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Posted to Maritime Musings (by on April 23, 2013

A small marine arthropod that continues to bedevil mariners

The lowly barnacle has intrigued and been detested by mariners from time immemorial.  It is a small arthropod with a complex life cycle.  Once the fertilized egg is released into the water by the female, it hatches into a nauplius – a one-eyed larva consisting of a head and a tail fan for locomotion.  After about six months of growth, it converts into a cyprid – a short-lived non-feeding larva that attaches to a solid object, such as a rock, a piling, or the hull of a ship.  The cyprid attaches head-first using its antennules and a proteinous substance.  The animal then transitions into the adult barnacle, never relocating again during its life.  Some species of barnacles grow their shells directly into the surface to which they have attached themselves.  Others use a stalk for attachment.  Although the barnacle seldom causes significant direct physical damage to the object to which it has attached itself, it can have deleterious effects, particularly since barnacles tend to colonize in large groups.  Significant barnacle growth on a ship’s hull adversely impacts its efficiency in moving through the water.  Thus, hulls require regular cleaning.  Various measures have been implemented over the years to deter barnacles and other marine growth.  Wooden-hulled ships frequently were sheathed with copper.  Steel-hulled ships for many years applied copper or tin based paint, but these were found to have adverse environmental impacts and have since been banned.  Hulls are now coated with more eco-friendly paints.  Barnacles present less of a problem for modern ships, but hulls must still be cleaned, albeit less often.  The adult barnacle is a suspension feeder.  It extends feathery appendages (actually modified legs) into the water column and draws plankton and other small material into its shell, where it is consumed.  Most barnacle species inhabit the intertidal zone, but some are found at depths of up to 2,000 feet.  The whelk is the only major predator of the adult barnacle.  It is able to grind through the hard shell and feed on the soft interior.    

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