Typically, when one thinks of pollution, images of garbage and oil spills may come to mind. The consequences of pollution are widespread. Understanding the ways, we impact our environment has led to changes in consumption and use, like reducing the consumption of fossil fuels, using metal straws and mineral based sunscreens.

However, there is a type of pollution that is just beginning to be discussed: sound pollution, also referred to as noise pollution. So, what is sound pollution? Webster’s Dictionary defines sound pollution as “environmental pollution consisting of annoying or harmful noise.” These annoying or harmful noises can constitute many things from recreational to military and scientific activities. Through the expansion of trade and exploration, anthropogenic sound has increased exponentially. The oceans ambient noise has been masked with the noise of shipping vessels and sound beams, disrupting a natural rhythm in this environment. In the marine environment, anthropogenic sound has caused changes in the natural behavior and/or physiology in marine invertebrates to marine mammals. For this reason, understanding what the causes are of excess sound, how anthropogenic sound has affected the marine environment and biota, and reducing the impacts are essential. Before discussing anthropogenic impacts on noise in the environment, understanding the behavior of sound in seawater is fundamental. Sound is type of mechanical energy that changes pressure through vibration during travel within a medium in the form of a wave. It produces a longitudinal wave and changes pressure through compression and decompression (Carroll, Przeslawski, Duncan, Gunning, & Bruce, 2017). Seawater is a more effective medium for sound to travel than air because it slows the absorption of sound. The sound detected from hydrophones or other auditory structures is the result of pressure changes.

Loud noises have a high amplitude and intensity. The sound pressure level (SPL) is used to compare the intensity or amplitude of two sound waves in decibels (dB) (Carroll et al., 2017; McCarthy, 2004). It is important to note, this measurement is relative to a logarithmic scale using the standard pressure reference in a medium (Carroll et al., 2017; McCarthy, 2004). In seawater, the reference standard of pressure is usually 1 µPa unless stated otherwise (Carroll et al., 2017; McCarthy, 2004). The number of pressure waves that pass a point in one second is the frequency and is measured in hertz (Hz) (Carroll et al., 2017). Differences in pressure, salinity, and temperature can affect the way sound moves. Sound waves move faster when pressure, temperature, and salinity is high and decrease as one lowers (Carroll et al., 2017). Sound intensity decreases the further it gets from its source because of absorption, scattering, and spreading effects. (Garrison, 2013). Generally, the longer it takes a sound wave to absorb, scatter, or spread, the greater distance the sound wave travels (Garrison, 2013). High frequency waves are more readily absorbed while low frequency sounds, less than 1,000 Hz, are absorbed more slowly.

Therefore, low frequency waves travel farther distances, upwards of thousands of kilometers (McCarthy, 2004). When considering the influence of sound on marine life several factors must be accounted for including duration, frequency, intensity, similarity to biological sounds, and the hearing sensitivity of species (McCarthy, 2004). It is equally important to recognize the ocean’s ambient noise. Ambient noise consists of a mixture of wind, waves, currents, surface weather, seismic activity, and biological activity (McCarthy, 2004). Geophysical and physical noise creates varying frequencies. For instance, seismic noise from volcanoes and tectonic plates produce low frequencies, usually below 100 Hz, whereas wind and waves produce frequencies between 100 and 50,000 Hz (McCarthy, 2004). Periods of precipitation can produce added noise at 100 to 500 Hz (McCarthy, 2004). The presence of sea ice and decrease ambient sound levels by preventing wind from interacting with the surface (McCarthy, 2004). Biological noise is created from many different taxa and activities. Intraspecific communication, foraging, predator-prey interactions, metabolic rate, reproduction, and larval development are some examples of physiological and biologically processes.

