It is not silent under the water! Shipping, piling works for the installation of wind turbines, seismic research, military exercises and the detonation of old munitions cause underwater noise. The disturbance may be of short or long duration.
In the worst case, this may be fatal or cause permanent hearing damage to some species. Underwater noise also disturbs the communication between the species, causes stress or changes the natural behaviour of the species. The impact will depend on both the nature of the noise as well as the susceptibility of the organism to the noise.
Marine mammals (cetaceans, dolphins, harbour porpoises) and fish (because of their gas-filled swim bladder) are particularly susceptible to explosions. Most invertebrates therefore suffer very little harm because they have no organs that are filled with gas. A number of other species are nevertheless in their early, embryonic development stages to a greater or lesser extent sensitive to acoustic pollution.
The management of the acoustic disturbance is one of the objectives of the Marine Strategy Framework Directive. Noise, as an environmental pressure, is being evaluated (environmental permits) as part of the environmental impact assessment of the projects.