Fake it till you make it – sounds of a healthy coral reef may help to restore it to its former glory

by Juliana Andrea Berner

The ocean – an image of vast tranquility and serenity. Despite this, the ocean can be quite a noisy place!

Coral reefs make up less than one percent of the ocean floor. However, coral reefs include a plethora of species with about 25 percent of all marine life calling this place home. The biodiversity is believed to be more immense compared to even the biodiversity in rainforests [1]. From this erupts a symphony of sound! From the crackling of snapping shrimp to the parrotfish scraping for food or even just the movement of crustaceans over the reef. Creating an enchanting and quite noisy paradise [4].

The animal in question

The main star of these coral reefs are the corals themselves. Corals are sessile animals – in other words, they are stationary animals when in their adult stage. While in larval form the coral can swim by moving the cilia on the surface of their bodies. However, these larvae are not the strongest of swimmers, so they more or less follow the current to find a solid substrate to settle down and undergo metamorphosis [3]. Adult corals come in a variety of size, shapes and even structures; from large reef-building structures to graceful flowing flowers and even small solitary individuals [1].

On a coral itself are coral polyps which are the animal side of the overall coral. These coral polyps are in a mutualistic symbiotic relationship with the photosynthetic zooxanthellae algae. The algae live in the tissue of the corals providing the algae protection against the environment and the compounds it needs for photosynthesis. In exchange, the algae produce food and oxygen for the coral to survive while a bonus ridding the coral of its waste [2].

Some environmental factors need to be in place for the corals to thrive:

● Sunlight; the algae in the coral needs to do photosynthesis

● Clear water; to let the sunlight reach the coral reef

● Warm water; corals require warm and stable water condition to live and survive

● Clean water; corals are sensitive to pollution and sediments

● And last but not least salt water; as corals require a certain balance of salt to water ratio [5]

What ails our coral friends?

As a well-known fact, our coral reef ecosystems are severely threatened. Some threats are natural due to disease, predators, and storms. While other threats are anthropogenic such as pollution, sedimentation, unsustainable fishing practices, and rise in water temperatures leading to ocean acidification. These threats can cause stress to the corals, leading to coral bleaching. Coral bleaching occurs when the coral expels their symbiotic zooxanthellae algae from their tissue, turning the coral completely white. However, this bleaching does not always mean the coral is dead. If the environment turns favourable to the coral may actually survive, but if the stress-inducing conditions persist the coral will eventually die [1].

But there is hope!

A study by Gordon et al. - an international team of scientists from the Universities of Exeter, Bristol, and the Australian Institute of Marine Science - showed just how important sounds are for the coral reefs. Their findings showed that the area equipped with a loudspeaker playing sounds of a healthy coral reef had an increase of around 50% in juvenile fish recruitment to the degraded coral reefs in just 40 days compared to the site equipped with a loudspeaker but playing no sounds, and a control site with no interference. A remarkable find! This enrichment of juvenile fish enticed other species to pop up and join this habitat [6]. This novel tool could be a helping hand in restoring the reef to its former glory. Banding this novel tool with other conservation efforts such as growing and planting healthy corals, removing invasive species that are detrimental to the coral reefs, and overall monitoring that are implemented to restore and build coral reefs. However, even with these conservation tools, the outer anthropogenic stressors need to be tackled for these ecosystems to fully thrive and stabilize [7].

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References

[1] National Oceanic And Atmospheric Administration. “Coral reef ecosystems.” National Oceanic And Atmospheric Administration, Updated Feb. 2019, https://www.noaa.gov/education/resource-collections/marine-life/coral-reef-ecosystems

[2] International Coral Reef Initiative. “What are corals?” International Coral Reef Initiative, N.D., https://www.icriforum.org/about-coral-reefs/what-are-corals/

[3] National Oceanic And Atmospheric Administration. “Are coral animals or plants?” National Ocean Service website, Updated 26 Feb. 2021, https://oceanservice.noaa.gov/facts/coral.html

[4] University of Exeter. “New Hope for Coral Reef Restoration From Playing Sounds of Healthy Reefs on Loudspeakers.” SciTechDaily, 29 Nov. 2019, https://scitechdaily.com/new-hope-for-coral-reef-restoration-from-playing-sounds-of-healthy-reefs-on-loudspeakers/

[5] Coral Reef Alliance. “What Do Coral Reefs Need to Survive?” Coral Reef Alliance, N.D.,
https://coral.org/coral-reefs-101/coral-reef-ecology/what-do-coral-reefs-need-to-survive/

[6] Gordon, Timothy A.C., Radford, Andrew N., Davidson, Isla K., Barnes, Kasey, McCloskey, Kieran, Nedelec, Sophie L., Meekan, Mark G., McCormick, Mark I., Simpson, Stephen D. “Acoustic enrichment can enhance fish community development on degraded coral reef habitat.” (2019) Nature Communications, Volume 10, https://doi.org/10.1038/s41467-019-13186-2

[7] The Nature Conservancy. “A Revolution to Save Coral Reefs.” The Nature Conservancy, N.D., https://www.nature.org/en-us/about-us/where-we-work/caribbean/stories-in-caribbean/caribbean-a-revolution-in-coral-conservation/