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Unravelling the ecological impacts of large-scale offshore wind farms in the Mediterranean Sea 

Author:  | Environment, Wildlife


  • Offshore wind farms (OWF) pose serious environmental risks to the Mediterranean Sea.
  • OWF models cannot be simply imported from the northern European seas to other seas.
  • OWF should be excluded from areas of high biodiversity and/or high valuable seascape.
  • OWF development should be forbidden in or in the vicinity of Marine Protected Areas (MPAs).
  • Biodiversity loss and climate change are interconnected and must be tackled simultaneously.

Abstract: The need for alternative energy systems like offshore wind power to move towards the Green Deal objectives is undeniable. However, it is also increasingly clear that biodiversity loss and climate change are interconnected issues that must be tackled in unison. In this paper we highlight that offshore wind farms (OWF) in the Mediterranean Sea (MS) pose serious environmental risks to the seabed and the biodiversity of many areas due to the particular ecological and socioeconomic characteristics and vulnerability of this semi-enclosed sea. The MS hosts a high diversity of species and habitats, many of which are threatened. Furthermore, valuable species, habitats, and seascapes for citizens’ health and well-being coexist with compounding effects of other economic activities (cruises, maritime transport, tourism activities, fisheries and aquaculture) in a busy space on a narrower continental shelf than in other European seas. We argue that simply importing the OWF models from the northern European seas, which are mostly based on large scale projects, to other seas like the Mediterranean is not straightforward. The risks of implementing these wind farms in the MS have not yet been well evaluated and, considering the Precautionary Principle incorporated into the Marine Strategy Framework Directive and the Maritime Spatial Planning Directive, they should not be ignored. We propose that OWF development in the MS should be excluded from high biodiversity areas containing sensitive and threatened species and habitats, particularly those situated inside or in the vicinity of Marine Protected Areas or areas with valuable seascapes. In the absence of a clearer and comprehensive EU planning of wind farms in the MS, the trade-off between the benefits (climate goals) and risks (environmental and socioeconomic impacts) of OWF could be unbalanced in favor of the risks.

Table 1. Summary of potential environmental effects of Offshore Wind Farms (construction, operation, and decommissioning stages combined) in the Mediterranean Sea translated into the 11 Good Environmental Status (GES) descriptors of the Marine Strategy Framework Directive.

