Pacific Oyster - Magallana gigas

The spread of Magallana gigas demonstrates firsthand the effects of climate change on species distribution. Recently held beliefs about the range of Pacific Oysters have already been proven outdated, as warming waters have allowed the species to spread further north (Cook et al, 2014). 
Pacific Oysters are up to 18cm wide with classic scalloped edge shells (Hughes, 2008), ranging in colours and shapes depending on the conditions in which they grow (Smithsonian Environmental Research Centre, 2024). An example of a Pacific Oyster reef is shown in fig. 1 (Nehls and Büttger, 2007). 

Native Range and Distribution:
The native range of the Pacific Oyster is known to stretch the West Pacific Coast, including Russia, Korea and China. It’s native range is theorised to stretch as far as Indonesia and Pakistan; however, this is unconfirmed due to confusion with other very similar species (Smithsonian Environmental Research Centre, 2024). 
In the UK, as with many countries, the species was introduced to be farmed in the 1960s (NNSS, 2012). Multiple wild populations have also managed to establish, having escaped from farmed sites, the first of which was recorded in 1965 (NNSS, 2012). 
It was believed up until the mid-2010s that the waters of Scotland were mostly too cold for Magallana gigas, however that assumption has been continuously proven wrong in the subsequent years. As shown in fig. 2, individuals can be found along the length of the West Coast, with the most northerly individual identified at 58.9o latitude (NBN Atlas, 2024). The species is less common along the East Coast, although two sighting were reported near Edinburgh in 2020 (NBN Atlas, 2024). 

Risks: 
The larval stage of the species is planktonic, meaning they can be transported by currents potentially thousands of kilometres (NNSS, 2012). As such, it is highly possible for the species to establish nearby to where they have been introduced. 
Although detrimental to native species, Pacific oysters can make for a profitable farmable species. They are highly adaptable, and resistant to disease, making them reliable stock for farming (Smithsonian Environmental Research Centre, 2024). 
Of course, being so adaptable, this means they tend to spread wherever they are introduced. They often grow in very dense groups, changing the characteristics of the environment around them (NNSS, 2012). As such, they may outcompete native species, destroy their habitat, or hybridise, and subsequently affect the industries that rely on native species. Additionally, the pacific oyster can act as a vector for many pathogens and parasites, which often do not affect itself, but can be devastating to less resistant species (Smithsonian Environmental Research Centre, 2024).

Control:
Once the Pacific Oyster is established in an environment, to the extent of forming reefs as in fig. 1, it is extremely costly to make even a small dent in the population. The more successful tactic is to remove individual oysters to prevent establishment (Hansen, Dolmer and Vismann, 2023). Promising results have been observed for the method of crushing individual oysters, while larger scale techniques are less successful. For example, the dredging of oyster reefs causes significant damage to the wider environment (Hansen, Dolmer and Vismann, 2023).
The current population in Scotland is perhaps still small and non-established enough to be tackled by smaller scale control methods. It is therefore crucial that management is undertaken now, to prevent the species establishing in the country.