We call this arrangement "commensalism" if the barnacles don't cause any harm to their host. However, this relationship becomes "parasitism" when too many barnacles cause the host to have trouble swimming, which can harm the host.
In Animal Partners, a sea turtle has quite a few questions for the barnacle who is riding on his back.
|illustration copyright Shennen Bersani|
text copyright Scotti Cohn
Sea Turtle's Lament
Barnacle, o barnacle,
where'd you come from, barnacle?
Were you born or were you hatched?
How'd we come to be attached?
We're not alike, as you can see.
Why are you so stuck on me?
And why my foolish fascination
with such a clingy, crude crustacean?