Rocks on the rocky intertidal covered by B. glandula.
B. glandula feeding on plankton in the water column.
|
Distribution
B. glandula has been found
along the Pacific coast from the Aleutian Islands of Alaska to Baja California,
Mexico. The books and studies referenced on this web page have mentioned
populations on Vancouver Island, San Juan Archipelago, the California coast
(Monterey, La Jolla), Puget Sound and Friday Harbor. These pictures are
all barnacles from the rocky intertidal shores near Juneau, Alaska including
Outer Point Beach and Fritz Cove.
Zonation
B. glandula lives in the high
to mid intertidal zone on both exposed and protected shore lines and extends
into brackish water areas. As they settle, they attach to rock,
wood, boat hulls and other animals such as the Blue mussel Mytilus
trossulus. The lower limit of their zone is set by a wide range
of predators.
What they eat
While under water, B. glandula feeds
by continually extending cirri out of the aperature in the operculum and
sweeping them out and down towards its mouth. Plankton in the current
is caught by setae on their appendages.
What eats them
Barnacles are prey for many shore animals.
Mollusks including limpets, nudibranchs (ex: Onchidoris) and whelks
(ex: Nucella lima) consumed them by infiltrating them between the
lateral wall plates. Other predators include nemerteans and echinoderms
(ex: Pisaster ochraceus, Pycnopodia helianthoides and Evasterias
troschelii)
The effect of P. ochraceus is great on barnacle
patches. As the amount of free space around B. glandula decreases,
predation by P. ochraceus increases thus reducing barnacle survivorship
in highly dense areas.
|