Log Transcript

While on watch for whales the other day, we spotted something unusual floating in the water, upon closer inspection we realized it was the shell of one of the most remarkable creatures in the sea, the Chambered Nautilus.

A relative of the octopus, squid and cuttlefish, the Chambered Nautilus is an ancient cephalopod. Represented by only a single genus, the chambered nautilus is an animal that has inspired poets and naturalists since olden times. The poem, The Chambered Nautilus' by Oliver Wendell Holmes published in 1858, still remains one of the most popular poems ever written about a sea creature.

The Nautilus is the only living cephalopod to retain an external shell, today, the fossilized shells of extinct cephalopods provide a good record of their evolution. There are 6 species of nautilus extending from the vast warm waters of the Indian Ocean to the tropics of the Pacific where it resides in the shadowless depths. The rarest and most enigmatic are found exclusively in the Bismarck Archipelago, here in Papua New Guinea, where the first was seen alive only in the last decade.

The Chambered Nautilus is unique to its family in many ways, it has anywhere from 60 - 90 very thin tentacles and very primitive eyes, which have been compared to a pinhole camera. Unlike many species of cephalopod that only live a few years and die after reproducing, the nautilus is believed to live twenty years or more. The male nautilus actually loses his reproductive organ during mating, breaking it off and placing it inside the female's mantle pouch, later growing himself a new one. They are propelled entirely by jet propulsion, using a siphon beneath the head to expel water from the mantle cavity. However, unlike some of their squid relatives who are able to reach speeds of 25miles per hour, faster than any other invertebrate, the nautilus is a comparatively slow swimmer and is predominantly a scavenger. It is rare to see these creatures in their natural habitat, as they usually only occur at a depth beneath which it is safe for humans to dive, typically around 500 - 650 feet (150 - 200 m).

The flat spiralling shell of the chambered nautilus is designed for a very specific function. The graceful swirls of the calcium shell house several distinct, ever-expanding compartments or chambers. The animal lives in the outermost and largest chamber, creating new and larger chambers, moving from old room to new room as it grows. Eventually, a shell that is more than 10 inches in diameter is created, an exquisite piece of work, even Pythagoras marvelled at the achievement of this logarithmic spiral, although it is a far cry from the 16ft shell of its extinct relative. A single tube called a siphuncle connects this series of chambers. This organ is used to pump fluids in and out of the chambers, it uses this system to control its buoyancy. Depending on the concentration of gases and fluids in each chamber, the nautilus will rise and sink in the water. Similar to the way a human diver will fill or expel air from a buoyancy vest to assist in ascent or decent.

Nautilus shells such as this one we found in the waters surrounding the Vitu Islands, are left empty when the animal has died, they can be found floating at the surface of the sea or washed ashore. The unique shell bears irregular brown stripes, which probably contribute to counter shading. Unfortunately the beautiful shell of this rare animal is often polished and sold in tourist shops and markets. Some shells may be collected from the beach, but it is highly likely that once the tourist demand is created, they are captured using traps at depth.

This is Genevieve Johnson speaking to you from the Odyssey in Papua New Guinea.

Log by Genevieve Johnson

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