Thursday, 20 March 2025

Master of Disguise: The Decorator Crab

Imagine yourself snorkeling through a lush kelp forest off the coast of Southern California. Sunlight filters through the dense canopy of the forest, casting shimmering patterns on the rocky seafloor below. The underwater world appears peaceful and still—until your gaze falls on what seems to be an ordinary-looking rock. 

Then… the rock moves.

At first, you assume it’s just the ocean’s current shifting the rock. But as you take a closer look, you realize it’s not a rock at all. It seems to be a crab, expertly hidden with bits of algae from its surroundings. Meet the decorator crab: a master of disguise and possibly the most stylish and secretive crab in our ocean.

What are decorator crabs?

Decorator crabs constitute several species of crabs that belong to the superfamily Majoidea, a group of crustaceans with a remarkable talent for camouflage. They use tiny, hook-like structures on their shells to attach pieces of algae, seaweed and other marine debris onto their bodies. But this isn’t just a quirky fashion statement—these natural accessories help decorator crabs avoid predators, like pacific halibut, octopuses and sea otters, by blending in with their surrounds. 

If they move to a new environment, decorator crabs will adapt their wardrobe to match. Some take their disguises a step further, attaching living organisms like sponges and venomous anemones to their carapaces—the hard upper shell that protects the crab’s vital organs. This not only helps the crabs blend in but also offers an extra layer of defense. Even when they shed their exoskeleton in a process called molting, some crabs will carefully transfer their decorations to their fresh shell.

Decorator Crab

You can also identify decorator crabs because they are decapods, meaning they have ten legs—two pinchers for feeding and four additional pairs of legs for walking. Decorator crabs are primarily omnivores and use their pinchers to pluck small algae out of crevices and off the sea floor. 

Decorator crabs are solitary animals for most of the year outside of mating season from May to September. You’ll find decorator crabs in shallow coastal waters around the world, from coral reefs and rocky shorelines to kelp forests, seagrass beds and tidal pools. You may have to keep a close eye out for decorator crabs, though, as their average size is only three to five inches across their leg span. 

How can you help decorator crabs?

While decorator crabs aren’t currently endangered, they depend on a thriving ocean to survive. Like all marine life, they face threats from pollution, habitat destruction and climate change. Protecting our ocean means protecting creatures like them.

Ocean Conservancy is dedicated to safeguarding our ocean from today’s greatest challenges, from plastic pollution to climate change. But we can’t do it alone. Visit the Ocean Conservancy Action Center to learn how you can help defend our ocean, its wildlife and the communities that depend on it.

The post Master of Disguise: The Decorator Crab appeared first on Ocean Conservancy.



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Master of Disguise: The Decorator Crab

Imagine yourself snorkeling through a lush kelp forest off the coast of Southern California. Sunlight filters through the dense canopy of th...