Abstract
The green macroalgal genus Codium (Chlorophyta, Codiales) is one of the most diverse genera in the world, comprising approximately 125 globally distributed species. Taxonomic studies on the Codium species found on the Western Australian coastline are mostly lacking. The genus displays a variety of morphologies, from globular to frond-like to erect and dichotomously branching. One subspecies, C. fragile subspecies fragile (Suringar) Hariot, is one of the most invasive seaweeds in the world, and is a major ecological and economic threat to the invaded habitat. It is a somewhat cryptic subspecies as it has a global distribution that overlaps morphologically similar native subspecies. This invasive alga was recently discovered in Princess Royal Harbour, Albany, Western Australia. Seventeen C. fragile ssp. fragile plants were collected from the Albany tug pen, and housed in a holding tank at 21° C. Two individual thalli were cultured at 20°C, 25°C and 28°C to determine their tolerance to increased water temperatures, and to gain insight into the subspecies potential spread in W.A. Culturing results indicate that at increased temperatures (> 25°C), the growth of Codium fragile ssp. fragile is strongly inhibited, indicating that its potential spread in W.A. may be temperature limited. To prepare a taxonomic account of the species occurring in W.A., specimens of Codium housed at the W.A. Herbarium (PERTH) were examined. Small portions of plants were removed and rehydrated in freshwater, and the utricles were excised and observed under a microscope to obtain anatomical measurements. On the basis of the PERTH collections, nineteen species of Codium occur on the coast of W.A. Thirteen of these have been documented previously, whilst five are, for the first time, described in detail based on W.A. specimens: C. arabicum Kützing, C. dwarkense Børgesen, C. fragile subspecies fragile (Suringar) Hariot, C. geppiorum O.C. Schmidt and C. platyclados R. Jones & Kraft. One species, from Nornalup Inlet on the south coast, appears to represent a new species, based on its morphology and analyses of its anatomical details. For all nineteen species, morphological and anatomical descriptions and illustrations are given, in addition to information on their local and worldwide distribution and habitat.