6.0 INVASIVE NON-NATIVE SPECIES
6.0 INVASIVE NON-NATIVE SPECIES
6.1 Species such as Common cordgrass (Spartina anglica) are widespread throughout much of the UK, whilst others such as the Mediterranean mussel (Mytilus galloprovincialis) and Orange Sheath Tunicate (Botrylloides violaceus) are confined to regional areas. Fourteen non-native species are found in Scottish waters19.
6.2 Non-native species become invasive where they become established and proliferate, and spread in ways that damage native biological diversity, including through habitat and food web alteration, out-competing native species, and hybridisation20. At present five species in Scottish waters are classified as invasive (Figure 6). These are Common cordgrass (Spartina anglica), Wire weed (Sargassum muticum), Darwin's barnacle (Elminius modestus), Stalked Sea Squirt (Styela clava), and Carpet Sea Squirt (Didemnum vexillum). They are known to spread readily and, once established, eradication is very difficult.
6.3 Non-native species can be introduced via a number of vectors, primarily shipping and aquaculture. It is estimated that 50% of non-native species in UK waters have been introduced by shipping21. Non-native species may be transported in ship ballast water or as fouling on hulls, anchors and chains.
6.4 Requirements to manage ballast water have been introduced by the International Maritime Organization. The International Convention for the Control and Management of Ships' Ballast Water and Sediments was adopted in 2004 but is not yet in force22. It sets out to control and regulate ballast water exchange. It stipulates distances from the nearest land and appropriate water depths in which ballast water can be exchanged, as well as setting standards for its quality. Marine Scotland Science and the Maritime and Coastguard Agency are working together to review ballast water treatment and management methods23.
6.5 Anti-fouling paints are used on vessel hulls to prevent the attachment of marine organisms, thereby reducing the likelihood of organisms being transported in this way. There are concerns about the environmental effects of biocides used in anti-fouling paints, and the International Convention on the Control of Harmful Anti-fouling Systems on Ships prevents the use of certain biocides, specifically tributyltin. Copper biocides have since become the most common biocide used in anti-fouling systems24.
Figure 6. Aquatic non-native species classed as invasive in British waters
6.6 Scotland's domestic ferry network does not include international connections and therefore would be unlikely to act as a vector for the introduction of non-native species into Scottish waters. However, where non-native and invasive species have become established in Scottish waters, the network could act as a vector for their distribution.
6.7 The key issue arising from the proposals in the Draft Ferries Plan is the increase in the number of vessel movements on existing routes. Additional vessel traffic on routes is expected to increase the risk of non-native and potentially invasive species being spread, particularly as they are introduced and become established in Scottish waters. The introduction of a new route could also increase the risk of invasive species being distributed to other parts of Scottish waters.
6.8 Increasing the likelihood of non-native and invasive species being spread could have significant adverse effects on biodiversity, particularly due to competition with native species and as a result of broader habitat changes.
6.9 Prevention of such effects will depend on the effective application of the following measures:
- use of anti-foulant paints on hulls
- implementation of controls such as the IMO convention on ballast water
6.10 The Scottish Government will explore, with ferry operators and others, the management of this issue and whether information should be collected. An update will be provided in the final Ferries Plan.