A shelly beach

My family met at Point Cook today for lunch because it was my step-mother's 19th birthday yesterday. No, my dad hasn't lost his marbles or succumbed to the charms of a teenager. She is actually 76 but was born on February 29. And hopes to celebrate her 21st in eight years time.

Now, I have to admit that, although Point Cook is not very far from home, I have driven past many times and never been there. I was pleasantly surprised. That's Melbourne on the horizon, just across Port Phillip Bay.

And on the sandy shore there were piles and piles of sea shells. My ignorance of all things marine is total, but I am curious to know why there are so many shells in this spot. Have a look at a map - Port Phillip Bay is huge, but it has a very narrow opening to the ocean. Does the shell debris come from the bay itself or does it get washed in all of the 50 kms from the ocean?