Balanus glandula Darwin, 1854 Common name(s): Acorn barnacle, white buckshot barnacle (when small)
Synonyms:
Phylum Arthropoda  Subphylum Crustacea   Class Maxillopoda    Subclass Thecostraca     Infraclass Cirripedia      Superorder Thoracica       Order Sessilia        Suborder Balanomorpha         Superfamily Balanoidea          Family Balanidae
	Balanus glandula attached to a cobble at Ala Spit, Whidbey Island.  Diameter approximately 1.5-2 cm
	(Photo by: Dave Cowles, September 2005)

How to Distinguish from Similar Species:  The sinuous line of contact between the terga and scuta distinguish this species from most other intertidal barnacles.  Semibalanus balanoides has a sinuous line of contact but also has no centripetal ridges at the interior base of the shell.  Chthamalus dalli has a straight, crosslike junction between the terga and scuta and the rostrum is overlapped by the rostrolaterals.

Geographical Range:  Aleutian Islands, Alaska to Bahia de San Quintin, Baja California; recently introduced at Puerto de Mar del Plata, Argentina.

Depth Range:  Intertidal, mostly in the upper half

Habitat:  Mainly on intertidal rocks.  Open ocean and protected waters.  Also common on pilings and on floats.

Biology/Natural History:  Often the most abundant barnacle in the upper half of the intertidal zone (can reach densities of up to 70,000 per square meter), and the most nearly ubiquitous barnacle species on the Pacific coast.  It can obtain oxygen both from the air and underwater.  Barnacles are hermaphrodites which fertilize one another internally by means of a long penis.  The eggs are brooded by the parent, and released as nauplius larvae.  Up to 6 broods of 1000-30,000 young may be produced per year from this species.  After 5 molts the larva becomes a nonfeeding cypris with 6 pairs of legs.  The cypris attaches itself to a substrate by an antennal gland and metamorphoses into the adult form.  Cyprids avoid rocks which Nucella lamellosa, an important predator, has recently crawled across, and also rocks with the red alga Petrocelis middendorffii.  Adult size is reached in 2 years and lifespan is about 10 years,  Barnacle molts are frequently seen debris in marine habitats.  Predators include oysterdrill snails such as Nucella lamellosa, the ribbed limpet Lottia digitalis (bulldozes and feeds on juveniles; barnacles 6.7 mm diameter have a refuge in size), seastars such as Pisaster ochraceous, Pycnopodia helianthoides, Evasterias troschelii, and Leptasterias hexactis, goldeneye ducks, gulls, and even the nemertean worm Emplectonema gracile and the barnacle nudibranch Onchidoris bilamellata.   Juvenile rockfish feed on the larvae swimming through kelp beds.  Competitors include Semibalanus cariosus and the mussels Mytilus trossulus and M. californiensis, to the shells of which it often attaches.  In many areas of the upper intertidal juveniles of this species compete with Chthamalus dalli juveniles by pushing them off the rock.  Chthamalus is usually common only in the zone above where Balanus glandula thrives.   Less common in estuaries.  While it has no eyes, this species is sensitive to light and will rapidly withdraw if a shadow passes over it.

Balanus glandula has recently become established in Japan and in Argentina.  In Japan it is directly competing with B. albicostatus.

The morphology of the feeding legs and penis of this species is highly plastic (Neufeld and Rankine, 2012).  Individuals transplanted to high flow areas grew legs which were 50% shorter and 25% wider than those in low flow and their penises were 25% shorter and 50% wider.  These differences were not seen between barnacles in high-density vs low-density sites, even though barnacles can only breed with individuals that they can reach with their penis.

References:

General References:
  Brandon and Rokop, 1985
  Carefoot, 1977
  Harbo, 1999
  Hinton, 1987
  Johnson and Snook, 1955
  Kozloff, 1993
  Morris et al., 1980
  Niesen, 1994
  Niesen, 1997
  O'Clair and O'Clair, 1998
  Ricketts et al., 1985

Scientific Articles:

Emlet, Richard B. and Steven S. Sadro, 2006.  Linking stages of life history:  how larval quality translates into juvenile performance for an intertidal barnacle (Balanus glandula).  Integrative and Comparative Biology 46:3 pp 334-346

Gilman, Sarah E., Jennifer W.H. Wong, and Shelly Chen, 2013.  Oxygen consumption in relation to body size, wave exposure, and cirral beat behavior in the barnacle Balanus glandula.  Journal of Crustacean Biology 33:3 pp 317-322

Kado, Ryusuke, 2003.  Invasion of Japanese shores by the NE Pacific barnacle Balanus glandula and its ecological and biogeographical impact.  Marine Ecology Progress Series 249: 199-206

Neufeld, Christopher J. and Cassidy Rankine, 2012.  Cuticle and muscle variation underlying phenotypic plasticity in barnacle feeding leg and penis form.  Invertebrate Biology 131:2 pp. 96-109.

Web sites:
 

This group is clustered on a cobble at Ala Spit.  Photo by Dave Cowles, September 2005

When individuals become too crowded, as on this rock, they grow in a tall, thin columnar formation.  Photo by Dave Cowles, September 2005

When individuals are dislodged from the rock they leave a calcified scar behind.  Photo by Dave Cowles, September 2005

Unlike Chthamalus dalli, Balanus glandula frequently grow on other substrates such as the wood of this stump.  Photo by Dave Cowles, September 2005.

Balanus glandula is usually white or gray-white, but these individuals growing on a stump are mostly brownish, probably due to overgrowth by diatoms or other algae.

These crowded individuals on an intertidal rock at Seal Beach, Oregon, have grown up to 10 cm tall.  Photo by Dave Cowles, September 2010

This large individual (2.5 to 3 cm long) is unusual in several ways.  Most barnacles are roughly as long as wide but this individual is nearly twice as long as wide.  Also, there are several young barnacles which have settled on the inside surface of the plates, although the original barnacle is still alive.
Photo taken by Dave Cowles, June 2011 in the upper midlittoral at Swirl Rocks between two rock walls.