How ‘Blue’ Is ‘Green’ Energy?

Abstract

Global offshore wind capacity has been increasing at 15–30% annually, aided partly by the establishment of the industry in China.There are over 90 tidal energy technology developers globally, with about half focusing on horizontal axis turbines that rotate in a plane perpendicular to the flow of the current.Over 200 companies are pursuing wave energy converter development, most commonly point absorber devices that convert the vertical motion of floats into electricity.Construction noise impacts are relatively well understood, but those from the operation of marine renewable energy devices remain largely unknown. Monitoring at demonstration sites and full commercial projects is needed to address this knowledge gap for future installations.Direct and indirect effects of installations on marine life depend on relative scales and interactions with impacts from other existing industries. Often perceived as environmentally benign, ‘green’ renewable energy technologies have ecological costs that are often overlooked, especially those occurring below the waterline. After briefly discussing the impacts of hydropower on freshwater and marine organisms, we focus this review on the impacts of marine renewable energy devices (MREDs) on underwater marine organisms, particularly offshore wind farms and marine energy converters (e.g., tidal turbines). We consider both cumulative impacts and synergistic interactions with other anthropogenic pressures, using offshore wind farms and the Taiwanese white dolphin (Sousa chinensis taiwanensis) as an example. While MREDs undoubtedly can help mitigate climate change, variability in the sensitivity of different species and ecosystems means that rigorous case-by-case assessments are needed to fully comprehend the consequences of MRED use. Often perceived as environmentally benign, ‘green’ renewable energy technologies have ecological costs that are often overlooked, especially those occurring below the waterline. After briefly discussing the impacts of hydropower on freshwater and marine organisms, we focus this review on the impacts of marine renewable energy devices (MREDs) on underwater marine organisms, particularly offshore wind farms and marine energy converters (e.g., tidal turbines). We consider both cumulative impacts and synergistic interactions with other anthropogenic pressures, using offshore wind farms and the Taiwanese white dolphin (Sousa chinensis taiwanensis) as an example. While MREDs undoubtedly can help mitigate climate change, variability in the sensitivity of different species and ecosystems means that rigorous case-by-case assessments are needed to fully comprehend the consequences of MRED use. Climate change is causing extensive and uncertain changes in the oceans, which bring new and sometimes severe challenges to marine life (see Box 1). Many nations view renewable energy (see Glossary) installations as part of their strategy to reduce carbon emissions and curb climate change [4REN21 Renewables 2018 Global Status Report. REN21 Secretariat, 2018Google Scholar]. Despite this, the environmental impacts of such installations should not be overlooked in the rush to meet political and economic targets. A previous review explored some of the impacts of wind power; hydropower; and, to a lesser extent, solar photovoltaic power on terrestrial environments [5Gibson L. et al.How green is ‘green’ energy?.Trends Ecol. Evol. 2017; 32: 922-935Abstract Full Text Full Text PDF PubMed Scopus (77) Google Scholar]. Here we consider potential impacts below the waterline and explore how environmentally benign, or ‘blue’, these ‘green’ energy technologies really are in marine ecosystems, using the available literature.Box 1Impacts of Climate Change on Marine LifeThe oceans are undergoing various physical changes, each with the potential for impacts on marine life. These include a broad warming of the oceans; reduced subsurface oxygen concentrations; ocean acidification; changes in sea level, sea ice extent, thermal stratification, and ocean circulation; and increased variability in local temperatures, with more frequent extreme oceanographic and atmospheric events (see review by [1Worm B. Lotze H.K. Marine biodiversity and climate change.in: Letcher T. Climate and Global Change: Observed Impacts on Planet Earth. 