ABSTRACT
The tropical and subtropical coasts of the world are lined with a highly specialized type of forested wetland system known as mangroves. Mangrove forests occupy intertidal zones and are adapted to regular inundation by a range of salinities (e.g., freshwater to oceanic) (Tomlinson 1986). The term “mangrove” is a descriptor of function, not phylogenetic relationship; there are nearly 75 species of mangroves within 20 different families that include small shrubs, palms, and trees (Duke 1992). Several morphological and physiological adaptations allow mangrove trees to survive the harsh conditions of coastal and estuarine life. Their highly vascularized root systems exclude salt from the soil water they utilize and pump oxygen down into anoxic sediments (Tomlinson 1986). Pneumatophores and knee roots project upward from the sediment, whereas prop roots and buttresses extend radially from trunks to provide stability in unconsolidated sediment and areas of high tidal action (Figure 7.1). Roots and leaves are also able to extrude salt to maintain the balance of cellular fluids that allow for normal biological function in saline environments. Mangrove trees also have a specialized form of reproduction through vivipary, i.e., after flowering and pollination, fruits germinate into seedlings, called propagules, while still attached to the tree. Propagules can then drop into the water and disperse via oceanic currents to colonize other suitable areas. This combination of traits has resulted in a pantropical distribution of mangrove forests along tropical and subtropical coastlines (FAO 2007; Giri et al. 2011).
