Behavioral and Physiological Responses of Sea Slug (Onchidium reevesii) to Low-Frequency Noise

A large amount of marine noise pollution from coastal industrial construction and the water transportation industry affects the growth and development of marine life, which is a big issue threatening marine organisms. However, most studies have focused on vertebrates, such as marine mammals and fishes, and little is known about the effects of noise on invertebrates. Therefore, the impacts of low-frequency noise (100, 300, and 500 Hz) on behavioral and physiological responsesof the sea slug (Onchidium reevesii) were investigated. Under laboratory conditions, sea slugs were stimulated with low-frequency noise at 100, 300, and 500 Hz for 1 h. Then, hemolymph enzyme activities (glucose, albumin, triglycerides, superoxide dismutase, catalase, and malondialdehyde) were measured, and mRNA expression of the hsp70 gene was detected in hemolymph and the nervous system by quantitative realtime polymerase chain reaction (qRT-PCR) analysis, while expression of the hsp70 protein was analyzed by immunohistochemistry. The results demonstrated that sea slugs were away from the stimulus source under the influence of low-frequency noise compared to the control group. Enzyme activities, as well as hsp70 gene mRNA and protein expression levels, were significantly higher in the noise-exposed groups than those in the control group. Overall, these changes indicate that low-frequency noise caused oxidative stress in sea slugs in vivo, and the oxidative damage gradually increased when the noise frequency was increased from 100 to 500 Hz.