What are the buoyancy control mechanisms of Chambered nautilus?

What are the buoyancy control mechanisms of Chambered nautilus?

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I'm currently working on an underwater robot and was hoping to use the principle used by the nautilus for buoyancy control. So how do the Chambered nautilus control its buoyancy?

The various species of nautilus use a combination of active transport of salts and passive diffusion of water for buoyancy (Denton and Gilpin-Brown 1966, Ward 1979, Greenwald et al. 1980). The chambers are filled with seawater. Salts from the seawater in the chambers is removed by a structure called the siphuncular epithelium. This process makes the chambered water hypotonic, meaning it has lower solute concentration relative to the animal. The hypotonic water then diffuses from the chambers into the blood, creating air pockets in the chambers. Greenwald and Ward (2010) have a recent summary of what is known about nautilus buoyancy, if you want to know more.

The diffusion of water in is not a rapid process. The maximum ascent and descent rate of Nautilus from depths appears to be about 3.0 m m$^1$ (Dunstan et al. 2011). This does not seem like an efficient process or rate of depth change for an underwater robot.

Literature Cited

Denton, E.J. and J.B. Gilpin-Brown. 1966. On the buoyancy of the peraly nautilus. Journal of the Marine Biological Association of the United Kingdown 3: 726-759.

Dunstan, A.J., et al. 2011. Vertical distribution and migration patterns of Nautilus pompilius. PLoS ONE 6: e16311. doi:10.1371/journal.pone.0016311

Greenwald, L., et al. 1980. Cameral liquid transport and buoyancy control in the chambered nautilus (Nautilus macromphalus). Nature 286 55-56.

Greenwald, L. and P.D. Ward. 2010. Buoyancy in NAutilus. Topics in Geobiology 6: 547-560.

Ward, P.D. 1979. Cameral liquid in Nautilus and ammontites. Paleobiology 5: 40-49.

As the siphuncle pumps cameral liquid out of a chamber, the pressure of the chamber falls and nitrogen, oxygen, and some carbon dioxide diffuse into the chamber. Sea water gas pressures are in equilibrium with atmospheric gases (oxygen and nitrogen) and are in equilibrium with nautilus blood. Hence as cameral liquid is pumped out of the chamber, gases enter from the blood. But it would make no difference to the buoyant state of the animal if gases entered or if there were a vacuum. The emptying mechanism relies on sodium pumps transporting salt out of the cameral liquid. There is no way to duplicate this biological mechanism in a mechanical system.

10 Chambered Facts About Nautiluses

Half a billion years before the first submarine left harbor, the ancestors of our modern nautiluses were already beginning to master the art of buoyancy control. How do these creatures work? Read on.


The chambered nautilus (Nautilus pompilius) is hands-down the most famous of these cephalopods. The orange-banded creature shares its genus with three other species, known as the Palau, bellybutton, and white-patch nautiluses (with a potential fourth, Nautilus repertus, though most scientists believe it's actually a large chambered nautilus). Meanwhile, the lesser-known Allonautilus genus contains two rarely-seen species—one of which we’ll discuss later on.

With shells that measure up to 10.6 inches in diameter, chambered nautiluses are the largest of the six, and bellybuttons—whose shells max out at 6.3 inches in diameter—as the smallest. Range-wise, these animals are all restricted east-west within the waters between Samoa and the Philippines, and north-south between Japan and Australia.


From the meaning of certain symbols to how to open child-proof lids, an octopus can remember a lot—and retain that knowledge long-term. Nautiluses, in contrast, aren’t regarded as being very bright in fact, until recently, it was believed that they weren’t capable of forming any memories whatsoever.

Marine biologists Robyn Cook and Jennifer Basil of Brooklyn College and the City University of New York, respectively, wondered if this assumption was true—so in 2008, the pair trained captive nautiluses to associate a flashing blue light with food. After a while, the animals reacted strongly whenever this signal came on, spreading their arms in eager anticipation. However, they stopped doing so the following day. Why? Presumably, the invertebrates had managed to forget everything they’d learned within a 24-hour period.


Squids and octopuses don't usually live long lives—in fact, most die after just two to three years. By comparison, nautiluses look like Methuselah: 17-year-old specimens have been caught, and biologists theorize that some can surpass 20 years old.


Nautilus shells have a series of chambers connected by the siphuncle—a tube made of tissue. A newborn nautilus starts life with four chambers, adding more and more as it grows (adults have 30 on average). The chambers contain a mixture of gas and seawater, and the siphuncle regulates how much of each is present within the chambers at any given time.

If a nautilus wants to descend, the siphuncle makes that happen by pumping sodium and chlorine ions into the chambers. Extra water then enters these compartments thanks to osmosis, making the animal less buoyant, and the nautilus sinks. To reverse this process and travel upward, the siphuncle simply removes ions from the chambers, and water consequently flows into the mantle cavity. As it leaves, gas bubbles start to diffuse, which lightens the shell.


The mantle cavity, a funnel below the eyes and present in all cephalopods, is connected to a muscular siphon. Nautiluses move forward and backward by aiming this tube and rapidly expelling water through it.


Nautiluses are usually found between 500 and 1000 feet below the surface, and within that range, their shells hold up quite well. But going too deep can be a fatal mistake. For chambered nautiluses, 2575 feet appears to be the limit. During one 1980 experiment [PDF], a captive specimen was subjected to the amount of pressure that it would naturally encounter at this depth. Moments later, the shell imploded, killing the creature instantly.


These short, clustered limbs help ensnare the fish, crabs, and carrion upon which the cephalopods dine. Speaking of mealtime, hungry nautiluses use scent to track down food because they can’t see very well (their eyes lack lenses) so their eyes are more akin to pinhole cameras, which, according to the book Animal Eyes, forces them to choose between “unusably dim or unusably blurred.”


