The correct answer is option 2: Tropical rain forests. Coral reefs are complex ecosystems found in warm, shallow waters with high levels of sunlight. They are known for their vibrant colors and the diversity of marine life that they support. Similarly, tropical rain forests are also known for their high levels of biodiversity and lush vegetation. Both coral reefs and tropical rain forests are considered to be the most biologically diverse habitats on Earth. They both provide important ecological services, such as carbon storage, oxygen production, and habitat for numerous species. While temperate forests, savannahs, and scrublands are all important ecosystems in their own right, they are not direct counterparts to coral reefs.