Create a stunning underwater scene featuring a realistic mermaid with long, flowing hair that dances gracefully in the water. Use a 24mm wide-angle lens with an aperture of f/4 to capture the expansive scene, focusing on the mermaid while slightly blurring the vibrant coral formations in the background. Set the ISO to 200 and shutter speed to 1/125s to maintain clarity and capture the movement of the mermaid and surrounding fish. The mermaid's shimmering tail should reflect the sunlight filtering through the surface above, creating a magical atmosphere with dappled light patterns on the ocean floor. Her expression should embody tranquility and joy, with a gentle smile as she swims effortlessly. Surrounding her are colorful fish darting playfully, their scales glinting in the light, and a gentle sea turtle gliding nearby, enhancing the serene ambiance. The background should be filled with vibrant coral formations, adding depth to the underwater landscape. In post-production, apply color grading to enhance the blues and greens of the water, while adding warm tones to the sunlight. Incorporate texture overlays to simulate the underwater environment, and add a subtle glow effect around the mermaid to emphasize her ethereal presence.