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rocky shore

Barnacles
Class Cirripedia

Feeding barnacles

Barnacles are often mistaken for snails because of their hard shells. However, barnacles as actually crustaceans.

'Cirripedia' means 'hairy foot'. There are about 900 species of barnacles.

The larvae of barnacles are shrimp-like and swim freely. Eventually, the larvae glue themselves head down onto a hard surface and develop an outer shell with an opening at the centre. At low tide, the opening is sealed by a series of plates. A barnacle without these plates is a dead barnacle!

Barnacle Food: When the tide comes in, barnacles open up their plates and extend their feathery, segmented legs to gather plankton from the water. The legs form a basket that scoops inwards where mouthparts scrape the edible particles off the legs and transfer these particles to the mouth.

Barnacles encrust any surface in the sea, including other animals such as whales and sea snakes. Some barnacles, however, have become parasites that live inside other animals.

Barnacle Babies: Barnacles are usually hermaphrodites, each barnacle having both male and female reproductive organs. However, they don't self-fertilise. Instead, they fertilise neighbouring barnacles. As these animals cannot move, this is achieved by having tremendously long male organs! Some have an organ that can reach another barnacle 7 shells away! In some species, a miniature male-only individual settles into the shell of a larger member of its species. Reduced to little more than a sack of sperm, the male relies on its 'host' for protection and sometimes even food, in exchange for fertilisation services.

Many barnacles brood their eggs, releasing the free-swimming larvae that look nothing like the adults. The first form is a nauplius which looks shrimp-like with antennae, an eye spot, jointed appendages and a shield-shaped body. The larvae spend some time drifting with plankton, moulting several times. Eventually, it changes form into a cyprid larvae which has a hinged hardened body with large antennae and more appendages. At this stage, it does not feed and uses its chemical and touch detectors to detect adults of its own species and suitable areas for it to settle down. When it finds the right place, it secretes a glue from special glands in its antennae to attach itself permanently. Barnacles tend to settle where others of their own species have already settled. For lovely animated diagrams of the larval stages of a barnacle, see Keith Davey's site. Here are fascinating photos of a barnacle larva on Image Quest 3-D Marine Library

Role in the habitat: Despite their hard shells, barnacles are eaten by crabs, drills and other predators. Dead barnacle shells provide hiding places for many small creatures. Sometimes you might see tiny mussels, small periwinkles and other animals hiding in the hollow shell of a dead barnacle.

Human uses: Barnacles are considered a menace to the shipping industry. An encrustation of barnacles soon develops over every ship hull. This reduces the speed of the ship and increases fuel consumption. Efforts to deter barnacle infestation include coating ship hulls with a toxic paint. However, this does not last and the toxic paint poisons the surroundings.

The barnacles' tendency to accumulate heavy metals in their shells, however, makes them useful as bio-indicators to measure water pollution.

The strong glue that barnacles use to cement themselves to the rock has been studied for use in dentistry for a similar protein cement to fit dentures. The glue has amazing properties: it hardens quickly under water and continues to work under pressure, in strong acids or alkalis and temperatures up to 225° C (440° F). The glue is so strong that even after the barnacle dies, its shell stays stuck to the rock.

quick facts
1-3cm common on rocks and hard surfaces

Classification:
Class Cirripedia
Subphylum Crustacea
Phylum Arthoropoda

See also ...
Barnacles of Chek Jawa and barnacle zonation

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.
Barnacles Inverted Invertebrates by Gordon Green on the Royal British Columbia Museum website: a quick, easy introduction to barnacles.
Cirripedia on the Canada's Aquatic Environments webpage on the University of Guelph website: an easy introduction to the more technical aspects of their morphology, metabolism, reproduction, ecology with an interesting section on their idiosyncracies and photos.
Love On the Rocks by Stephanie Greenman on the Wild California website: lots of easy-to-read details on the barnacles life cycle and strange mating habits, including the 'dwarf male'.
Barnacles: Living on the Edge by Wim van Egmond on the Microscopy UK website: brief introduction with lovely large photos of a feeding barnacle and the various stages of its life cycle.
The Secret Life of Barnacles by Phil Rainbow on the Fathom website: more detailed but still easy introduction with lots of photos, including how barnacles can be used as bio-indicators.
Class Cirripedia on Biomedia of the Glasgow University Zoological Museum on the Biological Sciences, University of Paisley, Scotland website: a brief introduction with explanations of the major classes, a glossary of terms and diagrams and photos.

Other references

Barnes, Robert D. & Ruppert, Edward E., 1996. Invertebrate Zoology. Harcourt College Publishers. 6th Edition. pp. 1056, G-1-16, I-1-30.
Pechenik, Jan A., 2000. Biology of the Invertebrates. McGraw-Hill Book Co., Singapore. 578 pp.
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.
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.

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