By Tracey B.
Goose barnacles live along beaches on the Pacific Ocean all the way from the southern coast of Alaska, south to Baja California (MARINe). They need a solid, hard substrate to attach to (rocks, driftwood, boats), and usually inhabit the middle intertidal zone in areas exposed to waves, as they need moving water to provide their food since they cement themselves permanently to rocks and cannot move (Jonker et al. 2014; University of California). They often occur in clusters, which provide a reproductive advantage, as well as some protection from predators and other disturbances. Goose barnacles are often found mixed with mussels (Mytilus californianus), and there is often competition for habitat space between goose barnacles and mussels.
Pollicipes pollicipes is a relatively large species in comparison with other intertidal barnacles, (acorn barnacles for example) (Watanabe 2010). They can grow up to eight centimeters tall, including their stalk. Their shell is comprised of 5 pieces, which are surrounded by scales, a tough peduncle which contains calcareous spicules (Morris et al. 1980). Goose barnacles have varying colour schemes, which are controlled mainly by their habitat. Colonies that grow in sun-exposed areas (driftwood or shallow water) have a dark grey or black peduncle and stalk, and sun-protected colonies (growing on the underside of rocks or deep in the water) instead have bright red stalks and peduncles (Lamb and Hanby 2005). The haemoglobin in the blood causes the sun-protected colonies’ red coloration. Sun-exposed colonies have a pigment which protects them from UV radiation in their stalks and peduncles, this pigment obscures the red from the haemoglobin in sun-exposed colonies (Lamb and Hanby 2005).
P. pollicipes are simultaneous hermaphrodites; instead of simultaneous cross-fertilization, they alternate between male and female rolls over time (Newman). Sexual maturity is reached at 1 year of age (Carefoot). During reproduction, the female moults and then lays eggs inside the new shell’s mantle cavity; to signal mating availability to nearby males; the female will release pheromones along with the eggs. In response to the pheromones, nearby males extend their penis up to seven shell diameters to fertilize the eggs (Newman). The fertilized eggs are held in the mantle cavity for approximately 30 days until they hatch into nauplius larvae and are expelled from the mantle cavity. There are six nauplius larval stages and one cyrid stage (Quintero et al. 2007). The naupliar stages have three pairs of limbs to aid in swimming and feeding. The cyrid larva is a strong swimmer, which does not eat; the role of these larvae is to find an attachment site before they die of starvation. (Newman). In sessile species such as goose barnacles, free-swimming larval stages are often the only chance for the organism to disperse the population and increase genetic diversity (Quintero et al. 2007). Factors such as ocean current, freshwater run-off, salinity, temperature, oxygen and phytoplankton availability are important in the dispersal and settlement of P. pollicipes larvae (Quintero et al. 2007). Cyprid larvae of the P. pollicipes species attach specifically to the base of an adult barnacle’s stalk of the same species (Quintero et al. 2007). Once the barnacle has cemented itself into place, it cannot remove itself from the attachment site and becomes a sessile organis, (Jonker et al. 2014). In this site, the barnacle grows from a juvenile to an adult, and may live to be 20-30 years old. Juveniles differ from adults in size and feeding behaviour; whereas mature barnacles hold their cirri in the water column, juveniles beat the cirri slowly in slow currents or still water. When in a fast current, juveniles hold their cirri still in the same manner as adults (MARINe). Feeding P. pollicipes uses six pairs of cirri to capture and eat prey, there are both large and small cirri, the large cirri are projected out into the water column to capture food in flowing water, and the small cirri are used periodically to scrape food off the retracted large cirri into the organism’s mouth. The barnacles are positioned such that they can obtain food from moving water, usually from waves that collide with the shore above them and then flow back to the ocean over the barnacles (Carefoot). This water brings the particulate organisms P. pollicipes feeds on within reach of their cirri; this includes things such as algae, organic sediment and plankton. Some gut analyses have shown a larger range of food matter, such as copepods, amphipods, crustacean and barnacle larvae, small clams and polychaetes, as well as cirripede moults (MARINe).
There are many dangers to goose barnacles; they are susceptible to oiling and disturbances (scraping off by boats, humans or animals stepping on them, the driftwood they are attached to getting beached). In addition to this, there are many natural predators of the goose barnacle, such as shore birds (gulls), sea stars, whelks, fish, and some species of nudibranch. One nudibranch in particular, Fiona pinnata, is a very small species, which attach on the stalk of the barnacle near where the shell plates join and rasps the flesh there until the barnacle opens, at which point the nudibranch can enter the barnacle to feed. P. pollicipesis considered a delicacy in many European countries, and so goose barnacles worldwide are harvested and exported for food. There are meagre protection programs in place in Canada to protect from overharvesting (University of California).
In European countries, there are myths linking goose barnacles to barnacle geese. Since barnacle geese are a migratory species that breeds in the Arctic in the summer and then return to Europe. The geese are similar in colour to the barnacles, and in the fall when the geese return, driftwood containing goose barnacles would be beached by storms, and so a connection was made. Some biologists of the 14th century affirmed this connection by dissecting the barnacles and finding “feathers and down” within the shells (probably the cirri and gills). Even though there was a lot of scepticism from other scientists of the era, the barnacle goose and the goose barnacle are named accordingly to this day.
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Quinteiro, J. Rodríguez-Castro, J. Rey- Méndez, M. 2007. Population genetic structure of the stalked barnacle Pollicipes pollicipes (Gmelin, 1789) in the northeastern Atlantic: influence of coastal currents and mesoscale hydrographic structures. Marine Biology. 153: 47-60.
Watanabe, J. M. 2010. Seanet: Phylum arthropoda; subphylum crustacea: rocky shore barnacles. Stanford University. [online] http://seanet.stanford.edu/RockyShore/Barnacles/. Accessed March 5, 2015.
Multi Agency Rocky Intertidal Network (MARINe). Pollicipes polymerus Sowerby. 1833. (online) http://www. marine.gov/research/coresurveys/pollicipes.htm. Accessed March 1, 2015.
University of California, Santa Cruz; Ecology and Evolutionary Biology. Pacific Rocky Intertidal Monitoring: Trends and Synthesis. [online]http://www.eeb.ucsc.edu/pacificrockyintertidal/target/target-species-pollicipes.html. Accessed March 3, 2015