A Review of Sea-Level Rise Effect on Mangrove Forest Species: Anatomical and Morphological Modifications

Abstract

Mangrove forests are among the most productive and biologically important ecosystems of the world, because they provide important and unique ecosystem goods and services to human society and coastal and marine systems, as stabilizing shorelines and reducing the devastating impact of natural disasters, providing breeding and nursing grounds for marine species, and food, medicine, fuel and building materials (Tomlinson, 1986; Giri et al., 2011). Mangroves are taxonomically diverse trees and shrubs that have evolved independently through convergence (Hogarth, 1999). The principal genera are Avicennia (Avicenniaceae), Laguncularia and Lumnitzera (Combretaceae), Nypa (Palmae), Bruguiera, Ceriops, Kandelia and Rhizophora (Rhizophoraceae), and Sonneratia (Sonneratiaceae) (Tomlinson, 1986). These plants have developed complex physiological, morphological and anatomical adaptations allowing survival and success in the high stress habitat where they inhabit (Hogarth, 1999). They can tolerate the stress of waterlogging and salinity prevailing in coastal environments influenced by tides and have adapted to wide salinity levels, may be influenced by local hydrology and episodic disturbance events (Doyle, 2003). The maximum concentration of soil water salinity that mangrove species can tolerate is suggested up to 155 ‰ with annual averages of 100 ‰ (Tomlinson, 1986). Mangrove forests are generally distributed along tropical coastlines of America, Africa and Asia between 25° N and 25° S, although this range extends beyond due to the movement of unusually warm waters from the equator, including the east coast of Africa, Australia, and New Zealand (Hogarth, 1999; McLeod & Salm, 2006). Nevertheless, sea-level rise in the future could be the biggest threat to mangrove ecosystems as climate change consequence (Giri et al., 2011). In the last century, sea-level has risen 10-20 cm mainly due to thermal expansion of the oceans and melting of glacial ice caused by global warming, with climate models predicting an accelerated rate of sea-level rise over coming decades from 0.09 to 0.88 m (McLeod & Salm, 2006). This will generate salinity concentration, along with rising CO2, and temperature, determining future species distributions, abundances, and viability (Kareiva et al., 1993; Yanez-Arancibia et al., 1998),