Cultivation of Gracilaria (Rhodophyta) in shrimp pond effluents in Brazil

Shrimp aquaculture produces a large amount of waste, including nitrogen and phosphorus. To investigate the utilization of those elements as sources of nutrients for the growth of the red seaweed, Gracilaria sp. J. Agardh, an experiment in shrimp pond effluents was carried out over a period of 5 months. The biomass varied significantly (P < 0.01), reaching a maximum of 2540 g m^?2 and a minimum of 380 g m^?2. The mean was 1418 ± 708 g m^?2. The higher biomass values occurred during the first 15 days and sometimes exceeded the initial inoculum by 190%. According to the results, production of 23.93 t ha^?1 year^?1 (dry weight) can be expected. anova showed significant differences in RGR (relative growth rate) values (P < 0.05). RGR varied from 8.8% per day to 1.8% per day. The fluctuation of nutrients was mainly influenced by pond fertilization frequency, with NH₄ being the most abundant nutrient. Correlations between RGR and environmental parameters during the study period were not significant (P > 0.05). We conclude that Gracilaria sp. can be cultivated in shrimp ponds effluents. However, despite this relative success, it is necessary to perform some adjustments regarding the utilized cultivation technique.