2nd edn. Elsevier, 2016: 195-212Crossref Scopus (19) Google Scholar] and L. Nunny and M.P. Simmonds, unpublished). Beyond direct impacts on physiology and mortality, such as those caused by exceeding the physiological tolerances of biota, there are numerous indirect impacts (e.g., changes in suitable habitat) and synergistic impacts (e.g., changes in the prevalence or severity of other threats for a given species) (see reviews by [1Worm B. Lotze H.K. Marine biodiversity and climate change.in: Letcher T. Climate and Global Change: Observed Impacts on Planet Earth. 2nd edn. Elsevier, 2016: 195-212Crossref Scopus (19) Google Scholar, 2Evans P.G. Bjørge A. Impacts of climate change on marine mammals.MCCIP Sci. Rev. 2013; 2013: 134-148Google Scholar]). As top predators, marine mammals may either suffer or benefit from changes in the distribution and abundance of prey species [2Evans P.G. Bjørge A. Impacts of climate change on marine mammals.MCCIP Sci. Rev. 2013; 2013: 134-148Google Scholar].There are many indications that range shifts are already occurring in several marine mammal species in response to changes in either physical oceanography or prey abundance [2Evans P.G. Bjørge A. Impacts of climate change on marine mammals.MCCIP Sci. Rev. 2013; 2013: 134-148Google Scholar,3MacLeod C.D. Global climate change, range changes and potential implications for the conservation of marine cetaceans, a review and synthesis.Endanger. Species Res. 2009; 7: 125-136Crossref Scopus (133) Google Scholar]. One study predicted that increases in water temperature will alter the ranges of 88% of cetacean species, with the changes expected to be detrimental for nearly half of these [3MacLeod C.D. Global climate change, range changes and potential implications for the conservation of marine cetaceans, a review and synthesis.Endanger. Species Res. 2009; 7: 125-136Crossref Scopus (133) Google Scholar].While many marine species may be able to adapt to the effects of climate change, some may have neither the necessary behavioural plasticity nor the ability to shift their range as required [2Evans P.G. Bjørge A. Impacts of climate change on marine mammals.MCCIP Sci. Rev. 2013; 2013: 134-148Google Scholar]. For example, in 21% of cetacean species, the predicted changes in range may place at least one geographically isolated population of the species at a high risk of extinction [3MacLeod C.D. Global climate change, range changes and potential implications for the conservation of marine cetaceans, a review and synthesis.Endanger. Species Res. 2009; 7: 125-136Crossref Scopus (133) Google Scholar]. The most seriously affected species and populations will be those that are constrained to small geographic ranges in fragmented or isolated habitat [2Evans P.G. Bjørge A. Impacts of climate change on marine mammals.MCCIP Sci. Rev. 2013; 2013: 134-148Google Scholar,3MacLeod C.D. Global climate change, range changes and potential implications for the conservation of marine cetaceans, a review and synthesis.Endanger. Species Res. 2009; 7: 125-136Crossref Scopus (133) Google Scholar]. The oceans are undergoing various physical changes, each with the potential for impacts on marine life. These include a broad warming of the oceans; reduced subsurface oxygen concentrations; ocean acidification; changes in sea level, sea ice extent, thermal stratification, and ocean circulation; and increased variability in local temperatures, with more frequent extreme oceanographic and atmospheric events (see review by [1Worm B. Lotze H.K. Marine biodiversity and climate change.in: Letcher T. Climate and Global Change: Observed Impacts on Planet Earth. 2nd edn. Elsevier, 2016: 195-212Crossref Scopus (19) Google Scholar] and L. Nunny and M.P. Simmonds, unpublished). Beyond direct impacts on physiology and mortality, such as those caused by exceeding the physiological tolerances of biota, there are numerous indirect impacts (e.g., changes in suitable habitat) and synergistic impacts (e.g., changes in the prevalence or severity of other threats for a given species) (see reviews by [1Worm B. Lotze H.K. Marine biodiversity and climate change.in: Letcher T. Climate and Global Change: Observed Impacts on Planet Earth. 