Layered Bone Holds Gas to Control Buoyancy

white and brown cuttlefish swims in waters with a black background

Biological Strategy

Cuttlefish

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Image: Naveen Manohar / Pixabay / Free non-commercial use

Modify Buoyancy

Buoyancy is an upward force exerted by air or liquid on a solid object that works against the object’s weight. A hawk glides through air and a duck floats on water due to buoyancy. Some living systems (such as fish eggs) can remain sedentary and therefore maintain the same buoyancy at all times. But most must adjust their buoyancy because they can’t survive long unless they change position. These living systems require strategies to not only be buoyant, but also adjust buoyancy level. They often modify buoyancy by adding or decreasing lift, or by changing their weight. For example, birds like condors that soar for a long time shift the directional orientation of their wingtip feathers to manage buoyancy. Fish alter the amount of air in their swim bladders to increase or decrease their weight, thus altering their buoyancy.

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Cephalopods

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).

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Cuttlefish control their buoyancy by changing the mix of liquid and gas within their multi-layered cuttlebone.

Introduction

Cuttlefish are renowned for their ability to control the colors and patterns on their skin. But equally important to their survival is the ability to control buoyancy nearly effortlessly.

The Strategy

The secret lies in their cuttlebone, a unique, lightweight, porous internal shell consisting of parallel sheets of a form of calcium carbonate, separated by numerous S-shaped pillars that create countless chambers filled with gas and liquid. These chambers are crucial for the cuttlefish’s buoyancy control.

When a cuttlefish needs to become more buoyant and rise up, it actively pumps liquid out of the cuttlebone chambers, allowing gas to fill the space. This gas, primarily nitrogen, comes from the cuttlefish’s body fluids, where it exists in dissolved form. Conversely, when the cuttlefish needs to decrease its buoyancy and sink, it draws liquid back into the chambers, which displaces the gas. This process is facilitated by the cuttlebone’s structure, which combines high compressive strength with minimal weight, enabling the cuttlefish to withstand significant external water pressure.

The many layers inside a cuttlebone are visible.

The Potential

The cuttlefish’s buoyancy control mechanism offers inspiration for numerous human applications. By mimicking the cuttlebone’s structure and function, engineers could develop advanced materials and technologies for underwater exploration. For instance, creating lightweight, strong, and adaptable materials could improve the design of submersibles, underwater drones, and buoyancy control devices.

Additionally, understanding the cuttlefish’s efficient buoyancy regulation could lead to innovations in energy-efficient underwater navigation systems, helping reduce the energy consumption of marine vehicles. This biomimetic approach emphasizes sustainability and efficiency, aligning with nature-inspired design principles that promote harmony with the environment.

Harnessing the strategies employed by cuttlefish could revolutionize underwater exploration and technology, offering new ways to navigate and study the ocean depths with greater efficiency and sustainability.

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Last Updated May 23, 2024

References

“The familiar internal shell or bone of the cuttlefish (Sepia officinalis L.) appears to function both as a skeletal structure and as a rigid buoyancy tank, enabling the cuttlefish to become more or less dense than seawater. Since an animal fractionally denser than seawater can only preserve constant depth by the expenditure of significant energy, the variable buoyancy tank role of cuttlebone confers a considerable advantage to the cuttlefish which can maintain a fixed position in water with little effort.” (Birchall and Thomas 1983:2081)

“The cuttlebone (which accounts for about 9% of the animal’s volume) is a hollow structure, divided by lamellae, containing both liquid and gas and the cuttlefish changes its density by varying the quantity of liquid within the porous structure of the bone.” (Birchall and Thomas 1983:2081)

Journal article

On the architecture and function of cuttlefish bone

J Mater Sci | 20/11/2004 | J. D. Birchall, N. L. Thomas

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Reference

“Cuttlefish (which look like bulgy squid) have a foamlike or corrugated cuttlebone containing a gas mixture at nearly constant pressure (fig. 5.1).” (Vogel 2003:97)

Book

Comparative Biomechanics: Life's Physical World, Second Edition

17/06/2013 | Steven Vogel

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