Renewable energy is a growing industry whose viability is increasing as the unsustainability and environmental pressures of conventional energy generation become more apparent. In the UK a large proportion of the future renewable energy production is planned to be generated in the marine environment from offshore wind, wave and tidal stream energy farms. At present there are a number of offshore wind farms already operational and some experimental wave and tidal stream devices are being tested; currently over 90 marine energy farms are planned or already installed. Each farm will contain an array of energy extraction devices (wind / tidal turbines or wave energy converters) amounting to 400 devices at some large sites. This represents a huge amount of offshore and coastal development and the installation of a large amount of artificial structure, not only of the device arrays but also from the installation of support technologies (e.g. cables, foundations and substations) and the expansion of harbours in order to service this industry.
There are a number of potential environmental impacts associated with the marine renewable energy industry. Some of these include: collision hazards of energy devices causing fatality or displacement to marine animals, noise from operation and installation interfering with the behaviour of acoustically sensitive species, and an increase in biodiversity to the local area as a result of the exclusion of destructive fishing activities. One negative impact that has received less attention from researchers and regulators is the potential for the marine renewable energy industry to facilitate the introduction and spread of non-native species.
Non-native species are considered to be one of the greatest threats to marine biodiversity and they can cause severe ecological and economic damage if they become invasive. For example, the invasive carpet sea squirt, Didemnum vexillum (Figure 1), overgrows organisms and has been shown to smother fish spawning grounds and reduce production in shellfish aquaculture. Any activity which may promote the invasion of this and similar species needs be investigated and potentially mitigated against. However, while there is legislation in place (e.g. Wildlife And Natural Environment (Scotland) Act 2011), and national strategies that attempt to reduce the introduction and impact of non-native species, the issue is not considered one of the major potential impacts of the marine renewable industry and therefore very little research has been done
Our scientific knowledge of invasion pathways and the known association of hard substratum nonnative species with artificial structure indicates a number of potential ways the marine renewable industry may facilitate the introduction and spread of non-native species.
Increased vessel activity during the installation and maintenance phases of development could cause non-native species introductions. Vessels are well known vectors of non-native species through hull fouling and ballast water exchange. Some of the highly specialised vessels used in the installation will be well travelled and therefore have a greater potential to bring in exotic organisms. If wettowed, the devices themselves may also act as vectors of non-native species introduction through hull fouling. Floating wave devices or floating wind and tidal turbines may be towed from construction or maintenance locations where they have been left quayside for sufficient time for hard substratum communities to form.
Marine renewable devices and support technologies provide hard substratum space for fouling nonnative species to colonise (Figure 2). Non-native species are often found in high abundance on submerged artificial structures. These novel habitats are widely thought to convey a competitive advantage to non-native species over indigenous species. In the case of soft sediment areas, where many energy farms are planned to be developed, installation of artificial structure will provide habitat for fouling non-native species in areas they are currently unable to settle. Provided they are capable of establishing populations in these exposed high energy environments, offshore artificial structures could aid secondary dispersal of non-native species. Populations of non-native species living on devices could source propagules to nearby natural habitat and networks of devices could link otherwise unconnected hard substratum habitats by providing a dispersal corridor for non-native species. The installation of a large number of renewable devices around the UK will also allow non-native species tolerant of offshore environments to expand their population size considerably, increasing propagule supply and strengthening their competitive advantage over native species. This will amplify the impacts of these non-natives on native biodiversity and the local economy.
In addition many of the areas with planned energy farms are located in parts of the UK where there is relatively low vector activity and a small number of non-native species, for example, northern Scotland. This therefore increases the likelihood that non-native species new to an area will be introduced by activities of the renewable industry and if they become established it increases the severity of the ecological and economic damage.
Surveys of biofouling communities growing on offshore wind turbines in the southern North Sea and navigation buoys in Scottish waters have been carried out to assess the presence and abundance of non-native species. A number of non-native species were found to be thriving on these offshore structures. Species with particularly high abundances include the invasive amphipod, Caprella mutica (Figure 3) and the marine midge, Telmatogeton japonicus. This confirms that some non-native species are capable of recruiting to hard substrata in exposed offshore environments and that they are likely to establish populations on marine renewable devices.
Researchers at the Environmental Research Institute and the Scottish Association for Marine Science are currently investigating ways in which to monitor and reduce the impact the renewable industry will have on facilitating the invasion of non-native species. So far this work has included the completion of a baseline survey for the presence and distribution of fouling non-native species within the Pentland Firth and Orkney marine energy park and the assessment of the detection abilities of different monitoring methods. Future work will investigate the potential introduction pathway of wet towed floating devices and also will assess how device material, habitat orientation and season affect non-native species composition. The results of this research will inform best practices for future monitoring programmes and suggest control measures which aim to reduce the introduction and spread of non-native species.
It is necessary to mention that although some non-natives are known to be damaging to the marine environment, the impacts of many of them (including those known to colonise renewable devices) are still unknown. Establishment of hard substratum fouling species, whether indigenous or not, on marine renewable energy devices may in fact provide benefits, such as increased productivity and additional food sources for fish species. With the potential for increased population size and increased spread of non-natives as a result of the marine renewable industry, regulators and statutory consultants need to fully understand both the positive and negative environmental impacts in order to give the best advice for focused management procedures.