The Trident is a merman accessory founded by a merman decades ago. It remains destroyed. It was taken by Zac until he put it back after Lyla became unconcious and then taken by Cam then destroyed by Zac. Only one Mermaid has touched the trident her name is Lyla. It was eventually be found by Zac because there are pictures of him and cam with it It is possible Zac will use this to fight the moons power so he could be affected but will fail (this never happened). It is the most powerful item in the sea. According to Rita, some time ago, a pod of mermen had control over the Trident, it was so powerful it gave them power over both the land and the sea. It took mermaids from all five oceans to defeat the mermen and they unlocked the chamber and put the trident in and then they locked the trident chamber and was not opened until 2013.
Zac used the trident as a personal mermaid detector so he could locate the moon pool. It tracked Aquata leaving the moon pool. If a mermaid touches it 5 minutes later they will grow weak. When Rita was standing in front of Zacs locker when it contained the trident she grew weak as it was drawing the life out of her. It tracks mermaids by the crystal lighting up when it is in range of a mermaid.