Why Are Some Seashells Thicker Than Others?

The shell of a cuttlefish typically doesn’t last more than a few months, while certain conch shells can survive for thousands of years if kept in the right conditions. The sheer variety of seashells has fascinated and inspired us for thousands of years. And one characteristic in particular that piques our curiosity is why some sea shells are thicker than others.

Some seashells are thicker than others because the animal that makes it requires a thicker shell to protect itself from predators, stay grounded against the current, or shield itself from external elements. The thickness of a shell depends on the species, its environment, and the temperature.

While it’s apparent that different species will possess shells of varying thicknesses, certain factors influence this characteristic. In this article, we’ll explore what factors determine the thickness of a sea shell.

What Determines a Shell’s Thickness?

Now we know that shells come in various shapes and sizes, and some tend to be thicker than others. But what determines the thickness of a sea shell?

A shell’s thickness is determined by the mollusk species, the environment it lives in and interacts with, and the temperature of the water in which it resides. Each species has unique requirements that determine the thickness of its shell.

Let’s look at these factors in detail.


The species of the mollusk is the greatest determinant of the shell’s thickness. This is perhaps the most obvious reason why different shells are built differently since each species has a set of unique requirements to fulfill. The density of the shell will depend on the creature’s food habits, mode of locomotion, and the way it interacts with its environment.

For example, the cuttlefish relies heavily on locomotion to catch prey and escape predators. This creature possesses a more flexible and mobile body than other mollusks so that it can dart about the water with ease. As such, cuttlefish shells tend to be thinner and more fragile than most others.

On the other hand, deep-sea clams and giant clams possess thick, heavy shells to anchor them into the sand and stop them from being washed up on shore. Additionally, the thick shells protect them from predators who may try to open them up to get to the soft interiors. While their heavier shells impede mobility, it keeps them safe from enemies.

However, some varieties of clams and oysters have thinner shells so that they can quickly bury into the ground when required. Their thin shells also allow them to move across the ocean floor with ease.

Another excellent example of a relatively thin-shelled mollusk is the horse conch. Most conches have thick, heavy shells that provide adequate protection against predators. The horse conch also has a thicker shell than most mollusks. However, their shell is thinner than most other conch shells.

This is because the horse conch is a carnivorous mollusk (unlike most conch species) and requires some mobility to catch its prey. So while they possess thick shells, the thickness is less than other conches.

Some mollusk species (especially a few conch shells) have developed the ideal mix between mobility and protection. As such, you’ll find shells that are spiked or sport sharp edges while remaining light and mobile. This design protects them from predators while allowing them to move easily.

This design is essential, or else they would be forced to drag a heavy shell behind them as they move.

There are several thousand species of mollusks across the world, and each possesses a unique shell thickness, depending on its species. This thickness is a reflection of the way they look for food and of their unique needs in a hostile environment.

Water Temperature 

As mentioned, the species of mollusk plays a crucial role in determining shell thickness and is the most important factor. However, depending on where you find them, the same mollusk may possess shells of differing thicknesses. And this variation in solidity can be due to a few reasons.

Presence of Predators

Mollusks living in waters with a higher concentration of predators tend to have thicker shells to protect them from natural enemies. And the highest concentration of marine predators typically occurs in tropical regions. More importantly, predatory activity increases as the waters get warmer because the energy demand is higher for creatures in this region.

As such, the mollusks in this region have responded by developing thicker shells to protect themselves from predators. So, if you pick up clams from frigid waters and tropical waters, the latter is likely to have thicker shells.

Additionally, tropical waters also provide an abundance of food to all sea creatures, and the survival rate of predators in this region tends to be higher. As such, there are typically more predators in this marine environment.


Another reason why temperature affects shell thickness is that mollusks in warmer regions need to devote less of their total energy to building their shells. Snails, clams, and other mollusks build their shells through a process called biomineralization.

During this process, mollusks absorb raw material from the surrounding waters and calcify them to create sturdy shells. This conversion of raw material is more efficient in warmer waters, as compounds are quickly and easily converted to the calcium used to build shells.

As such, sea shells in warmer regions tend to be thicker as the creatures here can afford to spend more energy during biomineralization.

In contrast, the calcification process is slower and more energy-demanding in colder regions. As such, the mollusks here limit the size and thickness of their shells to conserve energy for other life processes.

The slower rate of biomineralization and lower predatorial activity in colder regions means shells here tend to be thinner and lighter than those in warmer regions. Conversely, the increased availability of minerals and predators in warmer regions force the mollusks here to develop thicker shells.

CO2 Contamination

The two previous points are natural reasons that determine the thickness of a sea shell. However, humanity’s influence on marine environments also has an impact on the thickness of sea shells. And global warming, in particular, is one of the factors that determine the thickness of a sea shell.

As temperatures soar through the greenhouse effect, the presence of CO2 in the ocean begins to rise. As CO2 levels rise, the oceans tend to become more acidic, reducing the efficiency of the biomineralization process.

Additionally, an acidic marine environment affects the calcification process in shells, causing the calcium carbonate to dissolve. As such, oceans that have been impacted by CO2 contamination have mollusks with thinner shells. And while we are taking steps to reverse the damage, it may be a while before the oceans are less acidic and mollusks can start creating thicker shells again.

How To Find Thicker Sea Shells 

As a beachcomber or avid shell collector, it’s tempting to look for thicker shells. These specimens are best for decorating your home or for use in certain arts and crafts. Here are a few tips to help you find the best sea shells.

Visit Tropical Beaches

This point may be a no-brainer, but it’s worth mentioning. The best way to find thick sea shells is by visiting warmer beaches, as the mollusks here tend to produce thicker shells. Warmer beaches also mean more life in the ocean and a higher concentration of sea shells. As such, if you’re searching for shells, it’s best to visit tropical waters.

Search During Low Tide

If you have the option, consider visiting the beach during the new or full moon, when the tides are at their lowest and highest points. The highest high tides will bring more sea shells onto the beach, while the receding tides will expose a greater portion of the beach for you to search.

This phenomenon will ensure you have a greater variety of shells to choose from. Additionally, try visiting the beach as early in the morning as possible, during the first phase of the low tide. This period often reveals the most shells, and the beach is empty, so you can collect to your heart’s content. You can start when the tide begins to recede and follow it to its lowest point.

If possible, it’s also a good idea to visit the beach the day after a storm. Thicker and heavier sea shells tend to stay hidden and buried under water, and storms can churn the waters enough to loosen them up. As such, the day after a storm tends to reveal the most number of shells.

To learn more about which moon phases are best for shelling, check out my other article: What Moon Phase is the Best for Shelling?

Final Thoughts

In essence, the thickness of a sea shell depends on the species of mollusk that makes the shell and its unique requirements in that environment. Additionally, a shell’s thickness also varies based on its location on the earth’s surface and the temperature of the waters in that region.

Fortunately, humans are becoming aware of the environmental impact of greenhouse gases and taking measures accordingly. Hopefully, a shell’s thickness will only be impacted by natural factors in the future and not by our influence on the waters of our planet.

Alexander Picot

Alexander Picot is the principal creator of DiscoveryPit.com, a website dedicated to tips on finding and collecting precious items. Inspired by reading countless adventurer reports from the oldtimers, Alex is passionate about discovering hidden treasures and loves to share his experience with the rest of the world.

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