The last time I went on a cruise, I went to Key West, Grand Cayman and Cozumel. I collected something from each place. I got large pieces of rubble from Key West and Grand Cayman. I got a huge Queen Conch shell from the beach at Cozumel. This is a shell that is in the water for a long time but reasonably intact. It is very porous and makes an excellent addition to my aquascape. I got a colony of Green M. digitata (from my tank) growing on it at this time. My Yellow tail damsel pair uses it as a home and is spawning in there.
I got a bucket of water in my room and have a small air pump to keep it aerated for the week. Thus I only have these LR out of the water for about 2 hrs from the ship to home.
The next time I am going on a cruise, I will do the same thing. I did not go for volume, but got interesting pieces of ruble and rock.
Minh