Particle motion in the ocean helps determine what fish can hear

The ocean is a noisy place. Natural underwater sounds made by fish and invertebrates play an important role in coral reef inhabitants’ orientation, navigation, and more. Studies of such soundscapes can help researchers track biodiversity and impacts from marine traffic noise.

Fish mainly detect the back-and-forth vibration component of a sound field, or the particle motion, rather than the pressure waves of sound that mammals detect. However, most studies have explored the latter rather than the former in ocean soundscapes. Jones et al. investigated how particle motion could be used to understand what fish and invertebrates actually hear.

The researchers measured aquatic particle motion soundscapes at healthy and degraded coral reef sites by recording sound pressure with underwater microphones. Comparing adjacent microphones allowed them to calculate local particle motion.

The team compared the particle motion levels measured at the reefs to other research describing the levels fish and invertebrate species can detect. The results suggested that invertebrates, and fish in particular, may hear coral reef sounds best below 100 Hz.

“We were surprised to find that our soundscape data suggested fishes and invertebrates likely could only hear the less frequent and louder particle motion levels of coral reef sounds,” said author Ian Jones. “The sounds in their habitat they can detect may be limited to higher amplitude and less frequent sounds than previously thought.”

The researchers hope this work will encourage more studies of underwater soundscapes in different habitats with particle motion. Similar work could help scientists better understand the hearing abilities of different fish and invertebrate species, as well as how these animals communicate on reefs.

Source: “Soundscapes as heard by invertebrates and fishes: particle motion measurements on coral reefs,” by Ian T. Jones, Michael Gray, and T. Aran Mooney, Journal of the Acoustical Society of America (2022). The article can be accessed at https://doi.org/10.1121/10.0012579 .