The gooseneck barnacle is a
main food source the glaucous-winged gulls. The gulls eat them on exposed
shores, eating the head and leaving the stalk.
Gooseneck barnacles are also a food source for sea stars and whelks.
Gooseneck
Barnacle (Pollicipes polymerus)
Order: Thoracica
Family: Scalpellidae
GEOGRAPHIC
RANGE
The gooseneck barnacle
is found from the southern region of Alaska to Baja, California.
PHYSICAL CHARACTERISTICS
The gooseneck barnacle can be distinguished by its long neck, or stalk. This
part of its body is usually one inch long. The stalk has a leathery appearance
with a texture of small bumps.
The shell, or capitulum, of the gooseneck barnacle grows to be about two inches
long. It is made up of small plates, which enclose its soft body. Inside the
shell, the barnacle primarily consists of long segmented legs, intestines
and stomach. The gonads are held within the stalk. The stalk also contains
the gland that is used to produce the adhesive that allows barnacles to attach
to rocks so well.
The gooseneck barnacle ranges in color from reddish-brown to brownish-black.
It can reach up to eight inches in length.
FOOD HABITS
The gooseneck barnacle is a filter feeder. Since its head is attached to a
usually rocky surface, it feeds by extending its legs, or cirri, from its
"shell." It separates the valves of its shell and extends the feathery
cirri into the water when the tide is in, or when water runs down rocks.
The gooseneck barnacle often orients itself to face the current. This explains
why, when seen, most are facing the same direction.
Food is caught in a lassoing action of the cirri. Six pairs of cirri contract
and force the food down towards the mouth. Many small hairs that line the
sides of the segmented cirri help catch the food. These hairs also aid in
the movement of food towards the mouth. Since food may be hard to come by
at low tide, the gooseneck barnacle can use some of its cirri to pass food
to its mouth while using others to catch and hold onto new prey when food
is abundant.
The gooseneck barnacle will eat a variety of food and is not selective. Most
of its diet consists of small organisms such as plankton, cypris larvae, small
clams, hydroids and amphipods.
REPRODUCTION
The gooseneck barnacle is a hermaphrodite, meaning it is equipped with both
male and female reproductive organs. These organs mature at relatively the
same rate. Although it is hermaphroditic, it usually will not self-fertilize
unless there are no other barnacles within about eight inches. It is better
for them to crossbreed because it ensures the diversity of their population.
Once a female lays eggs, a pheromone is released letting those surrounding
males know that she is ready. One barnacle will release sperm into the shell.
Once the eggs in a neighboring barnacle are fertilized, they are brooded in
the mantle cavity. The gooseneck barnacle has a reproductive period of about
eight months, and produces about three to four broods. Thousands of free-swimming
larvae are then released into the ocean to fend for themselves. These larvae
are weak swimmers that spend their time feeding mostly on phytoplankton. Once
they reach the cyprid stage they are strong-swimming, non-feeding larvae,
with a sole purpose of finding a place to settle.
Gooseneck barnacles follow many cues for settlement. Once the cypris larvae
have undergone metamorphosis to juvenile barnacles, they will search for a
suitable home. They do so by receiving chemical cues from other established
barnacles, which tell them that there are good conditions. However, this could
be a problem when competing for space. They also have to take into consideration
the correct temperature, surface texture and current. All of these factors
are crucial for its survival.
Gooseneck barnacles are thought to reach maturity at the age of five, and
are considered fully grown at the age of twenty.
Source: Animal Planet.com
