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Dieren en planten

Crustaceans   Barnacles   Acorn barnacle   Bay barnacle   Volcano barnacle   Australasian barnacle   Goose barnacle   

Water en land

Sea regions   North Sea (biotope)   Coastal areas   Rocky coasts   Sea dikes (biotope)   Harbours (biotope)   Tidal flats and shallows   Biotope   

Mens en Milieu

Man and the environment   Water   Matter and materials   Seawater   Nutrients   Organic matter in the sea   Pesticides   Organotin compounds   
Barnacles andCaprella, foto fitis, sytske dijksen

Barnacles

At first sight, you aren't likely to think that barnacles and crabs are related. But they are just as much a crustacean as crabs, lobsters and amphipods. Their exterior calcareous skeleton is made up of four or 6 plates and resembles a miniature volcano. In fact, one of the relatively common species found in the North Sea is called the volcano barnacle. Two interior plates at the top open up, from which the barnacle sticks out six pairs of feathery limbs. These tentacles look like a fan and are used for filtering animal plankton out of the seawater. When mating, barnacles extend their long penises out of this opening and fertilize a neighboring barnacle. They close the plates during low tide, so that they can survive above water for a period of time.

  • Species
    Elminius modestus, foto fitis, sytske dijksen

    Most people are familiar with those barnacles known as acorn barnacles. This group attaches its shell directly to a hard surface, as opposed to others such as the goose barnacle, which stand on a stalk. Examples of acorn barnacles include the common (acorn) barnacle, the bay barnacle, the Australasian (or New Zealand) barnacle and the volcano barnacle.

  • The world inside out
    feeding barnacle, foto fitis, sytske dijksen

    When you look at a barnacle, you often only see the outer shell. The animal is hiding in its cone-shaped house. Only when the barnacle is under water, will it open up and stick its tentacles out of the cone. By waving these 'arms' back and forth, the barnacle catches plankton drifting by. These arms were not originally meant for catching food. They used to be legs. A barnacle is actually lying on its back in the cone and catches food with its legs.

  • Mating barnacles

    A barncle is both male and female, however, it can't mate with itself. And it can't just step out of its house to mate. Because it is fastened to the underground and can't move around, it has to make sure that when it attaches to a surface, other barnacles are in the vicinity. That is one of the reasons that you often find barnacles living in groups. Fortunately for them, they have found a solution to this problem. Every barnacle has a very long penis which can extend over its wall and enter a neighboring barnacle. The one to first reach the other with its penis becomes the male, the other one functions as female. There is a possibility that the following year the female is faster to act and will function as the male.

  • Larvae
    Larvae from barnacles, Ecomare

    Barnacle larvae develop first in the parent animal. Afterwards, they enter the seawater as a large group until they fasten themselves to a hard substrate. Sometimes this occurs so intensely that ship hulls underwater must be regularly cleaned.  If too many barnacles attach to a ship, it can cost a lot of fuel to motor. Barnacle growth on boats is combatted through the use of anti-fouling paints. In the past, some variations of this paint contained materials that are damaging to the environment, such as TBT. This substance was proven to damage the sexual organs of whelks. In the meantime, paints containing TBT are forbidden worldwide. It is even old layers must be removed.