Production of Ulva Sp. in Multitrophic Aquaculture in Earth Ponds

The cultivation of macroalgae in earth ponds could provide an optimal control on both quantity and quality of biomass. In previous studies the genus Ulva has proved to be an ideal candidate for growing in fish ponds since it withstands their considerable environmental fluctuations. This study assessed the biomass production and the SGR (specific growth rate) of green algae Ulva sp. cultivated in earth ponds facing the Ria Formosa lagoon (Southern Portugal). The growth and production performance were tested among: a) two different multitrophic systems (IMTA (fish +oyster + Ulva) and ‘Fish + Ulva’); b) four different initial densities (15 ,30, 50 e 60 g/m2); c) five production and harvest cycles (6, 7, 8, 9 e 15 days). The Specific Growth Rate (SGR) of Ulva sp. was found to be significantly different between the two multitrophic systems (p <0.05) and higher in the ‘Fish + Ulva’ system (19.3 ± 0.08% day-1) than in the IMTA system (16.7 ± 0.8% day-1). Also, there were significant differences between different densities and varied cultivating periods. Growth of Ulva sp. was dependent on both densities and time periods. The densities of 30g/m2 revealed to be the best among the four tested densities (23 ± 3.9 % day−1) whereas the optimal cultivating period was between seven and nine days (≈21 % day−1). The experiments on the production cycle indicated an optimal period of cultivation of about 8 days.