Mark D. Cyrus1,2, John J. Bolton2, Joseph A. De Prisco2, Michael Geldart2, Marissa Brink-Hull2, Brett M. Macey2,3
1Centre for Sustainable Tropical Fisheries and Aquaculture, College of Science and Engineering, James Cook University 4811, Australia
2Department of Biological Sciences, University of Cape Town, Rondebosch 7701, South Africa
3Department of Forestry, Fisheries and the Environment, Cape Town 8001, South Africa
Correspondence: Mark D. Cyrus, mark.cyrus@jcu.edu.au
In South Africa, several commercially operated land-based abalone farms employ integrated aquaculture (IMTA) technology to grow the local abalone, Haliotis midae, together with the seaweed Ulva lacinulata. On the studied farm, ammonia removal by Ulva enables routine continuous 50% water 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).
A series of experiments examined system water quality parameters at standard farm operation (50% recirculation), increased recirculation (75% recirculation), and the effects of short-term 100% recirculation, the latter designed to test the potential to prevent Harmful Algal Bloom (HAB) intake during external environmental events. At 50% recirculation, TAN removal across the Ulva biofilters ranged from 65-85% and pH ranged from 8.1 (daytime) to 7.5 (night). Data show 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 1 unit lower. 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%. The commensurate rapid and considerable decrease in pH however meant that the FAN increase was not as high as it would be at ambient seawater pH. Oxygen levels were not considered problematic at any stage in the experiments. 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.