The serpent who dwells at the bottom of the sea is probably a reference to the Leviathan (Isaiah 27:1). Leviathan is one of the Hebrew names for the sea monster of ancient Near Eastern Mythology that represented the forces of chaos held in check by the power of the creator deity. Here he is represented as a creature who is completely under God’s control.
3 If they hide themselves on the top of Carmel, from there I will search them out and take them; and if they hide from my sight at the bottom of the sea, there I will command the serpent, and it shall bite them.