Octopuses and squids employ suckers and hooks, which nautiluses lack. Instead, their arms are coated with a sticky substance that helps ensnare prey. Tiny hairs called cilia also help form viscous pads near the appendages’ tips.


“It’s really a very cool way not to get eaten,” earth scientist Peter Ward told Live Science. Last August, the University of Washington professor became the first person in 31 years to spot a rare nautilus species. Allonautilus scrobiculatus is easily recognized due to its odd defense mechanism: Thick, slimy fuzz coats the animal’s shell, making it too slippery for many fish and other predators to bite into.


Most cephalopod eggs are incredibly small: Those laid by the 50-pound giant Pacific octopus, for example, are about as big as a grain of rice. Around an inch long, chambered nautilus eggs dwarf the competition. Using her tentacles, a female will (presumably) affix the eggs to a hard surface, where they’ll hatch between nine and 12 months later.

Aquarium Science: Husbandry of the Nautilus: Aspects of its Biology, Behavior, and Care

A scientific look at the unusual nautiluses, including their eating habits, reproduction, and famously unique anatomy.

Keeping Cephalopods

The common misconception regarding the captive care of cephalopods is that long-term success is impossible. While it is true that keeping cephalopods is a difficult task, understanding their biology and natural behavior will enhance the success of the exhibition of these animals. The nautiluses are no exception. Though they may not have the chromatophores possessed by other cephalopods that enable color change, these deep-sea animals are a window into a world that most people will never see.

The nautilus differs from other cephalopods in many aspects both anatomically and behaviorally. The main body features of the nautilus are its shell, hood, and tentacles.

Similar to the cuttlebone in cuttlefish, the nautilus shell regulates the animal&rsquos buoyancy, while at the same time providing protection against predators. The calcium carbonate shell is made up of individual chambers, some of which are filled with gas and others filled with seawater. The chambers are interconnected by a tube, or siphuncle. The liquid-filled chambers release or take in sea water in order to maintain neutral buoyancy.

The body of the nautilus lies within the first chamber and can retract into this chamber if in danger. In the retracted state, the hood protects and conceals the animal from predators. This behavior is its only known defense mechanism. While most cephalopods possess an ink sac that can be used as a defensive tactic, the nautilus is without an ink sac.

Nautiluses are equipped with a total of 90 adhesive tentacles, without suckers, significantly more than any other cephalopod. Utilizing its 90 tentacles, the nautilus is able to feel around the ocean floor or rocks searching for prey. Vision in the nautilus is much less developed than in other cephalopods the eye lacks a lens and is constructed like the aperture of a pinhole camera (Hanlon & Messenger, 2005).

The last major difference between nautilus and other cephalopods is their life span. While most cephalopods have a life span of one to two years, the nautilus is thought to live up to at least 15 years, a very attractive characteristic for an aquarium animal.


Wild nautiluses have been observed to make diel migrations (Carlson et al., 1984 Ward et al., 1984). This type of behavior takes the nautilus from depths of 1200 feet at daybreak up to depths of 300 feet by sunset. Nautiluses can best be characterized as opportunistic feeders investigating food when detected. The actual feeding behavior of the nautilus can be described as sampling, searching, and sweeping.

There is evidence to support that the nautiluses detect prey by sampling lateral currents across the reef for chemical trails (O&rsquodor et al., 1993). After detecting prey with the use of large olfactory organs, the tentacles are used to locate and seize the prey. The diet of the wild nautilus includes crustaceans (including hermit crabs Ward & Wicksten, 1980), crustacean molts, nematodes, echinoids, and fishes (Saunders & Ward, 1987). There are accounts of cephalopod beaks and nautilus tentacles found in the gut as well (Hanlon & Messenger, 2005). It is not uncommon under aquarium conditions to witness cannibalism (Carlson, 1987) as is observed with other species of cephalopods.

The main focus in the feeding of nautiluses is to provide food that is high in calcium in order to sustain normal shell growth. The most common food offered to nautiluses in captivity is shrimp (with shell), squid, various types of frozen fish, and blue crab. Several different types of molts, such as lobster molts, have also been fed as an enrichment food. The lobster molt is taken quickly and consumed with no problems (molts are also a great source for calcium).

Shell Aberrations

A common and still misunderstood issue with captive nautiluses is aberrations of the shell. Over time, the shell does not grow normally and begins to degrade. Signs of this are black edging of the newly formed shell. There appears to be no adverse health issues associated with the shell malformation, and to date is merely an aesthetic problem.

Aquarium Care

Although nautiluses spend most of the time attached to the walls of the aquarium, they do occasionally jet around with minimal control, often running into the sides of the tank. For this reason the dimensions of their accommodations are important for the proper care and maintenance of nautiluses. For the average nautilus (less than 6 inches), the aquarium should be at least 3 feet long, 18 inches wide, and 2 feet deep to allow the animal to move around freely without constantly bumping into the sides of the tank however, when keeping multiple nautiluses or a single large nautilus, a bigger aquarium is required.

As with all cephalopods, a key ingredient in successful husbandry is proper filtration. Due to the high amount of solid and liquid waste produced, it is important to have a large biological filter bed or sand filter. A protein skimmer is also recommended to help manage the large waste load. UV sterilizers can be added to help minimize the spread of possible pathogens, which can be difficult to treat in cephalopods. A good rule to go by is to have a filtration system that is designed for a tank twice the size of the one the animal is in.

Another important aspect of keeping nautiluses alive is maintaining the water temperature between 50° and 70°F, using a chiller. For a more natural environment and to aid possible breeding, one can have the temperature gradually fluctuate between cooler and warmer temperatures over a 24-hour period. This will mimic diel migration, although this will be difficult without a computer controlling the heater/chiller. Because nautiluses live in the deep sea and receive only minimal light when migrating to the surface at night, there should only be enough light in the tank to view the animal. Actinic lights work well for this, as too much light can stress the animal.

