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 forms the substrate on which they live and which becomes a coral reef as it builds up over time. The calcium carbonate skeleton also protects the corals from predators. Scientists have categorized coral reef into three main types: fringing reefs, barrier reefs, and atolls. Their geographic range includes both tropical and temperate climatic zones, though they are most abundant in warm, shallow water. The geological range of coral reefs is from the Middle Ordovician to modern times.
Corals play an essential economic role for many coastal human communities, as they provide a habitat for fishers, physical protection from erosion, a source of marketable goods, and a destination for tourists. Unfortunately, coral reefs globally are showing signs of ecological degradation from pollutant runoffs of chemicals and human sewage, increasing sedimentation and eutrophication, damage from ships and divers, and increasing sea temperatures and ultraviolet radiation exposure. Coral reef ecosystem health is an important