Ulva australis

Lore & Background

Ulva australis was first described by Swedish botanist Johan Erhard Areschoug from samples collected in Southern Australia. Its general characteristics include a smooth surface, distromatic blades, lobed fronds, and a thallus color ranging from dark green to light grass green. It can be free floating or attached by a single holdfast, and its cells are irregularly arranged with rounded edges and shapes such as rectilinear, square, and pentagonal. Ulva rigida has sometimes been confused with this species.

The origin of Ulva australis has been a subject of study. DNA analysis showed that Ulva pertusa from Japan has almost identical DNA sequences to Ulva australis, with very small sequence divergence. The hypothesis that U. australis is an independent species was rejected because its natural habitat along the shoreline is suppressed by U. pertusa populations. It is concluded that Ulva australis is a species introduced to Australia that originated in Japan, though researchers hypothesize it was not directly introduced from Japan but from non-indigenous populations elsewhere in northeastern Asia.

Factors affecting its growth were tested experimentally: higher carbon dioxide (750 ppm) and nutrient levels (PES medium) increased growth and photosynthesis. Irradiance effects differed by life stage: germlings favored higher irradiance (100 μmol photons m−2 s−1), while other stages preferred lower irradiance (50 μmol photons m−2 s−1).

Reader's Guide

Ulva australis has been researched for several scientific properties. In environmental protection, it can absorb metals from polluted seawater, with a stronger absorption capacity for zinc compared to other metals. This allows it to be used as a biological tool to both monitor and remove metal pollution, though its absorption capacity has an upper limit and the thallus can be damaged by excessive pollution, requiring regular replacement.

In biotechnology and medicine, Ulva australis is rich in minerals, vitamins, and noncaloric dietary fiber. Its decoction has been used to treat hyperlipidemia, sunstroke, and urinary diseases. Sulfated polysaccharides from the alga show anti-hyperlipidemic, antioxidant, antiviral, immunomodulatory, and anti-radiation activities. Organic extracts exhibit radical scavenging activity and metal chelating activity, and the alga shows inhibitory effects on pathogenic factors of Alzheimer's disease, hyperpigmentation, Type-2 diabetes mellitus, and skin sagging.

In abalone aquaculture, replacing part or all of the traditional feed Undaria pinnatifida with Ulva australis improved abalone survival rates and reduced costs. The best results were achieved with a mixture of 60% Ulva australis and 40% Undaria pinnatifida, but even complete replacement caused no negative effects. However, Ulva australis has also caused problems: it contributed to green tides in Jeju Island and coastal areas of South Korea. Control measures include low salinity, low pH, temperatures above 30 °C, and oxidants such as hydrogen peroxide and sodium percarbonate, which cause rapid death of the alga.

Did You Know?

• It has almost identical DNA sequences to Ulva pertusa from Japan, leading to the conclusion it was introduced to Australia from northeastern Asia.
• The alga absorbs metals from polluted seawater, with a stronger capacity for zinc than for other metals.
• A mixture of 60% Ulva australis and 40% Undaria pinnatifida maximized abalone survival rate in feeding experiments.