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rocky shore

Barnacles of Chek Jawa
Class Cirripedia

Home zones: Immobile rock-dwellers survive best if they settle down on a good spot: one that is less often exposed at low tide or is cool and shady. These animals start life as free-swimming larvae. There is competition among these larvae for the best spots on a rock to settle down on. As a result, different species are found in distinct zones on a rock. This happens, for example, with barnacles.

Barnacle zonation: An ideal spot for a barnacle is lower down the rock where it gets wet more often. The further up a rock a barnacle settles, the hardier the barnacle must be to withstand longer periods out of water and the heat of the sun. The different species of barnacles are often found in zones on a rock.

Acorn barnacle
Balanus sp.
Family Balanidae
Acorn barnacles are medium sized (about 1cm across) and crowd the best spots lower down the rock.

Star barnacle
Chthamalus sp.
Family Chthamalidae
Star barnacles are smaller (about 0.5cm across) and settle higher up where the bigger Acorn barnacles are unable to colonise.

Volcano barnacle
Tetraclita sp.
Family Balanidae
Volcano barnacles are huge (about 3cm across) and are found where there is more water movement and where they are shaded from the sun. Volcano barnacles have thick shells which have an air-filled, honey-comb internal structure. This provides strength as well as insulation from the heat when exposed at low tide.

Barnacle zonation

Star barnacles

Acorn barnacles

Volcano barnacle

Internal structure of
Volcano barnacle

quick facts
1-3cm common on rocks and hard surfaces that are covered by water most of the time.

Classification:
Class Cirripedia
Subphylum Crustacea
Phylum Arthoropoda

See also ...
Barnacles in general

Links
Barnacles on Life on Australian Seashores by Keith Davey on the Marine Education Society of Australia website: Fact sheet on barnacles with lots of animated diagrams of barnacles at all stages of their development and details on various species of barnacles found in Australia.

Other references

Tan, Leo W. H. & Ng, Peter K. L., 1988. A Guide to Seashore Life. The Singapore Science Centre, Singapore. 160 pp. online version
Lim, S., P. Ng, L. Tan, & W. Y. Chin, 1994. Rhythm of the Sea: The Life and Times of Labrador Beach. Division of Biology, School of Science, Nanyang Technological University & Department of Zoology, the National University of Singapore. 160 pp.
Ng, Peter K. L. & N. Sivasothi, 1999. A Guide to the Mangroves of Singapore II (Animal Diversity). Singapore Science Centre. 168 pp. online version
Chuang, S. H., 1961. On Malayan Shores. Muwu Shosa, Singapore.225 pp., plates 1-112.
Davey, Keith, 1998. A Photographic Guide to Seashore Life of Australia. New Holland, Australia.144 pp.
Morten, Brian & John Morten, 1983. The Sea Shore Ecology of Hong Kong. Hong Kong University Press. 350 pp.

a companion website to the chek jawa guidebook website©ria tan 2003 www.wildsingapore.com

a companion website to the chek jawa guidebook
website©ria tan 2003 www.wildsingapore.com