Noise harming ocean invertebrates and ecosystems

Scientists reviewed hundreds of studies on the impact of noise on marine invertebrates (such as crabs, molluscs, squid, prawns and worms).

They concluded that noise caused by humans is harming invertebrates in numerous ways, from cellular level to entire ecosystems.

The international team, including Universitat Politècnica de Catalunya -- BarcelonaTech (UPC) and the University of Exeter, call for urgent research to investigate and mitigate these impacts.

"Many people are surprised to discover that invertebrates can even perceive sounds, but in fact sound is fundamental to their survival," said first author Dr Marta Solé, from UPC.

"Light doesn't travel very well in water but sound does, and invertebrates use sound in a variety of ways.

"Human activities -- especially shipping -- are changing the ocean soundscape rapidly, and our study brings together the latest evidence on the impacts of this."

The study highlights the multiple impacts of anthropogenic (human) noise on invertebrates:

• It can delay hatching and egg development in crustaceans, and significantly increase abnormalities and death rates among larvae of crustaceans, bivalves (eg mussels and oysters) and gastropods (eg snails).
• Low-frequency sounds can cause injuries and even death. For example, research has shown that sound from underwater explosions can kill blue crabs. After an increase of cephalopods (eg squid and octopus) washing up on beaches in Spain, research showed that noise had damaged their statocysts (hearing organs that help them navigate).
• Impacts on behaviour include many species displaying a "startle" reaction in response to loud sounds. Long-term exposure to noise also affects behaviour. For example, ship sounds limit the ability of shore crabs to change colour to camouflage themselves
• Physiological changes have also been discovered. For example, Mediterranean common cuttlefish showed changes in the protein content due sound exposure -- with some of the affected proteins related to stress. In another study, permanent high-level exposure to sound caused a significant reduction in growth rate and reproduction, an increase in aggressiveness and mortality rate, and a reduction in feed intake of shrimp.
• By changing the behaviour and health of predators and prey in complex food webs, noise can affect entire ecosystems -- and the researchers say more research is needed to investigate this.

Recent studies have revealed that a wide range of invertebrates are sensitive to sounds, especially via sensory organs whose original function is to allow maintaining equilibrium in the water column and sensing gravity.

Invertebrates can detect underwater sound through three types of sensory systems: "superficial" receptors on their body surface, internal "statocyst" receptors (equivalent of ears), and flexible "chordotonal" appendages that sense vibrations.

They can also produce sounds -- ranging from the "cough" of scallops to the creaks made by lobsters, crayfish, shrimps and crabs, possibly to ward off predators.

"Our study underlines that these animals exist in a rich underwater soundscape," said Dr Sophie Nedelec, from the University of Exeter.

"We urgently need to know more about the impacts of noise pollution on these animals and ecosystems.

"Considering that noise can affect invertebrates from cellular to ecosystems level, we need to bring together interdisciplinary expertise to embrace a holistic vision of the problem.

"Given the many pressures being caused by humans -- including from climate change and fisheries -- we must do everything we can to limit underwater noise."

Ships and boats are the main sources of marine noise, but a wide range of other activities including drilling, dredging and sonar also cause noise.

Seabed mining in international waters could be permitted for this first time later this year, and a recent study by Exeter researchers raised concerns about the noise impacts on wildlife.