Aquaculture Europe 2023

September 18 - 21, 2023


Add To Calendar 19/09/2023 11:30:0019/09/2023 11:45:00Europe/ViennaAquaculture Europe 2023IMTA IN ACTION: TWO DECADES OF GROWING THE GREEN SEAWEED ULVA IN INTEGRATED LAND-BASED SYSTEMS ON SOUTH AFRICAN ABALONE FARMSStolz 1The European Aquaculture Societywebmaster@aquaeas.orgfalseDD/MM/YYYYaaVZHLXMfzTRLzDrHmAi181982


John J. Bolton*1, Brett M. Macey1,2 , Mark D. Cyrus1,3, Marissa Brink-Hull1


1University of Cape Town, Rondebosch 7701, South Africa

2Department of Forestry, Fisheries and the Environment, Cape Town 8001, South Africa

3Centre for Sustainable Tropical Fisheries and Aquaculture, College of Science and Engineering, James Cook University 4811, Australia




 The first commercial system using abalone effluent to cultivate the green seaweed Ulva was built on an abalone farm in South Africa in 2002. Over 1000 tonnes fresh weight of Ulva was produced in South Africa in 2007, grown predominantly in abalone effluent, and the main reasons for this seaweed production was as additional feed for the abalone, as well as to provide bioremediation of the effluent  to enable partial water recirculation on a section of a single farm. Bolton et al. (2009) carried out a SWOT analysis of the use of these abalone/IMTA systems. After a further 15 years the aim of this contribution is to re-examine the findings of the analysis of Bolton et al. (2009) in the light of the subsequent development  of the abalone/Ulva IMTA commercial operations in South Africa.

Progress and strengths

The strengths previously documented are largely still applicable, and so we could say that the development of the South African abalone aquaculture industry, and the role of IMTA, has developed as predicted with no major changes.  The Ulva produced on abalone farms is not sold but is primarily utilised on-farm as feed addition. Thus, official government figures, the latest being 2718.10 tonnes in 2020, are an estimate. There are 5 farms (of the total of 14 commercial abalone farms in South Africa ) which operate  ca.  30m-long paddle raceways to cultivate Ulva . Four of these grow the Ulva in abalone effluent, and the other grows only in fertilised seawater. Thus production has increased by almost threefold in the last 15 years. Also in 2007 there was a newly  built section of a single farm operating on partial recirculation using Ulva , and since 2014 two entire new farms are operating on this principle. The success of these integrated operations is evidenced by the continuous fully commercial operation in various forms for more than 20 years. The integrated system warms the water for abalone cultivation resulting in increased growth rates, and there are demonstrated improvements in the microbiome and other aspects of system and animal health.

Problems and weaknesses

Apart from the COVID-19 pandemic, the major setback has been a large and unusual dinoflagellate bloom (HAB) in January 2017 resulting in losses of >250 tonnes of abalone at three farms. At least one  other farm successfully made use of the predicted potential of the IMTA system to switch to 100% recirculation. This can be done for at least 3 days without adverse effects on integrated farms . Lack of knowledge of the Ulva crop has been  largely  remedied, and most of the predicted weaknesses are well managed. 


These systems have indeed assisted with the continued expansion of  the local abalone industry , and integration is becoming widely acknowledged as a potential benefit both locally and internationally. Much work is being conducted on the benefits of Ulva as a component in formulated aquafeeds, as predicted. The stated benefits to sustainability of this system are becoming better recognised but are still far from being fully realised.


 Diseases and grazers have thus far proved amenable to successful management. The  predicted  two major threats  to IMTA expansion  still exist. The cost of using space to grow Ulva rather than profitable abalone was borne out by a farm which was designed as an IMTA system but was changed to a pure abalone cultivation shortly before construction. A main reason cited was potential for biosecurity risks with recirculation of water and/or seaweed through the system. Nevertheless, area under IMTA has considerably increased although some producers are still reluctant to integrate their operations due to these thus far unsubstantiated risks.


These South African abalone/Ulva integrated aquaculture systems are slowly becoming recognised as a leading example of IMTA in action. The benefits to the system with respect to biosecurity , both in water integration and seaweed as feed component, are increasingly being demonstrated. Nevertheless there is still the perception of recirculation as  a  disease transmission threat, which could slow further development.

 Aspects of these systems have been replicated in several other world regions, including in Europe and Australia. There are three main reasons for growing Ulva in these land-based systems:  1:  as a product (feed, feed component, biomaterial, human food etc.) ,  2:  to enable partial recirculation saving pumping costs,  3:  to bioremediate effluent for environmental benefits. In different regions/IMTA systems one or more of these benefits may dominate the reasons for integration. It seems very likely that the application of land-based , seaweed/invertebrate  integrated aquaculture will continue to be developed as a successful example of marine IMTA in South Africa and around the world.


 Bolton JJ, Robertson-Andersson DV, Shuuluka D & L. Kandjengo (2009). Growing Ulva (Chlorophyta) in integrated systems as a commercial crop for abalone feed in South Africa: a SWOT analysis. Journal of Applied Phycology 21: 575-583

This study received funding from the EU Horizon 2020 Research & Innovation Programme ASTRAL Project under Grant Agreement No. 863034