Pacific barnacle

Balanus glandula

Common name:

Pacific barnacle

Scientific name:

Balanus glandula

Alternative common names:

Acorn barnacle. 

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 Info

  • 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.