Aquascaping and Tankmates

Careful consideration should be used when deciding how to decorate the tank and choosing tankmates. Live rock can be used on the bottom and sides of the tank, but the mid and upper sections of the tank should be clear of obstacles that the nautilus could run into and damage itself. There should be no plastic dÉcor, as nautiluses have a habit of trying to bite/eat everything.

The nautilus is one of the few cephalopods with which other animals have been kept in the same tank with some success, but keep in mind that there is always the chance that those animals could become a snack. If choosing to have tankmates, make sure they are non-aggressive and can withstand the cold water and dim lighting nautiluses require. Possible tankmates include cardinalfish, squirrelfish, pinecone fish, flashlight fish, shrimp, sponges, snails, and non-stinging corals that can live in low light.


The understanding of nautilus reproduction has increased substantially in the past 20 years owing much to the pioneering work of Dr. Bruce Carlson at the Waikiki Aquarium (Carlson, 2000). There are two methods in determining the sex of a nautilus.

The first is best used on new animals not accustomed to captivity. By turning the animal upside-down, a horseshoe-shaped gland will be visible in females and will be green to brown in mature females. This technique, though, should only be used by advanced aquarists.

The second technique of sexing a nautilus is to locate the spadix, which is a large modified tentacle found on the left side of the male nautilus, adjacent to the mouth. The spadix is the mode of sperm transfer.

Nautiluses mate facing each other and may stay in that position for hours. The first embryo was discovered in 1985 and the first hatchling was obtained in 1988 (Norman, 2000). In captivity, female nautiluses may lay one to two eggs per month. The nautilus egg will take at least one year to hatch. The temperature of the egg-holding tank is crucial in the development of the embryo.

While most nautiluses are kept at temperatures of 64°F, the eggs actually develop at warmer temperatures, 70° to 75°F. Once hatched, the juvenile nautilus readily accepts food. Unfortunately, there has been no success in rearing adults from eggs as of yet.

Difficult but Rewarding

The task of exhibiting the nautilus can be very overwhelming when considering tank design, filtration units, and tank decor. Nevertheless, a keen awareness and understanding of nautilus biology and behaviors will assist you when you begin to assemble your tank. As Jacques Cousteau said, &ldquoThe impossible missions are the only ones which succeed.&rdquo


Carlson, B. A., McKibben, J. N., & DeGruy, M. V. 1984. &ldquoTelemetric investigation of vertical migration of Nautilus belauensis in Palau.&rdquo Pacific Science 38:183&ndash188.

Carlson, B. A., 1987. &ldquoCollection and aquarium maintenance of Nautilus.&rdquo In Nautilus: The Biology and Paleobiology of a Living Fossil. Plenum Press. New York, NY. pp. 563&ndash578.

Carlson, B. A., 2000. &ldquoBreeding chambered nautiluses.&rdquo In Cephalopods: A World Guide. ConchBooks. Hackenheim, Germany. pp. 24&ndash29.

Hanlon, R. T. & Messenger, J. B. 2005. Cephalopod Behavior. Cambridge University Press. Cambridge, United Kingdom.

Norman, M. 2000. Cephalopods: A World Guide. ConchBooks. Hackenheim, Germany.

O&rsquodor, R. K., Forsythe, J., Webber, D. M., Wells, J. & Wells, M. J. 1993. &ldquoActivity levels of Nautilus.&rdquo Nature 362:626&ndash627.

Saunders, W. B. & Ward, P. D. 1987. &ldquoEcology, distribution, and population characteristics of Nautilus.&rdquo In Nautilus: The Biology and Paleobiology of a Living Fossil. Plenum Press. New York, NY. pp. 137&ndash162.

Ward, P. D., Carlson, B. A., Weekly, M. & Brumbaugh, B. 1984. &ldquoRemote telemetry of daily vertical and horizontal movement of Nautilus in Palau.&rdquo Nature 309:248&ndash250.

Ward, P. D. & Wicksten, M. K. 1980. &ldquoFood sources and feeding behavior of Nautilus macromphalus.&rdquo The Veliger 23:119&ndash142.


Living systems use physical materials to create structures to serve as protection, insulation, and other purposes. These structures can be internal (within or attached to the system itself), such as cell membranes, shells, and fur. They can also be external (detached), such as nests, burrows, cocoons, or webs. Because physical materials are limited and the energy required to gather and create new structures is costly, living systems must use both conservatively. Therefore, they optimize the structures’ size, weight, and density. For example, weaver birds use two types of vegetation to create their nests: strong, a few stiff fibers and numerous thin fibers. Combined, they make a strong, yet flexible, nest. An example of an internal structure is a bird’s bone. The bone is comprised of a mineral matrix assembled to create strong cross‑supports and a tubular outer surface filled with air to minimize weight.

Modify Size/Shape/Mass/Volume

Many living systems alter their physical properties, such as size, shape, mass, or volume. These modifications occur in response to the living system’s needs and/or changing environmental conditions. For example, they may do this to move more efficiently, escape predators, recover from damage, or for many other reasons. These modifications require appropriate response rates and levels. Modifying any of these properties requires materials to enable such changes, cues to make the changes, and mechanisms to control them. An example is the porcupine fish, which protects itself from predators by taking sips of water or air to inflate its body and to erect spines embedded in its skin.

