In order to restore the ecology, they decided to play "music" outdoors

Produced by: Science Popularization China

Author: Earth's Gravity

Producer: China Science Expo

We have all listened to the sounds of nature, whether as a child or while traveling alone. These sounds are always nostalgic. Although these sounds may come from hundreds of different sources, they always make us feel inexplicably beautiful and harmonious.

With the rapid development of science and technology, these sounds from nature have not only become precious personal memories, but have also begun to become extremely important scientific research data, and even an important tool to help us restore the ecosystem.

Another wonderful use of acoustic monitoring

At first, scientists only conducted occasional and short-term sound data collection to study the distribution and habits of individual endangered or invasive species. For example, we often see bird observations and sound collection in some scientific news, and these collection activities are often occasional and short-term activities.

Scientists have proposed establishing long-term acoustic monitoring stations to collect and analyze the sounds of most animals near the monitoring stations . By distinguishing the sounds, they can determine which animal the sound belongs to, as well as the frequency and range of the animal's activities, thereby conducting a survey of animal diversity.

Traditional animal diversity surveys often require manual work, are time-consuming and labor-intensive, and may not necessarily collect all animal data. However, acoustic collection equipment is small and convenient, and does not disturb the environment much, so it is a very good method for animal diversity surveys. Based on this, Australian scientists have built an acoustic data collection network consisting of 360 permanent sound monitoring stations.

Australia's Acoustic Observatory Network

(Image source: Reference 1)

The installation of acoustic observation equipment is very simple

(Image source: Reference 1)

Moreover, this acoustic data can indeed fully reflect the diversity of local ecosystems, so it can naturally serve as an indicator for monitoring changes in local ecosystem diversity.

For example, French Island in Australia is often hit by wildfires. Scientists collected acoustic signals at the same location within 24 hours before and after the wildfire. The difference in the data can be clearly seen, and this data reflects the difference in local ecological diversity.

Comparison of acoustic data from the same location on French Island, Australia, before and after the bushfire.

(Image source: Reference 2)

After this idea came up, another idea naturally emerged: Is it possible to continuously play the sounds of an undamaged environment in a damaged environment to lure animals back to the damaged environment, so that the damaged environment can be quickly repaired.

This idea is not without reason, because we humans have had a long experience of using acoustic bait. The most familiar one to us may be the marine fishing industry, where fishing boats use acoustic technology to drive or lure schools of fish to specific areas. The technology of using acoustics to drive schools of fish appeared in my country during the Ming Dynasty. It is called the ancient technology of knocking on the boat. Fishermen knock on the boat boards to drive the fish together, and then set up nets to catch them. This technology has a very large catch volume, which once made fish species such as yellow croaker on the southeast coast of my country endangered, so it has been banned.

Acoustic fishing technology is to play the sounds of fish feeding, courting, and grouping in the water to induce the corresponding fish groups for fishing. This technology began to develop in the 1970s and has been very maturely applied in countries such as Japan, Russia, the United States, and Sweden.

However, the focus of scientists' recent research is not on how to lure fish, but on inducing specific responses in different animals , because many animals actually use sound signals to trigger different behaviors such as reproduction, migration, and alarm.

In research in these areas, some scientists have successfully used specific sounds to lure frogs, seabirds, bats, fish, etc. to different habitats; some scientists have studied using mating sounds to lure frogs and salamanders through underground tunnels of high-speed railways; and some scientists have studied using rainfall and frog calls to trigger frog reproductive behavior.

An experiment using sound to lure frogs to settle in areas without frogs. The black frame is the experimental area where no frogs had settled before, the asterisk is the location of the device that plays the sound, and the red and orange dots are frogs.

(Image source: Reference 3)

An attempt to protect the environment using sound

Based on these studies, scientists have successfully used sound to protect the environment, one of which is restoring oyster reefs.

Oyster reefs were once a common landscape in estuaries around the world. Oysters grew densely on reefs in shallow waters, forming large oyster reefs that provided habitats and refuges for multiple species and also provided natural breakwaters for estuaries.

However, due to overfishing and lime production, oyster reefs around the world have been severely degraded over the years. It is estimated that 85% of the world's oyster reefs have disappeared.

Oyster Reef

(Image source: Wikipedia)

Therefore, the world is exploring how to rebuild oyster reefs. The methods generally used are relatively expensive. First, sterilized dead oyster shells, concrete or limestone fragments need to be placed in the coastal shallows - because fishing often destroys the hard substrate in these places, and oysters need to attach to some hard substances to grow. Then artificially cultured oyster larvae are placed in these areas. But in fact, there are very few oyster larvae that can actually settle down, so the oyster reef restoration process cannot be achieved overnight. It needs to be placed and repaired year after year, which is both expensive and time-consuming.

A team of Australian scientists used the sounds they had recorded from normal reefs and repeatedly played them in areas where oyster reefs needed to be repaired. They found that within three months, the number of oyster larvae lured to settle there was 4.4±1.6 times that of the area where no sounds were played (control group). In March, the number lured was even 18 times that of the control group.

The area of ​​the oyster reef restoration experiment. The black star is the experimental area, the white star is the control area, and the lower right picture is the design of the underwater playback equipment

(Image source: Reference 4)

In addition, some scientists played the sound of normal coral reefs on damaged coral reefs, which lured a large number of fish communities living in the coral reefs, increasing the species richness of fish in the area by 50%. Since we are currently facing the crisis of coral reef degradation, this method also gives us more means to slow down the degradation of coral reef ecosystems.

Not only animals, sound even has effects on bacteria and fungi!

All of the above studies were conducted on animals. Recently, some scientists have discovered that sound is not only effective on animals, but also on bacteria and fungi.

In one experiment with Trichoderma harzianum (a fungus that can be used as a fungicide to inhibit the growth of other fungi and thus help the roots of plants grow normally), after playing white noise to them, they began to grow at an accelerated rate from the third day. During the five-day experimental period, their growth rate increased by 7 times and the number of spores increased by 4 times.

(a) is the fungus that received sound stimulation, (b) is the statistical result of (a), (c) (d) are the control group

(Image source: Reference 5)

Everyone loves music

This discovery is undoubtedly of great significance for the restoration of ecosystems on land. After all, soil ecosystems are the basis for the growth of plants and animals. Maybe one day in the future, when we walk in the forest, we will hear loud speakers playing white noise or Mozart or Beethoven, but that is not for us to listen to, but for the trees and soil to listen to.

References:

1.Roe P, Eichinski P, Fuller RA, et al. The Australian acoustic observatory[J]. Methods in Ecology and Evolution, 2021, 12(10): 1802-1808.

2.Znidersic E, Watson D M. Acoustic restoration: Using soundscapes to benchmark and fast-track recovery of ecological communities[J]. Ecology Letters, 2022, 25(7): 1597-1603.

3.James MS, Stockwell MP, Clulow J, et al. Investigating behavior for conservation goals: Conspecific call playback can be used to alter amphibian distributions within ponds[J]. Biological Conservation, 2015, 192: 287-293.

4.McAfee D, Williams BR, McLeod L, et al. Soundscape enrichment enhances recruitment and habitat building on new oyster reef restorations[J]. Journal of Applied Ecology, 2023, 60(1): 111-120.

5.Robinson JM, Annells A, Cando-Dumancela C, et al. Sonic restoration: acoustic stimulation enhances plant growth-promoting fungi activity[J]. Biology Letters, 2024, 20(10): 20240295.