Ulva australis

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).