Agri Kultuur March/ Maart 2016 - Page 77

house gas emissions and thus their carbon footprints. Ulva supplementation In South Africa most abalone farmers use large quantities of fresh kelp as feed and then supplement this with on-farm cultivated Ulva species. Feeding trials have shown that using on-farm cultivated Ulva that was previously grown in marine animal effluent, whether fed fresh only or supplied as a feed supplement with compound feeds, greatly improves abalone growth. This is most likely due to the higher protein content of the cultivated Ulva attained by culturing the seaweed in a high ammonia environment. Research investigating the growth of African catfish (Clarias gariepinus), dusky kob (Argyrosomus japonicas) and sea urchins (Tripneustes gratilla) on diets of Ulva species showed similarly that protein enriched treatments outperformed the wild, non-enriched treatments and the traditional diets previously used. Ulva as a biofuel South Africa is the first African country to demonstrate the feasibility of large-scale seaweed production, the subsequent biotransformation to liquefied petroleum gas (LPG), and their economic viability and the additional economic benefit from farming activities. Biogas produced from bacterial digestion is primarily a mixture of methane (53%) and CO2 (47%) and is comparable to LPG (60 – 70% methane), but better than LPG with regards to major harmful emissions of CO2, hydrocarbons and nitrogen oxide (NOx). In 2013, the South African government began the implementation of 20 – 50% biofuel renewable energy, using sugar cane and sugar beet as bioethanol feedstocks. We have demonstrated that Ulva as a methane source is better than traditional biogas feedstocks and the seaweed’s potential as a bioethanol feedstock is now being investigated overseas. Their high calorific values, vitamins, minerals and antioxidants make seaweeds popular products in Asian supermarkets. Photo: Gavin W. Maneveldt Ulva as a plant-growth stimulant About 1000 t of concentrates made from seaweed and worth about US$5 million annually, is used worldwide as plant growth stimulants and hormones for agricultural crops. These plant-growth regulators contain active ingredients such as Abscisic Acid, Auxins, Brassinosteriods, Cytokinins, Ethylene and Gibberellins, all of which are important polyamines responsible for promoting plant growth. Most of these plant-growth regulators are currently extracted from brown seaweeds like the South African sea bamboo Ecklonia maxima. This kelp dominates the west coast and is currently being harvested (about 100 t dry weight) for the extraction of plant-growth stimulants. More recently research on the potential of U. armoricana as a growth stimulant in some African leafy vegetables is being investigated as well as the suitability of incorporating cultivated Ulva species into existing kelp liquid concentrates. Ulva as a biofilter Our research has demonstrated the technical and economic viability of using Ulva species as biofilters for removing excess ammonium (90% removal efficiency) and other inorganic nutrients on aquaculture farms. This potential can be extrapolated to other marine environments to impact positively on moderately eutrophic waters. In our test trials, even though U. armoricana had high Cd, Cu and Zn levels after a double-dosing (200 g m-2) of fertiliser, these levels were still lower than the South African permissible limits for cultivated lettuce. U sing Ulva to mitigate against ocean acidification Of the many negative effects associated with ocean acidification a decrease of carbonate, which reduces the calcium carbonate (CaCO3) saturation state and potentially leading to shell dissolution in marine molluscs (that include abalone), is particularly concern- Flow-through, paddle-wheel raceways are the preferred method for growing Ulva. Photo: Deborah V. Robertson-Andersson