Final answer:
Option (d), 'Varied Aquatic Ecosystems: A Study in Marine Biodiversity,' is a suitable caption for comparing different marine ecosystems like coral reefs and ocean zones, emphasizing the diversity and complexity of life within these habitats.
Step-by-step explanation:
When comparing ecosystems such as a coral reef to a prairie, we can explore the remarkable diversity of life that each contains.
An appropriate photo caption that encompasses the comparison of different aquatic habitats, focusing on the marine ecosystems, would be option (d): "Varied Aquatic Ecosystems: A Study in Marine Biodiversity."
This caption highlights the variety of life forms and the interrelatedness within marine ecosystems such as oceanic zones, coral reefs, and estuaries, and captures the essence of biodiversity within these unique environments.