By Evangeline Wilby
When humans explore below the surface of the ocean, sound fuses into one background noise, but to marine life, this is a diverse array of sound that is essential to their existence. Specifically, the coral reef; a noisy habitat with a language scientists are yet to fully uncover (Honeyborne et al., 2017). Most people are familiar with whale song and dolphin whistles as being a part of these large cetaceans’ migration and communication, but sound is also essential for a much greater variety of organisms that are potentially less appreciated. Anthropogenic pressure such as noise pollution is therefore effecting marine populations and is an important area of study for conservation policy.
Noise affects the behaviour, physiology and physicality of marine life, leading to potentially devasting effects on fitness and ecosystem function due to auditory masking (perception of one sound being affected by the presence of another).
Most marine organisms can hear sound at a frequency of 100Hz – 1kHz, and most sound from human activity fits into this range. This can affect the ability of organisms to select appropriate habitats, forage, reproduce and detect predators, all of which they do by listening to the sound of the reef ecosystem (Ferrier-Pages et al., 2021). For example, research into coral reef larvae shows that they use sound from the reef to detect an appropriate habitat and settle there, being attracted to noises from fish and crustacea. These findings are important because they show auditory response in invertebrate phyla such as cnidaria, including jellyfish and anemones (Vermeij et al., 2010). Sharing of acoustic space by organisms is less studied in marine environments compared to terrestrial, highlighting the importance of research into noise pollution in the ocean for protecting marine habitats (Bertucci et al., 2020).
Clownfish use buzzing sounds to deter predators, such as coral trout. In a study, the audibility of these sounds were monitored as boats passed over the coral reef and this natural communication was lost, leaving the fish vulnerable to predation. These results have been replicated in many vocal species such as seabass, blue tuna, squid and lobsters (Honeyborne et al., 2017). Additionally, noise pollution is believed to be a major cause of stress and acoustic trauma in whales and dolphins, especially sonar systems used in submarine detection. This can cause stranding’s of such organisms. This stress can have further fatal impacts such as reduced immunity and lowered food intake coupled with increased metabolism which can cause a reduction in growth (Peng et al., 2015).
Noise pollution can also cause direct physical harm to the inner ear structure, damaging cochlear cells for up to 58 days after exposure to noise such as sound from a seismic air-gun. Additionally, permanent damage to sensory hair cells in the ear of many cephalopod species can be caused by noise pollution and lead to mass stranding’s. Even if the noise pollution doesn’t damage the ear structure beyond repair, it may alter the range for which the organism can hear sound, again affecting its crucial communication systems (Peng et al., 2015).
The behaviour of marine species is also affected by noise pollution, causing group living organisms to swim in a more tightly packed group. Additionally, it can induce various stress responses, for example, loggerhead turtles have been observed to induce a dive/avoidance response to anthropogenic noise (DeRuiter et al., 2010). However, some species have adapted their communication in response to noise pollution, such as humpback whales and bottlenose dolphins that have the ability to alter their courtship calls in the presence of certain unnatural sounds (Miller et al., 2000). This suggests that there is some ability to counteract noise pollution, but management policy and conservation strategy will need to play a major role in further protecting the vast diversity of marine species affected by noise pollution.
In order to protect the natural noise of the reef, one solution would be to remove old boats and vessels with the loudest engines. For example, in the port of Vancouver, there are reduced docking fees for ships that meet a certain standard in terms of reduced noise pollution (Honeyborne et al., 2017). Additional solutions include the making of marine protected areas where certain boats are not allowed. Studies here have shown that there is a higher level of acoustic diversity and complexity in protected areas compared to non-protected areas (Bertucci et al., 2016). Further studies in islands such as Bora Bora in French Polynesia have identified that acoustic diversity is much higher at night compared to the day, with a specific peak at dusk (Bertucci et al., 2020). This knowledge could be used to inform policy in the sense that boats would not be allowed in specific areas at night where communication could potentially be more important. Similarly, if there are known animal migration routes, then these can be protected from loud vessels.
Acoustic enrichment is an interesting innovation, that uses speakers playing ‘healthy coral reef’ sounds in an attempt to restore reef biodiversity. This was shown to recruit 50% higher species richness in comparison to reefs not using acoustic enrichment. However, this is only a potential solution to noise pollution, where as other conservation initiatives target multiple anthropogenic stressors (Ferrier-Pages et al., 2021). The United Nations Sustainable Development Goal 14 includes the aims to protect ‘life below water’. This an example of a move towards legislation against noise pollution and this is a step in the right direction for protection. However, further technological advances are also crucial, such as quieter boat motors and propellers, or electric engines, that also reduce fossil fuel consumption and therefore help to tackle further pressures on the reef.
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