Modify Density

In biology, density is measured as mass per unit volume, number per unit volume, or number per unit of area. This means that density changes when mass, volume, number, or area changes. Changing density can result in both challenges and opportunities. Modifying density or managing changes in density enables living systems to adjust to their environment because density also relates to other properties, such as pressure and buoyancy. For example, as a fish swims deeper in water, the outside pressure increases. This decreases the fish’s volume and therefore increases its density this, in turn, decreases its buoyancy. To keep from sinking, the fish adjusts to these density changes by using its fins to provide lift.

Modify Position

Many resources that living systems require for survival and reproduction constantly change in quantity, quality, and location. The same is true of the threats that face living systems. As a result, living systems have strategies to maintain access to shifting resources and to avoid changing threats by adjusting their location or orientation. Some living systems modify their position by moving from one location to another. For those that can’t change location, such as trees, they modify position by shifting in place. An example of an organism that does both is the chameleon. This creature can move from place to place to find food or escape predators. But it also can stay in one place and rotate its eyes to provide a 360‑degree view so that it can hunt without frightening its prey.

Optimize Shape/Materials

Resources are limited and the simple act of retaining them requires resources, especially energy. Living systems must constantly balance the value of resources obtained with the costs of resources expended failure to do so can result in death or prevent reproduction. Living systems therefore optimize, rather than maximize, resource use. Optimizing shape ultimately optimizes materials and energy. An example of such optimization can be seen in the dolphin’s body shape. It’s streamlined to reduce drag in the water due to an optimal ratio of length to diameter, as well as features on its surface that lie flat, reducing turbulence.


Class Cephalopoda (“head-foot”): Nautilus, squid, octopus, cuttlefish

Cephalopods are unique among mollusks, and even within the animal kingdom. They are lauded for their large brains and complex behaviors and are considered the most intelligent invertebrates. Among 800 species in 45 families, all are carnivorous and live in marine ecosystems. They all have a set of arms or tentacles, but only the nautilus retains an exterior chambered shell. Many species have chromatophores, which allow them to change color for defense, camouflage, or courting. They range from the size of a fingernail to just longer than a city bus (the mysterious giant squid).


To a beachgoer, a seashell is often simply an object of beauty. To a mathematician it may be an object of intrigue or inspiration. But to the creature that made it, a shell is predominantly a protection. It protects the organism from harm in the form of predators, rocks, and other inanimate objects in its environment. But it poses a bit of a problem, too: How does an animal grow when it’s encased in a container that can’t grow with it?

The chambered nautilus inhabits the most recently constructed chamber of its shell and uses the other chambers to regulate buoyancy.

The Strategy

The solution for the chambered nautilus (Nautilus pompilius) is simple and elegant. When it gets too large for its existing space, the (ultimately) volleyball-size nautilus adds on to the open end of its shell, expanding the diameter in a spiral configuration. And, in a remarkable and timely example of repurposing, it does not abandon its old space. Rather, it closes it off with a wall, creating a chamber that it uses to help stay buoyant as its body gets heavier.

Nautiluses live in the South Pacific, hundreds of meters beneath the surface of the ocean. They make their shell by mixing sugars, proteins, calcium, and other minerals, then adding the resulting crystallized material to the lip of the existing shell. But that’s not all. Every 150 days or so, a nautilus forms a membrane at its tail end that separates almost all of its body from the older portion of the shell. The one exception is a tube-shaped appendage called a siphuncle that extends back through the previously constructed chambers.

When first formed, a chamber is filled with fluid. But over time, as the growing nautilus adds bulk, the siphuncle sucks the fluid from the chamber. As a result, the shell becomes more buoyant, counterbalancing the added weight of the living animals to maintain neutral buoyancy (a condition of neither sinking nor rising).

Over the course of its life, a nautilus might add up to 30 chambers. In addition to gradually adjusting for its own increasing weight, it also can add or remove fluid from the old chambers more quickly to compensate for sudden changes such as a hefty meal or a sudden loss of part of its shell.

Over the course of its life, a nautilus might add up to 30 chambers.

The Potential

What lessons might we learn from the nautilus? The strategy of making and using closed chambers to take on and jettison a liquid already is used, and might be further applied, to regulate the position of submarines, drilling rigs, electricity-generating turbines and other manmade objects underwater.

Perhaps more universally applicable and generally beneficial, however, is this takeaway: It’s not always necessary (or even beneficial) to throw something away when it is no longer suitable for its original purpose. Rather, we might do well to consider whether an existing structure might be retained, added to, and ultimately repurposed to provide a new and valuable benefit.

Last Updated August 18, 2016


“[N]autiloids have an external shell forming a geometrical spiral and consisting of an organic matrix of calcium and other mineral compounds. The chambers are connected by the siphuncle, a strand of living tissue enclosed in a chitin tube that spirals from the posterior mantle through all preceding chambers of the shell, including the earliest one. As the animal grows, the shell aperture is extended and the body moves outward while the siphuncle is elongated before a new

septum and thereby a new chamber is built. Each new chamber is filled at first with a watery fluid, called cameral liquid, which is gradually removed by the epithelium of the siphuncle. This chamber formation cycle occurs at regular intervals until the animals are adult.” (Westermann et al. 2004: 930)

Shell growth and chamber formation of aquarium‑reared Nautilus pompilius (Mollusca, Cephalopoda) by X‑ray analysis

Journal of Experimental Zoology Part A: Comparative Experimental Biology | December 1, 2004 | Bettina Westermann, Ingrid Beck‑Schildwächter, Knut Beuerlein, Erhard F. Kaleta, Rudolf Schipp

Online Learning Center

In most geographic areas, the chambered nautilus migrates vertically at sundown from depths of 610 meters (2000 feet) to 91 meters (300 feet) to seek prey, returning to the deep ocean at sunrise.

The chambered nautilus, a cephalopod, is a relative of the ancient ammonoids and a modern relative of squid, octopus, and cuttlefish. Unlike its relatives, the nautilus has an external shell. It inhabits ocean waters close to the sea floor during the day, migrating to shallower water at night in search of prey.