Cetaceans are well known to use echolocation to communicate, navigate, and feed. Echolocation has a broad range of frequencies from 10 Hz to 200,000 Hz (McCarthy, 2004). In addition to cetaceans, some fish use low frequency sound for communication and is most pronounced when males are trying to attract females during breeding season (McCarthy, 2004). Other biological noise comes from daily activities, such as foraging and swimming. For example, the snapping shrimp can produce noise between 2,000 and 15,000 Hz when snapping its long front claw closed (McCarthy, 2004). Bubbles produced during photosynthesis also produce small pings when they pop (Freeman, Freeman, Giorli, & Haas, 2018). The combination of these affects make-up the ambient noise in the ocean. Nevertheless, humans are impacting natural sound. There are many sources contributing to anthropogenic noise in the marine environment. Perhaps the most common source is generated from recreational and commercial vessels.

Vessel activity produces three types of noise: high frequency sounds from the cavitation of the propeller blade, hydrodynamic noise from the passage from propeller to hull, and mechanical noise coming from the engine and gearboxes (McCarthy, 2004; Pine, Jeffs, Wang, & Radford, 2016). The sound frequency generated changes based on a vessels size, load type and weight, and speed (Pine et al., 2016). Low frequency waves generated mask biologically important sound waves, because they are within the audible range of many organisms, including dolphins, fishes, and crustaceans (Pine et al., 2016). For this reason, the masking of biological sounds in highly productive coastal areas near ports is a growing concern. A case study in Hauraki Gulf Marine Park near a port in Auckland City, New Zealand aimed to determine the extent of masking from increased anthropogenic noise in the embayment. Hauraki Gulf Marine Park is a large embayment that is highly productive and ecologically important (Pine et al., 2016). In 2000, the park was legislatively protected with the Hauraki Gulf Marine Park Act to protect the 25 species of marine mammals that make annual visits with 6 being resident species, over 80 fish species, and 700 invertebrate species. As of 2011, there are 132,000 recreational vessels and is expected to reach 183,000 by 2041 (Pine et al., 2016). The study concluded that small vessels moving about 9 km h-1 in shallow waters reduced bottlenose dolphin (Tursiops truncates) communication range by 26% and 58% in pilot whales (Globicephala macrorhynchus) within 50 m of the sound source (Pine et al., 2016). Another study looked at the raise in noise levels within the Strait of Georgia, BC in relation to the predator-prey relationship of the killer whale (Orcinus orca) and Chinook salmon (Oncorhynchus tshawytscha) and found that vessels increased noise by 10-15 dB (Williams et al., 2015). The Strait of Georgia, BC is a busy shipping route heading to the Port of Vancouver. The increase in noise could potentially impact the way O. orca communicates and finds prey as it reduces their range of communication (Williams, Clark, Ponirakis, & Ashe, 2014). Other anthropogenic sources impacting the marine soundscape include seismic surveys, construction, and use of sonar in military and scientific activities. Seismic surveys greatly contribute to our understanding of the structure, composition, and dynamics of the Earth’s crust as well as locating natural gas and oil in offshore sedimentary basins (Przeslawski, Brooke, Carroll, & Fellows, 2018). There are a few methods used in seismic surveying including sleeve exploders and gas guns, but most commonly used are airgun arrays (McCarthy, 2004). During these surveys, airgun arrays are towed behind a vessel and release compressed air in the form a bubble, which radiates through the water column until reflected off the seafloor and recorded through acoustic devices onboard the vessel (Przeslawski et al., 2018). These surveys produce high intensity, low frequency sound at regular intervals that can be detected hundreds of kilometers away (Carroll et al., 2017; McCarthy, 2004; Przeslawski et al., 2018). These arrays are within the audible range of many fishes and elasmobranchs and have been documented to induce a physiological response in cephalopods and decapods (Carroll et al., 2017). Coastal construction often consists of pile driving, which produces some of the most intense anthropogenic sound (Thompson et al., 2010). It is believed that sensitive cetaceans, such as harbour porpoises, within close range of pile driving could experience hearing threshold damage (Bailey et al., 2010; Thompson et al., 2010). During the construction of two wind turbines off the coast of Scotland, noise produced from pile driving was recorded 70 km away and possibly affected the behavior of bottlenose dolphins (T. truncates) and minke whales (Balaenoptera acutorostrata) up to 50 km away (Bailey et al., 2010). While the first piling event showed no difference in echolocation clicks, few to no clicks were recorded during the second piling event (Thompson et al., 2010). These results are believed to be a disturbance response due to comparison data of the following year (Thompson et al., 2010). Additionally, military and scientific use of sonar are sources of repeated anthropogenic sound.

