Scientists at Curtin University in Western Australia have shown that the seismic sound blasts made by airguns searching for new oil reserves under the ocean floor can kill large swathes of plankton.

The researchers surveyed zooplankton populations before, and 1 hour after, setting off an airgun near the south-east coast of Tasmania. They found that the sound burst created a 2-kilometre-wide “hole” in the zooplankton population. Within this area, zooplankton abundance dropped by two-thirds and the number of dead zooplankton more than doubled.

The scientists are not sure how the zooplankton died but think that the sound waves may have shaken and damaged the sensitive “hairs” they use for sensing the environment. This would make it harder to swim, find food and avoid predators.

Previous research has shown that such airguns cause behavioural changes and hearing loss in whales, dolphins and giant squid, impairing their ability to find food and communicate. But until now, it has been assumed that plankton are safe from seismic airguns, because they are too small to reflect the long sound wavelengths that are emitted.

The scientists are now researching how airgun-initiated declines in zooplankton populations affect other marine creatures, and how long it takes them to recover.