Simpson, S.D.

Coral reef fish larvae use sound to find suitable habitat during their vital settlement stage. Yet boat noise, which can cause stress and avoidance behaviour, and may cause masking via reduction of perceptual space, is common around coral islands and continental shelf habitats due to boat activity associated with fishing, tourism and transport of passengers and cargo. In a choice chamber experiment with settlement-stage coral reef fish larvae of the species Apogon doryssa, the directional responses of larvae were tested to 5 different noise types: Reef, Reef+Boat, Ocean, Ocean+Boat and White noise. The results showed that 69% of fish swam towards Reef playback compared with only 56% during Reef+Boat playback, while 44% of fish larvae moved away from Reef+Boat playback compared to only 8% during Reef playback. Significant directional responses were not observed during White noise, Ocean noise or Ocean+Boat noise playback. Overall, this study suggests that anthropogenic noise could have a disruptive effect on the response of fish larvae to natural reef sound, with implications for settlement and population dynamics in coral reef habitats disturbed by boat traffic. 

Free-swimming larvae of tropical corals go through a critical life-phase when they return from the open ocean to select a suitable settlement substrate. During the planktonic phase of their life cycle, the behaviours of small coral larvae (<1 mm) that influence settlement success are difficult to observe in situ and are therefore largely unknown. Here, we show that coral larvae respond to acoustic cues that may facilitate detection of habitat from large distances and from upcurrent of preferred settlement locations. Using in situ choice chambers, we found that settling coral larvae were attracted to reef sounds, produced mainly by fish and crustaceans, which we broadcast underwater using loudspeakers. Our discovery that coral larvae can detect and respond to sound is the first description of an auditory response in the invertebrate phylum Cnidaria, which includes jellyfish, anemones, and hydroids as well as corals. If, like settlement-stage reef fish and crustaceans, coral larvae use reef noise as a cue for orientation, the alleviation of noise pollution in the marine environment may gain further urgency. 

We compared catches of settlement-stage reef fishes in light traps attached to underwater speakers playing reef sounds with those of silent traps during a summer recruitment season at Lizard Island, Great Barrier Reef, Australia. Of the total 40191 reef fishes we collected, significantly more (67%; Wilcoxon and Binomial tests: p< 0.001) appeared in the traps with broadcast reef noise. Traps deployed with speakers consistently caught a greater diversity of species (Wilcoxon test: p< 0.001, total 81 vs 68) than did silent traps. This study provides a clear demonstration that the settlement-stages of a broad range of families of coral reef fishes are attracted to reef sounds