I recognize a couple of the cases listed above as a result of being a whitewater kayaker, and therefore having an interest in legal issues about the public right of navigation, and I looked at a couple of the cases I don't recognize. I didn't look at all of them, and all that I looked at are fairly general cases about the public's right to access lands "subject to the ebb and flow of the tide", a concept that dates back at least 1500 years to the code of Justinian. That right of access is predicated on the right to navigate on the seas. In some places that right, and the more evolved public trust doctrine, allows access for purposes beyond those that are directly or closely related to navigation. In others the public right is fairly limited.
For the most part it's a safe bet that everything below the mean high water mark is public property or that there's a public easement for at least some purposes. What a lot of people that know that don't realize is that having the right to be somewhere doesn't necessarily mean that you have a (useful) right to get there. You've got no right to cross private property simply because the property on the other side is public. You also may not have the right to cross publicly owned property, because despite noble ideas about property being owned "by the people" it's controlled by some governmental entity. When the property owner does allow access they're mostly free to allow it on their terms, and to control the uses the public makes of their property.
Even if the public trust doctrine is liberally applied there will still be limits on the uses the public can make of the intertidal zone, and the property owner (whether private or some public entity) will maintain control of the land above the high water mark. A good argument might convince the powers that be to allow diving, but if they don't want to allow it at a particular location I doubt that they can be compelled to. The nature of government is that you may have even fewer rights than you would with a private owner. Since everything below the low tide line is public you can probably dive right up to that line where it's adjacent to private property (even if you have to crawl in the sand). In front of a public beach the municipality can probably prohibit or restrict diving, as they commonly do with surfing or boating at beaches.
If you do find anything useful be sure to let us know.
