Baseline soundscapes of deep‐sea habitats reveal heterogeneity among ecosystems and sensitivity to anthropogenic impacts

Abstract

Underwater soundscapes, though invisible, are crucial in shaping the biodiversity of marine ecosystems by acting as habitat‐specific settlement cues for larvae. The deep sea has received little attention in soundscape research, but it is being targeted for mineral extraction to feed the ever‐growing needs of our society. Anthropogenic impacts on soundscapes influence the resilience of key shallow‐water habitats, and the same likely applies to the deep. Japan is a forerunner in deep‐sea mining, but virtually no deep soundscape baselines exist for Japanese waters. Here, we report baseline soundscapes from four deep‐sea locations in Japan, including the Suiyo Seamount hydrothermal vent, the abyssal plain around the Minamitorishima Island home to manganese nodule fields and muds rich in rare‐earth elements, twilight depths off Sanriku, as well as a typical bathyal system in Suruga Bay. Long‐duration audio recordings were visualized and factorized by an unsupervised machine learning model, revealing differing characteristics among the habitats. Two locations near the coast are highly influenced by shipping noise. The Suiyo vent is characterized by low‐frequency sounds from venting, and the abyssal Minamitorishima is quiet with a flat spectral shape. Noise from observation platforms is likely sufficient to alter soundscape characteristics, especially in offshore locations, suggesting offshore mining‐targeted areas are susceptible to impacts from anthropogenic noise. We argue that the monitoring of soundscapes is an indispensable component for assessing potential mining impacts on deep‐sea ecosystems. Our results establish reference points for future soundscape monitoring and assessment in Japanese waters as well as similar ecosystems globally.

Acoustic twilight: A year‐long seafloor monitoring unveils phenological patterns in the abyssal soundscape

“…Comparable observations of evening choruses in the deep sea have also been reported globally, including in the western Pacific Ocean (Lin et al 2021) and the eastern Indian Ocean (Cato 1978). Furthermore, these evening choruses have been detected across a wide range of depths, ranging from 277 m (Lin et al 2021), and430-490 m (McCauley andCato 2016), to 1000 m (Cato 1978), and even down to the deepest recorded depth of 5500 m (Chen et al 2021). In the Perth Canyon, western Australia, an evening chorus detected in the frequency range of 1.89 to 2.67 kHz was inferred to be associated with mesopelagic fishes of the family Myctophidae (McCauley and Cato 2016).…”

“…Despite their potential significance, deep-sea soundscapes face a drastic alteration due to impending mining activities (Miller et al 2018;Christiansen et al 2020). Projected noise levels from such operations are expected to exceed existing ambient noise levels, which could extensively alter soundscapes across a vast region and diverse habitats (Chen et al 2021;Williams et al 2022). There is also a high risk that noise pollution from mining operations and shipping activities will mask biological sounds, making these auditory cues imperceptible to deep-sea organisms (Lin et al 2019).…”

“…LTS is an effective visualization tool for spectral and temporal variations in long-duration audio recordings, and its efficacy in delineating the heterogeneity of deep-sea soundscapes has been discussed (Chen et al 2021). Following the methodologies of Chen et al (2021), we generated a median power spectrum (10 Hz frequency resolution) for each 1-min fragment. Given the recording duty cycle, this yielded 12 median power spectra per day.…”

“…The extraction of median power spectra ensures the spectral representation of continuous sound sources, including environmental sounds, biological choruses, and shipping noise (Chen et al 2021). To enhance signal-to-noise ratios (SNRs) of biological choruses, we measured n 5 (f ): the 5 th percentile at each frequency bin f to represent the background noise level.…”

“…For example, Dziak et al (2017) identified a noisy hadal environment at Challenger Deep-the Earth's deepest known locationresonating with sounds produced from storm-induced waves, marine mammals, shipping activities, and geophysical airgun surveys. Another case in point is the abyssal soundscape off Minamitorishima Island, which transforms from daytime quietude to a vibrant biological chorus after sunset (Chen et al 2021). Furthermore, the soundscape recorded at mid-ocean ridges showed tidal modulations, suggesting pressure-induced variations at hydrothermal vents (Crone et al 2006).…”