This is a very informative link regarding sea lice.
http://www.fau.edu/safe/sea-lice.html
Having grown up near the Gulf, lived in BWI and scuba dive I try to be prepared for "stings" when we know we are going into the water. DH once got terrible stings from sea wasps in Honduras on a night dive, I carry a lovely Man o' War scar myself, etc.
I always make sure to pack things for stings-meat tenderizer, hydrogen peroxide,asprin,benedryl(sp?) just as a precaution.
Severe allergic reation is a primary concern-a big one especially if you are sensitive.
The other concern is secondary infections from scratching or having open sores. Staph is a big concern today. If you do get stings cover them up with big t-shirts or drag out that flowered mumu whatever works! Be careful about sitting/lounging on uncovered beach chairs, etc to avoid picking up germs left by other people. Think carefully about going into the water if you have open sores. The old wive's tale about salt water helping to heal doesn't always apply to sea water-we on the Gulf also have the extra bonus of fleash-eating bacteria in the waters during hot weather.
I hope this info helps.
Sea lice should only be a small concern-
I think of them like the potential for ants at your picnic they may be there, maybe not-, enjoy your trip, but be prepared.