Several commercially operated land-based abalone farms in South Africa employ integrated aquaculture (IMTA) technology to grow the local abalone, Haliotis midae, together with the seaweed Ulva lacinulata. The studied farm routinely operates at 50% water recirculation, where ammonia removal by Ulva enables continuous recirculation. Ulva is also harvested and used as supplementary feed. The farm is divided into platforms, each containing four independent modular clusters, which consist of a single paddle raceway containing ca.1 ton Ulva (volume 300,000l) linked with ca. 10, 000 -15,000 kg of abalone within 42 tanks (volume of each tank 8,000l).
In this study a series of experiments examined system water quality parameters at standard farm operation (50% recirculation), increased recirculation (75%), and the effects of short-term 100% recirculation. The latter designed to test the potential to prevent Harmful Algal Bloom (HABs) intake during external environmental events. At 50% recirculation, TAN removal across the Ulva biofilters ranged from 65-85% and pH ranged from 7.8 (daytime) to 7.4 (night). Data suggested a strong positive linear relationship between TAN removal and TAN load to the biofilter, with %TAN removal higher during the day. No significant differences in temperature, pH, TAN or FAN were observed between the 50% and 75% recirculation clusters. At 100% recirculation, temperature was consistently 1°C higher, and pH was around 0.5 unit higher. TAN and FAN increased rapidly at 100% recirculation, with TAN values ranging from 0.3-0.8 mg l-1 compared with values less than 0.1mg l-1 at 50%. Oxygen levels were not considered problematic at any stage in the experiments and increase at 100% recirculation. It is clear from the data that this system could feasibly run for extended periods at 75% recirculation, with relatively little effect on water quality compared with 50% recirculation.