2nd edn. Elsevier, 2016: 195-212Crossref Scopus (19) Google Scholar, 2Evans P.G. Bjørge A. Impacts of climate change on marine mammals.MCCIP Sci. Rev. 2013; 2013: 134-148Google Scholar]). As top predators, marine mammals may either suffer or benefit from changes in the distribution and abundance of prey species [2Evans P.G. Bjørge A. Impacts of climate change on marine mammals.MCCIP Sci. Rev. 2013; 2013: 134-148Google Scholar]. There are many indications that range shifts are already occurring in several marine mammal species in response to changes in either physical oceanography or prey abundance [2Evans P.G. Bjørge A. Impacts of climate change on marine mammals.MCCIP Sci. Rev. 2013; 2013: 134-148Google Scholar,3MacLeod C.D. Global climate change, range changes and potential implications for the conservation of marine cetaceans, a review and synthesis.Endanger. Species Res. 2009; 7: 125-136Crossref Scopus (133) Google Scholar]. One study predicted that increases in water temperature will alter the ranges of 88% of cetacean species, with the changes expected to be detrimental for nearly half of these [3MacLeod C.D. Global climate change, range changes and potential implications for the conservation of marine cetaceans, a review and synthesis.Endanger. Species Res. 2009; 7: 125-136Crossref Scopus (133) Google Scholar]. While many marine species may be able to adapt to the effects of climate change, some may have neither the necessary behavioural plasticity nor the ability to shift their range as required [2Evans P.G. Bjørge A. Impacts of climate change on marine mammals.MCCIP Sci. Rev. 2013; 2013: 134-148Google Scholar]. For example, in 21% of cetacean species, the predicted changes in range may place at least one geographically isolated population of the species at a high risk of extinction [3MacLeod C.D. Global climate change, range changes and potential implications for the conservation of marine cetaceans, a review and synthesis.Endanger. Species Res. 2009; 7: 125-136Crossref Scopus (133) Google Scholar]. The most seriously affected species and populations will be those that are constrained to small geographic ranges in fragmented or isolated habitat [2Evans P.G. Bjørge A. Impacts of climate change on marine mammals.MCCIP Sci. Rev. 2013; 2013: 134-148Google Scholar,3MacLeod C.D. Global climate change, range changes and potential implications for the conservation of marine cetaceans, a review and synthesis.Endanger. Species Res. 2009; 7: 125-136Crossref Scopus (133) Google Scholar]. For example, hydropower in freshwater systems alters water flow, affecting aspects of marine circulation, ice cover, size of freshwater plumes, and nutrient flux (e.g., [6Prinsenberg S.J. Effects of the hydroelectric developments on the oceanographic surface parameters of Hudson Bay.Atmosphere-Ocean. 1983; 21: 418-430Crossref Scopus (15) Google Scholar, 7Prinsenberg S.J. Effects of Hydro-electric Projects on Hudson Bay’s Marine and Ice Environments. Hudson Bay Programme, Department of Fisheries and Oceans, Dartmouth, NS, Canada1994Google Scholar, 8Carriquiry J.D. et al.The effects of damming on the materials flux in the Colorado River delta.Environ. Earth Sci. 2011; 62: 1407-1418Crossref Scopus (19) Google Scholar]). Additionally, anaerobic decomposition of flooded vegetation in deep reservoirs formed above large dams often produces biologically toxic methylated mercury (e.g., [9Bodaly R.A. Johnston T.A. The Mercury Problem in Hydro-electric Reservoirs with Predictions of Mercury Burdens in Fish in the Proposed Grande Baleine Complex, Québec. James Bay Publication Series, 1992Google Scholar,10Leino T. Lodenius M. Human hair mercury levels in Tucuruí area, state of Pará, Brazil.Sci. Total. Environ. 1995; 175: 119-125Crossref PubMed Scopus (53) Google Scholar]) that can have serious consequences for fish and other wildlife both in the reservoir and downstream [11Scheuhammer A.M. et al.Effects of environmental methylmercury on the health of wild birds, mammals, and fish.Ambio. 