Offshore: potential effects

AuthorDirectorate-General for Environment (European Commission)
Guidance on Wind Energy Developments and EU Nature Legislation 93
Guidance on Wind Energy Developm ents and EU Nature Legislation
6.1 Introduction
This chapter reviews the main types of impacts that offshore wind energy developments could have on habitats
and species protected under the Habitats and Birds Directives. The scope of the two D irectives is clarified in
Chapter 2.2.1, while the concept of assessing significance is explained in Chapter 3.1.
The purpose of this chapter is to provide developers, NGOs, consultants and competent national authorities
with an overview of the potential impacts on different groups of EU-protected habitats and species. These
potential impacts should be considered when developing or reviewing an offshore wind energy plan or project.
However, as the identification of likely significant effects is always case specific, the real impact of a wind
energy development on protected species and habitats will be highly variable.
Effects from offshore wind energy developments may arise in one or m ore of the five main phases of wind
energy development:
pre-construction (e.g. meteorological investigations, exploratory studies into sediment stability, and seabed
construction (e.g. transport of material by vessels and construction of monopile110 foundations; turbines;
grid connection cables; fixed/floating turbines; etc. );
operation (including maintenance);
repowering (changing the number, type and/or configuration of turbines in an existing wind farm);
decommissioning (removing the wind farm or individual turbines).
When assessing the significance of effects, it is important to bear in mind that they may arise from the entire
project footprint (including any associated infrastructure, such as grid cables), and may even arise from the
onshore aspects of offshore projects (e.g. arrangements for landfall and onshore transmission).
The effects on habitats and species may be temporary or permanent. They may result from activities within or
outside the boundaries of a Natura 2000 site. For mobile species, the impacts m ay potentially affect individuals
well away from the associated Natura 2000 sites, such as marine m ammals or seabirds foraging at large
distances from the breeding colony. Significant ef fects may arise from the plan or project alone, and may occur
at different times during the project’s lifec ycle. Plans and projects acting in combination may produce
cumulative effects. These effects will be of growing importance, as offshore wind energy is projected to grow
to meet renewable energy targets.
In the next subchapters, the main types of impacts are described for the major receptor groups111. An overview
is given in Table 6-1. In some instances, an impact may be positive, e.g. the creation of a new habitat or reef
effects (see Box 6-1).
Box 6-1: The reef effect of offshore wind-farm foundations
The reef effect is one of the possible effects of offshore wind-farm foundations on marine biodiversity. It is particularly
significant in
marine areas without rocky soils such as large parts of the North Sea. Underwater constructions may function
as artificial reefs, and the foundations may be colonised by a range of organisms. Although there is evidence that wind
farm structures are associated with greater diversity of benthic organisms (Lindeboom et al.,
2011) and increased
densities of commercially significant fish (Reubens et al.,
2013), this may also alter the characteristics of local species
composition and biological structure (Petersen & Malm, 2006). This potentially positive effect for marine biodiversity
110 There are different types of wind turbine foundations. Most frequently, monopiles are used; these are quite simple
structures, made up of a thick steel cylinder that is anchored directly to the sea bed. Other foundation types are a.o.
jacket pin piles foundations with a lattice framework that feature three or four sea bed anchoring points or gravity
111 Key receptor groups such as seabirds, marine mammals and marine habitats which potentially experience an impact
of the offshore wind energy developments
94 Guidance on Wind Energy Developments and EU Nature Legislation
should be taken into account when considering options for decommissioning. Fowler et al. (2018) highlight the potential
negative effects, including to groups such as marine mammals, of full removal of structures from the marine environment
(as currently required in line with OSPAR Decision 98/3; Jørgensen, 2012). Partial removal of these
structures can have
the potential advantage of providing a continued
reef habitat. However, the potential biological communities that could
be established on the wind-farm structures should be carefully assessed in relation to the
conservation objectives of the
site, including their effects on protected species and habitats, not least through the potential introduction of invasive ali
species that could be established on newly built structures.
