A thila is a coral formation that rises steeply from the atoll floor and reaches to between 5m and 15m of the water surface - often it's a spectacular underwater mountain that divers fly around like birds. The top of a thila can be rich in reef fish and coral, while the steep sides have crannies, caves and overhangs, which provide shelter for many small fish, and larger fish come, in turn, to feed on the smaller fish.
A giri is a coral formation that rises to just below the water surface. It has many of the same features as a thila, but the top surface may be too shallow to dive.
Thilas and giris are found inside kandus, where the nutrient-rich currents promote soft-coral growth. They also stand in the sheltered waters inside an atoll, where the sea is warmer and slower moving. Hard-coral structures on sheltered thilas and giris suffered most from the 1998 coral bleaching, and have been the slowest to recover.
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