Barnacles
With the exception of several parasitic species, barnacles are a group of sessile crustaceans adapted to live in brackish or salt water environments. Barnacles have a hardened cuticle, forming a shell consisting of calcium carbonate. Most anchor themselves to submerged surfaces using a strong natural adhesive and feed by extending appendages through the shell to sift food from the water.
While barnacles demonstrate a high tolerance to fluctuating environments they are particularly sensitive to low salinity and at concentrations of 5 ppt or below all cirral activity ceases. In order to cope with emersion in freshwater barnacles are able to close their opercular valve for extended periods. Some species such as Semibalanus balanoides are able to enter ‘salt sleep’. In this state all motor activity ceases and respiration is reduced allowing the organism to survive for up to three weeks.
The Acorn or Bay Barnacle (Balanus improvisus), shown in figure 5 opposite, has one of the widest salinity tolerance ranges of any species. The precise reasons behind this broad tolerance are unclear but it is believed B. improvisus can alternate between being a passive osmoconformer and an active osmoregulator.
Barnacles expertly cope with variable environmental conditions through a process known as ‘phenotypic buffering’ in which a functional phenotype is maintained despite external disturbances. Such plastic responses enable the barnacle to tolerate environmental disturbance without genotypic changes occurring through selection.
With the exception of several parasitic species, barnacles are a group of sessile crustaceans adapted to live in brackish or salt water environments. Barnacles have a hardened cuticle, forming a shell consisting of calcium carbonate. Most anchor themselves to submerged surfaces using a strong natural adhesive and feed by extending appendages through the shell to sift food from the water.
While barnacles demonstrate a high tolerance to fluctuating environments they are particularly sensitive to low salinity and at concentrations of 5 ppt or below all cirral activity ceases. In order to cope with emersion in freshwater barnacles are able to close their opercular valve for extended periods. Some species such as Semibalanus balanoides are able to enter ‘salt sleep’. In this state all motor activity ceases and respiration is reduced allowing the organism to survive for up to three weeks.
The Acorn or Bay Barnacle (Balanus improvisus), shown in figure 5 opposite, has one of the widest salinity tolerance ranges of any species. The precise reasons behind this broad tolerance are unclear but it is believed B. improvisus can alternate between being a passive osmoconformer and an active osmoregulator.
Barnacles expertly cope with variable environmental conditions through a process known as ‘phenotypic buffering’ in which a functional phenotype is maintained despite external disturbances. Such plastic responses enable the barnacle to tolerate environmental disturbance without genotypic changes occurring through selection.