Barnacles start life as larvae or ‘cyprids’ that swim around freely in the water. These cyprids must attach themselves to a hard substrate in order to complete the transition to adult life. When the cyprid finds an appropriate hard substrate to settle on it starts to attach itself using a ‘cement’.
A cyprid larva
Illustration: Jo Taylor / Source: Museum Victoria
The cement is released through the tips of the antennules (the first of two pairs of antennae). The cement is produced in glands at the base of the antennules, passes through ducts running up the centre of the antennule, and is released through the tip. The glands are regenerated and remain active throughout life. As the barnacle grows, the cement glands increase in size and become more complex. The broad base of the barnacles (where they are attached to the rock or substrate) continually develop secondary cement pores close to the growing margin, from which concentric rings of cement are released. The cement, which provides strong adhesion, is released as a clear liquid that hardens into an opaque, rubbery solid. It is composed of ‘quinone-tanned proteins’.
So a barnacle larva finds a nice-looking place to call its home, lands head-first and releases cement out of its antennules. It then spends its life stuck to the ground, flapping its legs about in a ‘hand-stand’ position!
Barnacles attached to a rock
Photographer: Rudie Kuiter / Source: Aquatic Photographics
Rocks are not the only places where barnacles settle. They also end up on wharf pilings and on the underside of boats. Many barnacles on a boat’s hull will slow it down and add considerably to the fuel bill because of the drag. Nautical engineers and chemists have developed anti-fouling paints that deter barnacle cyprids from settling. The poisonous chemicals in these paints, copper or tributyl-tin (TBT), leach into the water and do more than kill the barnacles – they are toxic to many other marine animals, and the use of TBT has been banned for small boats in harbours in many countries.