(Photograph) ©2010 Gary McDonald

Acorn Barnacle

Balanus spp.





Balanus is a very successful genus consisting of 1,445 identified species, 900 of them being acorn barnacles (1). Found worldwide in tropical or temperate waters though limited to upper-mid rocky intertidal zone by desiccation and predation (4). Studies by Joe Connell during his time at UCSB on Balanus balanoides, an acorn barnacle species, and Chthamualus stellatus provided incredible insight on interspecific competition (4). Acorn barnacles undergo three phases throughout their life cycle; a pelagic Nauplius larva, a non-feeding pelagic Cpyris larva, and ending in a sessile adult (3). Upon finding a suitable substrate cement glands within the antennae produce a glue that secures the barnacle (1). The exterior shell, composed of six fused plates, are also created by the barnacle upon settling (2). Cirri, modified thoracic legs, extended out of the shell filter feeding for plankton and also facilitating gas exchange (2).


(1) "Acorn barnacle." Acorn barnacle, Rocky Shores, Invertebrates, Balanus sp at the Monterey Bay Aquarium.

(2) "Acorn Barnacle." Slater Museum of Natural History. 

(3) "Barnacle larvae." Scripps Oceanography.

(4) Connell JH. The Influence of Interspecific Competition and Other Factors on the Distribution of the Barnacle Chthamalus Stellatus. Ecology. 1961;42(4):710–723.

(Photograph) ©2010 Gary McDonald



  • rocky intertidal