NUTRIENT REMOVAL AND GROWTH CAPACITIES OF GREEN MACROALGA Ulva flexuosa CULTIVATED IN DIFFERENT SEAWATER ENRICHMENT SYSTEMS INCLUDING BIOFLOCS

Biofiltration systems such as biofloc and macroalgae cultivation systems are the most innovative systems  in the removal of nitrates and phosphate s in from aquaculture effluents. The use of these systems has a high capacity to secure sus tainable aquaculture . The purpose of this study was to evaluate  removal  of nitrogenous compounds, phosphate and growth of  green macroalga Ulva flexuosa in the cultivation systems with or without biofloc .

In order to reach the aim  U. flexuosa individuals were cultivated at a total of 12 carboy  cultivation systems .  During the experiment,  three treatment groups were  conducted with 3 replicates :  in the first group,  U. flexuosa  was cultivated in seawater only (SW);  in the second group,  U. flexuosa  was cultivated  in seawater with PES (Provasoli's Enrichment Solution) at a concentration of 10 ml PES.l^-1 (SW + );  in the third group,  U. flexuosa  was cultivated  in  a biofloc  with shrimp  effluent  seawater obtained  from  shrimp, Litopenaeus vannamei , prod uction  unit and ;  in  the  fourth threatment group  was  only including  a  biofloc  seawater  (BFT-WS)  without Ulva .   The experiments were started at  the Ulva density of 2 g.l^-1 at the carboys.  At the beginning of the experiments, the  total ammonia nitrogen, nitrite, nitrate and phosphate concentrations of 0.0; 0.02; 0.51 and 0.0 mg.l ^-1 were found for the SW treatment, and 0.05; 0.04; 6.0 and 0.34 mg.l^-1 for the SW + treatment, and 0.02; 0.28; 28.5 and 1.25 in the BFT and BFT-WS treatment groups, respectively .  During the 20 days of the experimental period, constant aeration, artificial illumination and photoperiod of 12 hours  of light:dark cycles were applied .  Addition to biomass yield of Ulva, water quality parameters w ere measured periodically and  at the end of the experiments  the average  temperature, dissolved oxygen, salinity and PH measure s were  recorded as 19.8 °C, 8.4 mg.l^-1 , 28.4 ppt and 8.4,  respectively.

T he  highest biofiltration capacities of nutrients and higher biomass yields  of Ulva  were found in SW and SW+ treatment groups  compare to BFT and BFT-SW groups.  In the BFT treatment, Ulva showed a negative relative growth rate (TCR -0.73), probably due to the contamination  of the system with microalgae that probably caused a competition for nutrients and light availability  between Ulva and microalgae.  The  microalgae contamination  was  also  observed  in BFT-SW  treatment  group. Therefore, it was  concluded that the biofloc systems limite the performance of  U. flexuosa by limiting the light  and nutrients which are  necessary for  high Ulva growth and it was suggested that  further studies  should be conducted  to  design new system models where biofloc and Ulva flexuosa  cultivation works together for the high capacity nutrient removal of aquaculture effluents.