Mangrove wetlands are extremely important to the ecology of sub-tropical coastal zone ecosystems. Mangroves flourish in salty environments because they are able to obtain freshwater from saltwater. Some have the ability to block absorption of salt at their roots while others secrete excess salt through their leaves, allowing them to flourish where other trees would die. Mangroves, with the impenetrable root system, keep Biscayne's waters clean and clear by slowing the water that flows into the bay from the land, allowing the sediment carried by the runoff to settle out. Additionally, mangroves help to stabilize the coast and protect it from tropical storms and hurricanes. The roots also provide shelter and protection for many marine organisms, while the tree branches provide breeding and nesting areas for birds. Leaves fall from mangroves year round. The leaves break down to become food for many organisms including commercially important species of fish, shrimp, and the Florida Spiny Lobster. The prop roots of red mangroves support an extensive invertebrate community, consisting of sponges, tunicates, mollusks, and polychaete worms among many others. Without healthy mangrove forests, Florida's recreational and commercial fisheries would drastically decline. Mangroves stretch along 14 miles of shoreline of Biscayne National Park's western edge.
There are total of 6,905 acres of mangrove wetlands within Biscayne National Park. Many species found within Biscayne's mangroves are of special concern due to their conservation status, notably the American Crocodile, Crocodylus acutus , and the West Indian Manatee, Trichechus manatus . There are 3 types of mangroves that inhabit the park's shoreline. The red mangrove, Rhizophora mangle , thrives around muddy coastlines where its spreading roots reach outward toward the ocean in water as deep as 3 feet. These prop roots grow in mass thickets. The black mangrove, Avicennia germinans , is found in mostly salty, saturated soils, with a lot of silt along the tidal shoreline. It prefers higher and dryer soils than the red mangrove. It is characterized by it's cigar-shaped pneumatophores sticking out the soil all around the truck. The white mangrove, Laguncularia racemosa , is normally found further inland than the red and black mangroves. The base of its leaves have two salt-excreting glands near the leaf blade which allow it to get rid of excess salt. The white mangrove is the least cold tolerant of the three species. A typical example of a black swamp community can be found along Biscayne Bay at Card Point. Black swamps are basin forests made up mostly of black mangroves due to the salinity tolerance of Avicennia . This community is rare in Dade County, most often found in shallow basins with occasional tidal flush. Glasswort ( Salicornia spp.), saltwort ( Batis maritima ), and sea purslane ( Sesuvium portulacastrum ) are common understory plants in open areas.