Removal of nitrogenous wastes excreted by lobsters in a closed culture systems by two species of seaweeds, Gracilaria corticata and G.verrucosa was studied. Both species removed ammonia-N more readily than nitrites and nitrates. Among the two species. G.verrucosa was more efficient in uptake of ammonia-N (100%) compared to G.corticata (72.3%). The experiment shows that the seaweeds Gracilaria sp. can be used in maintaining water quality in closed culture systems by ready uptake of nitrogenous wastes excreted by the cultured organisms. The advantages of water reuse systems incorporating biological agents such as seaweeds for water management in closed culture system is outlined. The potential of developing doubly productive farming system by integrating seaweeds with other marine organisms is discussed.