Communication in aquatic animals
Interspecies communication is most common between prey and predator or between animals engaged in mutualistic symbiotic relationships.
[7] Aquatic invertebrates such as lobster, crabs and shrimps have external sensory hairs and internal statocysts as their sound-detecting organs.
Coastal or oceanic species are more likely to use visual signals than species inhabiting the riverine or turbid environment, due to the poor light transmission in turbid areas or in areas with increasing depth and high habitat complexity.
[15][14] It is suggested that some fish and cephalopods can actively produce and regulate polarised light patterns for communication purposes using light-reflective structures on their bodies.
Some semi-aquatic mammals have adaptations for visions (larger eyes, tapetum) that allow them to see and potentially communicate using visual signals even in low light conditions.
[14] In some fish, mantis shrimp and squid, their eyes have a specific photoreceptor structure/orientation that is thought to give them the ability to detect polarised light.
[16][17] Unlike in the air, the specific light spectral bandwidth and intensity changes across water habitats.
The spectral sensitivity of an animal's retinal photoreceptors appears to depend on the colour of the water they live in and can sometimes shift when they move to a different location to maximise visual acuity.
Crustaceans can release urine containing chemical signals anteriorly through a pair of nephron-pores[23] and can also deposit pheromones on their body surface which are produced by their tegmental glands.
It is suggested that the multi-ciliated cells around the rim of their nasal cavities generate a water flow to increase chemical detection.
On land, sea otters and pinnipeds often perform ‘nosing’ behaviours at prominent scent glands which indicate some level of detection of chemical signals.
[21] However, it has been found that the semi-aquatic star-nosed mole and water shrew can detect chemicals underwater by exhaling air bubbles onto objects or scent trails and re-inhaling the bubbles which now carry the chemical signals back through the nose.
[26] Chemical signals are used for: As water is a much better electrical conductor than air, electrocommunication is only observed in aquatic animals.
[28] Electric fish can also modify the frequency, amount, duration, silent periods, amplitude and chords of their EOD.
Electrical signals are used for: Tactile communication, also known as touch, is limited for very short distances as it requires physical contact.
[14] Animals detect touch by the somatosensory system which responses to changes at the surface or inside the body.
The mechanoreceptors in the somatosensory system can be found the skin surface of most aquatic animals, as well as on the vibrissae of pinnipeds or on the hair of whales.
For example, when the fire-bellied toad is attacked, it will adopt a defensive pose and exhibit its bright-coloured belly to the predator.
An example of this is the mutualistic symbiotic relationship between the goby, a small bottom-dwelling fish, and an alpheid, or snapping, shrimp.
