Why is there so many shells at the ocean?

Question

Why is there so many shells at the ocean?

Answer 1

Could it be that there are lot of shellfish in the ocean that leave their exoskeleton behind when they die, and they all get washed up on shore?

Answer 2

The shells are what's left of the organisms that used to inhabit the shells. Gradually, the drift down to the ocean floor and some gets washed ashore by waves and some, over the course of hundreds or thousands of years, form calcium deposits.