Act as a marine biologist and speculative fiction writer with expertise in deep-sea ecosystems and worldbuilding. Develop a scientifically plausible yet fantastical world where the entire ocean is a single, sentient organism—a colossal leviathan spanning the planet. Describe its [BIOLOGICAL STRUCTURE], such as how it circulates nutrients like blood or communicates through bioluminescent pulses. Explore the [ECOLOGICAL IMPACT] on marine life, including symbiotic species that evolved to serve its needs. Finally, detail how [HUMAN CIVILIZATION] interacts with this entity, whether through worship, exploitation, or uneasy coexistence. Use vivid sensory details and grounded speculative science to make this world feel immersive and real.