Boat Noise And Coral Reef Fish

Coral reefs are home to a variety of fish species. Past studies have shown that coral reef fish use the natural sounds of reefs (such as sounds from the activities of the inhabitants and the waves) to guide where they will rest for their larval settlement stage. If noise from passing boats disrupts these natural  reef sounds, then it may also disrupt the settlement patterns of the fish. The authors of this study, which is published in the Marine Ecology Progress Series, investigate this idea through an experiment involving the coral reef species Apogon doryssa (longspine cardinalfish).

In this experiment, the researchers placed individual Apogon doryssa larvae in large chambers within a lagoon. For the first five minutes, each larva could swim freely in the chamber. Then, for one minute, a speaker at one end of the chamber played one of five sound clips: 1) Reef, 2) Reef+Boat, 3) White noise, 4) Ocean noise, or 5) Ocean+Boat. Finally, the chamber was divided into three parts (near the speaker, in the middle, and far from the speaker). The researchers noted the location of each larva at this time.

The results of the experiment were as follows: “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.”

The results indicate that fish tend to steer toward natural reef sounds. But, when reef sounds are mixed with boat sounds, significant proportions of fish move both toward and away from this sound combination. This variety of response may be due to individual differences between the fish or even due to random scattering because of fear.

The authors use these results to suggest that boat noise does indeed disrupt the settlement process of coral reef fish. They propose that this disruption could threaten the survival of the fish as “larvae may spend a longer time swimming in the plankton, resulting in increased energetic costs and predation risk.” As a result, the authors suggest that fisheries and fish conservationists should take the effects of boat noise into consideration in their work.