Effects of shrimp cage farming on sediment nutrients in a subtropical estuary

The objective of this study was to evaluate the effects of shrimp (Litopennaeus vannamei) cage farming on sediment nutrients concentration. The farm were located in a subtropical estuary (Guaratuba Bay) in the south of Brazil and held 300 cages (size: 3.6m x 3.6m x 2m) made of PVC distributed over an area of approximately 4200m². Shrimps were fed with two types of commercial feeds, one developed specifically for shrimp and other for fish. Five sampling points were defined, one was located at the center of the farm area, one was set 1000m away from the farm, in an area with similar hydrodynamics conditions, and the others were located 200m away from the culture in west, northeast and southwest directions. During one year, monthly sediment sampling was performed at each station. Carbon (C), phosphorus (P), calcium (Ca²+), and potassium (K+) concentrations were determined. The results consistently indicate that in the studied shrimp farm the nutrients concentration increased significantly below the cultivation cages. We also obtained an indication that under the studied conditions the raise in the levels of nutrients can reach distances in the range of 200m.