I agree that this is more a question for scientific fact than opinion.  I'm not sure that one day would help the coral reefs and beaches.  Yes, we should protect these delicate areas.  We should do what we can to preserve and maintain corals and beaches.  I'm just not sure that one day a week would really help.  Perhaps one month a year or some other, lengthier time period might be more effective.  This would be an interesting area for scientific research.

I don't think that laypeople can really say anything relevant on this subject.  This is not an opinion sort of a thing.  Instead, it depends on actual scientific data.  Scientists need to be the ones to determine whether such a day off would actually do anything for the beaches.  If they say it would, then the public should decide if the benefit to the beaches would outweigh the costs.

I have vacationed on Singer Island in West Palm Beach, FL for a couple of years, and many of the beaches there are nesting grounds for loggerhead sea turtles.  One morning we got up really early to see them hatching (so amazing!), and I got to speak to one of the Sea Turtle Conservationists that was there to oversee the hatching.  She had some really interesting observations about the fragile quality of the ecosystems on these reefs and how quickly the natural reefs were dying out.  For many of these natural beach areas, the damage has been done.  Less foot traffic and human-interaction would probably help, but in some cases, the damage is sadly irreversable. 

I agree with post #2's ideas about rotating beach management of hours.  On the state beaches, this ideas would certainly be feasible.  The mega-deluxe super condo hotels with their beach front property would probably not embrace this plan. 

This is a good question. I think it would be good, in general, for people to think about the impact of humans on the environment. Our footprint can do a lot of harm and has already done a lot of harm. All one needs to do is to think about things like global warming. In addition, some of the damage is irreversible. So, a policy that seeks to protect the environment or beeches in this case is a great idea. 

As for closing all beeches for one day, this might be a little drastic and may have a lot of public uproar, because tourism is how Hawaii makes money. In light of this, it is possible to think of other alternatives. Perhaps there can be a system that is implemented where some beeches are closed and some are opened. This type of arrangement can be a good middle ground.