Table 6-1 Overview of potential types of impacts on major offshore receptor groups
Potential impacts of offshore wind energy developments
Marine habitat loss
Marine habitat disturbance and degradation
Smothering from suspended sediments falling out of suspension
Creation of new marine habitats
Changes to physical processes from the presence of new structures
Contaminant release or mobilisation of historic contaminants
Electromagnetic fields
Underwater noise disturbance
Reef effects
Habitat loss and degradation
Disturbance and displacement
Barrier effect
Indirect effects
Attraction (e.g. roosting opportunities)
Marine mammals
Habitat loss and degradation
Noise disturbance and displacement (pile-driving noise and
noise from
Acoustic impairment (injuries from underwater noise)
Communication masking
Collision with vessels
Barrier effect
Reduction of fishing pressure (no fishing zones)
Water quality changes (contaminants + marine waste)
Electromagnetic field effects on navigation
Indirect effects
Reef effect
Disturbance and displacement
Barrier effect
Loss/ shifting of flight corridors and roost sites
Indirect effects
Other species
Noise disturbance and displacement
Electromagnetic fields
Heat effects
Creation of new habitats
Water quality changes (contaminants + marine waste)
Indirect effects
Compared to onshore wind energy, there are clearly differences in the nature of some activities associated
with offshore wind energy development. These differences include the use of vessels to access sites and
certain impact mechanisms which are unique to the aquatic environment such as underwater noise. However,
the principles underpinning the mitigation measures for onshore wind also app ly to offshore wind. These
principles are outlined in the bullet points below.
The ‘mitigation hierarchy’ applies, wh ich means that measures to avoid negative effects in the first place
must be considered and implemented before measures to reduce negative effects. It is also good practice
to apply these measures at the source before considering m easures for the receptor.
Guidance on Wind Energy Developments and EU Nature Legislation 95
The best way to minimise negative effects on EU-protected habitats and species is to locate projects away
from vulnerable habitats and species (a practice known as ‘ macro-siting). This can best be achieved
through strategic planning at administrative, regional, national or even international level, in particular
through the maritime spatial plans drawn up under the Maritime Spatial Planning Directive 112.
Transboundary effects are very relevant in offshore wind energy, not only due to cumulative effects (e.g.
on bird migration) but also because many wind farms are located close to the borders of the European
Economic Zones (EEZ) of other Member States (or even cross-border projects in the future). According to
the ESPOO Convention and the Protocol on Strategi c Environmental Assessment (SEA Protocol, Kyiv
(Jendroska et al., 2003113)), the parties of the Convention are obliged to inform each other of transboundary
effects and to take transboundary eff ects into account in their planning. Cooperation between the Mem ber
States and with countries outside the EU is also required when developing maritime spatial plans.
Monitoring is not in itself a mitigation measure, but it is necessary to validate whet her measures to avoid or
reduce significant effects are effective.
Mitigation measures must not be confused with compensatory measures, which are intended to
compensate for damage that may be caused by a plan or project. Compensatory measures can only be
considered in relation to the criteria set out in Article 6(4) of the Habitats Directive.
6.2 Habitats
6.2.1 Introduction
Ten habitat types (or habitat-type complexes) listed in Annex I of the Habitats Directive are treated as marine
habitats for reporting purposes, and two of these are considered as priority habitat types (marked with *):
sandbanks which are slightly covered by sea water all the time [1110]
Posidonia beds (Posidonion oceanicae) * [1120]
estuaries [1130]
mudflats and sandflats uncovered at low tide [1140]
coastal lagoons* [1150]
large shallow inlets and bays [1160]
reefs [1170]
submarine structures made by leaking gas [1180]
Boreal Baltic narrow inlets [1650]
submerged or partly submerged caves [8330].
The above habitat types include coastal habitats, habitats of shallow seas, and habitats of deeper offshore
waters (European Commission, 2013). Because offshore wind energy developments require access to the
land (‘landfall’) onshore habitats also need to be considered when assessing offshore projects (see Chapter
5.2). Baseline data to support an appropriate assessm ent should be collected using the best available
methods. Examples of baseline-survey methods are summarised in Box 6-2.
Box 6-2 Baseline survey for benthic habitats
Surveys are likely to be required to delineate Annex I habitat areas within the footprint of wind energy developments and
within a delineated buffer zone. Detailed guidance on survey methods are sometimes available at national level114
Surveys for Annex I habitats could be part of a wider characterisation survey for the purposes of an environmental impact
112 Directive 2014/89/EU of the European Parliament and of the Council of 23 July 2014 establishing a framework for
maritime spatial planning; OJ L 257, 28.8.2014, pp. 135145.
113 Jendroska, Jerzy & Stec, Stephen. (2003). The Kyiv Protocol on strategic environmental assessment. 33. 105-110.
114 See for example: ‘Standard Investigation of the Impacts of Offshore Wind Turbines on the Marine Environment (StUK
offshore-wind-turbines-marine-environment_en.pdf?__blob=publicationFile&v=6 and ‘Marine Monitoring Handbook’:

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