i've had them come back from a very dead looking state. These things are responsible for a lot of coral atoll islands because they wash up on newly formed land. I think they're prety dang tough. LOL. I love my mangroves, but I am prettty convinced you would need hundreds of them to actually impact nutrient export. To Steve's point, plants only consure nutrient when they grow and mangroves grow very slowly. One errant leaf will also set you back, though they are prey easy to keep tack of. In the end, for nutrient export chaeto can't be beat, but Mangroves are awesome in and of themselves.