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Acorn Barnacle

Although they may not look alike at first glance, barnacles are crustaceans just like crabs, lobsters, and krill! Unlike most crustaceans, however, adult acorn barnacles cannot move around – they’re fixed in place.

 

Acorn barnacles live among the rocky shores of the north Atlantic Ocean as well as the north-east Pacific Ocean. They begin their lives as free-floating larvae, which eventually settle on a surface like a rock, ship hull, or whale. Then, the larva seeks out another acorn barnacle, “walking” with its antennae until it does so. Once the larva is settled, it cements itself to the surface and begins to grow its protective shell, committing to never moving again! The shape of this shell – like an acorn – is what earned this barnacle its name.

So, how does the barnacle survive if it can’t move? Adults are suspension feeders, using special feathery appendages called cirri to catch and eat plankton and other tiny particles floating in the water. And while they cannot run away from predators, they can tightly close the plates on their exterior shell if danger is near. Acorn barnacles do not have eyes, although they do have eyespots that help with sensory detection such as changes in light that may indicate that a threat is nearby. Because they cannot move to find mates, they make sure to settle very close to other barnacles so that they can reproduce with nearby neighbors.

 

 

While their population has not been assessed, acorn barnacles are known to be resilient and can adapt well to changing conditions.  They are the most common type of barnacle.

 

 

Protecting and restoring our oceans benefits wildlife around the world. By speaking up and working together, we can create real, measurable change for oceans and marine life. Learn more about Oceana’s campaigns to protect and restore marine biodiversity and abundance here.

 

 

Animal Diversity Web 

Buckeridge JS. Opportunism and the resilience of barnacles (Cirripedia: Thoracica) to environmental change. Integrative Zoology, 7: 137-146. https://doi.org/10.1111/j.1749-4877.2012.00286.x 

Schmidt PE, Bertness MD, and Rand DM. (2000) Environmental heterogeneity and balancing selectionin the acorn barnacle Semibalanus balanoides. The Royal Society, 267: 379-384. https://doi.org/10.1098/rspb.2000.1012 

 

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