The three correct answers that accurately describe coral reefs are:
- Coral reef ecosystems are among the most biodiverse on Earth.
- Coral reefs are sturdy structures that can exist for thousands of years.
- Coral reefs often are located in nutrient-poor waters.
(Note: The third answer about nutrient-poor waters is typically correct as coral reefs thrive in clear, warm, and nutrient-poor waters, which allows for the symbiotic relationship with zooxanthellae algae.)