The world’s coral reefs provide an incredible source of biodiversity, they protect coastlines from erosion and extreme weather such as storms and provide jobs for those in the local community surrounding the reef. Unfortunately, these aquatic ecosystems have faced a myriad of threats over recent decades.
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Increasing levels of sea pollution, destructive fishing methods such as those that utilize dynamite, global warming, and the rising acid pH of the ocean have had a detrimental impact on the world’s coral reefs. Now, emerging evidence warns of another threat that may further jeopardize the future of the world’s coral reefs. Noise pollution is raising new concerns over the security of coral reefs, which scientists are already struggling to revive from intensive damage.
Ships and drills prevent baby coral from finding their way home
New data shows that sound is vitally important to the health of coral reefs. Baby corals begin life as swimming larvae and navigate back to the reef to settle by listening to the subtle sounds of the aquatic life on the reef. Human activity is loud in the oceans, existing in the forms of ship and boat engines and drills used in oil and gas retrieval. These sounds that are not native to the aquatic environment mask the softer sounds that come from life on the reef, making it difficult for baby coral to find their way home.
Previously, research had been published demonstrating that noise pollution in the ocean increases the mortality of juvenile fishes during a critical period. Around 60% of young fish who live on coral reefs die within their first two days of life. Several years ago, scientists found that boat and ship noise further exacerbates this high mortality rate by decreasing the activity of juvenile fishes, leading to them swimming out of the reef at decreased distances.
Young fish who swim out further are more likely to learn about their environment and predators faster, therefore, those who remain close to the reef have reduced chances of survival. Now, scientists are surprised that noise pollution not only threatens the survival of fish who live on reefs but of the coral itself.
Recent evidence that has emerged as the result of a research project conducted in the Caribbean has shown that the survival chances of coral larvae are also negatively impacted by noise pollution. Baby corals start life as tiny larvae that spend their first days swimming in the waters that surround the reef. In order to survive, they must quickly find a place to land and make home. To guide them, the tiny larvae use sounds from the reef as cues. However, if masked by noise pollution, the larvae fail to hear these vital auditory cues.
In the new research, the researchers developed a device known as a “choice chamber” which offered the larvae a choice of two or more conditions, allowing them to move towards their preferred condition. The team placed coral larvae in the chamber and played them recordings of the coral reef. The results show that the noise of the reef induced a strong attraction in the larvae as they sought to find a habitat.
While it remains unclear how the tiny larvae, which look like miniature hair-covered eggs, detect sound, scientists have hypothesized that the vibrations caused by the sound cause motion in the tiny hairs that allow the larvae to hear.
Because the sound of the reef is vitally important to fish and coral, there is an urgent need to monitor and regulate the levels of sound pollution in key aquatic environments, such as coral reefs. Ships, drilling, and even small boats and seismic testing all contribute to noise pollution that can drown out the sounds of the reef and reduce the chances of survival of fish and coral.
The importance of protecting coral reefs
Coral reefs are sometimes referred to as “the rainforests of the sea”. Coral reefs are rich and diverse ecosystems, they are home to a quarter of all aquatic species although they occupy just 1% of the ocean’s surface. As well as being a valuable source of biodiversity, they also support local communicates that live near the reef by providing jobs in the sectors of tourism and fishing. The reefs protect shorelines from erosion.
Finally, coral reefs are becoming increasingly important for drug discovery. More and more, scientists are looking to marine invertebrates as a source of compounds to use in the development of novel therapeutics. AZT, the world’s first drug against AIDS, was developed from a chemical found in the Caribbean sea sponge.
It is important that governments and key stakeholders are aware of the danger that noise pollution poses to coral reefs and that monitoring and strategic interventions are established as a matter of urgency.
- Ferrier-Pagès, C., Leal, M., Calado, R., Schmid, D., Bertucci, F., Lecchini, D. and Allemand, D., 2021. Noise pollution on coral reefs? — A yet underestimated threat to coral reef communities. Marine Pollution Bulletin, 165, p.112129. https://www.sciencedirect.com/science/article/pii/S0025326X21001636
- McCormick, M., Allan, B., Harding, H. and Simpson, S., 2018. Boat noise impacts risk assessment in a coral reef fish but effects depend on engine type. Scientific Reports, 8(1). https://www.nature.com/articles/s41598-018-22104-3
- Velasquez Jimenez, L., Fakan, E. and McCormick, M., 2020. Vessel noise affects routine swimming and escape response of a coral reef fish. PLOS ONE, 15(7), p.e0235742. journals.plos.org/plosone/article?id=10.1371/journal.pone.0235742