Behavior Human impacts

Ocean Commotion and Hearing Loss in Bobtail Squid

Putland RL, Mooney TA and Mensinger AF (2023) Vessel sound causes hearing loss for hummingbird bobtail squid (Euprymna berryi). Front. Mar. Sci. 10:1151605. doi: 10.3389/fmars.2023.1151605

Most people have a hard time concentrating in noisy environments, for example, having to work with a loud construction site right outside your window. Now imagine you were a marine organism living in the ocean where sound travels about five times faster than in the air – and shipping vessels were continuously passing by and the sea floor was being drilled for oil. You would probably never be able to concentrate and get anything done. Unfortunately, this is the case for many marine environments in the Anthropocene.

The Squid and the Ocean

Ambient ocean sounds are used by many marine organisms to navigate their environment, locate food, communicate, and avoid their predators. However, human-made sounds, which are getting louder, noisier and more persistent in the ocean, are blocking natural ocean sounds. This in turn is negatively affecting foraging, movement, predator-prey interactions, mating, and physiology in various marine organisms, such as squid.

Figure 1. Hummingbird Bobtail Squid on the sandy bottom in shallow coastal waters.

Hummingbird bobtail squid (Euprymna berryi) live in the sand and are a key species in shallow coastal water food webs, an environment that is frequented by boat noises and is therefore heavily affected by anthropogenic noise pollution. Squid ‘ears’ comprise hair-filled statocysts that can detect sounds from predators and prey, as well as environmental sounds which they use for navigation. These sounds range in frequency from 100-1000 Hz, and also match the frequency of boat sounds. Bobtail squid have the highest sensitivity to sounds ranging from 300-500 Hz.

Hearing Loss Experiments

Figure 2. Experimental tank setup (not to scale). 2: Underwater speaker ; 4: Hydrophone; 6: Recording and reference electrodes; 10: Acoustic isolation chamber; 11: Vibration isolation table.

In a recent study, researchers exposed bobtail squid (at different stages of development – juvenile, mid-adult, and adult) to short durations (15 minutes) of high intensity boat sounds to understand the effect of anthropogenic noise on squid behaviour. They found that the bobtail squids sensitivity to sound was impaired after exposure to boat sounds at all stages of development. Although there was no permanent damage to their statocysts, the squid did not respond normally to sounds after exposure; the squid were able to recover from the noise after a few hours. Furthermore, the squid reduced their ventilation rate after exposure – a potential defence mechanism that allows them to avoid detection by predators.

A reduced sensitivity to sound in adult squid may reduce their ability to navigate their environment – to avoid predators and detect prey. In younger, juvenile squid, reduced sound sensitivity may restrict them from finding a suitable habitat to live in; this is especially critical to the squids lifecycle – if the juvenile squid don’t reach adulthood, the bobtail squid population could decrease rapidly.

Solution to Noise Pollution?

Hummingbird bobtail squid amongst many other marine species are facing rapid change in their lifestyles due to increasing noise pollution in the ocean. We do know that the squid can recover from loud noises, but we are yet to figure out the point at which the damage is irreversible. It is important that we understand how much human-made noise is too much in the squid and other affected species so that new policies can be put in place to reduce the intensity and the persistence of noise for their protection.

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