The applications of sonar include the detection of vessels, schools of fish, and shipwrecks, as well as measuring water depth and current and mapping the ocean floor (McCarthy, 2004). Sonar frequency ranges from a few hundred hertz to hundreds of kilohertz, however each task has an optimal frequency (McCarthy, 2004). The use of sonar used by the navy has the potential to impact animals within a 3.6 million km2 area (Nabi et al., 2018). Additionally, mid-frequency active (MFA) sonar used in military exercises produce frequencies from 1-10 kHz and are associated with mass strandings of beaked whales (DeRuiter et al., 2013; Goldbogen et al., 2013). These sources can produce more intense sounds in the marine environment affecting the fauna. Marine mammals that use echolocation are believed to be impacted the most by anthropogenic sound and therefore appear in more publications. Even though more publications mention cetaceans, our understanding on them is limited. This is due to the short amount of time they spend at the surface, as well as a poor understanding of their hearing sensitivity (Johnson & Tyack, 2003). Cetaceans are thought to have sensitive hearing and are highly vocal creatures using sound to communicate, forage, navigate, learn about their surroundings, and detect potential predators (Nabi et al., 2018). Echolocation can occur in any frequency, but the different whale sub-classes gravitate toward specific frequencies. For instance, odontocetes, or toothed-whales, mostly vocalize above 2 kHz while mysticetes, or baleen whales, primarily vocalize under 2 kHz (Payne & Webb, 1971). Anthropogenic sound induces behavioral and physiological changes that effect reproduction and functional ecology. Although marine mammals do not have the ability to prevent masking from intense anthropogenic noise, they do have adaptations that allow them to prevent masking from ambient sounds in the local environment (Nabi et al., 2018). Such adaptations include modifying frequency ranges, increasing vocalization levels, and changing the temporal pattern (Nabi et al., 2018). Sound-induced behavioral changes are the most common response to biological masking. Silencing, increased song or dive length, diversion from sound source, disruption of activity, and stranding are some examples of behavioral changes (Johnson & Tyack, 2003; Nabi et al., 2018). These behavioral changes are believed to play a roll in the reproductive success of all marine mammals (Nabi et al., 2018). During breeding seasons, masking or silencing the mating song or displacing them from critical breeding grounds will decrease the success of attracting a mate (Nabi et al., 2018). Displacement from breeding grounds can occur over long periods, as in one study that found vessel and dredging noise displaced Gray whales from breeding grounds for 10 years (Nabi et al., 2018). Reductions in vocalizations are commonly seen near seismic surveys and other sources of intense noise like in the construction of two wind turbines of the coast of Scotland (Thompson et al., 2010). Vessel activity has been documented to lower foraging capability which can contribute to decreased reproduction rates and decreased immunity (Nabi et al., 2018). Sound can also cause physiological responses, including increased cortisol levels and hearing loss (Nabi et al., 2018). Experiments on captive animals show a direct correlation of increased cortisol levels and noise (Nabi et al., 2018). Intense sound can reach species specific threshold shifts leading to permanent (PTS) or temporary (TTS) hearing loss depending on the duration and intensity of the noise (Nabi et al., 2018). Hemorrhages in the cochlear duct consistent with acoustic injuries have been found in beached beaked and Cuvier’s beaked whales confirming hearing loss (Nabi et al., 2018). Cetaceans close in proximity to sonar, pile driving, seismic surveys, and explosives are at an increased risk of hemorrhages and embolisms (Nabi et al., 2018). Although much research has focused on cetaceans, other taxa are also affected by these sources. Publications involving sound pollution effects on fish have been increasing the past few decades (Williams et al., 2015). However, the auditory system of fish has been extensively studied (Carroll et al., 2017). Fish have a broad range of hearing capabilities due to interspecific variability in auditory structures (Carroll et al., 2017). In bony (teleost) fish, hearing results from particle motion of the three main auditory components, collectively called otolithic organs (Carroll et al., 2017). Sound is an important indictor in both adult and larval forms.

