Final answer:
Coral reefs are indeed organic and formed by the calcium carbonate skeletons of coral organisms. They create diverse ecosystems essential to marine life and shoreline protection. The statement about coral reefs being organic is true.
Step-by-step explanation:
The statement that coral reefs are considered organic because they were once made of living creatures is true. Coral reefs are formed by the calcium carbonate skeletons of coral organisms, which are marine invertebrates in the phylum Cnidaria. These organisms form colonies in shallow tropical waters and have a mutualistic relationship with photosynthetic algae, which need sunlight for photosynthesis. Coral reefs provide a crucial ecosystem for many marine species and play a significant role in protecting shorelines.
The exoskeletons of both living and dead corals comprise most of the reef structure, offering protection to a diverse array of marine life. Reefs support about one third of the world's marine fish species despite making up only one percent of the marine habitat. The Great Barrier Reef is a prime example of such a diverse and vital ecosystem. However, coral reefs face numerous threats, including unsustainable harvesting for the pet trade and other human-induced damages, making their conservation a critical environmental concern.