In the sea, variations in the properties of seawater such as temperature, pressure, and salinity all have significant effects on the speed of sound propagation. Both the speed and the path upon which sound propagates are dependent on the characteristics of the medium through which it travelling. One important feature of sound is its transmissibility in various mediums. Frequency, wavelength, and intensity are the main parameters used to describe the characteristics of sound.
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Knowledge of the feature of sound is essential to a full understanding of the impacts of sound on marine organisms. In this paper, we summarize (1) the sources of biotic and abiotic sound undersea and the characters of anthropogenic sound, (2) the significance of sound to marine organisms, and (3) the effects of anthropogenic sound on various aspects of different species to elucidate the current understanding of noise pollution in the sea and the gaps in our current knowledge. However, the mechanisms underlying these effects are still poorly understood. A number of studies have shown that the effects of anthropogenic sound on marine organisms can range from no influence to immediate death depending on the differences in the intensity and frequency of the noise and the distance from the noise source. There is growing international concern regarding the impact of anthropogenic noise on marine organisms.
Noise may cause stress in animals, increase the risk of mortality by unbalancing predator-prey interaction, and interfere with sound-based orientation and communication, especially in reproductive contexts.
Consequently, the level of underwater background noise worldwide has increased correspondingly due to increased anthropogenic activities, which gives rise to a new kind of pollution: noise pollution. has continued to grow in the last century. Without doubt, anthropogenic sound from cargo ships, sonar, seismic testing, drilling, pile drivers, recreational holiday ships, and etc. In fact, sound plays a vital role in the lives of many marine organisms in this undersea world. However, with the deepening of the investigation of this “world,” the reality has proven not to be as silent as was initially thought. The French documentary The Silent World, co-directed by the famous French oceanographer Jacques-Yves Cousteau and director Louis Malle in 1956, presented a multi-colored and wonderful undersea world full of life and energy that satisfied the curiosity of audiences at the time. In addition, further studies are needed to reveal in detail the causes for the detected impacts.
Moreover, the scarcity of studies carried out with other species and with larval or juvenile individuals severely constrains the present understanding of noise pollution. However, since different sampling methodologies and unstandarized measurements were used and the effects of noise on marine organisms are dependent on the characteristics of the species and noise investigated, it is difficult to compare the reported results. Studies showed that anthropogenic noise can cause auditory masking, leading to cochlear damage, changes in individual and social behavior, altered metabolisms, hampered population recruitment, and can subsequently affect the health and service functions of marine ecosystems. In general, the studies about the impact of noise on marine organisms are mainly on adult fish and mammals, which account for more than 50% and 20% of all the cases reported. In this review, the source and the characteristics of noise in the sea, the significance of sound to marine organisms, and the impacts of noise on marine organisms are summarized. With the growing utilization and exploration of the ocean, anthropogenic noise increases significantly and gives rise to a new kind of pollution: noise pollution.
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