Sea Lice... I didn't run into any when we snorkeled in Nassau and St. Thomas. However I use to run into them all the time when I SCUBA dove in West Palm/Miami. There are a few easy ways to lessen the impact, first you can buy whats called a "skin" from any snorkeling/watersports/dive shop... they run between $20-$60.00 depending on what kind you want. The cheapy will work. It looks like a wetsuit but it is made from lycra similar to bathing suit material. This will keep Sealice and Sun Burns away. =o)
If you get sea lice its not really that bad, its not like "lice" in your hair. They are jelly fish eggs that get into your skin and you only really feel them when you shower in fresh water. A quick way to get rid of the sting these cause is to use vinegar. Or this may sound gross but in a bind another acidy liquid that we carry with us all the time will work.... if you get the drift.
They really aren't that bad and will go away quickly, like I said they are only aggrivated by fresh water.
BE SURE to wear plenty of sun block and reapply often in St. Thomas the sun was Brutale! We got blisters withen a 1/2 hours time... except me in my "skin"... =o)