the rich diversity is in part due to the of coral reef extending along its coastline; these fringing reefs are 5000–7000 years old and are largely formed of stony acropora and porites corals. the reefs form platforms and sometimes lagoons along the coast and occasional other features such as cylinders (such as the blue hole (red sea) at dahab). these coastal reefs are also visited by pelagic species of red sea fish, including some of the 44 species of shark.