Introduction Mangrove Ecosystems and it’s Status
The word “Mangrove” is derived from the Portuguese word “Mangue” and a English word “Grove” The corresponding French words are “Manguler” and “Paletuvier” (Macnae, 1968 ; Kethiresan & Bingham, 2001). It is believed that all these words originated from the Malaysian word “manggi manggi” meaning “above the soil”. This word is no longer used in Malaysia but is used in eastern Indonesia to refer to Avicennia species (Kethiresan & Bingham, 2001).
Mangrove ecosystem is referred to as Mangrove Tidal Forests (Mepham & Mepham,1985; Jayasooriya, et. al, 2006), Inter-tidal Forests (Saenger, et al., 1983; Jayasooriya, et. al, 2006) or Coastal woodlands (Saenger, 1983; Jayasooriya, et. al, 2006).
The term mangrove is simply used to describe a wide variety of taxonomically unrelated tropical trees and shrubs which share common characteristics. It is an assemblage of halophytic, evergreen, woody plants and shrubs which live between the sea and the land that are regularly flooded by tides (Miththapala, 2008). The mangrove environment exists in conditions of high salinity, extreme tides, strong winds, high temperature and muddy, anaerobic soils. Mangroves are the only group of plants which have highly developed morphological and physiological adaptations for those extreme environmental conditions (Kathiresan & Bngham, 2001).
Mangroves perform a vital ecological role, providing habitats for a wide variety of species and mangrove forests together with their adjacent intertidal environments are among the most productive ecosystems on earth and play a vital role as the major primary producer in estuarine ecosystem (Zara, et al, 1996, Bhatt Kathiresan, 2012). It also supports to increase secondary and detritivorous production within the ecosystem. The muddy and sandy sediments of the mangrove ecosystems are home to a variety of epibenthic, infaunal and meiofaunal invertebrates as well it provides breeding and feeding grounds for a large variety of fish species with good protection (Kathiresan Bngham, 2001). Mangrove ecosystem have also been considered as low cost and high efficiency wetland system for the treatment of municipal waste water (Liu, et al., 2009). The mangrove ecosystem limits the impacts of storm surges and protects coastal areas from storm impacts (Das & Crepin, 2013).
Destruction of mangrove will accelerate release of the large quantities of stored carbon and increase global warming and other climate issues (Ramsar Secretariat, 2001; Kristensen et al., 2008; Gilman, et al, 2008). According to the products and services provided by the mangrove ecosystem, the value of it has been estimated to be USD 200,000 – 900,000 ha ‘(Wells, et al.; 2006,Gilman, 61(21,2008).
Mangrove forests are found in very hostile environments with wide fluctuations of temperature and salinity. The plants found in mangals are generally categorized as true mangroves or core/exclusive mangrove species and mangrove associates. True mangroves can be found only in mangrove areas or the areas containing high salinity and the associates can be found in mangrove areas as well as other freshwater marshes (De Silva & De Silva, 2006).
Mangroves are strictly restricted to the tropical and few warm temperate countries between latitude 30° north and 30° south, with the largest proportion found between latitude 5° north and 5° south (Bhatt & Kathiresan, 2012 ). The estimated spatial extent of the mangroves in the world is about 18 million hectares spreading across 123 countries and territories (FAO, 2007). Nearly 75% of world’s mangrove ecosystems occur in just 15 countries. About 90% of mangroves are found in developing countries, though they are nearing extinction in 26 countries. Their long term survival is threatened by fragmentation of the remaining ecosystems. Due to this ecosystem services of mangroves will be lost entirely within the 3next 100 years (Duke, 2007). Globally, mangrove habitats continue to disappear, the annual rate of loss was 0.66% between 2000- 2005 (FAO, 2007).
Adaptations of Mangroves
The mangrove environment has some special physicochemical characteristics of salinity, tidal current, winds, high temperature, and muddy anoxic soils. Plants of the environment are able to adapt themselves to particularly all types of adverse conditions (Kathiresan & Bngham, 2001). Mangrove species have developed many morphological and physiological adaptations to survive in the intertidal habitat. In general mangrove species share four important traits that allow them to live successfully in adverse environmental conditions. The most obvious adaptation is the development of aerial roots such as pencil roots (Avicinnia sp.), peg roots or pneumatophores (Sonneratia sp.), knee roots (Bruguiera sp.), plank roots (Xylocarpus sp.) and prop roots (Rhizophora sp) (Plate 1) associated with gas exchange in this anaerobic soil conditions of the mangrove environment (de Silva, 2006).
The fruits or propagules of many mangrove species are viviparous, which means that young individuals start growing trees and a root while attached to the parental trees. It is a critical morphological adaptation to survive in the muddy habitats. Proagules when dropping at low tide, will be planted by themselves under the parental tree or when dropping at high tide they can move away from the parental trees. This mechanism is an important strategy to maintain the vegetation structure and the composition or the vegetation structure dynamic of the mangrove ecosystem (Plate 2).