Chambered Nautilus


CLIMATE CHANGE: Not Applicable

At the Aquarium

The chambered nautilus is not currently exhibited at the Aquarium.

Geographic Distribution


The nauilius in most geographic areas spend daylight hours near the bottom of coral reef deep slopes to depths of 450 m (1500 ft) migrating vertically at night to shallower waters of about 90 m (300 ft) or less to seek prey. Recent studies have shown that individual population and habitat characteristics may determine daily vertical migrations of regional nautilus populations. Factors such as requirement for buoyancy regulation, preferred feeding habitat and predator avoidance may combine to create vertical migration patterns best suited to each distinct population and location.

Physical Characteristics

This cephalopod with an external shell is considered primitive compared to its relatives, the octopus, squid, and cuttlefish. Its shell, which is produced by its mantle, is divided into compartments, ranging from four in a newly-hatched nautilus, to 38 or more in mature individuals. As the animal grows, its body moves forward and a wall called a septum is produced that seals off the older chambers. The body is contained in the last compartment—the newest and largest of them all. The animal can completely withdraw its body into its shell, closing the opening with a leathery hood. A nautilus does not have suckers on its tentacles like an octopus does. Instead its tentacles are lined with alternating grooves and ridges that allows it to grip objects.

The beautiful nautilus’ shell is white to orange, with white stripes and a central, black whorl.

The shell of adults is 20-25 cm (8-10 in) in diameter.

This nocturnal opportunistic feeder eats shrimp, crabs, fishes, dead animals, and occasionally another nautilus. It is believed that prey is detected by smell since the animal lacks good vision. Food is captured by its retractable tentacles and passed to its mouth where a beak-like jaw tears it into pieces. Its radula, a file-like feeding structure, further shreds the food before it is swallowed.


Little is known about nautilus reproduction in the wild. Most information is based on observations made of animals in protected environments. The nautilus takes 5-10 years to reach sexual maturity, a very long time when compared to most other cephalopods. The male uses his tentacles to hold onto the female’s shell while using a specially modified arm to transfer a sperm packet into the female’s mantle cavity. The female lays several eggs, one at a time. Each emerges covered with layers of membranes that form a leathery protective covering. She uses her tentacles to attach each egg to a hard surface where it remains for 9-12 months before emerging as a 3 cm (1.2 in) hatchling. The eggs and hatchlings of the chambered nautilus are the largest of all cephalopods.


In addition to protecting the animal’s soft body, the shell has another important function which is to provide enclosure of a system that enables the nautilus to control its buoyancy. The older closed chambers of the shell contain an argon-nitrogen gas mixture and a liquid saline solution. The chambers are connected by a tube called a siphuncle that gives the nautilus the ability to change the ratio of liquid to gas which modifies its weight. These changes can result in whatever buoyancy it chooses: positive, negative, or neutral and are much like a submarine filling or emptying its dive tanks.

The nautilus moves in a see-saw motion using “jet propulsion” by alternately pulling water into the mantle cavity within the shell and blowing it out the muscular, flexible siphon beneath the tentacles. The way the siphon directs the water stream controls the animal’s forward, backward, and sideways movements.


Little changed over the past 500 million years, the chambered nautilus is considered a “living fossil”, like the horseshoe crab and the coelacanth. The relatively primitive creature swimming in the ocean today has been traced back to a time before there were bony fishes, and before dinosaurs roamed the earth.

The eyes of a nautilus are poorly developed compared to the complex ones of most other cephalopods. The simple, pinhole eyes lack lenses and probably form blurry images at best.


Unlike most other cephalopods that have a short life span, the chambered nautilus can live 16 or more years.


Although the ornamental shell trade continues to threaten nautilus populations and has resulted in major declines in localized populations, currently protection is still lacking except in Indonesia which banned collection in 1987.

June 2014: The U.S. Fish and Wildlife Service (USFWS) convened a workshop to address the biology and protection of the chambered nautilus. At that time chambered nautilus were not protected internationally under the IUCN Red List of Threatened Species because of lack of sufficient evidence about the populations. They also were not listed under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) or protected specifically under U.S. domestic laws. The USFWS funded funding research to gain a better understanding of their current status and the impact of nautilus fishing and trade on wild populations. The USFWS collaborated with the National Marine Fisheries Service (NMFS), other range countries, researchers, and others in this study.

September 2016: Delegates to the 17th meeting of CITES will discuss and vote on protection of the chambered nautilus and if approved, will assign Appendix 1 or ii levels of protection. This nautilus species will then be projected in international trade. The USFWS has announced that the Service will support protection of this nautilus.

Special Notes

Chambered nautili are known as living fossils because they have remained virtually unchanged for millions of years.In 1997-98 paleontologists used DNA techniques to compare tissues from today’s animals to those of millions-of-years-old fossil nautiloids, dating to the time when California and Washington State were under the ocean. These studies confirmed the belief that the species Nautilus pompilius is a living fossil. The chambered nautilus (Allonautilus and Nautilus species) is the only living descendent of a group of ocean creatures that thrived in the seas 500 million years ago when the earth’s continents were still forming. It is even older than the dinosaurs!

Named after the chambered nautilus, the USS Nautilus launched in 1954 was the first nuclear-powered submarine in the world. This cephalopod was also the subject of Oliver Wendell Holmes’ famous poem, The Chambered Nautilus. The line of exercise equipment called the Nautilus&trade got its name from its pulleys that are shaped like the cross-section of a nautilus shell.

