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