Coral reef fish that are exposed to motorboat noise grow up smaller and less able to dodge predators, new research shows.
Scientists played either boat noise or natural reef sounds to a species from the Great Barrier Reef called the spiny chromis, both as embryos and soon after hatching.
Fish exposed to boat noise at both stages were less likely to respond to a simulated predator attack - and those that did were more likely to swim towards the predator.
The study, by the University of Exeter, University of Bristol and James Cook University, also found that fish exposed to boat noise after hatching were 7% shorter on average than those exposed to reef sounds.
Commenting on the possible reasons for these effects, Exeter's Dr Sophie Nedelec said: "We know from previous research that motorboat noise affects parental care behaviour, including oxygenating eggs by fanning during the embryonic phase, which is linked with their survival.
"If exposure as embryos sensitises them to noise, it's possible that they respond more strongly to noise as juveniles.
"For example, it could cause stress or affect feeding, creating cumulative effects that lead to poor assessment of risk and decision making, and smaller body size."
Predator response
The fish in the study were divided into four groups and exposed to either motorboat noise or reef sound playback in tanks during the embryo and post-hatching stages of their lives - or one of each (either boat noise as embryos then reef noise as juveniles, or vice versa).
Sound exposure was carried out for up to 78 days.
No sounds were played to the fish for 24 hours before the predator test, or during the test itself - so the results reveal how noise affects fish in the longer term, rather than as a momentary distraction.
The predator response was tested by a weight being dropped onto the water's surface. For a spiny chromis, the natural reaction to a threat is to twist into a "C" shape then burst away from the danger.
In the groups of fish exposed to natural reef sounds for at least one stage of development, about 80% reacted in this way to the simulated predator. Of these, about 20% made the mistake of swimming towards the predator.
But among the fish exposed to motorboat noise as both embryos and juveniles, only 68% responded to the predator - and 40% of these swam towards it.
Dr Nedelec said: "Our results show that exposure to motorboat noise during early development can affect growth and disrupt the escape response of juveniles, even when the escape occurs in relatively quiet conditions.
"Limiting motorboat traffic close to reefs during the breeding season may reduce these effects and protect reef fish - thereby helping to preserve coral reefs, which are valuable and vulnerable ecosystems worldwide."
The study was funded by the Natural Environment Research Council.
