Modelling a reef as an extended sound source increases the predicted range at which reef noise may be heard by fish larvae

Abstract

Underwater sound emanating from reefs has been shown to be attractive to pre-settlement larval stages of fish and crustaceans, but its ecological importance depends on the range at which this cue can be detected by these larvae. Here we show, through field measurement and modelling, that the spatially extended sound source of a reef creates a surrounding zone, which extends for a distance offshore equal to the length of the reef, within which there is almost no loss in the sound level. Beyond this zone, the sound level decreases with cylindrical spreading plus any seafloor attenuation. This 'reef effect' means that the sound from a reef would be detectable at a much greater distance from the reef than would be estimated from a spot measurement near the reef or by using theoretical models of sound spreading from a point source. The greater reach for sound emanating from a reef means that reef noise could play a greater role in directing larval reef fishes and crabs to suitable settlement habitats than previously estimated.

Coral reef soundscapes : spatiotemporal variability and links to species assemblages

“…The lack of agreement with cylindrical or spherical spreading predictions has been demonstrated on temperate reefs and has been postulated to be a result of a "reef effect" (Radford et al, 2011b), whereby levels do not attenuate as quickly as predicted because the reef is not a single point source but instead is composed of a "chorus" of many sound sources (fish, snapping shrimp). However, aural and visual inspections of our coral reef recordings collected far from the reef indicated no discrete detectable sounds of biological origin, which suggests that at greater distances from the reef such sounds might be buried in the environmental noise floor.…”

“…Loud choruses of reef sounds may be detectable from hundreds to thousands of meters from the reef (Radford et al, 2011b;Mann et al, 2007;Cato, 1980). A study by Egner and Mann (2005) proposed that sergeant major damselfish (Abudefduf saxatilis) would likely be able to use coral reef sounds as a significant navigation cue up to 500 m away.…”

“…Bioacoustic larval settlement studies (Simpson et al, 2004(Simpson et al, , 2005Radford et al, 2011a;Stanley et al, 2011; and investigations of the distances over which reef sound cues may travel have measured those cues in terms of pressure (Radford et al, 2011b;Piercy et al, 2014), leaving responses to particle motion poorly understood. For example, Radford et al (2011b) modeled a reef as an extended sound source and found that reef sound pressure propagates much further than predicted by a point source.…”

“…For example, Radford et al (2011b) modeled a reef as an extended sound source and found that reef sound pressure propagates much further than predicted by a point source. However, without acoustic particle motion data, the sound cues available to settling larvae remain largely unknown.…”

Wind Conditions on the Great Barrier Reef Influenced the Recruitment of Snapper (Lutjanus carponotatus)

“…Larvae were counted at high tide, so the box was extended out to the west by 5 km to account for the larvae that would have been transported into the capture area with the tidal excursion over 6 h as the tide went out. The capture distances used are conservative given Radford et al (2011) detected reef noise 5 km from a reef and larvae can likely smell OTI from several kilometers away (Wolanski and Kingsford, 2014). The Self-Seeding rate (% SS) was subsequently calculated as the percentage of the total number of settlers counted around OTI that had originally been seeded from OTI.…”