Larvae fully develop otolithic organs within 2 days of hatching to orient themselves (Carroll et al., 2017). Furthermore, fish that possess gas-filled chambers, like swim bladders, can have indirect sound stimulation through pressure changes, extending their detectable frequency range (Carroll et al., 2017). Adversely, fish with gas-filled chambers are more susceptible to pressure-mediated injuries (Carroll et al., 2017). However, the physical effects of sound pollution in teleost fishes is not as well understood has behavioral effects (Carroll et al., 2017). Like cetaceans, fish can experience PTS and TTS when exposed to intense sound, but PTS is less likely because fish are able to regenerate lost or damaged sensory cells (Carroll et al., 2017). Physiological effects are mostly due to increased stress levels, which are indicated by ventilation rates and cortisol levels (Carroll et al., 2017). Low frequency sounds induce stress and behavioral effects, such as reduced foraging and predator avoidance, distribution changes, increased swimming speed, and alarmed reactions (Carroll et al., 2017; Nedelec et al., 2016). These effects have been documented to be reduced as exposure continues due to habituation. To illustrate, a field experiment on juvenile Dascyllus trimaculatus in the French Polynesia, showed short-term behavioral and physiological changes in response to a motorboat playback, but were reduced within one week of exposure (Nedelec et al., 2016). This is likely a result of habituation, but it is not seen in all species (Nedelec et al., 2016). Species that do become accustomed to noise may be more prone to overfishing or exposure to disease, so it may not be advantageous (Nedelec et al., 2016). In elasmobranchs, auditory structures resemble teleost fishes, but possess an addition organ called the macula neglecta (Carroll et al., 2017). Elasmobranchs are highly sensitive to low frequency sound (~ 20 Hz to ~ 1500 Hz) probably due to an evolutionarily adapted response of irregular vibrations produced by injured fish (Arthur A., 2001; Carroll et al., 2017). Abrupt intense noise can cause elasmobranchs to withdrawal from a sound source when they are within 10 m even when favorable noise is present (Arthur A., 2001). Like teleost fishes with gas-filled chambers, they may be susceptible to barotrauma, but other effects are not known (Carroll et al., 2017). Further research is needed on all fishes to determine the extent of sound pollution. Specifically, invertebrates have been underrepresented in sound pollution publications and research that has been done, primarily focuses on crustaceans (Carroll et al., 2017). Some marine invertebrates detect sound through a sensory organ called a statocyst, which form during the larval stage, but the effects on larval stages are not well documented (Carroll et al., 2017). Like otolithic organs in fish larvae, these statocyst help the larvae orient themselves so it is possible anthropogenic sound affects the success of these organisms (Carroll et al., 2017). Other sensory structures include setae in decapods and epithermal hair cells in cephalopods (Carroll et al., 2017). Like elasmobranchs, invertebrates do not have swim bladders, therefore they rely on particle motion for sound sensory (Carroll et al., 2017). Intense sound from seismic surveys is thought to be the cause of anatomical damage, but there is limited research to support this (Carroll et al., 2017). Although, there have been studies that have shown acoustic trauma to the statocyst in lab experiments. For example, four species of cephalopod had statocyst trauma after two hours of continuous sound in a 200-liter tank (Carroll et al., 2017). Like fish, there is more evidence of behavioral responses in invertebrates.

