Eutrophication Could Lead to More Silent Seas, Study Finds

A new study from the University of Adelaide revealed that excessive nutrients washing into the sea from cities, towns and agricultural lands are changing the sounds made by marine life, potentially disrupting the navigational cues of fish and other marine creatures.

The study, published in the journal Landscape Ecology, suggests that eutrophication caused by run-off of nutrients from adjacent lands is causing the "soundscape" of marine ecosystems to be more silent. Excessive nutrients washing into the sea could have a negative impact in kelp forests and sea grass beds. Kelp forests and sea grass beds function as nursery habitats for many marine species. They also play a crucial role in commercial fishing and maintenance of marine biodiversity.

"We know that sound is very important for some species of fish and invertebrates to find sheltering habitats in reefs and seagrass beds," explained Ivan Nagelkerken, associate professor at University of Adelaide's Environment Institute and lead author of the study, in a press release. "The demise of biological sounds is likely to have negative impacts on the replenishment of fish populations."

For the study, the researchers compared audio recordings of marine ecosystems degraded by eutrophication and healthy ecosystems. The researchers discovered that the marine ecosystems with excessive nutrient pollution are more silent compared to healthy marine ecosystems.

Furthermore, audio recordings of the polluted waters have the same pattern of sound reduction as the high-carbon dioxide underwater volcanic vents, which show what water conditions are predicted to be like at the end of the century under global ocean acidification.

With their findings, the researchers recommend the use of marine soundscape as a new cost-effective monitoring tool to evaluate 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," said Sean Connell, professor at University of Adelaide and co-author of the study, in a statement.