What is the natural marine animal

How do animals hear underwater?

Each animal species has adapted to its habitat in the course of evolution. Their sense organs have also specialized or regressed accordingly. The hearing of the various sea creatures has adapted very differently to the conditions under water in order to detect, localize and interpret sounds from their surroundings. Some animals that live in aquatic environments, such as marine mammals, are already fairly well known from research about how they hear underwater. For diving birds, on the other hand, there is so far only little knowledge about the hearing abilities.

Marine mammals

The main hearing characteristics of marine mammals and land mammals are similar. However, the entire anatomy of marine animals has adapted to life in the water during evolution and, of course, hearing as well.

In seals, the outer auricle has receded or has completely disappeared, and whales no longer have an outer auricle. Not only the skull structure of today's whales is very different from that of other mammals; Her hearing system has also changed significantly and adapted to marine life. The auditory canal of whales, for example, is considered to have no function in transmitting sound. Toothed whales, to which the dolphins belong, transmit sound to the middle ear via their specially adapted lower jaw, which is surrounded by fatty tissue. Additional adjustments to the basilar membrane in the inner ear mean that toothed whales are particularly good at perceiving the high-frequency sounds that they also use for echolocation [1]. Baleen whales, on the other hand, mainly use the bony structures for the transmission of sound waves; Especially low-frequency tones can be perceived optimally in this way [2].

fishes

Fish have developed different systems for perceiving sounds. Small ear stones made of lime in the fish's inner ear, so-called otoliths, are set in motion by sound waves. Since they are denser than the body of the fish, they move more slowly and the difference between the movement of the otoliths and the sensory hairs that are stimulated by the movement is perceived as sound [3].

Fish whose swim bladder is in close proximity to the inner ear or is even connected to it can use the swim bladder as a resonance body and thus have greater hearing sensitivity.

In addition to the auditory system, fish also use the mechanosensory side line to detect water currents that can also be caused by sound waves. The linear sensory organ consists of many fine sensory hairs in small channels under the skin surface, with which the fish perceive the finest pressure and flow differences in the immediate vicinity and thus coordinate themselves in large swarm structures [4].

Marine invertebrates

Marine invertebrates cannot actually hear. However, it is assumed that they can perceive the vibrations and (particle) movements generated by sound waves. Most crustaceans use fine sensory hair on their bodies. Some marine invertebrates also have mechanoreceptors in their leg joints or antennae that are connected to the central nervous system. Vibrations that are transmitted through water or substrate can be felt by the animals and they help them to grasp their surroundings. Researchers also assume that the statocyst, the equilibrium organ of marine invertebrates, detects the smallest movements using sound waves and thus also helps with noise recognition [5].

[1] Ketten, DR (1994). "Functional analyzes of whale ears: adaptations for underwater hearing". Conference: OCEANS '94. 'Oceans Engineering for Today's Technology and Tomorrow's Preservation.' ProceedingsVolume: 1. DOI: 10.1109 / OCEANS.1994.363871.

[2] Cranford TW and Krysl P (2015). "Fin Whale Sound Reception Mechanisms: Skull Vibration Enables Low-Frequency Hearing." PLoS ONE 10 (1): e0116222. DOI: 10.1371 / journal.pone.0116222.

[3] Putland RL, Montgomery JC and Radford CA (2018). "Ecology of fish hearing." Journal of Fish Biology 95 (1). DOI: 10.1111 / jfb.13867.

[4] Popper, AN and Fay, RR (1993). "Sound Detection and Processing by Fish: Critical Review and Major Research Questions (Part 2 of 2)." Brain Behavior and Evolution 41 (1): 14-38. DOI: 10.1159 / 000316111.

[5] Popper, AN, Salmon, M and Horch, KW (2001). "Acoustic detection and communication by decapod crustaceans." Journal of Comparative Physiology 187 (2): 83-9. DOI: 10.1007 / s003590100184.