2007; 36: 12-18Crossref PubMed Scopus (689) Google Scholar]. This process also initially generates considerable greenhouse gases, meaning that hydropower installations can take decades just to reach net impact levels similar to those of conventional energy production [12Kemenes A. et al.Methane release below a tropical hydroelectric dam.Geophys. Res. Lett. 2007; 34: L12809Crossref Scopus (152) Google Scholar, 13Fearnside P.M. Pueyo S. Greenhouse-gas emissions from tropical dams.Nat. Clim. Chang. 2012; 2: 382-384Crossref Scopus (135) Google Scholar, 14Kahn J.R. et al.False shades of green: the case of Brazilian Amazonian hydropower.Energies. 2014; 7: 6063-6082Crossref Scopus (40) Google Scholar]. Several technologies that are designed specifically for installation in marine environments, referred to as marine renewable energy devices (MREDs), can have more direct impacts (see [15IWCIWC Scientific Committee workshop on interactions between marine renewable projects and cetaceans worldwide.J. Cetacean Res. Manage. 2012; 14: 395-415Google Scholar]). These technologies include offshore wind turbines, marine energy converters and ocean thermal energy conversion devices (although the last of these is substantially less developed than the others and is not discussed further here). Offshore wind farms are currently the most prevalent, although they do not actually extract the energy from the ocean itself. However, several truly marine energy technologies are in varying stages of development. Some MREDs are nearing economic competitiveness with conventional energy production methods (e.g., [16Magagna D. Uihlein A. Ocean energy development in Europe: current status and future perspectives.Int. J. Mar. Energy. 2015; 11: 84-104Crossref Scopus (185) Google Scholar]), despite discriminatory tax and subsidy regimes around the world (e.g., [17Redman J. et al.Dirty Energy Dominance: Dependent on Denial. How the U.S. Fossil Fuel Industry Depends on Subsidies and Climate Denial. Oil Change International, 2017Google Scholar]). This will likely lead to the rapid proliferation of MREDs globally (as demonstrated by offshore wind farms), with countries selecting the technologies most suited to local oceanic conditions to meet looming national renewable energy targets. Therefore, it is important to explore and understand the expanding potential for environmental impacts from such technologies. European leadership in offshore wind farm development has been matched by efforts to understand and mitigate its impacts on marine life, primarily marine mammals (see [18Verfuss U. et al.Review of offshore wind farm impact monitoring and mitigation with regard to marine mammals.Adv. Exp. Med. Biol. 2015; 875: 1175-1182Crossref Scopus (11) Google Scholar]). With percussive pile-driving being used to push wind turbine foundations into the seafloor, noise during construction was identified early on as a potential threat to coastal marine mammals. Typical impacts include displacement and, at close ranges, hearing damage, such as temporary or permanent threshold shifts in hearing sensitivity [19Lucke K. et al.Temporary shift in masked hearing thresholds in a harbor porpoise (Phocoena phocoena) after exposure to seismic airgun stimuli.J. Acoust. Soc. Am. 2009; 125: 4060-4070Crossref PubMed Scopus (168) Google Scholar, 20Tougaard J. et al.Pile-driving zone of responsiveness extends beyond 20 km for harbor porpoises (Phocoena phocoena).J. Acoust. Soc. Am. 2009; 126: 11-14Crossref PubMed Scopus (146) Google Scholar, 21Dähne M. et al.Effects of pile-driving on harbour porpoises (Phocoena phocoena) at the first offshore wind farm in Germany.Environ. Res. Lett. 2013; 8: 025002Crossref Scopus (127) Google Scholar, 22Russell D.J.F. et al.Marine mammals trace anthropogenic structures at sea.Curr. Biol. 2014; 24: R638-R639Abstract Full Text Full Text PDF PubMed Scopus (76) Google Scholar]. Stress responses and masking (including obscuration of sounds from prey species and conspecifics) are additional concerns because marine mammals depend on sound for nearly all life functions [23Thompson D. et al.Current Status of Knowledge of Effects of Offshore Renewable Energy Generation Devices on Marine Mammals and Research Requirements. Scottish Government, 2013Google Scholar]. Percussive pile-driving is intermittent and produces primarily (although not exclusively) low-frequency noise [24Wang Z. et al.Assessing the underwater acoustics of the