Pacific barnacle

Pacific barnacle

Balanus glandula

Common name:

Pacific barnacle

Scientific name:

Balanus glandula

Alternative common names:


The Pacific barnacle is an acorn barnacle, occurring in the high-mid intertidal zone of rocky coastlines. Here it can be one of the most abundant solitary animals, reaching densities of more than 70 000 individuals per square metre.

Additional Information

Where does this species come from?

Pacific coast of North America.

What is its invasive status in South Africa?

NEMBA Category 3.

Where in South Africa is it a problem?

Cape Town in the Western Cape.

How does it spread?

Spread via larvae in shipping ballast water or hull-fouling.

Why is it a problem?

It invades rocky shores. It out-competes the indigenous African chthamalus species – Chthamalus dentatus – and as a result this species is currently rare on the Atlantic South African shores.

What does it look like?

Description: It is a small barnacle, up to 8mm in diameter. The shell is brown-grey in colour and smooth. The operculum (gill cover) is oval.

Habitat: Mainly on intertidal rocks, in the open ocean and protected waters.

Breeding: Mothers brood eggs, which are released into the water as larvae. These planktonic larvae undergo five moults to become a non-feeding cypris with six pairs of legs. Cyprids attach to a suitable substrate (avoiding potential predators or competitors) and metamorphose into adult form. They reach adult size in about two years.

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