A sea moss farm! In St. Lucia there is a drink called sea moss. To make it they harvest a particular kind of moss from the sea, sun dry it, grind it up, mix it with water and some other stuff, and then sell it. You'll often see it at a roadside stand as a "local juice" but it is also bottled. It is thick and creamy and pretty good. The moss does grow in the sea naturally but it is economically valuable enough that some people also encourage it to grow by placing empty soda bottles on strings between sticks, providing a nice surface that the moss can attach itself too and also a relatively easy way to harvest it.