Coral reef soundscapes may not be detectable far from the reef

Abstract

Biological sounds produced on coral reefs may provide settlement cues to marine larvae. Sound fields are composed of pressure and particle motion, which is the back and forth movement of acoustic particles. Particle motion (i.e., not pressure) is the relevant acoustic stimulus for many, if not most, marine animals. However, there have been no field measurements of reef particle motion. To address this deficiency, both pressure and particle motion were recorded at a range of distances from one Hawaiian coral reef at dawn and mid-morning on three separate days. Sound pressure attenuated with distance from the reef at dawn. Similar trends were apparent for particle velocity but with considerable variability. In general, average sound levels were low and perhaps too faint to be used as an orientation cue except very close to the reef. However, individual transient sounds that exceeded the mean values, sometimes by up to an order of magnitude, might be detectable far from the reef, depending on the hearing abilities of the larva. If sound is not being used as a long-range cue, it might still be useful for habitat selection or other biological activities within a reef.

Ontogenetic change in predicted acoustic pressure sensitivity in larval red drum (Sciaenops ocellatus)

“…Data for the left sagitta otolith are shown. Kaplan and Mooney, 2016;Nedelec et al, 2016). In our modeling, the morphology of red drum larvae produced a significant increase in the amplification of the acoustic stimulus at the otoliths in the presence of the bladder.…”

“…Thus, there can be ecological consequences to a larva's sensitivity to pressure and how this sensitivity changes ontogenetically. We may therefore underestimate the consequences of changing soundscapes for larval settlement and survival if we assume that particle motion is the only relevant acoustic stimulus (as in Mann et al, 2007;Kaplan and Mooney, 2016;Nedelec et al, 2016). The small sizes of larval body plans warrant consideration that they are pressure sensitive.…”

Habitat degradation negatively affects auditory settlement behavior of coral reef fishes

“…Lower levels of attraction and settlement to postdegradation soundscapes might be facilitated by quieter reef sound propagating over a smaller area, resulting in detection by fewer fishes (see refs. 16 , 17 , and 29 for discussions of the spatial scale of reef-sound propagation). Alternatively, young fishes might exhibit qualitatively different behavioral responses to pre- and postdegradation reef soundscapes, irrespective of detectability.…”

Listening forward: approaching marine biodiversity assessments using acoustic methods

“…Sound directionality may also be determined by measuring acoustic particle motion (velocity or acceleration) [ 244 ]. As technology has improved, measurements of particle motion have become increasingly common [ 245 , 246 ] and, as a direct cue for fauna, it is important to test particle motion measurements of the soundscape to investigate its relationship with biodiversity and acoustic communication. In addition, the instrumentation used to measure particle motion offers an alternative method to sound source localization that requires fewer individual sensors (compared with a hydrophone array) and may improve signal detection in noise (e.g.…”