Nutrient pollution emptying into the oceans from cities, towns and agricultural land is changing the sounds made by marine life—and potentially upsetting navigational cues for fish and other sea creatures, a University of Adelaide study has found.

The research found that marine ecosystems degraded by "eutrophication," caused by runoff from adjacent land, are more silent than healthier comparable ecosystems. The typical marine soundscape comes largely from the snapping of shrimps, but also the rasping of sea urchins and fish vocalizations.

The typical marine "soundscape" comes from the snapping of shrimps, the rasping of sea urchins and fish vocalizations. Image credit: Pixabay.PhD graduate Tullio Rossi, Associate Professor Ivan Nagelkerken and Professor Sean Connell, from the university’s Environment Institute, studied kelp forests and seagrass beds in South Australia’s St. Vincent’s Gulf. Many have been impacted by excessive nutrients washing into the sea. They compared audio recordings of these polluted waters with audio recordings at natural high-CO2 underwater volcanic vents, which show what water conditions are predicted to be like at the end of the century under global ocean acidification. They found the same pattern of sound reduction in both locally degraded ecosystems and those that show what oceans are expected to be like under climate change.

“Kelp forests and seagrass beds are important ecosystems for commercial fishing and maintenance of marine biodiversity,” notes Nagelkerken, who adds that they also function as nursery habitats for a range of species. “We know that sound is very important for some species of fish and invertebrates to find sheltering habitats in reefs and seagrass beds. The demise of biological sounds is likely to have negative impacts on the replenishment of fish populations.”

The study also suggests that soundscapes may be a suitable management approach to evaluating the health of ocean ecosystems.

“Because ocean acidification acts at global scales, local reduction of nutrient pollution as a management intervention will strengthen the health of our marine ecosystems and set them up for coping better with global climate stressors,” says Connell.