Marine animals have many different ways to interpret the world
Like us, marine animals depend on their senses to interpret the world around them. But the ways in which they taste, touch, smell, see and hear are quite different from what we know. Some use feet rather than tongues to sample their meals, while others detect noise and vibrations with their skin instead of ears. Such adaptations may seem bizarre to us topside dwellers, but in the ocean, they provide the sensory advantages needed to find prey, escape predators, or communicate with a potential mate. Let’s take a look at some of the unusual ways that marine animals have developed their senses.
Touch, color, smell, sound, taste, it all changes when water is added. Those who make their home in the aquatic realm have come up with unique adaptations that heighten and focus the senses. Antennas, eyes, nostrils, gills, tassels… everything has a purpose and plays a special role in what sea dwellers perceive — and it varies from species to species.
For the octopus, touch is very important. The arms of the octopus are covered in tiny suction discs. They provide grip, but are also highly sensitive feelers that pick up even the subtlest of sensations. These discs also serve as chemoreceptors, allowing an octopus to ‘taste’ what it is touching, while other sensors at the end of each arm detect smells. Octopus often can be seen squeezed in tight places, like the one in this bottle, or sticking an arm into a crevice to search for a morsel of food without ever having to look.
Do you enjoy a relaxing massage or a facial? Something similar happens at the underwater cleaning stations. When a predator or a ‘stressed client’ comes to get cleaned, the cleaner fishes fan their fins over their skin, which calms them down and encourages them to stay longer. And so begins the relationship between cleaner and host. A soothing touch can be a powerful tool for anyone, but especially on the coral reef, where the cleaners use it to earn their food.
The Mantis Shrimp sees the world in ways no other animal can. Each eye is divided into three distinct sections that work together to provide trinocular depth perception – we humans only have binocular vision, and need both eyes to accomplish that. It is all but impossible to sneak up on a mantis shrimp, as they have the equivalent of eyes in the back of their head. While we can move our eyes left and right a bit, the mantis shrimp’s eyes are placed on stalks that allow each eye to pivot individually and look forward, back or to the side.
Each of the mantis shrimp’s complex eyes contains up to 10,000 visual elements grouped into 16 different types of photoreceptors – 12 more than humans possess. Half of these receptors process what we consider the normal visual light spectrum, the other half interpret ultraviolet and polarized light, including something known as circular-polarized light. Physicists use circular polarization for high-tech radio wave transmissions, and astronomers study it in starlight, but the mantis shrimp is the only known animal in the world to tap into this unique light source. Fitting for an animal with a truly otherworldly appearance.
Most fish have well-developed eyes on the sides of their heads. This placement allows them to see in all directions. In the case of blennies and gobies, it also creates some very funny expressions, since they can move each eye independently. They often perch on rocks and coral branches to look at their surroundings — one eye looking in one direction, the other eye a different way.
Nudibranchs sense the world mainly through smell. On top of their heads are two antenna-like appendages called rhinophores, which are responsible for detecting smell. And though these chemical scents are dissolved in seawater, the nudibranch can detect them in extremely small quantities. The hair-like structures on the rhinophores increase surface area for better reception, and the entire appendage can be retracted when the animal is threatened. These unique sensory systems guide the nudibranchs to their food, away from a predator, or eventually to a mate.
Morays have an excellent sense of smell (which compensates for their bad eyesight), and their nares (nostrils) are developed into tubes. They use their great olfactory system to find and catch their prey. Some species, like the blue ribbon eel above, have nostrils that expand in a fan-like shape to capture more of the passing scents.
Most fish have taste buds on their lips, tongue, and all over their mouths. The abundance and sensitivity of the tasting cells placed around the mouth means they can taste their food simply by touching it with their lips.
Instead of tongues, goatfishes have barbels, which are whisker-like structures covered in taste buds. Goatfish can often be seen digging through the sand with their barbels extended, searching for invertebrates and worms to eat. They can taste taste their meal before it even reach their mouths. Catfish are also equipped with barbels, which enable them to find food in the sand and especially in bad visibility when they can’t see. This gives them the advantage of taste-testing as they travel along.
Although fish do not have external ears that are obviously visible, their hearing is very well developed and they can hear even faint underwater sounds with great clarity. Many fishes make and communicate using sound. It is also thought that the fishes swimming bladder can also act as a sound detector, vibrating and passing sounds to the inner ear.
Fish posses another sense, which is like a cross between hearing and touch. The organ responsible for this is the lateral line, a hair cell-based sensory system that detects water motion and vibration using organs known as neuromasts. The fish’s lateral line receives signals stimulated in a front-to-back sequence, which gives the fish much more that simple auditory information, including the ability to “feel” the other fish around it for social schooling, avoiding obstacles, and detect predator and prey.
Rays and sharks have specialized electroreceptors or electric field sensors (ampullae of lorenzini), which form a network of jelly-filled pores on their skin. These sensory organs are finely tuned to help them sense electrical stimuli, and they are so sensitive that if there were no other distortions in the water, a shark could detect the heartbeat of a fish 500 miles away! It is thought that sharks may use this sense to navigate the oceans by tapping into the Earth’s magnetic field.
Many fishes can see in the ultraviolet spectrum. Most damselfishes have ultraviolet coloration, which they appear to use as an alarm signal to signal others of their species. It means this little fish (and most other fishes in his Damselfish family) can see and display a wider spectrum of colors than we can, which is remarkable when you consider how colorful coral reefs are.
Taste, smell, sight, touch, hearing and much more… The underwater world is full of wonders, with different perceptions, unusual methods of communication and bizarre animal behavior. As divers, we can only begin to imagine how the creatures surrounding us experience us humans through their senses.