Creature Feature: Northern Rock Barnacle

The Northern Rock Barnacle (Semibalanus balanoides) also known as the common rock barnacle is found fastened to rocks in the low intertidal zone to the shallower waters of the subtidal area.  This is the most commonly found barnacle in this area and can be identified by its rough grayish white shell.  It does not have a calcareous base as some other barnacles do. 

The barnacle is an arthropod and a crustacean, meaning it is related to crabs and lobsters.  It does not have a hard exoskeleton so must build a shell around itself for protection. It is the only crustacean that is stationary for its entire life.  Once the barnacle is finished with its planktonic larval stage, it will glue itself head down onto a rock substrate where it will create the shell around itself. It will not move from this spot for its entire life cycle.

Rock barnacles are hermaphroditic (both male and female).  They reproduce sexually but do not release their eggs and sperm into the open water; rather their fertilization is internal wherein one barnacle acts as the male and will reach to another barnacle that will act as the female and accept the sperm and brood the eggs within their shell. Once the eggs are hatched they will be released into the water.  A single adult barnacle may release up to 10,000 larvae into the water.  When these larvae settle, they may chose something other than rocks to attach to, such as the hulls of boats, lobsterpots and even slow moving or fairly stationary creatures such as Horse mussels.  The cement they secrete to attach themselves to things is very strong and currently being studied for possible use in dental applications.

 

Diagram of the internal anatomy of the Rock barnacle; though note the Northern Rock Barnacle does not have a calcerous disk on the bottom.

 

Colony of rock barnacles. Note the gastropod; Dogwinkles are known to feed quite frequently on barnacles.