The chamber formation cycle in Nautilus macromphalus

The chamber formation cycle in externally shelled, chambered cephalopods consists of mural ridge formation, secretion of the siphuncular connecting ring, septal calcification, and cameral liquid removal. Radiographic observation of the chamber formation cycle in specimens of Nautilus macromphalus allows direct observation of the various processes of the chamber formation cycle in a chambered cephalopod, and gives direct measures of rates. New chamber formation in N. macromphalus initiates when slightly more than half of the cameral liquid has been removed from the last formed chamber. At this volume, the liquid within the chamber drops from direct contact with the permeable connecting ring to a level where it is no longer in direct contact and must move onto the connecting ring due to wettable properties of the septal face and septal neck. This change from “coupled” to “decoupled” emptying coincides with the formation of a mural ridge at the rear of the body chamber, in front of the last formed septum. With completion of the mural ridge, the septal mantle moves forward from its position against the face of the last formed septum and attaches to the new mural ridge, where it begins calcifying a new septum in front of the newly created, liquid-filled space. Emptying of the new cameral liquid from this space commences when the calcifying septum has reached from one-third to two-thirds of its final thickness. The cessation of calcification of the septum coincides with a liquid volume in the new chamber of approximately 50%, at which point the cycle begins anew. During the chamber formation cycle apertural shell growth appears to be continuous. Since apertural shell growth is the prime factor leading to increased density in seawater, and hence decreased buoyancy, the period in the chamber formation cycle between the onset of septal calcification and the onset of emptying would be a time of greatly decreasing buoyancy. This is avoided by the removal of decoupled liquid from previously produced chambers. In this way constant neutral buoyancy is maintained. The time between chamber formation events in aquarium maintained N. macromphalus appears to be between 70 and 120 d.

In the Spotlight

The chambered nautilus, Nautilus pompilius, is listed as threatened under the Endangered Species Act.

In addition, all chambered nautiluses are vulnerable to international trade and are listed under Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora. All seven species, in two genera Nautilus and Allonautilus, are listed under CITES.

Conservation Efforts

At the 2016 meeting of the Conference of the Parties to the Convention on International Trade in Endangered Species of Wild Fauna and Flora, the Parties agreed to include the entire nautilus family of chambered nautilus in Appendix II of CITES. The United States—joined by Fiji, India, and Palau—submitted the proposal for consideration (PDF, 31 pages) at the meeting.

A global treaty, CITES protects species from becoming endangered or extinct because of international trade. The inclusion of the family Nautilidea in CITES Appendix II will help ensure that the international trade in these species is legal and sustainable.

The U.S. Fish and Wildlife Service is the government agency designated under the Endangered Species Act to carry out the provisions of CITES. NOAA Fisheries provides guidance and scientific support on marine issues given our technical expertise. Learn more about U.S. FWS efforts under CITES for the chambered nautilus.

What are the buoyancy control mechanisms of Chambered nautilus? - Biology

Effective January 2, 2017: The entire family of chambered nautiluses (Nautilidae), which includes two species from the genus Allonautilus (A. perforatus and A. scrobiculatus) and five species from the genus Nautilus (N. belauensis, N. macromphalus, N. pompilius, N. repertus, and N.stenomplahus), has been listed in CITES Appendix II. This means that CITES documentation will be required for import and re-export of these species and items made from them.

Information to assist in complying with U.S. CITES regulations is available for commercial traders.

Chambered nautiluses (Allonautilus and Nautilus species) are the only living descendants of a group of ocean creatures that thrived in the seas 500 million years ago when the earth&rsquos continents were still forming. They are even older than the dinosaurs! Chambered nautiluses are known as living fossils because they have remained virtually unchanged for millions of years.

Among the last representatives of the ancient lineages of cephalopods (animals with no backbones but with tentacles or arms), chambered nautiluses are easily distinguished from their closest living relatives -- the octopus, squid, and cuttlefish -- by their distinctive external coiled shells. A feat in molluscan evolution, the internal chambers of their shell provide a buoyancy mechanism to facilitate movement that inspired the inventor of the earliest modern submarine to name the invention &ldquoNautilus.&rdquo

These marine mollusks are found in the coastal reefs around Southeast Asia and Australia, including the U.S. territory of American Samoa. Chambered nautiluses grow slowly, maturing around 10-15 years of age. They produce a small number of eggs that require at least a year-long incubation period. These deep-sea scavengers spend much of their time hovering along the reef at depths of 100-300 meters (330-990 feet), dangling their tentacles as they move along in search of food. They have up to 90 retractable, suckerless tentacles with grooves that secrete mucous to help in obtaining food and attaching to the reef face when resting.

Chambered Nautilus Species

Scientific Name

Common Name

Crusty nautilus or King nautilus

Emperor nautilus or Pearly nautilus

Taxonomic Classification
Phylum: Mollusca
Clss: Cephalopoda
Order: Nautilida
Family: Nautilidae

**Effective January 2, 2017, the family Nautilidae is protected under Appendix II of CITES.**

Laws & Regulations

Nautilus in the Wild. Credit: USFWS

The United States, along with Fiji, India, and Palau, submitted the proposal to protect these species and worked closely with other countries and non-governmental organizations to gain support for the Appendix II-listing proposal.

Read the proposal we submitted to include the Family Nautilidae in Appendix II at CoP17 and the 2-page fact sheets about the proposal, available in English, French, and Spanish.

As of January 2, 2017, the listings have gone into effect and CITES documentation will be required for import and export of these species and items made from them. Information on how to comply with the U.S. CITES regulations is available for commercial traders.

Read our blog to learn about the events leading up to CoP17.

Learn more about the outcomes of CoP17.

Threats & Conservation Status

Harvested primarily for their beautiful shells, and not as a source of food, chambered nautiluses are sold as souvenirs to tourists and shell collectors, and as jewelry and home decoration items. Living animals are taken for public aquariums and research. The reef habitat where they live is also subject to pollution, destruction, and degradation and coral reefs are prone to being overfished for a variety of reef species that live there.

