Bacteria in shrimp pond sediments: their role in mineralizing nutrients and some suggested sampling strategies

Strategies for sampling sediment bacteria were examined in intensive shrimp , Penaeus monodon (Fabricius), ponds in tropical Australia. Stratified samp ling of bacteria at the end of the production season showed that the pond c entre, containing flocculated sludge, had significantly higher bacterial co unts (15.5 X 10(9) g(-1) dw) than the pond periphery (8.1 X 10(9) g(-1) dw) , where the action of aerators had swept the pond floor. The variation in b acterial counts between these two zones within a pond was higher than that between sites within each zone or between ponds. Therefore, sampling effort should be focused within these zones: for example, sampling two ponds at s ix locations within each of the two zones resulted in a coefficient of vari ation of approximate to 5%. Bacterial numbers in the sediment were highly c orrelated with sediment grain size, probably because eroded soil particles and organic waste both accumulated in the centre of the pond. Despite high inputs of organic matter added to the ponds, principally as pelleted feeds, the mean bacterial numbers and nutrient concentrations (i.e. organic carbo n, nitrogen and phosphorus) in the sediment were similar to those found in mangrove sediments. This suggests that bacteria are rapidly remineralizing particulates into soluble compounds. Bacterial numbers were highly correlat ed with organic carbon and total kjeldahl nitrogen in the sediment, suggest ing that these were limiting factors to bacterial growth.