Survey of Wild Pacific Oyster Crassostrea gigas in Scotland

Global sea surface temperatures have accelerated in the last few decades (IPCC, 2007). Some of the most rapid increases have been seen in the NE Atlantic (IPCC, 2007), where increases of up to 1 oC have been recorded (Hawkins et al., 2003, Inall et al., 2009) and mean seawater surface temperatures have risen by 0.57 oC per decade since 1975 (Inall et al., 2009). Furthermore, an increase in magnitude and frequency of short-lived, high temperature events is predicted (Meehl & Tebaldi, 2004), which could cause significant changes in marine hard substrate communities (Sorte et al., 2010). Periodic increases of 2 oC have been observed off the west coast of Scotland (Inall et al., 2009). This warming seawater has been linked to the northwards spread of certain non-native species in the UK, such as the Pacific oyster Crassostrea gigas (Thunberg, 1793) (Maggs et al., 2010). A recent report suggests that it is highly likely that ‘wild’ populations of C. gigas will continue to expand northwards and become established on the west coast of Scotland by the 2020s (Cook et al., 2013). Until recently, it was thought that the northern most ‘wild’ populations of C. gigas in Great Britain were located in Lough Foyle, North coast of Northern Ireland (Kochmann et al., 2012). However, C. gigas was recently reported from the Firth of Forth on the east coast (Smith et al., 2014) and the Solway Firth (Clair McFarlan, Solway Firth Partnership, pers. comm.) and Loch Fyne (J. Khan-Marnie, SEPA, pers. comm.) in south-west Scotland. The presence of wild populations of the Pacific oyster Crasssostrea gigas was assessed in eleven regions in Scotland. An extensive, co-ordinated survey programme was undertaken between March and September 2014. Sixty locations were surveyed on the west and east coasts of Scotland using a standardised protocol and specific factors, previously associated with the presence of C. gigas, were recorded. Sites were chosen based on regions; (i) where ‘wild’ C. gigas had already been found , (ii) where C. gigas was commercially cultivated and (iii) where suitable habitat and environmental conditions (e.g., summer seawater temperatures and water retention rates) existed for spawning, thus increasing the probability of the region supporting ‘wild’ populations.