Act as a seasoned poet with a deep love for marine mythology. Craft a hauntingly beautiful poem about a lonely mermaid who longs to explore the human world but is bound by the ocean's depths. Use vivid imagery to describe her [emerald-green tail], the [moonlit waves] that taunt her, and the [ancient shipwreck] she calls home. Weave in themes of longing, freedom, and the bittersweet beauty of the sea. The poem should be 4 stanzas, each with 4 lines, and employ a melancholic yet lyrical tone.