Integrate the provided primary subject image into a vivid and detailed underwater coral reef scene. The final composition should depict the subject gracefully positioned amidst a thriving marine ecosystem. The scene must include a diverse array of intricate coral formations, such as vibrant branching corals, undulating sea fans, and robust brain corals, rendered with realistic textures and a spectrum of natural underwater hues. Populate the environment with various species of colorful tropical fish, including schools of iridescent reef fish, elegant angelfish, and playful clownfish, actively swimming around and interacting with both the coral and the integrated subject. Ensure the lighting replicates natural underwater conditions, with subtle caustics and dappled sunlight filtering from the surface, creating a sense of depth and clarity in the water. The overall aesthetic should be a photorealistic portrayal of a pristine and lively coral reef environment.