Why is the Kraken a troll?

Excuse me, but I have a question that's been bugging me for quite some time. I've noticed that in many legends and folklore, the Kraken is often described as a type of troll. This puzzles me, because the Kraken is typically portrayed as a giant sea monster, while trolls are usually associated with being ugly, clumsy, and living in caves or forests. So, why is the Kraken considered a troll? Is there some historical or cultural reason for this association? Or is it just a matter of different traditions and interpretations?