In Australia, it has been predicted that M. gigas may displace Saccostrea glomerata (Gould, 1850), the native Sydney rock oyster, in both mid- and low intertidal zones (Krassoi et al. 2008) where it is also known to alter native species assemblages (Wilkie et al. 2012).

In the Northern Hemisphere, M. gigas continues to spread toward the poles, facilitated by the warming of sea surface waters (Rinde et al. 2016; Thomas et al. 2016; Townhill et al. 2017).

The Pacific oyster, Magallana gigas, has a white and purple elongated shell, with an average shell length of 15 – 20 cm. It is among the largest of all oyster species globally, with extreme examples reaching up to 450 mm in length (Huber 2010: 180). M. gigas, as with many other ostreid species, possess shells that are morphologically highly variable, often as a function of their substrate (Poppe and Goto 2000). This variability can make species identification challenging (Dridi et al. 2008).

M. gigas is an important aquaculture species throughout the world. Native to Japan, it was introduced intentionally to, North America, Europe, New Zealand, and Australia to establish oyster aquaculture industries. M. gigas was intentionally introduced to southern Tasmania, Western Australia, and Victoria in the mid-1900s, and was found in New South Wales in the 1960s. It is well established in Tasmania, South Australia and parts of NSW. It did not establish in Western Australia and is not common in Victoria.