Behavioral responses in cephalopods consist mostly of startled reactions, such as inking and jetting (Carroll et al., 2017). Startled reactions in decapods has been observed, but only when individuals are with 10 cm of the sound source (Carroll et al., 2017). Other behavioral changes seen are righting times and foraging. A field experiment found that shore crabs (Carcinus maenas) aggregated around food less when exposed to elevated sound levels, than common shrimp(Crangon crangon), but neither species had a reduced feeding rate (Hubert et al., 2018). Another experiment looked at C. maenas behavior and physiology when exposed to vessel activity playback. This experiment found C. maenas was more distracted from food, took longer to find shelter during a predatory event, righting themselves, and elevated oxygen consumption (Williams et al., 2015). Cephalopods may experience lower respiration rates like those observed in Octopus ocellatus when exposed to sound between 50-150 Hz (Carroll et al., 2017). Invertebrates make up most of the fauna, but our understanding of the effects of sound pollution needs further study. Though there are gaps in our understanding, policies to alleviate sound pollution effects are underway. Research on ocean acoustics began during World War II for military advances (Williams et al., 2015). Journal publications began in the 1940s but were concentrated on ocean noise not impacts (Williams et al., 2015). Publications on the impacts of anthropogenic sound to marine life became more important in 1990s (Williams et al., 2015). Payne et al. were one of the first to suggest whales were being affected by anthropogenic noise in 1971 (Williams et al., 2015). A report from the Worldwatch Institute, a non-profit public policy research organization, released in 1993 is one of the earliest references to sound as an environmental pollutant (McCarthy, 2004). Due to the distances sound can travel, it is classified as a transboundary energy and a pollutant under the 1982 United Nations Convention on the Law of the Sea (UNCLOS) providing a framework for future policies (McCarthy, 2004). UNCLOS has been ratified by 138 states and the European Union and requires protection and preservation of the marine environment (McCarthy, 2004). With that in mind, international policies involving ocean noise are minimal (Merchant, 2019). This is partly due to uncertainty in the economic cost of implementing these policies (Merchant, 2019). There are other organizations that could play a future role in policy formation including the United Nations Environmental Programme, The International Maritime Organization, and International Whaling Commission, all of which have addressed noise in the past (McCarthy, 2004). Currently, there is not enough public awareness on sound pollution to further policy abatement (McCarthy, 2004). Although they do not lower the amount of noise pollution, there are a few forms of mitigation, such as spatiotemporal restrictions and introduction of additional noise (Merchant, 2019). Spatiotemporal restrictions are based on the short-range detection of marine mammals while the introduction of additional noise of less intensity aims to deter animals before high intensity sound begins (Merchant, 2019). Incentive-based and command-control measures as well as Marine Protected Areas could be the solution to lowering sound pollution effects in the future (McCarthy, 2004; Merchant, 2019). Many marine animals use low frequency sound for intraspecific communication, foraging, predator-prey interactions, navigation, and environmental awareness. Even though our understanding is incomplete on their auditory mechanisms, we are beginning to understand how they respond to anthropogenic sound through the trophic levels.

The combination of geophysical and biological noise makes the ocean a noisy place by nature. Organisms here have evolved to utilize sound instead of sight due to its propagation through water. Anthropogenic activities producing low frequency sound, like vessel activity, affects marine fauna because it is within their audible range masking important sounds. Some species, like D. trimaculatus , can become habituated to this noise, but this may not be beneficial. Other behavioral effects such as noise avoidance and silencing can be destructive to reproduction, mortality, distribution, and interspecific interactions. Seismic surveying and pile driving are contributors to intense low frequency noise, which pose physical dangers although may not be as consistent as vessel activity.

When intense low frequency noise reaches an organism’s threshold, PTS, TTS, or death can occur. This is believed to be the cause of whale strandings. The effects of stress caused by anthropogenic sound increases cortisol levels and respiration rates in many taxa. Although, sound is not directly seen as an environmental pollutant, it can have effects on populations and ecosystems.

