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Soundscapes consist of any sound coming from physical, biological and man-made sources. The physical sounds come from physical forces, such as rocks falling, wind, or breaking waves, and biological sounds are created by actual organisms. Thus, the soundscape of an ecosystem has the potential to provide useful information regarding its structure. There have been several studies looking at bird calls in combination with other sounds convey information about different environments. However, in the marine realm, the effectiveness of soundscapes to provide this information is still somewhat up in the air. Many studies have shown that juvenile fishes and larvae utilize acoustic cues to recruit to reefs, which possibly suggests that more diverse sound is connected to healthier habitats. Several studies looking at reefs before and after degradation from storms and/or ocean acidification examine this idea, and come to the conclusion that damage caused by climate change has a negative effect on these marine soundscapes, overall producing quieter and less complex sounds. This could create a negative feedback loop in which quieter, less diverse soundscapes attract fewer organisms, resulting in even more declension and ultimately weakening reef resilience.
Ocean acidification can substantially reduce the sound level and frequency in a marine soundscape. A study in 2016 (Tullio et al.) examined the frequency and magnitude of the snaps of snapping shrimps at two natural CO2 vents in Italy and one in New Zealand. Researchers found that after three to four months of CO2 exposure, the frequency(snaps per minute) and sound pressure level (SPL) had been substantially reduced. The study found that this is due to a “CO2-induced disruption of soniferous behavior”. Snapping shrimps are among the loudest marine invertebrates, and the most common organism present in a soundscape. This behavior change could potentially decrease larval orientation and recruitment, bolstering the aforementioned feedback loop. Another study from 2018 (For further reading, see Gordon et al.) reached similar conclusions. Researchers compared soundscapes of 10 lagoonal reefs before and after damage from Cyclone Ita, Cyclone Nathan, and the mass bleaching event in the Great Barrier Reef in Australia. The post degradation soundscapes were around 15 dB and 1µPa quieter, with less acoustic complexity, acoustic richness, snap rates, and SPLs than their predegradation counterparts. Once again, this augments the activity of a destructive feedback loop, in which reduced recruitment leads to further degradation.
The majority of work done on marine soundscapes has focused on coral reefs, but they are not the only ecosystems threatened by global changes. Oyster reefs are also negatively affected by ocean acidification, storms, and warming temperatures. These reefs provide important habitats for many marine species, including nurseries for juveniles. They also filter water and cycle nutrients, and their complex structure protects coastlines from storms. Similar to coral reefs, oyster reefs also exhibit intricate soundscapes, hinting at the potential influence the difference in sounds has on larvae orientation, and in this case, especially for mollusks. The next question is how we combat the effects of climate change on these environments. A study published in 2013 tested oyster larval settlement in the presence and absence of reef sounds (Lillis et al.). It found that in both laboratory conditions and in the field (off the coast of North Carolina), larval settlement was significantly higher in the presence of reef sounds. These findings highlight the need for further exploration into the connection between soundscapes and larval recruitment, which could tell us a lot about sound as a possible indicator of ecosystem structure. Perhaps we can use this information to delve into how to monitor and utilize reef sounds to influence recruitment and strengthen reef resilience.
Post by Eve Adelson, Bioacoustics team