GES descriptor Effects of the offshore wind farms References
#1. Biodiversity:
The quality and occurrence of habitats and the distribution and abundance of species are in line with prevailing physiographic, geographic and climatic conditions
Loss of fragile benthic marine and coastal habitats important for biodiversity, particularly in protected areas Gill, 2005; Perrow, 2019; ICES, 2021
Disturbance to sensitive and threatened species (birds, mammals, sea turtles and fish) due to piles, anchors and cables (including the effects of electromagnetic fields and artificial lights, and entanglement risks). The OWF may cause species injury or death, changes in their behavioural response (attraction to and avoidance of the turbines) and/or changes in habitat. Zettler and Pollehne, 2006; Vermeij et al., 2010; Benjamins et al., 2014; Bergström et al., 2014; Leopold et al., 2015; Goodale and Milman, 2016; WWF, 2014, WWF, 2019; Stanley et al., 2020; Hutchison et al., 2020; Taormina et al., 2020; De Jong et al., 2020; Jones et al., 2021; Anderson et al., 2021, Farr et al., 2021
As floating wind farms expand in size and increase in distance from the shore, longer and higher capacity subsea cables are required to interconnect facility components to each other, to the seafloor, and to the shore. This may increase the extent of electromagnetic fields in the water column and potentially interact with a great diversity of marine organisms. Benjamins et al., 2014; Farr et al., 2021.
For floating wind farms, midwater mooring lines and floating substructures may similarly act as fish aggregation devices and settlement surfaces for invertebrates and algae, thus altering species composition in pelagic communities. Additional concerns are the potential for marine mammal collision and entanglement with these mooring lines and subsea cables Benjamins et al., 2014; Farr et al., 2021.
Risk of accidents (associated with natural hazards, such as storms and extreme events, and wind turbine accidents, including fire, the aerogenerator itself falling into the sea and ship collisions) Biehl and Lehmann, 2006; Asian et al., 2017
Artificial reef effect: when wind farms are built in areas with homogenous seabeds, the installation of foundations and piles may provide space for settlement, shelter and foraging for some species (positive effect) ICES, 2008; Vaissière et al., 2014; Hammar et al., 2016; Degraer et al., 2020; Mavraki et al., 2021
Habitat destruction on nearshore and inland fragile areas (estuaries, coastal lagoons, large shallow inlets and bays, etc.) due to the building of new terrestrial/ coastal infrastructure This study
#2. Non-indigenous species:
Non-indigenous species introduced by human activities are at levels that do not adversely alter the ecosystems
New, artificial substrates favor the colonization of non-indigenous species Glasby et al., 2007; Duarte et al., 2013; De Mesel et al., 2015
#3. Commercial fish and shellfish:
Populations of all commercially exploited fish and shellfish are within safe biological limits, exhibiting a population age and size distribution that is indicative of a healthy stock
Effects on exploited species due to sound, vibrations and electromagnetic fields from cables Zettler and Pollehne, 2006; Bergström et al., 2014; Leopold et al., 2015; Hutchison et al., 2020
In the absence of fishing (usually forbidden within wind farms), biodiversity and the abundance of benthopelagic and benthic species using OWF for shelter and as feeding grounds may increase, with potential spillover effects (positive effect) Halouani et al., 2020; Degraer et al., 2020; Gill et al., 2020; Mavraki et al., 2021.
OWF will alter the dynamics (periodicity, access to areas occupied by wind farms) of scientific fishery resource surveys, thus affecting the stock assessment and management of fishery resources Methratta et al., 2020.
#4. Food webs:
All elements of the marine food webs, as far as they are known, occur at normal abundance and diversity and at levels capable of ensuring the long-term abundance of the species and the retention of their full reproductive capacity
Colonization by new (atypical) communities (sessile benthic species) that may modify food webs and biogeochemical cycling Wilhelmsson and Langhamer, 2014; Coolen et al., 2020; Dannheim et al., 2020
Increase of suspension feeders leading to changes in local primary production Slavik et al., 2019; Mavraki et al., 2020
#5. Eutrophication:
Human-induced eutrophication is minimised, and especially its adverse effects, such as biodiversity losses, ecosystem degradation, harmful algae blooms and oxygen deficiency in bottom waters
#6. Sea-floor integrity:
Sea-floor integrity is at a level that ensures that the structure and functions of the ecosystems are safeguarded and benthic ecosystems in particular are not adversely affected
Habitat alterations due to the installation and dismantling of pile foundations, cables, and anchors, the scour of the seabed, and the strumming of the cables Gill, 2005; Wilhelmsson and Langhamer, 2014; Slavik et al., 2019; Perrow, 2019; Degraer et al., 2020; Coolen et al., 2020; ICES, 2021
Floating OWF require mooring and anchoring systems consisting of heavy chains to keep their substructures stationary, and in some cases, the use of suction anchors that may require scour protection through rock dumping, affecting sea-floor integrity. Statoil, 2015; Defingou et al., 2019; Farr et al., 2021
#7. Hydrographical conditions:
Permanent alteration of hydrographical conditions does not adversely affect marine ecosystems
Changes in atmospheric and oceanic dynamics leading to alterations in local primary productivity and carbon flow to the benthos, and changes in larval transport pathways. Oceanographic processes that could be affected by offshore wind farms include downstream turbulence, surface wave energy, local scour, inflowing currents and surface upwelling. Christensen et al., 2013; Clark et al., 2014; Ludewig, 2015; Carpenter et al., 2016; Grashorn and Stanev, 2016; Floeter et al., 2017; van Berkel et al., 2020, Lampert et al., 2020; Dannheim et al., 2020; Gill et al., 2020; Akhtar et al., 2021
Turbulent mixing generated by turbine structures and wind reduction that can modify ocean vertical mixing and, in turn, stratification patterns Ludewig, 2015; van Berkel et al., 2020; Miles et al., 2020
While the floating OWF may initially have a smaller impact on the underwater hydrodynamics than a fixed OWF, the higher emerged structure (up to 250 m) could significantly modify the wind field This study
#8. Contaminants in the marine environment:
Contaminants are at a level not giving rise to pollution effects
Contamination from chemical emissions, including organic compounds such as bisphenol A and metals such as aluminum, zinc, and indium from corrosion and biofouling protection measures and sacrificial anodes Kirchgeorga et al., 2018; De Witte and Hostens, 2019; Farr et al., 2021
Pollution from the industrialization of the coastline, including the associated hydrogen plants GIZ, 2020; WindEurope, 2021, Khan et al., 2021
Pollution from accidents Biehl and Lehmann, 2006; Asian et al., 2017
Floating OWF may hold internal tanks that may contain both solid ballast and ballast water typically dosed with sodium hydroxide, a chemical compound that is toxic for aquatic organisms European Commission, 2007; Statoil, 2015
#9. Contaminants in seafood:
Contaminants in fish and other seafood for human consumption do not exceed levels established by Community legislation or other relevant standards
#10. Marine litter:
Properties and quantities of marine litter do not cause harm to the coastal and marine environment
#11. Energy, including Underwater Noise:
Introduction of energy, including underwater noise, is at levels that do not adversely affect the marine environment
Changes to water quality: increase in local water turbidity arising from suspended solids Gill, 2005; Perrow, 2019; ICES, 2021
Significant marine noise and vibration from turbines and mounting structures (including floating OWF, which require mooring and anchoring systems consisting of heavy chains to keep their substructures stationary) Gill, 2005 Statoil, 2015; Perrow, 2019; Defingou et al., 2019; Stanley et al., 2020; ICES, 2021; Jones et al., 2021; Farr et al., 2021
Emission of electromagnetic fields can affect electrosensitive species, such as marine mammals and bottom dwelling species (e.g., elasmobranchs and decapods) Zettler and Pollehne, 2006; Bergström et al., 2014; Leopold et al., 2015; Hutchison et al., 2020

Josep Lloret, Institute of Aquatic Ecology, University of Girona, Catalonia, Spain
Antonio Turiel, Elisa Berdalet, Ana Sabatés, Josep-Maria Gili, Institut de Ciències del Mar (CSIC), Barcelona, Catalonia, Spain
Jordi Solé, Department of Earth and Ocean Dynamics, University of Barcelona, Catalonia, Spain
Alberto Olivares, Rafael Sardá, Centre d’Estudis Avançats de Blanes (CSIC), Girona, Catalonia, Spain
Josep Vila-Subirós, Department of Geography, University of Girona, Catalonia, Spain

Science of The Total Environment, Volume 824, 10 June 2022, 153803

Unravelling the ecological impacts of large-scale offshore wind farms in the Mediterranean Sea

This material is the work of the author(s) indicated. Any opinions expressed in it are not necessarily those of National Wind Watch.

The copyright of this material resides with the author(s). As part of its noncommercial educational effort to present the environmental, social, scientific, and economic issues of large-scale wind power development to a global audience seeking such information, National Wind Watch endeavors to observe “fair use” as provided for in section 107 of U.S. Copyright Law and similar “fair dealing” provisions of the copyright laws of other nations. Queries e-mail.

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