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Offshore wind: drop in the ocean or energy tsunami?

Marine life: contrasting effects of offshore wind

Anaïs Marechal, science journalist
On January 19th, 2022 |
4 mins reading time
3
Marine life: contrasting effects of offshore wind
Nathalie Niquil
Nathalie Niquil
CNRS Research Director at the Laboratory of Biology of Aquatic Organisms and Ecosystems
Key takeaways
  • One of the best-known effects on marine biodiversity during wind turbine operation is the artificial reef effect. If the wind farm is closed to fishing, or less visited, a nature reserve-effect can occur.
  • Species such as algae, mussels and anemones fix themselves onto the hard structures of the turbine and their presence attracts other species.
  • However, the construction stage is the one that most affects marine species negatively. Driving piles into the seabed is extremely noisy and the effects of this noise remain significant even 10 years later.
  • Degradation of turbine components also has an effect on the biomass present on-site. Corrosion of metal structures or electromagnetic fields caused by energy flow from the cables seem to have little impact though.

Do installed off­shore wind tur­bines harm marine biodiversity?

One of the best-known impacts on marine bio­di­ver­si­ty dur­ing the oper­a­tional phase of wind tur­bines is the arti­fi­cial reef effect. This is when new species, such as mus­sels, crabs, anemones, and var­i­ous fish – depend­ing on the geo­graph­i­cal loca­tion – begin to set­tle around the wind tur­bine. The lay­er of rock that pro­tects the cables, masts and their foun­da­tions pro­vide a hard sub­strate that encour­ages eco­log­i­cal nich­es and enrich­es the com­plex­i­ty of the habi­tat, thus fur­ther attract­ing new species. The arti­fi­cial reef effect has been well doc­u­ment­ed in Bel­gian wind farms, which have been oper­a­tional for ten years, and it has been observed in many oth­er man-made con­struc­tions at sea. The new habi­tat is rich­er in bio­di­ver­si­ty and in ani­mal and plant biomass.

If the wind farm is closed to fish­ing, or sel­dom vis­it­ed, a reserve-effect can be added. As in the case of a marine pro­tect­ed area, the wind farm may allow for bet­ter renew­al of fished species’ stocks. The bio­mass of these species may increase at the periph­ery of the wind farm.

So, could the pres­ence of wind tur­bines increase the num­ber of fish?

Do the num­bers of ani­mals increase, or do they sim­ply clus­ter in the wind farm? This ques­tion is cur­rent­ly being debated.

For ben­th­ic species, which attach them­selves to sur­faces, the increase in bio­mass and pro­duc­tion is clear­ly estab­lished. Algae, mus­sels and anemones that set­tle on hard struc­tures attract oth­er species in a cas­cade along the food chain. Our numer­i­cal sim­u­la­tions show that this cas­cade is like­ly to reach top preda­tors at the top of the food chain, poten­tial­ly increas­ing their numbers.

Obser­va­tion of marine mam­mals pro­vides some evi­dence of this: in the North Sea, satel­lite mon­i­tor­ing shows that seals are attract­ed to wind farms. How­ev­er, it should be not­ed that this cas­cade effect depends strong­ly on the ini­tial pop­u­la­tion1. The seal pop­u­la­tion in the North Sea has been increas­ing nat­u­ral­ly for sev­er­al years, and the reef effect poten­tial­ly rein­forces this growth. In the case of pop­u­la­tions liv­ing in poor con­di­tions, a wind tur­bine may in fact wors­en the phenomenon.

Do birds and bats risk collisions?

Feed­back from Bel­gian wind farms2 has revealed the great uncer­tain­ty con­cern­ing this risk. For onshore wind farms, sci­en­tists count the num­ber of ani­mals on the ground, but this is more dif­fi­cult to do for off­shore wind farms. Stud­ies are under­way to devel­op instru­ments to this end. It is impor­tant to make these mea­sure­ments: some pro­tect­ed bird species may be sub­ject to a very lim­it­ed num­ber of col­li­sions per year3.

Is the con­struc­tion of a wind farm a par­tic­u­lar­ly risky time for marine species? Is it pos­si­ble to lim­it the effects?

Yes, all experts agree that this is the stage that most affects marine species. The noise lev­els gen­er­at­ed dur­ing pile-dri­ving are very high, and these effects are con­sid­ered to be the most impor­tant even after ten years.

