How sea squirts perceive underwater noise
Shipping, construction work and other human activities are altering the acoustic conditions in our planet's seas. Sound pressure is often examined to determine the effects that this underwater noise has on marine organisms. However, these observations may not be thorough enough for creatures that live on the seafloor.
Underwater noise, caused by shipping, construction, and other human activities, is altering acoustic conditions in the world's seas. Researchers from the University of Bochum's Department of General Zoology and Neurobiology are studying how sea squirts, small tunicates that live on the seafloor, react to this noise. Unlike previous observations, which focused on sound pressure, the researchers discovered that sea squirts respond to vibrations rather than pressure.
In their study, published in Marine Biology, the team found that these animals contract mainly in response to vibrations between 50 and 800 hertz, primarily when substrate vibrations are below certain thresholds. Even when underwater sound pressure exceeded 130 decibels, sea squirts did not show comparable reactions if substrate vibrations stayed below the reaction thresholds.
The researchers believe that specialized ciliated mechanoreceptor cells in the siphons, particularly in the coronal organ, are responsible for detecting these mechanical stimuli. However, more studies are needed to determine if these receptors are stimulated by particle motion in water or vibrations through the substrate and mantle.
The findings suggest that mechanical components of underwater sound should be more closely considered when examining benthic organisms, and future studies aim to identify which mechanical stimuli are actually perceived and how they are processed by sensory and neural systems.
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