Complex sentence: As Ecco recovers, he discovers that the Asterite's powers have left him (indicated by the return of his need to surface for air), and his fellow dolphins explain that something has killed the Asterite and is now spreading fear among the ocean life.
Split into simpler sentences: As Ecco recovers, he discovers that the Asterite's powers have left him (indicated by the return of his need to surface for air). His fellow dolphins explain that something has killed the Asterite and is now spreading fear among the ocean life.