getwet2:
The "Sea Itch" you are talking about is probably what they call "Sea Lice" and that's the larva of the thimble jelly fish.
Yes, the itch is from the thimble larva, but its not this case with Sea Wasps.
The Sea Wasps that are found occasionally on Cayman night dives are genuine stinging jellyfish. They're usually roughly a little larger than a Thimble jellyfish that you'll encounter in the springtime, but they trail four (4) long stinging tentacles that can be 6" long and these pack a good punch.
Here's a fuzzy photo of a pretty dense swarm that we had on a night dive last year. This was ~4ft off our starboard rear quarter and ~7ft from the exit ladder. Note: every white dot here is one Sea Wasp; I think I've counted 90-something of them in this image:
To surface right through this mess would not be fun.
If you get stung, the topical treatment is vinegar.
But the best medicine is to prevent getting stung. Three things work well here:
1.
Minimize risk
Your exposed skin is the problem. Cover it up with a polartech, lycra or full length tropical wetsuit. Diving nude is for Masochists.
2.
Plan Ahead:
They're attracted to lights, so in your dive briefing, very, very emphatically tell all divers to
NOT spend any time directly under the diveboat with their lights blazing: they should spread out away from the boat so as to prevent the wasps from finding the boat and congregating at your dive exit.
3.
Surface Smartly:
First, when doing your safety stop, try to do it with the minimum amount of lights on, to prevent attracting them to the water between you and your exit point.
Next, they'll usually be worst right near the surface, and even the lights on the diveboat will pull some of them in, so after you finish your safety stop,
"blow a hole" through them to clear your exit. You do this by letting rip on your regulator's purge button a big, healthy burst of air - - usually, ~5 seconds is enough, but if you're pretty sure its going to be nasty (like you had a class of AOW's all sitting under the boat for a {bleeping} hour), try a 10-15 second long blast of air.
This blast of air will of course rise and it will carry the water column along with it. This rising water can't go any further "up" than the surface, so it then spreads out. All of this water flow causes a flushing action that "blows a hole" through any wasps that were hanging out near the surface where you're about to surface, and then pushes them away from your exit.
Feel free to give yourself another short blast of air on the way up, maybe 3ft before breaking the surface. Once you're at the surface, get out of the water smartly and promptly before the buggers can swim their way back into the clear water that you created.
For multiple divers surfacing, keep using the same spot over and over. This keeps pushing the wasps the same "away" direction and will make a cleaner hole.
4.
Post Dive: I've seen divers seem to do all of the above perfectly, then get nailed a few minutes later while they're stripping off their wetsuit. The problem can be traced back to them not promptly getting all of the way out of the water: they stand on the ladder, hip-deep and allow the wasps to get onto their wetsuit. They then go strip it off 5 minutes later and get zapped and can't figure out why.
Lesson here is that #3's "GET OUT" means GET ALL THE WAY OUT of the water.
Follow the above, and when all of the other divers are looking for vinegar, you'll be saying, "Were there sea wasps on that dive?"
-hh
