Some places don't allow you to collect anything from the beach because it detracts from the beauty and the experience of what one would expect of a seashore. With that being said you can buy the seashells and other neatful things some made in art form while others just what was picked up from the shore.
I can understand this to an extent as you don't want people picking up live creatures and taking them home only to die a terrible death... I mean if you lived on the beach would you want someone picking you up and taking you home in a box to live out the rest of your life in nothingness all alone with no real purpose?
For me, I would rather create art without disturbing anything if I can and keep the photos, art, paintings, anything I've created as a long lasting memory of the beauty and good memories I had. Respect for the ocean is a big deal not just because it's about others but about your self and your safety. It doesn't take much for an undercurrent/ sleeper wave to pull you under that would take one of your great memories and turn it into a nightmare or worse. Take the time research and learn about the things you love (the ocean) and you'll be fine. mean while enjoy one of my memory art.