Sev­er­al strate­gies can lim­it these effects. Using dou­ble cur­tains of bub­bles dur­ing pile-dri­ving reduces noise pol­lu­tion. It is also impor­tant not to car­ry out work dur­ing crit­i­cal peri­ods such as calv­ing or repro­duc­tion, par­tic­u­lar­ly for pro­tect­ed species. Final­ly, the noise lev­el can be increased very grad­u­al­ly, which allows sen­si­tive species to be scared away and not harmed. Sim­u­la­tions show that the cumu­la­tive effect of all these mea­sures can reduce the neg­a­tive impact on species by up to 97%.

I would add that it is impor­tant to avoid con­struct­ing tur­bines in areas of eco­log­i­cal inter­est or areas that are par­tic­u­lar­ly well con­served. Instead, wind pow­er should be devel­oped in areas that have already been heav­i­ly impact­ed by human activ­i­ties. The devel­op­ment of off­shore wind pow­er seems to me to be impor­tant to lim­it green­house gas emis­sions: our sim­u­la­tions show that the con­se­quences of cli­mate change are much more far-reach­ing than the localised effects cre­at­ed by wind turbines.

Are there any risks relat­ed to chem­i­cal pol­lu­tion or the under­wa­ter trans­port of electricity?

Under­wa­ter met­al struc­tures are prone to cor­ro­sion at sea. Gal­van­ic anodes – con­tain­ing most­ly alu­mini­um – are often used; their dis­so­lu­tion in water pro­tects the foun­da­tions of wind tur­bines. Their pres­ence has some­times been accused of being a sig­nif­i­cant source of metal­lic pol­lu­tion, but it seems that the degree to which they are dilut­ed is enough to lim­it these effects. Work is under­way, how­ev­er, to ver­i­fy this result.

Elec­tric cables and sub-sta­tions gen­er­ate, for their part, elec­tro­mag­net­ic fields. Their effects have been stud­ied for sev­er­al years: the first results show very localised fall­out. And ini­tial field and lab­o­ra­to­ry stud­ies show that, at the inten­si­ties observed, the impact on ani­mals is very low4.

Off­shore wind tur­bines, unlike land-based wind tur­bines, have been lit­tle stud­ied with regards their envi­ron­men­tal impact. The SEM-REV test site at Cen­trale de Nantes, off the coast of Le Croisic, has allowed, for the first time in France, the envi­ron­men­tal impacts to be mea­sured in situ for three years, tak­ing into account the con­struc­tion, oper­a­tional and main­te­nance phas­es5. After a year of oper­a­tion, the ben­th­ic com­mu­ni­ties in the vicin­i­ty of the wind tur­bine and its infra­struc­ture – the anchor­ing sys­tem and the elec­tri­cal cable – are in very good health. The anchor lines, float and cables have been colonised by mus­sels, anemones and corals. Only one non-native (and there­fore new) mol­lusc species has been observed. Lob­sters, con­ger eels and Dun­ge­ness crabs have also been found in the new habi­tat. The impact on these species and the fish caught has not yet been eval­u­at­ed. Final­ly, we not­ed that bats are attract­ed to wind tur­bines. We can­not make any reli­able obser­va­tions con­cern­ing bird pop­u­la­tions, how­ev­er, in the absence of an appro­pri­ate mea­sur­ing tool.

1D’après une dis­cus­sion avec Cécile Vin­cent, chercheuse en écolo­gie au Cen­tre d’études biologiques de Chizé
2Degraer, S., Bra­bant, R., Rumes, B. & Vigin, L. (eds). 2020. Envi­ron­men­tal Impacts of Off­shore Wind Farms in the Bel­gian Part of the North Sea: Empir­i­cal Evi­dence Inspir­ing Pri­or­i­ty Mon­i­tor­ing, Research and Man­age­ment. Series ‘Mem­oirs on the Marine Envi­ron­ment’. Brus­sels : Roy­al Bel­gian Insti­tute of Nat­ur­al Sci­ences, OD Nat­ur­al Envi­ron­ment, Marine Ecol­o­gy and Man­age­ment, 131 p.
3D’après une dis­cus­sion avec Sophie de Gris­sac, chercheuse en écolo­gie à France Energie Marine
4D’après une dis­cus­sion avec Antoine Car­li­er, chercheur en biolo­gie marine au lab­o­ra­toire d’écologie ben­thique côtière de l’Ifremer
5Rey­naud, Marine, Le Bouhris, Enored, Soulard, Thomas, & Perignon, Yves. (2021). Rap­port de suivi envi­ron­nemen­tal de l’éolienne flot­tante FLOATGEN, site d’essais SEM-REV. Zen­o­do. https://​doi​.org/​1​0​.​5​2​8​1​/​z​e​n​o​d​o​.​5​6​59296