How to replace Mangrove estuaries?

[archman]

I've always been under the impression that a multispecies ecosystem thrives better than monospecies ecosystem.

You are correct. The key difference with things with mangroves is that they ARE the habitat. The most important factor for organisms that create habitat (kelp, cordgrass, seagrass, coral) is abundance and size. You want a whole mess of the things around, in order to provide the basic habitat structure for all the other critters. That's where the high diversity comes in.

Now if you have multiple habitat-creating species present (ie. tropical rainforest), that'll really jack up your biodiversity.