world’s largest vibration hammer (OCTA-KONG) and its potential effects on the Indo-Pacific humpbacked dolphin (Sousa chinensis).PLoS One. 2014; 9: e110590Crossref PubMed Scopus (26) Google Scholar,25MacGillivray A.O. Underwater noise from pile-driving of conductor casing at a deep-water oil platform.J. Acoust. Soc. Am. 2018; 143: 450-459Crossref PubMed Scopus (6) Google Scholar]. Therefore, masking will be more problematic for animals using lower frequencies, such as baleen whales, than for small echolocating cetaceans (dolphins and porpoises) that generally exploit higher frequencies. Additionally, masking may be more pervasive at larger distances from the source due to the way impulsive sound propagates and spreads out in complex environments. Concerns over masking are also greater for concurrent piling, vibratory pile-driving, and noise produced during the operation of a wind farm [26Madsen P.T. et al.Wind turbine underwater noise and marine mammals: implications of current knowledge and data needs.Mar. Ecol. Prog. Ser. 2006; 309: 279-295Crossref Scopus (232) Google Scholar]. Operational noise is at lower frequencies and much lower levels than construction-related noise, comparable to or in most cases lower than noise from most ships. It is even less problematic in European waters, where low-frequency baleen whales are now much less common than they were in the past, having been decimated by historical whaling. Elsewhere, operational noise may remain a concern because the hearing ranges of most baleen whale species are thought to peak below 1 kHz [27Erbe C. Hearing Abilities of Baleen Whales. Defence R&D Canada, 2002Google Scholar]. These frequencies may also be relevant for underwater communication by certain pinniped species [28Sabinsky P.F. et al.Temporal and spatial variation in harbor seal (Phoca vitulina L.) roar calls from southern Scandinavia.J. Acoust. Soc. Am. 2017; 141: 1824-1834Crossref PubMed Scopus (10) Google Scholar]. Ongoing monitoring of sound from offshore developments along the Atlantic coast of the USA may soon offer opportunities to assess possible impacts of wind energy development on some baleen whales (e.g., [26Madsen P.T. et al.Wind turbine underwater noise and marine mammals: implications of current knowledge and data needs.Mar. Ecol. Prog. Ser. 2006; 309: 279-295Crossref Scopus (232) Google Scholar,29Petruny L.M. et al.Getting it right for the North Atlantic right whale (Eubaleana glacialis): a last opportunity for effective marine spatial planning?.Mar. Policy Bull. 2014; 85: 24-32Crossref PubMed Scopus (11) Google Scholar]). Finally, offshore wind farms alter the benthic habitat. This can change the scale and composition of prey aggregations with knock-on consequences (good or bad) for marine mammals (e.g., [30Mikkelsen L. et al.Re-established stony reef attracts harbour porpoises Phocoena phocoena.Mar. Ecol. Prog. Ser. 2013; 481: 239-248Crossref Scopus (27) Google Scholar,31Petersen J.K. Malm T. Offshore windmill farms: threats to or possibilities for the marine environment.Ambio. 2006; 35: 75-80Crossref PubMed Scopus (102) Google Scholar]). Of the various MREDs that extract energy from the ocean, marine energy converters (tidal stream generators or tidal range energy converters and, to a lesser extent, wave energy converters) are the most developed and thus merit discussion here. Optimal tidal energy sites tend to coincide with complex, biologically rich coastal habitat [32Polagye B. et al.Environmental Effects of Tidal Energy Development. US Department Commerce, NOAA Tech. Memo, 2011Google Scholar,33Garel E. et al.Applicability of the “frame of reference” approach for environmental monitoring of offshore renewable energy projects.J. Environ. Manage. 2014; 141: 16-28Crossref PubMed Scopus (10) Google Scholar], due in part to high transport rates of larval invertebrates and nutrients to the higher photic (sunlit) zone (e.g., [34Palardy J.E. Witman J.D. Water flow drives biodiversity by mediating rarity in marine benthic communities.Ecol. Lett. 2011; 14: 63-68Crossref PubMed Scopus (37) Google Scholar,35Sánchez-Garrido J.C. et al.Modeling the impact of tidal flows on the biological productivity of the Alboran Sea.J. Geophys. Res. Oceans. 