Why is shark bay a world herritage site?

Shark Bay was granted world heritage status in 1991. It is listed under criteria vii, viii, xi, and x. It is a place of great natural beauty as well as a home to stromatolites which are the oldest forms of life on earth. It is a great sanctuary for all types of life, containing great biodiversity. It is home to 5 kinds of different mammals, it is used as a migratory point for humpbacks, among other whales. Sharks and Manta Rays are also observed within the Bay. It is also home to the Wooramel Seagrass Bank which is the largest structure of its type in the world and contains 12 different species of seagrass.