibition was carried out during a school science fair on the theme Life in the water, with elementary school students in a public school in the rural area of the municipality of Nísia Floresta / RN. Considering the high values of NT and Chl-a and the dominance of cyanobacteria in the Guaraíras lagoon, the water quality of this environment tended to eutrophicate. Differently from what was expected, the results reveal the decrease in the productivity of the nurseries and the quality of the water in the BFT system, due to weaknesses in the management, especially of the OD and SS parameters. For a BFT system to be truly sustainable, it is essential to strictly follow technical management principles. The richness and dominance of phytoplankton species in the studied environments were represented by the group of cyanobacteria in all environments (> 90% of the total biomass). Regarding the cultivation modes, the conventional system showed greater species richness and lower phytoplankton density, the reverse was observed in the BFT system. The relative contribution of cyanobacteria was more representative in conventional nurseries and the greatest richness was identified in natural environments. Potentially toxic and off-flavor producing cyanobacteria such as circular Anabaenopisis, Aphanizomenon gracile, Aphanocapsa delicatissima, Cylindrospermopsis raciborskii, Oscillatoria sp., Planktothrix sp., Pseudanabaena sp. and Snowella sp., emphasizing the importance of these microorganisms as bioindicators of water quality in cultivation and in the natural environment. The result of the questionnaire showed that 79% of the students had not heard about sustainability. Regarding aquaculture, 73% of students were unaware of what they were referring to and 79% reported not knowing what shrimp farming was. The interactive exhibition proved to be a potential tool to foster interest and discussion on socio-scientific aspects of curricular content, contributing to the development of students' critical thinking and more meaningful learning. In this way, the school exercises its role in building the relationship between the environment and citizenship, strengthening the awareness that the environment is a common public heritage and, its defense, a political right of all citizens.