2015; 120: 7329-7345Crossref Scopus (14) Google Scholar]). Such habitat provides predictable foraging opportunities for marine mammals [36Zammon J.E. Tidal changes in copepod abundance and maintenance of a summer Coscinodiscus bloom in the southern San Juan Channel, San Juan Islands, USA.Mar. Ecol. Prog. Ser. 2002; 226: 193-210Crossref Scopus (22) Google Scholar, 37Zammon J.E. Mixed species aggregations feeding upon herring and sandlance schools in a nearshore archipelago depend on flooding tidal currents.Mar. Ecol. Prog. Ser. 2003; 261: 243-255Crossref Scopus (57) Google Scholar, 38Jones A.R. et al.Fine-scale hydrodynamics influence the spatio-temporal distribution of harbour porpoises at a coastal hotspot.Prog. Oceanogr. 2014; 128: 30-48Crossref Scopus (30) Google Scholar, 39Benjamins S. et al.Confusion reigns? A review of marine megafauna interactions with tidal stream environments.Oceanogr. Mar. Biol. 2015; 53: 1-54Google Scholar], and thus marine mammals and tidal energy developments are prone to co-occur [40Hastie G.D. et al.Harbour seals avoid tidal turbine noise: implications for collision risk.J. Appl. Ecol. 2017; 55: 684-693Crossref Scopus (22) Google Scholar]. Much has been learned from the many small evaluation marine energy converter installations in Canada, the USA, the UK, Sweden, and France. Current concerns over converter technologies focus primarily on physical interactions with marine mammals and other marine life (e.g., collision with structures or moving parts), although considerable uncertainty exists regarding the nature and scale of such interactions [32Polagye B. et al.Environmental Effects of Tidal Energy Development. US Department Commerce, NOAA Tech. Memo, 2011Google Scholar,33Garel E. et al.Applicability of the “frame of reference” approach for environmental monitoring of offshore renewable energy projects.J. Environ. Manage. 2014; 141: 16-28Crossref PubMed Scopus (10) Google Scholar,41Inger R. et al.Marine renewable energy: potential benefits to biodiversity? An urgent call for research.J. Appl. Ecol. 2009; 46: 1145-1153Google Scholar, 42Copping A. et al.Annex IV 2016 State of the Science Report: Environmental Effects of Marine Renewable Energy Development Around the World. Pacific Northwest National Laboratory, 2016Google Scholar, 43Onoufriou J. et al.Empirical determination of severe trauma in seals from collisions with tidal turbine blades.J. Appl. Ecol. 2019; 56: 1712-1724Crossref Scopus (8) Google Scholar]. While we are not aware of any recorded instances of marine mammals colliding with turbine blades, the probability of making such observations is low, meaning that the uncertainty surrounding this risk will persist (see [44Copping A. et al.Understanding the potential risk to marine mammals from collision with tidal turbines.Int. J. Mar. Energy. 2017; 19: 110-123Crossref Scopus (6) Google Scholar,45Schmitt P. et al.A tool for simulating collision probabilities of animals with marine renewable energy devices.PLoS One. 2017; 12: e0188780Crossref PubMed Scopus (7) Google Scholar]). Converters may also exclude animals from important habitat due to perceived or physical barriers [39Benjamins S. et al.Confusion reigns? A review of marine megafauna interactions with tidal stream environments.Oceanogr. Mar. Biol. 2015; 53: 1-54Google Scholar,40Hastie G.D. et al.Harbour seals avoid tidal turbine noise: implications for collision risk.J. Appl. Ecol. 2017; 55: 684-693Crossref Scopus (22) Google Scholar]. Noise from operating turbines may also change the behaviour of marine mammals and other marine fauna, cause masking, and induce stress responses [33Garel E. et al.Applicability of the “frame of reference” approach for environmental monitoring of offshore renewable energy projects.J. Environ. Manage. 2014; 141: 16-28Crossref PubMed Scopus (10) Google Scholar,39Benjamins S. et al.Confusion reigns? A review of marine megafauna interactions with tidal stream environments.Oceanogr. Mar. Biol. 2015; 53: 1-54Google Scholar,46Samuel Y. et al.Underwater, low frequency noise in a coastal sea turtle habitat.J. Acoust. Soc. Am. 2005; 117: 1465-1472Crossref PubMed Scopus (39) Google Scholar, 47Wilhelmsson D. et al.Greening Blue Energy: Identifying and Managing the Biodiversity Risks and Opportunities of Offshore Renewable Energy. International Union for Conservation of Nature, 2010Google Scholar, 48Leeney R.H. et al.Environmental impact assessments for wave energy developments – learning from existing activities and informing future research priorities.Ocean Coast. Manag. 