Pacific mussel

Semimytilus algosus

Common name:

Pacific mussel

Scientific name:

Semimytilus algosus

Alternative common names:

Bisexual mussel

Pacific mussel is a marine mussel that has invaded South Africa’s west coast. The present geographic range of pacific mussel in South Africa extends some 500 km, from Groenriviersmond in the north to Bloubergstrand in the south. It has become a dominant intertidal organism on wave-exposed rocky shores across this region.

Additional Info

  • Where does this species come from?

    Chile

    What is its invasive status in South Africa?

    NEMBA category 1b

    Where in South Africa is it a problem?

    Western Cape

    How does it spread?

    Spread by ballast water.

    Why is it a problem?

    It’s an invasive mussel that has become a dominant intertidal organism on wave-exposed rocky shores across the region of West coast (Western Cape Province). It’s much more abundant intertidally than either of the indigenous mussels Aulacomya ater and Choromytilus meridionalis, which have become largely confined to sublittoral and sand-inundated habitats respectively.

    What does it look like?

    Description: Pacific mussel exists as 2 morphotypes: a thick, smooth shell and a thinner, ringed shell. Habitat: The thick-shell morphotype is mostly found on compact, rocky platforms, whereas the thin one is found on emergent rocks. Breeding: The pacific mussel attaches eggs to rocks or substrate or bear live young, the distance between adult population and juveniles will be small and thus determine the population size of embryos and larvae.