Since Poseidon is a god from Ancient Greek, there are no records or stories of what Poseidon fears, and most people do not believe in Greek gods anymore. However, since he is immortal, my guess would be being tortured and placed in Tartarus.
A soul
jelly fish are his biggest fear because when he was making those creatures one of them stug him he was really scared
nothing
kronos
no
Poseidon does not fear Zeus, he respects his older brother because he is the king of the gods in Greek Mythology (Zeus is Jupiter, Poseidon is Uranus in Roman mythology).
In Greek mythology, Hades feared losing control of the Underworld, as well as experiencing betrayal from other gods or from mortals seeking to escape his domain. Additionally, Hades feared challenges to his authority and power by potential adversaries.
Poseidon feared nothing.
a war of the gods
Quite possibly, as Cronus the father of Poseidon swallowed him shortly after birth.
a war of the gods
Poseidon was afraid of this brother Zeus. (actually, he was afraid of the sky, because Zeus ruled it.. )
Poseidon ruled in the sea which surrounds the entire city of Greece and he was considered the god of the seas
Poseidon fears betrayal and losing his power. He desires respect and acknowledgment of his authority as the god of the sea. He needs people to honor and worship him to maintain his influence and control over the oceans.
Sailors feared Poseidon, because they believed him to be the cause of earthquakes.
Poseidon's Greek name was Poseidon. Poseidon's Roman name was Neptune.
he is poseidon