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

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.