Sea Hares Die Off Due to Boat Noise

Sea hares are shown to die off and cease embryonic development when exposed to boat noise, according to new research, in line with previous studies which have suggested that marine noise can affect animal movement and communication.

Scientists from the Universities of Bristol and Exeter and the école Pratique des Hautes études (EPHE) CRIOBE in France studied sea hares, specifically the sea slug Stylocheilus striatus. These creatures usually hatch from their eggs to swim away and later feed on toxic alga, but unfortunately noise from passing traffic overhead can disturb this natural process.

The study, conducted in a coral reef lagoon in French Polynesia, found that when exposed to playback of boat noise, more eggs failed to develop and those that hatched were more likely to die off.

"Traffic noise is now one of the most widespread global pollutants," lead author Sophie Nedelec, a PhD researcher at the University of Bristol and EPHE, said in a statement. "If the reproductive output of vulnerable species is reduced, we could be changing communities and losing vital ecological functions. This species is particularly important because it eats a toxic alga that affects recruitment of fish to coral reefs."

Noise from boats can spread far and wide, and recent research has increasingly indicated that noise from human activities can affect the behavior and physiology of animals. But this study is the first to provide evidence of its impact on larval survival.

"Boat noise may cause stress or physically disrupt cells during development, affecting chances of survival," explained co-author and marine biologist Dr. Steve Simpson.

Using controlled field experiments, the researchers placed nearly 30,000 eggs in plastic tubes. Half of the eggs were placed next to speakers emitting boat noises, while the other half listened to peaceful coral-reef ambient noise. The boat noise playback resulted in a 20 percent drop in survival rates for the embryos.

"This is the first indication that noise pollution can affect development and survival during critical early life stages. Growing evidence for the impact of noise on animals suggests that consideration should be given to the regulation of human activities in protected areas," added co-author Dr. Andy Radford.

Currently, human-made, or anthropogenic, noise is now recognized as a global pollutant, appearing in national and international legislation.

Therefore, it's no surprise that environmentalists in New Jersey were asking the local court to halt research plans to bombard the ocean bed with loud noise as means for studying sea level rise and ocean sediments, for fear that it would harm marine life, including whales and dolphins.