Finding ways to maintain enterprises and economic cost while reducing noise impacts proves to be challenging and lacks incentives towards finding a solution. REFERENCES Arthur A., M., Jr. (2001). The acoustical biology of elasmobranchs. Environmental Biology of Fishes, (13), 31. Retrieved from http://ezproxy.fau.edu/login?url=http://search.ebscohost.com/login.aspx?direct=true&AuthType=ip,cookie,url,uid&db=edsovi&AN=edsovi.00009238.200106010.00007&site=eds-live&scope=site Bailey, H., Senior, B., Simmons, D., Rusin, J., Picken, G., & Thompson, P. M. (2010). Assessing underwater noise levels during pile-driving at an offshore windfarm and its potential effects on marine mammals. Marine Pollution Bulletin, 60(6), 888-897. doi://doi.org/10.1016/j.marpolbul.2010.01.003 Carroll, A. G., Przeslawski, R., Duncan, A., Gunning, M., & Bruce, B. (2017). 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L., John, C., Friedlaender, A. S., Hazen, E. L., . . . Tyack, P. L. (2013). Blue whales respond to simulated mid-frequency military sonar. Proceedings of the Royal Society B: Biological Sciences, 280(1765), 20130657. doi:10.1098/rspb.2013.0657 Hubert, J., Campbell, J., van der Beek, Jordy G, den Haan, M. F., Verhave, R., Verkade, L. S., & Slabbekoorn, H. (2018). Effects of broadband sound exposure on the interaction between foraging crab and shrimp – A field study. Environmental Pollution, 243(Pt B), 1923-1929. doi:10.1016/j.envpol.2018.09.076 Johnson, M. P., & Tyack, P. L. (2003). A digital acoustic recording tag for measuring the response of wild marine mammals to sound. IEEE Journal of Oceanic Engineering, 28(1), 3-12. doi:10.1109/JOE.2002.808212 McCarthy, E. (2004). International regulation of underwater sound : Establishing rules and standards to address ocean noise pollution. Boston: Springer. Retrieved from http://ezproxy.fau.edu/login?url=http://search.ebscohost.com/login.aspx?direct=true&AuthType=ip,cookie,url,uid&db=nlebk&AN=119740&site=eds-live&scope=site Merchant, N. D. (2019). Underwater noise abatement: Economic factors and policy options. Environmental Science and Policy, 92, 116-123. Nabi, G., McLaughlin, R. W., Hao, Y., Wang, K., Zeng, X., Khan, S., & Wang, D. (2018). The possible effects of anthropogenic acoustic pollution on marine mammals’ reproduction: An emerging threat to animal extinction. Environmental Science and Pollution Research, 25(20), 19338-19345. doi:10.1007/s11356-018-2208-7 Nedelec, B., Nedelec, S. L., Mills, S. C., Lecchini, D., Simpson, S. D., & Radford, A. N. (2016). Repeated exposure to noise increases tolerance in a coral reef fish. Environmental Pollution, 216, 428-436. doi:10.1016/j.envpol.2016.05.058 Noise pollution. (2019). Retrieved from https://www.merriam-webster.com/dictionary/noise%20pollution#medicalDictionary Payne, R., & Webb, D. (1971). Orientation by means of long range acoustic signaling in baleen whales. Annals of the New York Academy of Sciences, 188(1 Orientation), 110-141. doi:10.1111/j.1749-6632.1971.tb13093.x Pine, M. K., Jeffs, A. G., Wang, D., & Radford, C. A. (2016). The potential for vessel noise to mask biologically important sounds within ecologically significant embayments. Ocean and Coastal Management, 127, 63-73. doi:10.1016/j.ocecoaman.2016.04.007 Przeslawski, R., Brooke, B., Carroll, A. G., & Fellows, M. (2018). An integrated approach to assessing marine seismic impacts: Lessons learnt from the gippsland marine environmental monitoring project. Ocean & Coastal Management, 160, 117-123. doi://doi.org/10.1016/j.ocecoaman.2018.04.011 Thompson, P. M., Lusseau, D., Barton, T., Simmons, D., Rusin, J., & Bailey, H. 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