Yet, chambered nautilus biology does not lend itself to recovering from overfishing or adjusting to habitat destruction. These are slow-growing marine invertebrates – they take 15-20 years to reach maturity. They also lay only one egg at a time and they produce a small number of eggs annually that take about 1 year to incubate that swim along the ocean reef. They do not swim in the open ocean and cannot move between habitats that are separated by deep ocean.

The primary threats to family Nautilidae include:

• targeted, market-driven harvest for international trade in their shells
• habitat degradation throughout much of their range
• predation by bony fishes, octopus, and possibly sharks and
• risks associated with ecotourism.

Given their slow growth, late maturity, low reproductive output, and low mobility, chambered nautiluses are particularly vulnerable to overfishing. These threats make it difficult for them to recover from overharvest or catastrophic events.
Research scientists have had little success breeding these animals in captivity eggs will hatch but the young do not live long enough to reach maturity. Little is known about nautilus populations in the wild. The very first population estimate was made only in 2010.

Watch a chambered nautilus and its unique way of moving in this video from the Monterey Bay Aquarium.

Chambered nautilusesare bottom scavengers and eat shrimp and crabs, but their diet in the wild is largely unstudied. They are nocturnal, making daily migrations up and down the
continental shelf. Their up to 90 tentacles do not sting their prey, but stick to it.

Natural predators of nautilus include the octopus, which can bore a hole right through the nautilus&rsquo shell to reach its soft body parts in the outermost chamber. Teleost fish, such as triggerfish and grouper, prey on nautilus in shallow waters, and other species such as sharks and snappers may also prey on nautilus.

The nautilus shellappears front and center on the emblem of New Caledonia. Nautilus jewelry figured strongly in Australian aboriginal culture both for bartering and was incorporated into hunter-gatherer folklore.

International Research

Toward a better understanding of the Impacts of Trade on Chambered Nautiluses

The U.S. Fish and Wildlife Service and the National Marine Fisheries Service have collaborated with range countries and species experts for several years, contributing funding to research that would help us better understand chambered nautilus biology and the effects of harvest and international trade. See more about our efforts and results.

Learning more about Chambered Nautilus Populations/Biology

For population research, we signed a Cooperative Agreement with the University of Washington (Seattle, Washington) to enlist the services veteran nautilus expert, Dr. Peter Ward, and fellow researcher Dr. Andrew Dunstan (currently of Queensland Parks and Wildlife Service, Australia) to conduct population and livelihood research in four locations (American Samoa, Fiji, Australia, and the Philippines). The aims were to estimate population sizes, to understand the importance of chambered nautilus harvesting to local fisheries, and to evaluate the effects of fishing by comparing fished and unfished populations. None of the research methods involved intentional killing of any chambered nautiluses and the non-lethal trapping and research methods were designed to minimize disturbance and incidental mortality. The research protocol was very similar to that used by Dunstan when he formulated the first chambered nautilus population estimate in 2010. Fieldwork began in 2012 at a location where commercial nautilus fishing has occurred (the Philippines) and three other locations where no commercial fishing has occurred (American Samoa, Fiji, Australia). Among the findings were that chambered nautiluses have low population numbers even where they have never been commercially harvested and that the meat of chambered nautiluses is not considered an important food source to local populations.

Results: Comparative Population Assessments of Nautilus sp. in the Philippines, Australia, Fiji, and American Samoa Using Baited Remote Underwater Video Systems (2014)

Investigating the Impact of International Trade

The World Wildlife Fund, Inc.-TRAFFIC North America conducted a year-long trade study to gather data on the levels of exploitation and the extent of global trade. Prior to the CITES listing, there were no global statistics on the extent of trade in chambered nautiluses, although trade has been reported on nearly every continent. The goal of this project was to obtain information on and characterize the dynamics and levels of trade both where the animals are harvested and where the products are sold. The focal countries for harvest research were the Philippines and Indonesia and destination countries studied included the United States, Europe and China. The report demonstrated that harvest and trade of chambered nautiluses was poorly regulated and that the United States was among the major importers and re-exporters of chambered nautilus products [and called for better monitoring of international trade in chambered nautiluses].
Results: An investigation into the trade of Nautilus (2016)

Working with Species Experts

NOAA Fisheries and U.S. Fish and Wildlife Service held a joint workshop that brought together many of the leading chambered nautilus researchers to discuss biological trends and trade data. Through eight presentations, participants explored present and historical population information and the impacts of international trade on wild populations. Discussions covered a range of topics, including population estimates, laboratory studies, demographics, life history characteristics, captive breeding, and trade trends.

Visit the NOAA Fisheries chambered nautilus website for more information on U.S. research to assess the impact of harvest and international trade on these iconic species and useful links to news and information.

"Nautilus Girl" Gretchen Grooge wears a nautilus
Halloween costume.
Credit: Courtney Googe

Kids Take Action for Nautilus

Save the Nautilus is a non-profit organization, started by some inspiring young conservationists that is dedicated to conserving and funding for chambered nautilus research.

See their video blog of their amazing adventure when they traveled to American Samoa with researchers for a week of chambered nautilus population studies!

Read our blog about Gretchen Googe, the Nautilus Girl, and her enthusiastic work to raise awareness these amazing creatures.

Mankind Benefits From Nuclear Energy and Radiation

Marine propulsion

Work on nuclear marine propulsion started in the 1940s, and the first test reactor started up in the United States in 1953. The first nuclear-powered submarine, USS Nautilus , put to sea in 1955. This led to the development of reactors and propulsion systems mostly for naval vessels in several countries. Today over 140 vessels are powered by about 180 small nuclear reactors and more than 12,000 reactor-years of marine operation has been accumulated.

