Abstract
Aquaculture activities can affect water quality and phytoplankton composition. Our study aimed to estimate phytoplankton density and composition in relation to environmental factors impacted by aquaculture. We analyzed water quality and phytoplankton from 35 sites in a tropical lagoon, including inside aquaculture ponds, at wastewater discharge points, within 300 meters of these points, and farther out in the lagoon. Measurements were taken after aquaculture activities started in March and again in July. In both periods, total nitrogen (TN), total phosphorus (TP), chlorophyll-a (chl-a), and turbidity decreased from the aquaculture ponds to the farther lagoon areas. Principal component analysis showed that nutrients, turbidity, and chl-a were key factors in aquaculture ponds, while salinity, temperature, pH, dissolved oxygen (DO), and water depth influenced water quality outside the ponds. Phytoplankton density was higher in July than in March due to aquaculture characteristics. Redundancy analysis indicated that phytoplankton typical of inorganic, turbid, shallow lakes were present throughout, whereas marine phytoplankton characterized the open water area. Phytoplankton in aquaculture ponds was dominated by Oscillatoria spp., while Thalassiosira spp. dominated outside the ponds. We also identified indicator genera for two connected lagoons. Although constant water exchange prevented the identification of specific indicator phytoplankton groups for aquaculture activities, this revealed the impact of wastewater from aquaculture ponds on the natural environment in the lagoons.