Cultivation of Gracilaria (Rhodophyta) in shrimp pond effluents in Brazil E Marinho-Soriano, C Morales & W S C Moreira Departamento de Oceanografia e Limnologia, UFRN ± Laborato Ârio de Macroalgas, Praia de Ma Äe Luiza, Brazil Correspondence: E Marinho-Soriano, Departamento de Oceanografia e Limnologia, UFRN ± Laborato Ârio de Macroalgas, Via Costeira, Praia de Ma Äe Luiza, s/n, Natal RN 59014-100, Brazil. E-mail: lmacroalgas@dol.ufrn.br Abstract Shrimp aquaculture produces a large amount of waste, including nitrogen and phosphorus. To in- vestigate 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 5months. The biomass varied significantly (P < 0.01), reaching a maximum of 2540gm 2 and a minimum of 380gm 2 . The mean was 1418 + 708gm 2 . The higher biomass values oc- curred during the first 15 days and sometimes exceeded the initial inoculum by 190%. According to the results, production of 23.93 tha 1 year 1 (dry weight) can be expected. anova showed signifi- cant 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 NH 4 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 rela- tive success, it is necessary to perform some adjust- ments regarding the utilized cultivation technique. Keywords: Gracilaria, biomass, growth rate, effluents Introduction Intensive aquaculture has contributed to environ- ment degradation, with visible effects such as increases in particulate organic matter and chem- ical changes such as dissolved oxygen reduction and increased nitrogen and phosphorus concentrations in water (Beveridge 1996). In Brazil, shrimp culture has expanded considerably in the last few years, mainly in the north-east region, which accounts for 97% of total production. In 1999,15000 ton of shrimp were produced from 5000ha of ponds, with predictions of 105000 ton from 35000ha of cultivated area in 2003 (Ca Ãmara 2000). The main species of marine shrimp cultivated commercially in Brazil is the white shrimp, Lithopenaeus vannamei, from the Pacific American coast. In general, shrimp culture produces a large amount of waste, including dissolved nitrogen and phosphorus, that is released to the aquatic environ- ment without treatment. To explore the use of these elements as sources of nutrients, and at the same time to reduce discharges to the environment, sea- weed cultivation in shrimp pond effluents appears to be a viable approach. Indeed, seaweeds have been identified as marine plants capable of treating animal culture effluents efficiently (Qian, Wu, Wu & Xie 1996; Troell, Ronnback, Halling, Kautsky & Buschmann 1999; Nelson, Gleen, Conn, Moore, Walsh & Akutagawa 2001; Jones, Dennison, & Preston 2001). Polyculture of several species of animals and sea- weeds has been used traditionally in aquaculture. Such systems are based on the concept that excre- tions of one organism provide the nutrients for an- other (Buschmann, Troell, Kautsky & Kautsky 1996). Previous studies have showed enhanced growth of seaweed and shrimp in coculture (Chiang 1981; Shan & Wang 1985; Wei 1990). In combined cultures, productivity depends on the Aquaculture Research, 2002, 33, 1081±1086 ß 2002 Blackwell Science Ltd 1081