Thursday, May 3, 2007

Barnacles: Pimples on a Rock

Three NAKED Facts

Thoughtful question: Let's take a closer look at these pimples. Do you think they are living animals? Which animals are alive and which are dead?

NF#1: A living barnacle has a door over the opening in its shell. A dead one has a gaping hole. The glue produced by the barnacle is so strong that its shell usually remains stuck even after it's dead.

Interactive activity: Even after the barnacle is dead, other animals may shelter in the remaining empty shell. Let's see what other animals are living in the empty shell.

Interactive activity: Gently feel the shells. Are they sharp? They are very sharp! If you slip and get scratched by barnacles, you can get a nasty cut. So don't walk on rocks.

Thoughtful question: Can you guess what kind of animals barnacles are? Are they snails? Would you believe me if I told you they are like crabs?

NF#2: Barnacles are crustacea, like crabs and shrimps. Inside the shell is an animal with feathery legs. When the tide is high and the barnacle is submerged, the little doors on the shell open up and the feather legs stick out to gather bits of food. There's diagrams of what the barnacle looks like on the inside, in the Chek Jawa guidebook pg 50.
When it first comes out an egg, the barnacle larva looks like a tiny shrimp. When it finds a good place to settle down, the larva glues its head to the surface and builds a shell around itself. There a diagram of the shrimp-like larva in the Chek Jawa guidebook pg 49.

NF#3: Barnacles will grow on any hard surface immersed in seawater. Barnacles are even found on other animals such as whales and sea snakes. There are often even barnacles on top of other barnacles!

Corny joke: If you stayed long enough in seawater, barnacles will also grow on you!

Barnacles are considered a menace to the shipping industry as they grow on every ship. This reduces the speed of the ship and increases fuel consumption.

Too Much Information
Provide only if asked, or if you are desperately having to entertain a group while waiting for the tide to go down/rain to stop, etc.

Winner of the Most Manly Marinelife Award: 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!

Corny joke: This is like a husband 'doing' a neighbour's wife 7 apartments 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.

Human uses for barnacles:
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.

Are barnacles used to make oyster omelette or 'or luak'?
This is a common misconception. The ingredient in that dish is indeed oysters and NOT barnacles.

What are the different kinds of barnacles on our shores?

Star barnacle (Euraphia sp.) have star-shaped shells. About 0.5-1cm, sometimes seen, usually near the high water mark as they are tougher than the other bigger barnacles.

Acorn barnacle (Balanus sp.) have walls made up of plates. About 1cm, common, often found lower down on large boulders and hard surfaces.

Volcano barnacle (Tetraclita sp.) the walls are not made up of plates and has a ridged patten of bumps or short lines. The thick shell has an air-filled, honey-comb internal structure. This provides strength as well as insulation from the heat when exposed at low tide. (There is a photo of this structure in the Chek Jawa guidebook, pg 49)

Other barnacles include Goose barnacles (Lepas sp.) which is clam-like with thin shells made up of five white plates. A leathery stalk attaches the animal to a hard surface. These stalked barnacles grow on objects such as large logs that float in the open sea. These barnacles usually die once they are stranded on the beach.
The parasitic barnacle (Thompsonia sp.) grows through the body of the host crab like a root system. The parasite does not kill the crab but it does affect the crab's reproductive system such that the crab becomes infertile. The parasitic barnacle eventually produces egg sacs that emerge through the crab's joints, seen in the photo above. A crab infected by parasitic barnacles tends to be covered with seaweeds and other encrusting animals, including non-parasitic barnacles. It generally doesn't look very healthy.

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