Temporal Variability in Acoustic Behavior of Snapping Shrimp in the East China Sea and Its Correlation With Ocean Environments

Abstract

The snapping shrimp sound is known to be a major biological noise source of ocean soundscapes in coastal shallow waters of low and mid-latitudes where sunlight reaches. Several studies have been conducted to understand the activity of snapping shrimp through comparison with surrounding environmental factors. In this paper, we report the analysis of the sound produced by snapping shrimp inhabiting an area where sunlight rarely reaches. The acoustic measurements were taken in May 2015 using two 16-channel vertical line arrays (VLAs) moored at a depth of about 100 m, located ∼100 km southwest of Jeju Island, South Korea, as part of the Shallow-water Acoustic Variability Experiment (SAVEX-15). During the experiment, the underwater soundscape was dominated by the broadband impulsive snapping shrimp noise, which is notable considering that snapping shrimp are commonly observed at very shallow depths of tens of meters or less where sunlight can easily reach. To extract snapping events in the ambient noise data, an envelope correlation combined with an amplitude threshold detection algorithm were applied, and then the sea surface-bounced path was filtered out using a kurtosis value of the waveform to avoid double-counting in snap rate estimates. The analysis of the ambient noise data received for 5 consecutive days indicated that the snap rate fluctuated with a strong one-quarter-diurnal variation between 200 and 1,200 snaps per minute, which is distinguished from the periodicity of the snap rate reported in the euphotic zone. The temporal variation in the snap rate is compared with several environmental factors such as water temperature, tidal level, and current speed. It is found that the snap rate has a significant correlation with the current speed, suggesting that snapping shrimp living in the area with little sunlight might change their snapping behavior in response to changes in current speed.

Circadian and Tidal Changes in Snapping Shrimp (Alpheus brevicristatus) Sound Observed by a Moored Hydrophone in the Coastal Sea of Western Jeju

“…In a previous study on the correlation between underwater noise and sea level at Ieodo, the underwater noise also changed according to the tidal change and the phase of the moon [37]. Although the study of prawns conducted in the same sea area did not show circadian characteristics, the snap rate of prawns changed according to the tidal change (Table 2) [31]. According to the soundscape for various fish species such as Miichthys miiuy (brown croaker) and Lophius piscatorius (angler), there was a noticeable change with the tide but not with the moon phase.…”

“…Unlike this study, the snap rate was quantitatively expressed by analyzing the data measured a short period at depths where visible light rarely enters. Although there is a seasonal difference in the measurement period in May, a snap rate of 200 to 1200 times occurred, and the snap rate changed according to the sea level [31].…”

“…Then, the long-term pattern was added by the moving average value of 90 days (six cycles of the moon phases). A MATLAB function was employed for wavelet calculation with the wavelet type 'Morlet' [16,[30][31][32][33][34][35]. This wavelet analysis provides a good balance between time and frequency localization.…”

“…They have a strong coherence with semidiurnal (0.5 day, K2 = 0.50) and diurnal (1 day, K1 = 1.00) periods. Therefore, the semidiurnal tide from the principal lunar and solar components and the diurnal tide from lunisolar and principal lunar periods affect the snap rate [31,36]. Longer periods, such as 15 days (lunar Figure 6 presents the wavelet analysis to show the coherence between the snap rate of snapping shrimp and the tidal level.…”

Sounds of a changing sea: Temperature drives acoustic output by dominant biological sound-producers in shallow water habitats

“…Snapping shrimp typically live in dense aggregations hidden within the substrate of many coastal ecosystems (e.g., coral reef, sponges, rubble, oyster beds, rocky shores), together producing a continuous audible crackling sound (Johnson et al 1947;Mathews, 2007). Snapping shrimp acoustic activity is often the major determinant of ambient sound levels in coastal seas (Everest et al, 1948;Johnson et al, 1947;Lillis et al, 2014;Kaplan et al, 2015), and variation in snapping shrimp acoustic output has been found to account for much spatiotemporal soundscape variation, both in sound levels and frequency content, within temperate and tropical benthic marine ecosystems (Radford et al 2008;Radford et al 2010;Lillis et al 2014;Staaterman et al 2014;Butler et al 2017;Lee et al, 2021). This spatiotemporal variability of snapping shrimp sound production likely influence a range of acoustically-mediated animal activities, including navigation and habitat selection by settlement-stage fish and invertebrate larvae (Simpson et al, 2008;Lillis et al, 2013), and perhaps even functions as an auditory cue for migrating cetaceans to avoid rocky shorelines (Allen, 2013).…”