Biotopes like this aren't very common, but can be really cool. They normally require a huge amount of research to find things that will do well in the size of tank you have and if you are trying to do FOWLR
The regulations around you will also be important, as bribo stated, since it is illegal in many areas to just go and start grabbing stuff from the beach and ocean. It depends on where you are on what is ok and what isn't. In Hawaii, the fines are pretty hefty and can even include jail time if I remember correctly. So please look into this before starting the project.
Here is a quick link to one of the early biotope tanks I read about. Real quick read and might give you some ideas.
Jacob Dixon’s Puget Sound biotope is a cool as it is awesome