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Several environmental factors may interfere in the behavior of mole crab (Emerita brasiliensis Schmitt, 1935), such as the discharge of urban pollutants on the shore, which can be toxic. During a study of the impact of human activities on a beach in Southern Brazil, opportunistically it was tested if burying behavior of the mole crab were affected after an accident causing the discharge of urban effluents. When comparing the period before (two days) and after (one day) the accident, there was a substantial increase in the concentration of ammonia in the seawater, but pH, water temperature, salinity, and the microclimatic conditions remained stable. During the increased ammonia phase, we captured individuals of smaller size, but the latency in an burying test conducted in an aquarium, immediately after the capture, remained unaltered. The discharge of organic pollutants seems affected the surf zone, where small individuals were more abundant, supposedly males and juveniles but not adult females. The maintenance of burying latency by males and juveniles seems to suggest a greater physiological resistance to a short term contamination by ammonia.