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Decorator crab

Loxorhynchus crispatus

On view at the Aquarium inKelp Forest

Meet the decorator crab

If you see a rock moving in one of our exhibits, look closer. It might be a decorator crab that has camouflaged itself with tiny algae and animals like anemones, sponges and bryozoans. The crab selects pieces of algae and small animals from its habitat and fastens them to hooked, Velcrolike bristles called setae on the back of its carapace, or upper shell.

Animal type

Invertebrates

Size

Up to 5 inches (12.7 cm)

Diet

Algae, sponges, small crustaceans, bryozoans

Range

Northern California to Baja California

Relatives

Kelp crabs, sheep crabs, dungeness crabs, other crabs; Family: Epialtidae

Natural history

As long as the crab stays in the neighborhood, it blends in and looks at home. Large decorator crabs don’t decorate as much as smaller crabs. But plants and animals may still settle, take hold and grow on the decorator crab’s shell without help.

Close-up of a decorator crab covered in strawberry anemones
A decorator crab on the sandy seafloor covered in strawberry anemones

Conservation

The decorator crab isn’t in danger. However, oil spills and runoff of pesticides, used oil, paint solvents and other chemicals endanger its habitat. As stewards of the ocean, we must carefully dispose of hazardous materials like these or, better yet, use environmentally-safe products.

Cool facts

  • The decorator crab is an important food source for some fishes, including croakers and cabezon.
  • A crab’s shell doesn’t grow, but the crab does. To solve this dilemma it must molt as it grows, shedding its old exoskeleton and forming a new, larger one. The old shell loosens as a new one forms beneath it. When the old shell splits, the soft animal crawls out. Before its new shell hardens, the crab absorbs water and expands to a size larger than before the molt. While the new shell is hardening, the crab hides from predators.  Once they’ve reached sexual maturity, decorator crabs stop molting.
  • The decorator crab recycles its living decorations during the molting process. It removes the anemones, sponges and other decorations from its old shell and uses them to adorn its new shell.

Meet the decorator crab

Head-on view of a decorator crab

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