Semibalanus cariosus (Pallas, 1788)
Common name(s): Thatched barnacle, Rock barnacle, Horse barnacle
|Synonyms: Balanus cariosus|
|Semibalanus cariosus from a rock near Lopez Island. Diameter about 1.5 cm.|
|(Photo by: Dave Cowles, July 2006)|
How to Distinguish from Similar Species: This is the only species locally that has the strong thatchlike external appearance. A bit farther south, Tetraclita rubescens has a similar appearance but it is a pinkish red color and has only 4 plates.
Geographical Range: Bering Sea to Morro Bay, Central California; Japan
Depth Range: Mid intertidal to shallow subtidal. Especially common (even dominant) in the low intertidal, below the densest band of Balanus glandula and near Mytilus trossulus or M. californianus.
Habitat: Attached to rocks, floats, or pilings. Not often found around fresh water. Especially common on steep shores with much current and waves in our area but on the open coast it is found in cracks and protected locations.
Biology/Natural History: Farther south this species grows individually, but here in the Pacific Northwest aggregations can sometimes be so dense that the thatched appearance is not immediately evident. The barnacles grow very tall and narrow when densely aggregated. Competitors for space include Halichondria panicea (crumb of bread sponge), Mytilus trossulus, and Mytilus californianus. When the barnacles are small they may be bulldozed off the rocks by grazing limpets such as Lottia digitalis. The large size of adults likely protect them from some predators such as Nucella lamellosa or the seastars Pisaster ochraceous and Pycnopodia helianthoides. Eggs are brooded in the winter and the cyprid larvae settle in the spring (fall and winter on the open Washington coast). The larvae preferentially settle near adult barnacle shells. Lifespan up to 15 years.
These barnacles appear to have been eaten by native tribes in SE Alaska in some coastal locations during an extended time period. At other times, mussels were a more common food in the same regions.
|Main Page||Alphabetic Index||Systematic Index||Glossary|
Carefoot, 1977 (as Balanus cariosus)
Johnson and Snook, 1955 (as Balanus cariosus)
McConnaughey and McConnaughey, 1985
Morris et al., 1980
O'Clair and O'Clair, 1998
Ricketts et al., 1985
Moss, Madonna L. and Jon M. Erlandson, 2010. Diversity in North Pacific shellfish assemblages: the barnacles of Kit-n Kaboodle Cave, Alaska. Journal of Archaeological Science 37: pp 3359-3369
These individuals, on a vertical rock face, are abut 2 cm diameter. Photo by Dave Cowles July 2007