2014; 99: 14-22Crossref Scopus (40) Google Scholar]. For example, recent playback experiments at a tidally active site in Scotland found that the tagged harbour seals (Phoca vitulina) avoided the area, maintaining a separation distance of up to 500 m from the sound source, even though the overall numbers of seals using the site did not change [40Hastie G.D. et al.Harbour seals avoid tidal turbine noise: implications for collision risk.J. Appl. Ecol. 2017; 55: 684-693Crossref Scopus (22) Google Scholar]. Similarly, experiments in Washington State (USA) found reductions in both sightings and acoustic detections of harbour porpoises (Phocoena phocoena) during some playback periods, although simulated turbine sounds had no significant effect on harbour seal presence [49Robertson F. et al.Marine Mammal Behavioral Response to Tidal Turbine Sound.2018Crossref Google Scholar]. These studies suggest that the noise from turbine operations could impact the use of core foraging areas by some marine mammals. Very few studies are available on wave energy converters, but at least some types appear to have very low noise emissions [50Tougaard J. Underwater noise from a wave energy converter is unlikely to affect marine mammals.PLoS One. 2015; 10: e0132391Crossref PubMed Scopus (9) Google Scholar,51Robinson S.P. Lepper P. Scoping Study: Review of Current Knowledge of Underwater Noise Emissions from Wave and Tidal Stream Energy Devices. The Crown Estate, 2013Google Scholar]. However, much like wind farms, construction of marine energy converter installations is likely to be the most acoustically complex and loudest phase, involving not just higher sound pressure levels (relative to operational levels) but often also impulse-type sounds [32Polagye B. et al.Environmental Effects of Tidal Energy Development. US Department Commerce, NOAA Tech. Memo, 2011Google Scholar,49Robertson F. et al.Marine Mammal Behavioral Response to Tidal Turbine Sound.2018Crossref Google Scholar]. Accordingly, temporary displacement of harbour porpoises from demonstration turbine sites during construction has been reported (e.g., [52Keenan G. et al.SeaGen Environmental Monitoring Programme Final Report. Report produced for Marine Current Turbine Ltd. Royal Haskoning, 2011Google Scholar,53Copping A. et al.An international assessment of the environmental effects of marine energy development.Ocean Coast. Manag. 2014; 99: 3-13Crossref Scopus (51) Google Scholar]). Construction of the world’s first commercial-scale converter installation in Scotland [4REN21 Renewables 2018 Global Status Report. REN21 Secretariat, 2018Google Scholar] may provide insight into the population-level consequences of such displacement. The direct and indirect effects of converter installations (such as those of other MREDs) will likely depend on project scale, phase of development (construction versus operation), specific device structure, site characteristics, species present, (local) population sizes and densities, proportion of each population’s total distribution that overlaps the project area, and how the animals use the area [40Hastie G.D. et al.Harbour seals avoid tidal turbine noise: implications for collision risk.J. Appl. Ecol. 2017; 55: 684-693Crossref Scopus (22) Google Scholar,48Leeney R.H. et al.Environmental impact assessments for wave energy developments – learning from existing activities and informing future research priorities.Ocean Coast. Manag. 2014; 99: 14-22Crossref Scopus (40) Google Scholar]. Accordingly, risk assessments for marine energy converters and other MREDs will need not only to incorporate both direct effects (e.g., disturbance, displacement, injury, or mortality from noise and collisions) and indirect effects (e.g., changes in prey availability), but also to consider how the particular animals present in the area will respond to the specific activities and structures associated with any given development. MREDs have impacts on various non-mammalian marine s