Physiological effects of anthropogenic sound on aquatic animals: where are we and what is next?

Many aquatic animals have a well-developed sense of hearing as sound is important for communication underwater. However, this trait leaves them susceptible to injury, and physiological and behavioral impacts from exposure to intense or persistent anthropogenic sounds. We provide an overview of the current state of knowledge on the physiological effects of five main sources of anthropogenic sound: marine traffic, seismic exploration, pile driving, other industrial activity and sonar. Our understanding of impacts varies greatly by sound type and taxon, although the studied species do not represent the full taxonomic diversity. Exposure to ship sounds has been best studied in fish and it generally leads to responses along the stress response cascade, while few studies have been conducted on its physiological effect on invertebrates or marine mammals. Effects of exposure to seismic sound show mixed impact across taxa. Pile driving sounds have been shown in captive studies to result in hearing impairment in marine mammals and can cause injury to fishes. Lethal impacts have been documented from naval sonar on marine mammal species. Currently, physiological impacts from other industrial sound sources are poorly documented across taxa. Overall, given the limited number of species examined in sound impact experiments, it is crucial to establish categorizing principles and guidelines and modeled response pathways to improve management strategies, especially as new sound threats continue to emerge in our changing world.