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 by several specialized scientific organizations, a new analysis was carried out by the Marine Environmental Sciences Laboratory, in order to assess the impact of the noise associated with the phase construction of offshore wind turbines at Coquille Saint-Jacques and La Praire.

Behavior of adult scallops:

It should be noted first of all that we never revealed any lethal effect of pile driving or drilling noises on adult scallops even if the experiments lasted up to two months of exposure to anthropogenic noise (> 180 dB).

The SOMME design office coordinated research as part 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 embarks on its valves. These sensors make it possible to describe by signal processing (applied mathematics):

  • the audiogram of a scallop shell (In vitro, Tinduff and Océnopolis). It reacts to sounds with a frequency between 1 and 800 Hz max. The scallop shell means a structure which is comparable to an ear;
  • the behavior of this animal when we talk about valvular movements, jumps, swimming, and rotations. The scallop is a nocturnal animal (In situ), the opening of the CSJ valves 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 work (boat positioning, drilling itself) thus made it possible to (i) validate an innovative monitoring method; (ii) acquire new knowledge about the biology of this species (behavior); (iii) to remove the main doubts as to the impacts of drilling on the behavior of scallops (no mortality, no observation of changes in behavior revealing a real impact). The results show a slight change in behavior upon arrival of the drillboat (installation, Jack-up). This behavioral modification is no longer noted during the drilling phase. It would be useful to continue these studies to consolidate this initial information.

Today, it remains to be demonstrated that sediment vibrations and particle movements linked to boat sounds (long term), or to pounding and drilling (more transient) have no 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 then metamorphose to return to the bottom and never leave it. In order to estimate the impacts of driving and drilling noise 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 It was first necessary to imagine and then build an adequate experimental system. This work has been done. We then carried out bioacoustic experiments in this pioneering system in 8 ponds allowing fine control of the physical (temperature, salinity, ambient noise, turbidity) and biological (predation, competition) parameters of the environment. The use of tanks therefore allows observations that are impossible in the natural environment, but it also represents a technical challenge due to the problems of sound reverberation and resonance of the tanks. We therefore developed and tested at Tinduff (CSJ Hatchery) a tank allowing both larval breeding and the diffusion of known sounds not distorted by the tank itself. The system was named the Larvosonic (in publication).

Note 1:
It should be noted here that metamorphosis is truly a pivotal moment in the development of a mollusk since it marks the beginning of benthic life. Science shows that the successful completion of this phase determines the rest of the life cycle. The fixation process which follows metamorphosis includes prospecting behaviors influenced by numerous environmental factors which ultimately intervene in the selection of benthic habitat. If it does not meet optimal conditions, which are highly variable depending on the species, a larva is capable of extending the duration of its larval phase. This delay in metamorphosis is a risky bet (increased predation, dispersal on unsuitable bottoms and cessation of feeding). Reducing this delay also reduces larval dispersal.

Note 2:
The results presented here concern the responses of larvae and post-larvae to noise imposed in plexiglass enclosures. During these experiments everything happens as if the shell or clam larvae remained at a fixed distance from the sound source (driving or drilling). Obviously, in nature and particularly in the bay of Saint-Brieuc, strong tidal currents continually move pelagic larvae which cannot remain at a constant distance from a sound source during work at fixed points. The “scenario” imagined here is therefore not realistic and maximizes the potential impacts of construction noise from wind farms on the youngest stages of CSJ and Praire.

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

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

Point 1: Impacts on larvae and post-larvae.
The response of young CSJ stages to anthropogenic noise depends both on the stage of development and the type of sound emitted, with the youngest larvae being generally more resistant and the pediveligerous larvae (capable of metamorphosing) being the most sensitive.

It should be noted once again that the excess mortality detected (see below) is very low (1.5 – 4%) since the survival rates are always greater than 96% regardless of the experiment considered for an exposure of four days.

has. At the pediveligera stage, we show that drilling noise increases mortality (which remains less than 4%), delays metamorphosis and reduces their feeding capacity (filtration rate). Conversely, those of pile driving have no detectable effect on mortality or on feeding but accelerate metamorphosis. We therefore suggest that drilling noise, in our experimental conditions, has a short-term negative effect on these larval stages.

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

In addition, the inhibition of metamorphosis by drilling goes hand in hand with a reduction 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 therefore modulate the dynamics of metamorphosis and these effects are contrasted depending on the nature of the sounds, which would indicate that the larvae react differently, depending on their development, to continuous and impulsive sounds or to differences in the frequency composition of the sounds. issued. This research work should be continued.

Note 4:
Studies suggest that the marine acoustic landscape could provide information about the environment that a larva must choose or escape 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 might postpone its metamorphosis, leading it into a 'desperate' state to randomly settle later further away.

Point 2: Maternal Effects.
We demonstrate for the first time that during the reproductive phase, exposure of adults to pile driving noises (during the entire period of gametogenesis) induces complex maternal effects on CSJ offspring. Although their exposure to pile driving noises did not induce mortality at the sound levels tested, nor a modification of the lipid content of the adult scallop muscle, nor that of its growth, we observed much more subtly a reduction in the size of the gonad with increasing sound level and at the same time fewer atretic eggs (normal process of “digestion” of eggs to use reserves) and a better hatching rate. Very interestingly, the resulting larvae have better performance (growth, metamorphosis) at pre-metamorphic stages. At the post-larvae stage, however, these performances are identical between the different batches.

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

Main results concerning larvae/post-larvae of Venus verrucosa (Praire):

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

By using two distinct rearing temperatures (15 and 20°C) which reflect spring periods (15°C) or max. summer (20°C) in the English Channel, batches of physiologically different larvae (contrasting lipid contents) were produced.

  • At the veliger stage (at this stage a large can eat), only the noise 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.
  • At the pediveligerous stage (just before metamorphosis, feeding on the decline), noise from pile driving and drilling both reduce mortality and larval settlement without changing the dynamics of metamorphosis. In addition, they reduce the retention of essential fatty acids when metabolism is high (20°C). It then seems that increasing the temperature amplifies the effect of sound, which is not expressed at 15°C. The differences with the results obtained on the CSJ clearly reflect that responses to anthropogenic noise are different from one species to another. This variation between species in the way they respond to variations in their environment is a near constant in marine ecology.

It then seems that increasing the temperature amplifies the effect of the sound. This effect of the impact of noise cannot be expressed at 15°C. It is probably the same under this temperature (the season therefore seems important). Energy reserves, depending on the seasons, are an element of explanation that is obviously at play. It will also be noted that temperature, unlike sound, modulates all the performance criteria of a clam larva, once again emphasizing the importance of thermal factor in the development of bivalve larvae.

We demonstrate here that the joint effects of temperature and anthropogenic sounds depend on the stage of development and modulate the performance of larvae at the pediveliger stage, acting on the dynamics of metamorphosis. At this stage, our results demonstrate interactions between temperature and sounds and this indicates that the response to noise is linked to the physiological state of the larvae and therefore does not have an exclusive link with noise alone.

Note 6:
We would also like to point out that stimulation of metamorphosis by a beating 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 indicator of a poorly adapted environment, then the larva could postpone its metamorphosis, leading it to a “desperate” state. But paradoxically our results show that in the shell as in the mussel (another study) anthropogenic noise can stimulate metamorphosis at the place where the noise pollution is emitted and therefore potentially stimulate pre-recruitment at the source of the pollution (more bivalve at the source of the noise!).