When you play bonuses, you can find rewards for sunken treasures, including wild bonuses, discount bonuses, free game features and re-spins.
When dolphins appear, they will appear on reels 2 and 4, where they replace all symbols except the scattered treasure chest symbol. However, if the dolphins appear on reels 2 and 4 at the same time, they will trigger a re-spin feature where they unfold to cover all reels 2 and 4, while reels 1, 3 and 5 are re-spin five times.