Summary of recent work on the impact of noise

Marine Environmental Sciences Laboratory

As part of the impact studies regularly carried out by Ailes Marines and several specialized scientific organizations, a new analysis was conducted by the Laboratoire des Sciences de l'Environnement Marin to assess the impact of noise associated with the construction phase of offshore wind turbines on the Coquille Saint-Jacques and the Praire.

Adult scallop behavior:

It should be noted first and foremost that we never revealed a lethal effect of pile-driving or drilling noise in adult scallops even though the experiments lasted up to two months of exposure to anthropogenic noise (> 180 dB).

The SOMME study office has coordinated research in the framework of a new collaboration between organizations (MHNN, CNRS, INP Grenoble, WHOI, Ecloserie du Tinduff) on the development of a method involving position and movement sensors that the animal carries on its valves. These sensors allow to describe by signal processing (applied mathematics):

  • the audiogram of a scallop (In vitro, Tinduff and Océnopolis). It reacts to sounds whose frequency is between 1 and 800 Hz max. The scallop hears through a structure that is similar to an ear;
  • the behavior of this animal when it comes to valvular movements, jumps, swims, and rotations. The scallop is a nocturnal animal (In situ), the opening of the valves of the CSJ is maximum at night (In Vitro and In situ). Movements are very frequent at the end of the night.

In the Bay of Saint-Brieuc, a pioneering study on the behavior of scallops carried out in 2021 during drilling operations (boat positioning, drilling itself) made it possible to (i) validate an innovative monitoring method; (ii) acquire new knowledge on the biology of this species (behavior); (iii) remove the main doubts about the impacts of drilling on the behavior of scallops (no mortality, no observation of behavioral changes revealing a real impact). The results show a slight change in behavior upon the arrival of the drilling vessel (installation, Jack-up). This behavioral change is no longer noted during the drilling phase. It would be useful to continue these studies to consolidate this first information.

Today, it remains to be demonstrated that vibrations of the sediment and particulate movements linked to the sounds of boats (long term), or to pile driving and drilling (more transient) do not have an impact on the behavior of scallops.

Creation of an original experimental device, the Larvosonic. Larval ecology

The marine bivalves studied here are born in open water. They first have a pelagic larval life and then metamorphose to find the bottom and never leave it.
In order to estimate the impacts of pile-driving and drilling noises associated with the installation phase of offshore wind farms on the biology and ecology of the larvae of two species of bivalves (the scallop and the clam), we had to first imagine and then build an adequate experimental system. This work has been done. We then conducted bioacoustic experiments in this pioneer system in 8 tanks allowing a fine control of the physical (temperature, salinity, ambient noise, turbidity) and biological (predation, competition) parameters of the environment. The use of ponds allows observations that are impossible in the natural environment, but it also represents a technical challenge because of the problems of sound reverberation and resonance of the tanks. We have therefore developed and tested at Tinduff (CSJ Hatchery) a tank allowing both larval rearing and the diffusion of known sounds undistorted by the tank itself. The system was named the Larvosonic (in publication).

Remark 1:
It should be noted here that metamorphosis is really a pivotal moment in the development of a mollusk since it marks the beginning of the benthic life. Science shows that the good progress of this phase determines the continuation of the life cycle. The settlement process that follows metamorphosis includes exploration behaviors that are influenced by many environmental factors that ultimately play a role in the selection of the benthic habitat. If it does not encounter optimal conditions, which are highly variable depending on the species, a larva is able to prolong the duration of its larval phase. This delay of metamorphosis is a risky bet (increased predation, dispersion on unsuitable bottoms and stop of feeding). Reducing this delay is also reducing the larval dispersion.

Remark 2:
The results presented here concern the responses of larvae and post-larvae to imposed noises in Plexiglas enclosures. During these experiments, everything happens as if the shell or clam larvae remained at a fixed distance from the sound source (beating or drilling). Obviously, in nature and particularly in the Bay of Saint-Brieuc, strong tidal currents continuously move pelagic larvae that cannot remain at a constant distance from a sound source during work in fixed points. The "scenario" imagined here is therefore unrealistic and maximizes the potential impacts of wind farm construction noise on the youngest stages of CSJ and meadowlarks.

Note 3:
The results presented here concern the responses of larvae and post-larvae to anthropogenic noises, excluding boat noises (fishing or work at sea) recognized elsewhere as impacting invertebrates.

Main results for larvae/post larvae Coquille St Jacques (CSJ):

Item 1: Impacts on larvae and post-larvae.
The response of young CSJ stages to anthropogenic noise depends on both developmental stage and type of sound emitted, with younger larvae being more resistant overall and pediveliger larvae (able to metamorphose) being the most sensitive.

