Many marine animals like fish and whales rely on acoustic signals to communicate and to understand their environment. Noise pollution can have negative impacts on individual animals, but what are the larger-scale ecological consequences of anthropogenic marine noise?
David Attenborough’s Blue Planet II TV series in 2017 brought the ocean into our living rooms and exposed millions of people to current issues in marine conservation. In one memorable scene, a family of clownfish battled to be heard over high levels of anthropogenic noise in their surroundings. The parents were unable to communicate with their offspring, making the family more vulnerable to predation. This scene highlighted one impact of marine noise pollution, but this is a much broader and more pervasive issue than a brief moment of television drama can convey.
Changing perceptions of marine noise pollution
Pollution is often perceived as being an issue primarily about the release of harmful chemicals into the environment. Because chemical pollution (for example from oil spills and agrochemicals) presents a more visible threat to marine wildlife, it has historically eclipsed scientific and public conversation around other forms of pollution. The importance of noise pollution in marine ecosystems has gone largely unnoticed by scientists, governments and the public until relatively recently. But anthropogenic noise has the potential to be just as challenging an issue for the natural world, with sources of pollution coming from all kinds of human activity in the marine environment, including leisure, transport, military operations, and the acquisition of fossil fuels.
Although marine noise pollution has only been an established field of scientific enquiry for a little over two decades, studies in this field have already found anthropogenic noise to be harmful to a range of animals including fish,
cephalopods, corals and zooplankton. Marine noise pollution is now recognised by the scientific community as a global issue that has far-reaching physiological and behavioural consequences across these groups. These consequences can include damage to hearing¹, impaired vocal communication² and even direct mortality.³
The costs of marine noise
So far, most of the research into the consequences of marine noise pollution has focused on its behavioural effects on animals like fish, dolphins and whales. For example, orcas have been shown to alter their vocalisations in response to anthropogenic noise in their vicinity.² This might affect the signals being shared between members of a pod, thus having potential impacts on social bonding. Cetaceans have also been found to avoid noisy sites in the ocean⁴, suggesting that these animals may be unable to feed at sites that are subject to high levels of noise. Loud noises have also been found to induce stress responses in fish which can affect their foraging behaviour and thereby decrease their food intake.⁵
These behavioural impacts probably have adverse influences on the fitness of individual animals. However, so far there has been very little research into the long-term, ecosystem-scale consequences of anthropogenic noise. It is likely that the toll on individuals has cumulative impacts on animal communities, which in turn could be affecting whole marine ecosystems.
It is also important to recognise that behavioural influences are not the only consequences of anthropogenic marine noise. Recent studies have found evidence for effects of noise pollution which may have major ecological impacts such as direct mortality of zooplankton after exposure to sounds from seismic air guns³ (devices which survey the seabed using noisy blasts of compressed air). Zooplankton are at the lower trophic levels of the food web, meaning that they are important in supporting many other organisms in marine ecosystems. Therefore, the loss of zooplankton from marine environments probably poses a great threat to marine conservation efforts. However, as yet there is very little scientific data addressing the long-term ecological effects of marine noise pollution.
The need for long-term data
The paucity of evidence for large-scale ecological effects of marine noise pollution may reflect the more recent recognition of the topic, hence the lack of useful long-term datasets. We should not take the dearth of scientific evidence for ecological effects as an indication that noise pollution is ecologically harmless. It is highly unlikely that events, such as the loss of zooplankton, could occur without causing major damage to an ecosystem. Future studies of marine noise must look into its potential long-term effects, beyond behavioural changes in individuals. It will be much easier to draw the attention of governments and the public to this issue once we have established the true ecological costs of anthropogenic marine noise.
How can we mitigate noise impacts in the marine world?
There are multiple potential strategies which could be implemented to reduce noise pollution and minimise its impact on marine life. We can help to relieve the problem by creating quieter protected areas of the ocean⁶, where human activity is restricted. Additionally, industries which rely on the practices which create lots of marine noise may be more willing to reduce their impact if economic incentives are offered to help them change, or if regulations are put in place to restrict their activities. Such industries should be encouraged to use the quietest equipment possible, while also implementing tools such as bubble curtains (underwater walls of bubbles surrounding noisy sites like offshore drills⁷), which help to shield marine wildlife from anthropogenic noise. Illustrations and explanations of bubble curtains can be found here.
Ultimately, it may be necessary for people to abandon some of the most polluting practices and to seek less damaging alternatives.
Marine noise pollution is an emerging field in conservation which demands our attention. It poses a serious threat to marine ecosystems, requiring urgent co-ordinated action from governments and businesses around the world. In order to get this issue the international recognition it deserves, conservation scientists must pursue the relevant long-term ecological data necessary to establish the scale of the issue.
1. Scholik, A; Yan, H (2002) Effects of Boat Engine Noise on the Auditory Sensitivity of the Fathead Minnow, Pimephales promelas. Environmental Biology of Fishes, Dordrecht, v.63(2), pp.203-209. https://link.springer.com/article/10.1023/A:1014266531390
2. Holt, MM; Noren, DP; Veirs, V; Emmons, CK; Veirs, S (2009) Speaking up: Killer whales (Orcinus orca) increase their call amplitude in response to vessel noise. The Journal of the Acoustical Society of America, v.125(1), pp.EL27-32. https://www.ncbi.nlm.nih.gov/pubmed/19173379
3. McCauley, RD; Day, RD; Swadling, KM; Fitzgibbon, QP; Watson, RA; Semmens, JM. (2017) Widely used marine seismic survey air gun operations negatively impact zooplankton. Nature Ecology & Evolution, v.1(7), pp.195. https://www.nature.com/articles/s41559-017-0195
4. Williams, R; Erbe, C; Ashe, E; Beerman, A; Smith, J (2014) Severity of killer whale behavioral responses to ship noise: A dose–response study. Marine Pollution Bulletin, v.79(1), pp.254-260. https://www.sciencedirect.com/science/article/pii/S0025326X13007376
5. Voellmy, IK; Purser, J; Flynn, D; Kennedy, P; Simpson, SD; Radford, AN (2014) Acoustic noise reduces foraging success in two sympatric fish species via different mechanisms. Animal Behaviour, v.89, pp.191-198. http://www.bio.bris.ac.uk/research/behavior/Vocal_Communication/pdfs/Fish_foraging_comparison.pdf
6. Williams, R; Erbe, C; Ashe, E; Clark, CW (2015) Quiet(er) marine protected areas. Marine Pollution Bulletin, v.100(1), pp.154-161. https://www.sciencedirect.com/science/article/pii/S0025326X1530028X
7. Wursig, B.; Greene, C.; Jefferson, T. (2000) Development of an air bubble curtain to reduce underwater noise of percussive piling. Marine Environmental Research, v.49(1), pp.79-93. https://www.sciencedirect.com/science/article/pii/S0141113699000501