Acorn barnacles
Barnacles are crustaceans that live attached to rocks and
are the only crustaceans that remain fixed in one spot for life.
They are strongly related to goose barnacles
reproductiion of barnacles
the difficulties the poor barnacle faces, permanently glued to an underwater rock or hull.
Barnacles, however, actually copulate with each other. They manage this feat with an amazing penis that is capable of seeking out partners and mating with them.
Barnacle attached to rock near a rockpool.
enemies of the barnacle
Barnacle are eaten by the common whelk, a large snail.
The whelk is capable of boring through the shell of bivalves and barnacles,
Young seastars are capable to open the barnacle valves.
how barnacles eat
Barnacles have appendages, called "cirri", they use for straining algae from the seawater. When the cirri are drawn back, the food is scraped off into the mouth.
The cirri are in fact modified thoracic legs and are long and feathery. Plankton, mostly algae are filtered out from the water, but also mud particles are ingested.
attached to rocks
The barnacle has a free floating juvenil stage,as planktonic larvae.
That free moving period ends when these larvae meet a rock.
It will glue itself with an strong glue to that rock and starts to build a house of cement produced by cement glands.
Barnacles transform from a freefloating stage to a sessile live, attached to a rock or the hull of a boat. They even attache to slowly moving animals: e.g. a crab or a whale.
fouling on hulls
The accumulation of barnacles and goose barnacles on boats
is called fouling and reduces the speed of a boat.
It will also increase fuel consumption. Mechanical removing the barnacles
is a costly operation and removing it without damaging the
hull can be next to impossible.
Its much easier to use anti-fouling bottom paint, commonly known as bottom paint.:
This is a toxic paint used to prevent the attachment of these organisms.
Certain forms of this paint, although effective, can be harmful to
other marine life if not applied and removed properly.
If a boat is longer then 25 meter the toxic TBT was added to the anti-fouling paint.
tributyltin of TBT
For 40 years TBT was used as a biocide in bottom paint.
The use of TBT has come to a stop in the western world,
but is still the most effective and cost efficient,
and it is being used in countries with poor regulation enforcement, like the Caribean Islands.
The danger of TBT used on the ship hulls was found to leach into, and severely damage, the marine envirronment.
TBT has has a strong toxic and long lasting impact to invertebrate development: snails, worms, barnacles and bivalves
and all the higher animals that depend on them as a food.
Skipjack tuna sea-otters and dolphins accumilate the TBC in there bodies.
The common whelk has almost dissapeared because of the use of TBC.
imposex
The common whelk has almost dissapeared because of the use of TBC.
These animals were affect by TBC causing imposex.
Imposex is a disorder in sea snails caused by the toxic effects
of TBT. TBT cause female sea snails like the common whelk to develop male sex organs
Reproduction of the seasnails comes to a stop. 
1 Acorn barnacles
2 goose barnacles