Mangroves can help us solve some of the world’s most pressing environmental problems, including improving fish stocks and protecting cities from hurricanes.
The term mangrove is used both to refer to an entire ecosystem type and to the primary group of species within that ecosystem. The red mangrove (Rhizophora mangle) grows along the Atlantic coast in regions with minimum temperatures above freezing. Along with other species that can tolerate saline environments and fluctuating water levels, Rhizophora mangle forms dense mangrove communities that protect and stabilize low-lying coastal lands.
Rhizophora mangle has many intriguing qualities that allow it to thrive in the difficult conditions of the tidal zone. James’ photo clearly shows one of these adaptive traits: the stilt roots (rhizophores). Technically, rhizophores are specialized root-bearing branches; in Rhizophora mangle they begin to develop at about two years, and sprout from the tree’s trunk. These roots prop up the 20 meter tall red mangrove, and anchor it against dramatic tides, waves, and even tropical storms. The rhizophores grow downwards (through air or water) until they reach an object on which to anchor, then form many smaller roots that attach to the soil or reef. Not only does this root system provide an excellent anchor for its mangrove tree, it also slows the flow of water, causing sediment to settle out and slowly build up new land. A post on Biomimicry Norway questions whether we could use Rhizophora mangle‘s approach to stabilize our own construction projects — perhaps many, differently-sized stilts would work better than the pillars that we typically use for supporting structures in wet environments.
Another of Rhizophora mangle‘s unusual adaptations is its viviparous propagule. Like other viviparous species, red mangrove seeds do not undergo extended periods of dormancy as most seeds do. Instead, they germinate while the seed is still enclosed in fruit and attached to the tree. By the time the propagule detaches from its parent, it is already a seedling and measures about 23 cm. Amazingly, this seedling can float on the ocean for over a year before finding land and getting “planted” into soft mud in a suitable habitat.