Ok, as promised, this is what the mangroves look like now (freshwater tank, but should actually do a bit better in brackish. Flowering plant is one in the same family as African violets). I know most folks use small tanks, so I doubt you'd fit more than one per.
'Batophora oerstedi' is apparently another plant/algae that can survive in brackish conditions:
see http://macroalgae.org/portal/taxa/index.php?taxon=18649
and
https://www.flickr.com/photos/jsjgeology/16326642277/
University of Michigan
Catalog #: 678864
Occurrence ID (GUID): f8cf9567-3b11-404d-b4e9-9acef82d1940
Taxon: Batophora oerstedii J.Agardh
Family: Dasycladaceae
Collector: Albert J. Bernatowicz 51-864
Date: 05 February 1951
Locality: Bermuda, Emily Bay, south side of Saint David Island
32.370233 -64.671492 +-148m