© Joseph Dougherty. All rights reserved.
Pollicipes polymerus (Sowerby, 1883)
They can live 20 years, or more. As they grow they make new calcareous plates protecting their bodies. When first secreted, these plates are shiny and pearlescent. After repeated high tides and battering waves (with sand and rocks), the pearly shells become pitted and dull.
It is found, often in great numbers, on rocky shores on the Pacific coasts of North America.
Gooseneck barnacles compete with a number of other organisms in a complex struggle for survival in the limited available space in their rocky intertidal habitat. The first colonisers of bare rock are usually annual algae, soon to be followed by perennial species including coralline algae. Gooseneck barnacles, sea mussels and several species of acorn barnacles soon follow. Further competition is provided by sea palms, the large holdfasts of which may smother or squeeze out the molluscs and barnacles. Sea palms may settle on the mussels and may be carried away in storms, taking the mussels with them. Gooseneck barnacles may limit the colonisation of mussel recruits by feeding on their larvae. In areas where gooseneck barnacles predominate they may dominate until some are swept away in storms and allow in other species. In the long term, the mussels usually come to dominate as their byssal threads are able to overgrow all the other sessile organisms.