Nuclear propulsion has proven technically and economically essential in the Russian Arctic where operating conditions are beyond the capability of conventional icebreakers. The power levels required for breaking ice up to 3 m thick, coupled with refuelling difficulties for other types of vessels, are significant factors. Russia's nuclear fleet, with six nuclear icebreakers and a nuclear freighter, has increased Arctic navigation from 2 to 10 months per year, and in the Western Arctic, to year-round.

The Russian LK-60 icebreakers now being commissioned are “universal” dual-draught (10.5 m with full ballast tanks, minimum 8.55 m), displacing up to 33,540 t (25,450 t without ballast), for use in the Western Arctic year-round and in the eastern Arctic in summer and autumn. They are 173 m long, 34 m wide, and designed to break through 2.8 m thick ice at up to 2 knots. The wide 33 m beam at waterline is to match the 70,000 t ships they are designed to clear a path for, though a few ships with reinforced hulls are already using the Northern Sea Route. The LK-60 is powered by two RITM-200 reactors of 175 MWt each which together deliver 60 MW at the three propellers via twin turbine-generators and three electric motors.

In 1988, the NS Sevmorput was commissioned in Russia, mainly to serve northern Siberian ports but more recently as a freighter for fresh food from east coast across the north of Siberia to the west. It is a 61,900 t LASH carrier (taking lighters to ports with shallow water) and container ship with ice-breaking bow. It is powered by a similar KLT-40 reactor to that used in the ice-breakers, delivering 32.5 propeller MW from the 135 MWt reactor, and it needs refuelling only every 15 years.

Nuclear power gives submarines and large naval ships unmatched performance. The Russian, US and British navies as well as Russian icebreakers until the latest models rely on steam turbine propulsion, the French and Chinese in submarines use the turbine to generate electricity for propulsion. All power plants are pressurized water reactors (PWR), except the ill-fated Russian Alfa class.

With increasing attention being given to greenhouse gas emissions arising from burning fossil fuels for international air and marine transport, particularly dirty bunker fuel for the latter, and the excellent safety record of nuclear-powered ships, it is likely that there will be renewed interest in marine nuclear propulsion. Large bulk carriers that go back and forth constantly on few routes between dedicated ports could be powered by a reactor delivering 100 MW thrust. The world's merchant shipping is reported to have a total power capacity of 410 GWt, about one third that of world nuclear power plants. So far, exaggerated fears about safety have caused political restriction on port access.

The Chambered Nautilus

My love affair with the nautilus began as love affairs often do. a book fell on my head while I was visiting the public library in 9th grade. I was 14 and had always collected seashells with my mother or grandmother when we went for walks on the beaches off the Atlantic and Gulf of Mexico where I grew up. I always gravitated towards the nonfiction section and even more accurately the science section with lots of books on nature. This particular book that “magically” fell on my head was all about the chambered nautilus and various cephalopods that were considered odd. These creatures, including the living fossil we know as the chambered nautilus, are considered among the most difficult to study, in or out of captivity.

I read that book back-to-back twice and immediately started drawing and studying every cephalopod I could get information on. At the time, I was actually headed towards a career in mortuary science and by 12th grade I was the only woman in my high school getting acceptance letters from mortuary science schools. I switched gears soon after graduating and decided to become a zoologist and literally dive into everything related to the sea. Of course, we did not have any of the species of nautilus off either coast of Florida, so in my many dives, I studied deep living echinoderms, sharks, and one of my favorites, the horseshoe crab. Do you ever feel like there is a force in nature that pulls you towards it? That is what the nautilus and argonautidae species have done to me. I teach about them in my marine biology classes, and I advocate for them through educating people to not purchase either of these species in shell shops or overseas, where you do not know if they have been found on the beach or collected alive.

The chambered nautilus is a nocturnal slow-growing marine invertebrate of seven different species that are voracious hunters. They do not reach maturity for 15 to 20 years and lay a single egg that takes a year to incubate. The chambers inside a nautilus shell allow the nautilus to control the buoyancy, salinity levels, and gas exchange within the animal, so that it can dive to depths of 1,000 feet. They are not utilized for their meat but are collected for their beautiful shell, which has drastically affected their population in their natural habitat. This living fossil did not even have an estimated population count until 2010 and the overfishing of them for their shell and habitat loss through the devastation of the world’s oceans has pushed them towards becoming an endangered species. Our lack of understanding towards these and other creatures of the deep has irreversably damaged this wonderful being among many others along the shores, in our forests, and in the world’s oceans.

The paper nautilus is on the decline as well. This amazing little pelagic octopus creates the most lovely casing for its young to incubate in and then releases it to the sea when they have hatched. They are a wonderful introduction to sexual dimorphism as the female can be up to 600 times larger than the male! They are known as the “seafaring octopus,” and their paper thin cradles can be found along the beaches of the east coast of North America and tropical and sub-tropical seas. There has been a rise in ocean acidification, which has drastically affected the delicate shells of these and other marine mollusks due to our carbon pollution and reduction of the pH levels of the world’s oceans.

But…there is hope. There are choices you can make as a living organism on this planet to not take more than you need, to understand that every piece of organic material you pick up from your peaceful beach walks was once an intricate part of a complex system, which should be respected and not coveted. If you cannot live without a nautilus or paper nautilus in your collection, educate yourself about where it came from. You can find these lovely seashells in vintage collections like I do or antique stores if you’re lucky, and you will not have to carry the possible guilt of supporting the further decline of these amazing animals.

No live shelling: Be sure shells are empty and sand dollars, sea stars, and sea urchins are no longer alive before you bring them home.

Watch the video: Episode 4 - Staterooms (May 2022).


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