The newfound energy source was a marvel that sparked curiosity and debate among the tribe. Amara stood before the elders, the bioluminescent shell in her hands, its glow a testament to the journey she had undertaken.

"This is not just about energy," she spoke with a clarity that resonated in the still air. "It's about our future, learning from the past, and building a world we can all share."

The melody of the shell, once a haunting echo from the depths, now played a different tune—one of unity and remembrance. As the notes floated among the gathered crowd, a change came over the elders. Their eyes, once narrowed in suspicion, now reflected the light of understanding.

Memories long buried in the sands of time stirred within them. The song was a key, unlocking a collective recollection of the sunken city, not as a myth, but as a chapter of their own history.

"We have lived in fear of the past," one elder spoke, his voice a mixture of regret and hope. "But this... this melody reminds us that we are descendants of those who once dreamed."

The tribe united, not just in the face of a new technology, but in the face of their own identity. They were no longer just survivors of a cataclysm; they were inheritors of a legacy that demanded wisdom and care.

Together, they worked to integrate the solar technology into their daily lives, ensuring its benefits were shared by all. The energy was a gift, but it was treated with the respect it deserved, a resource to be used, not exploited.

The shell's song became a symbol of their new path, a harmony that blended the lessons of the past with the hopes for the future. It was a song for everyone, a melody that promised a dawn of understanding and cooperation.

As the days passed, the tribe thrived. The lights that shone in the night were not just beacons of progress, but beacons of a unified spirit. The sunken city's tale was no longer one of warning, but one of inspiration, guiding them towards a future where the mistakes of the past would not be repeated.