An Unwelcome Antarctic Visitor

Despite our increasing knowledge of the risks of introducing alien species into the Irish environment, the numbers of records of priority invasive species, new to Ireland has increased steeply over the past ten years. 

Graph of Invasive Alien Species Number in Ireland from 1800 to 2010 (data source, see reference 1)

Over half of these priority invasives are plants, but there are increasing number of alien marine animals being recorded. Few of these have come as far as the Orange Tipped Sea Squirt, Corella eumyota, which is native to the cooler waters of the Southern Hemisphere. Here, it has a circumpolar distribution within the temperate and sub-polar regions (Chile, Antarctic Peninsula, South Africa, Australia and New Zealand) (2). It was first recorded off the coast of France in 2002, and has been since recorded in Spain in 2003 and England in 2004 (3, 4). C. eumyota was first recorded in Ireland in 2005 and 2006 (5), and while it is not yet considered as a potential invasive here, this may soon change.
 

Orange Tipped Sea Squirt, Corella eumyota

C. eumyota is a solitray ascidian that attaches itself flat to a substrate. Adults range in size from 2 – 4 cm, but larger individuals are common (2). Colouration is variable, but an orange tinge is often common, lending it its common name. Shape is variable, depending on the shape of the substrate, but given a flat substrate, a oval form is the most common. The main risk posed by C. eumyota is that of biofouling, clogging up pontoons, nets and cages in harbours (2). This also poses a risk to mussels and oyster farming, as C. eumyota has been found associated with these and other bivalves in Spain (2,5). Large aggregates on commercial mussel beds would reduce their productivity dramatically (2). C. eumyota also threatens native ascidians through competition, where clumps of them growing together can reduce water flow (2).

References:

1. http://apps.biodiversityireland.ie/InvasivesBrowser/
2. Nagar et al., 2010. Aquatic Invasions 5 pp. 169-173
3. Arenas et al., 2006. Journal of the Marine Biological Association of the United Kingdom 86 pp. 1329-1337
4. Varela et al., 2008. JMBA2 – Biodiversity Records 1: e59
5. Minchin, 2007. Aquatic Invasions 2 pp. 63-70