I shoot around/across water a lot, and after much fiddling taking test shots with and without, I find a high quality UV filter can make an improvement in certain situations, or at least no detrimental difference I can see. The caveat would be shooting into the sun. There, one less layer of glass always seems to be an improvement. So, between either finding a slight improvement to no negative change plus the protection aspect, I put a high quality UV filter on most all my lenses. And as would be expected around water, I have a CPL for every lens. I've settled on B+W, but there certainly are several other good makers. I think this is an area you do get what you pay for, and if you do use filters, you need good ones. An earlier post made reference to the Lens Rental blogs on UV filters. Here are a couple links worth a quick read - informative and entertaining:
an "accidental" discovery of UV filter quality differences:
Lens Rentals | Blog
and a more scientific review with actual measurements:
Lens Rentals | Blog
and I know there are many other articles and tests out there - you can go nuts on this topic. As they point out in the Lens Rental blogs, "not enough bandwidth" to sort this one out. I'd say grab a good quality filter for your favorite lens and go play in situations that match what you shoot, and put it on a tripod and take some controlled pictures and see where you land. Worst thing that happens is you take it off.