It's not so much the water, it's that the chances of the person checking your carry-on will actually know enough about corals to completely understand what it is. I can definately see someone, who's only seen Finding Nemo, think only the worst if someone tried to bring an anenome as a carry-on. Nail clippers for instance are not allowed as carry-on. A corner of one of my books can do more damage than one of those things
.
And, I don't recognize the name of your future sister-in-law. What department does she work in?