The effects of ocean acidification on fish orientation and soundscapes. Graphic: Dr Tullio Rossi

By Ivan Nagelkerken, Sean Connell, and Tullio Rossi
19 September 2016

(Australian Geographic) – Despite appearances, the oceans are far from silent places. If you dunk your head underwater you’ll hear a cacophony of sounds from wildlife great and small, crashing waves, and even rain. And it’s louder still for creatures attuned to these sounds.

However, humans are changing these ocean soundscapes. Our recent research showed that changes caused by people, from ocean acidification to pollution, are silencing the seas' natural noises. (We’re also filling the oceans with human noise).

This is bad news for the species that depend on these noises to find their way. […]

Humans are increasingly dominating the physical and chemical environment. We are altering the carbon cycle through the burning of fossil fuels and the nitrogen cycle by extracting vast amounts of nitrogen for food production and releasing it as waste. Large amounts of this carbon and nitrogen liberation end up in the ocean.

About one-third of the carbon dioxide that humans emit into the atmosphere dissolves in the ocean, leading to increased seawater acidity (or ocean acidification). This is an obvious problem for animals that produce a calcium carbonate shell or skeleton (such as corals, some plankton, and snails). Remarkably, ocean acidification also alters the behaviour of many animals by messing up their brain functioning.

Earlier studies (see also here) have shown that ocean acidification can change the response of fish larvae to settlement habitat sounds by deterring them rather than attracting them.

Two of our recent studies (see also here) showed that ocean acidification not only affects sound reception, but also the sounds that ocean ecosystems produce. If we don’t reduce greenhouse gas emissions, rocky reefs could be much quieter in 2100 than now. And snapping shrimps are the reason.

Coastal discharge of nutrients from sewage plants and catchment runoff also degrades kelp forests and seagrass beds. These coasts are more silent than their healthy counterparts. [more]

The silencing of the seas: how our oceans are going quiet



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