It should be noted again that the excess mortality detected (see below) is very low (1.5 - 4%) since the survival rates are always above 96% whatever the experiment considered for a four day exposure.

a. At the pediveliger stage, we show that drilling sounds increase mortality (which remains below 4%), delay metamorphosis and decrease their feeding capacity (filtration rate). Conversely, pile-driving noises have no detectable effect on mortality or feeding but accelerate metamorphosis. We thus suggest that drilling noise, under our experimental conditions, has a short-term negative effect on these larval stages.

b. At the post-larval stage (very young shell on the bottom), no excess mortality is detected depending on the nature and level of the sounds (as in adults!), and we show that drilling sounds increase the growth rate and reduce the concentration of lipid contents (energy) while pile-driving sounds have no observable effects.

Furthermore, the inhibition of metamorphosis by drilling goes hand in hand with a decrease in energy reserves, in the sense of a prolongation of the pelagic phase.

Conversely, beating accelerates metamorphosis so that scallop larvae settle with energy reserves that have not yet diminished.
Anthropogenic noises imposed over several days thus modulate the dynamics of metamorphosis and these effects are contrasted according to the nature of the sounds, which would reflect that larvae react differently, depending on their development, to continuous and impulsive sounds or to differences in the frequency composition of the sounds emitted. This research work should be continued.

Note 4:
Studies suggest that the acoustic seascape may provide information about the environment a larva must choose or flee before metamorphosis. We wish to emphasize here that the stimulation of metamorphosis by a beating sound might not be positive at the pediveliger stage (ecological sense) if the sound is emitted in a habitat unfavorable to young bivalves. Conversely, if a sound is interpreted by a larva as an indication of an unsuitable environment, then the larva could postpone its metamorphosis, leading it in a 'desperate' state to settle randomly later on.

Point 2: Maternal effects.
We demonstrate for the first time that during the reproductive phase, exposure of adults to pile driving noise (during the whole gametogenesis period) induces complex maternal effects on the CSJ offspring. Although their exposure to pile-driving noise did not induce mortality at the tested sound levels, nor did it alter the lipid content of the adult scallop muscle, nor its growth, we observed much more subtly a reduction in gonad size with increasing sound level and in parallel fewer atresic eggs (normal process of egg "digestion" for reserve utilization) and a better hatching rate. Interestingly, the resulting larvae have better performance (growth, metamorphosis) at the pre-metamorphic stages. At the post-larval stage, however, these performances are identical between the different batches.

Parental exposure to pile-driving sound thus modifies the sensitivity of the offspring to the same sound, without clearly contributing to a more or less well adapted response. To be continued...

Main results for Venus verrucosa (Praire) larvae/post larvae:

Note 5:
The physiological state of marine invertebrate larvae is largely based on their lipid content (energy reserve). Thus, energy metabolism modulates many parameters of a larva's life, be it its survival, its behavior or its response to stress factors. The physiological state, described by the lipid content, fluctuates mainly in response to two factors: food and temperature.

Using two distinct rearing temperatures (15 and 20°C) that reflect spring (15°C) or maximum summer (20°C) periods in the Channel, batches of physiologically different larvae (contrasting lipid contents) were produced.

  • At the veliger stage (at this stage a large one can eat), only the sound of pile driving increases the retention of essential fatty acids in the lipid membranes (in the cells!) without interaction with temperature while drilling has no impact.
  • In the pediveliger stage (just before metamorphosis, feeding on the decline), both pile-driving and drilling noises reduce mortality and larval fixation without altering metamorphic dynamics. In addition, they decrease retention of essential fatty acids when metabolism is high (20°C). It seems then that the increase in temperature amplifies the effect of bran, which is not expressed at 15°C. The differences with the results obtained on the CSJ reflect that the responses to anthropogenic noise are different between species. This variation between species in the way they respond to variations in their environment is a near constant in marine ecology.

It seems then that the increase in temperature amplifies the effect of the sound. This effect of the impact of the sound cannot be expressed at 15°C. It is probably the same under this temperature (the season thus seems important). The energy reserves, season dependent, are an element of explanation obviously in play. It should also be noted that temperature, unlike sound, modulates all the performance criteria of a clam larva, underlining once again the importance of the thermal factor in the development of bivalve larvae.

We show here that the joint effects of temperature and anthropogenic sound are developmental stage dependent and modulate larval performance at the pediveliger stage, affecting the dynamics of metamorphosis. At this stage, our results demonstrate interactions between temperature and sound and indicate that the response to noise is related to the physiological state of the larvae and is therefore not exclusively related to noise alone.

Remark 6:
We also wish to point out that the stimulation of metamorphosis by a threshing sound may not be positive at the pediveliger stage. Indeed if the sound is emitted in an unfavorable habitat errors in the choice of the place of fixation will have serious consequences on its future.

But conversely, if a sound is interpreted as an indication of a poorly adapted environment, then the larva could postpone its metamorphosis, leading it into a "desperate" state. But paradoxically our results show that in the shellfish as in the mussel (other study) an anthropic noise can stimulate metamorphosis at the place where the noise pollution is emitted and thus potentially stimulate pre-recruitment at the source of the pollution (no more bivalves at the source of the noise!).