2. australia
the great barrier reef

sometimes referred to as the tropical rainforests of the seas, coral reef ecosystems are highly diverse, productive aquatic marine communities. coral reefs are biogenic deposits formed by coral, marine invertebrates belonging to the phylum cnidaria and class anthozoa. coral are sensible animals living primarily in colonies of individual polyps. two main types of extant corals are hard rayed stony corals subclass zoanthiniaria, order scleractinia and soft corals order alcyonaria. nearly all corals live in symbiotic relationships with zooxanthellae algae, which rely on the coral for protection and for access to the light necessary for photosynthesis. in return, the algae provide the coral with food and food also give their distinctive colors. other marine invertebrates and fishes live in the coral reef community, which provides shelter, food, and a habitat for nurseries.
coral secrete a hard calcium carbonate skeleton, which fo...