Non-native species

My group's work on non native species has developed because of local issues with locally introduced non natives:

In 2006 the non native slipper limpet Crepidula fornicata was accidentally introduced into the Menai Strait, the body of water separating north Wales from the island of Anglesey.  The Menai Strait supports the UK's largest mussel fishery, hence the arrival of Crepidula was a real cause for concern. Fortunately prompt action by the Countryside Council for Wales and the Bangor Mussel Producers Association, and probably some good fortune, meant this potentially invasive species did not establish but this temporary arrival prompted Katrin Bohn's Phd investigating the factors limiting the northward spread of Crepidula (Bohn et al 2012 PDF; Bohn et al 2013a PDF;Bohn et al 2013b PDF)

In 2008 School of Ocean Sciences Masters student Kate Griffith discovered the first GB record of the invasive colonial ascidian Didemnum vexillum in Holyhead marina on the north coast of Anglesey (Griffith et al 2012).  This prompted our work on marinas as hotspots of non native colonisation within the ALIENS project, the ecology of Didemnum vexillum and practical and policy issues of biosecurity.                                                 

Didemnum vexillum

Didemnum vexillum is a colonial ascidian well known as a problematic invasive species worldwide.The arrival of D. vexillum in North Wales and the subsequent threat to the UK’s most important mussel fishery in the nearby Menai Strait instigated eradication procedures by the Country Side Council for Wales (now Natural Resources Wales-NRW).  At the same time we have worked closely with NRW to conduct both field and laboratory experiments to better understand the ecology of this invasive ascidian as well as to work on more practical issues of biosecurity.

Eradication and biosecurity

Surveys throughout Wales have confirmed that to date (February 2014)  D. Vexillum is confined to the marina in Holyhead and has not dispersed to surrounding habitats. Two eradication attempts over the period 2009-2012, described in our paper in Marine Policy (Sambrook et al In press), have thus far failed to eliminate D vexillum from the marina although they have no doubt limited the potential for wider colonisation. The sequence of events at Holyhead, where a large investment of time and resource has been targeted at a very localised colonisation by an important non-native, does emphasis the difficulty of managing marine non-natives once introduced.  Focus on biosecurity is clearly paramount and we have been working on two projects, one to trial an in water quarantine facility and the other to determine the most effective means to establish an early warning system for coastal non natives.

Comparison of the environmental tolerances of native and non-native colonial ascidians

 As part of the GAME project we examined the ecological tolerance of D. vexillum in contrast to a similar, locally distributed colonial ascidian. Msc student Federike Gröner exposed both D. vexillum and the cosmopolitan colonial ascidian Diplosoma listerianum to chronic and episodic hyposalinity stress (Groner et al 2011). D. vexillum exhibited lower mortality rates and greater growth under osmotic stress than D. listerianum, suggesting a competitive advantage under future scenarios of climate change.  Taking a wider view, our work contributed to a global comparison of environmental tolerance in non native marine invertebrates which indicated that stress tolerance could be a general property of succesful invaders (Lenz et al 1011).