1. What is mangrove? (Definition)
The word “mangrove” refers to tropical plants and their communities growing in the inter-tidal zone, and their area along the coast-line (e.g. seashore, estuaries, lagoons and river banks and is influenced by tidal condition. According to FAO (1952) mangrove is defined as trees and bushes growing below the high-water level of spring tides (see tide at picture above. It taken by KeSEMaT in its Arboretum - Teluk Awur Jepara Central Java).
Mangrove includes a large variety of plant families that adapt to particular environment Tomlinson (1986) classifies mangrove species into (three) groups, i.e. major component, minor component and mangrove associates.
2. Where is mangrove found? (Habitat)
Large mangrove trees are found along muddy sheltered shorelines free form ordinary strong winds currents (e.g., mouth of big rivers). They can also grow on sandy and rocky shores, coral reefs and oceanic islands. While brackish water is not essential for mangrove’s growth, it thrives if there are plentiful supplies of fine sediments and fresh water.
Dense wide spread mangroves forests grow at the mouth of big rivers in the tropics, but in an area where mountains come close to the seashore, the forest growing along the coastline is limited and narrow in size. The extent of mangrove forest is most influenced by hinterland topography.
There is a close relationship between water conditions and mangrove vegetation. Mangrove may, in some places, show a certain degree of zonation tending to change from water edge towards inland. However, this sometimes depends on the undulation of the forest floor or creeks within the area which is typically schematic and generalized profile of a tidal flat in Bali and Lombok.
3. Where is mangrove distributed? (Distribution)
There are many species of mangrove around the equator. The farther away from the equator, the fewer the mangrove species are, and the smaller the trees will be. The northernmost location of mangrove is the southern Kyushu Island of Japan, where there is only one species (Kandelia candel) is found while the southernmost location is New Zealand’s North Island where the only one species Avicennia marina is identified.
There are approximately 70 species of true mangrove species (major and minor component). 40 of them grow in Southeast Asia; approximately 15 in Africa; and about 10 in America.
Soemodihardjo (1993) substantives that mangrove in Indonesia consists of 15 families, 18 genera, and 41 species and 116 associates. Hence, a total of 29 true mangrove species have been found in Bali and Lombok.
The world’s total mangrove area estimated using remote sensing technology, is approximately 18.1 million ha (ISME, 1997). The data obtained from IUCN in 1983 indicates that the mangrove area covers a total of 16.9 million ha. It should be understood, however, that this figure does not cover all countries. On the basis of studies conducted by FAO/UNDP (1982), the total mangrove area in Indonesia was 4.25 million ha. By 1996 the figure decreased to 3.53 million ha as mangrove forests have been rapidly deforested/degraded due to land conversion and over utilization of resources due to rapid population growth and vast economic development along the coastal areas.
4. What is the structure of mangrove? (Structure)
Dominant elements of mangrove forests are trees growing up to over 30 m tall, many of which form a dense closed canopy. Many other plants and fauna species are also typical or exclusive to mangrove forests. Local topographical and hydrological characteristics, type and chemical composition of soils and tidal regime determine the type of mangrove ecosystem established at any given places.
As indicated earlier mangrove species are classified into three: major component, minor component and mangrove associates. Below is an outline of the three classifications.
Major components: develop morphological specialization, e.g. aerial root system and special physiological mechanism for salt exclusion to suit the mangrove environment. The components are taxonomically isolated from terrestrial relatives occurring only in mangrove forests and forming pure stands, but never extending into terrestrial communities.
Minor Components (coastal plants): are not conspicuous elements of vegetation which may occupy peripheral habitats and which rarely form pure stands.
Mangrove associates: never grow in true mangrove communities and may only be found in terrestrial vegetation.
5. What characteristic do mangrove species have? (Morphological Characteristic)
Remarkable morphological characteristic of mangrove species appear in their root system and fruits as elaborated below.
The soil of mangrove habitat becomes anaerobic (air-free) when it is under water. Some species develop a typical root system called aerial root suitable for anaerobic soil conditions.
There are several types of aerial roots, i.e., stilt, pneumatophores, knee-, and plank-roots. Aerial roots serve gas exchange function and air storage for respiration during submersion.
All mangrove species produce fruits usually dispersed by water. The fruits take several shapes such as cylindrical, round, and bean-like.
1. Viviparous seeds
Rhizophoraceae (Rhizophora, Bruguiera, Ceriops, and Kandelia) form cylindrical (stick-like) fruits commonly known as viviparous seedlings. Rhizophoraceae seeds germinate in the fruits and the hypocotyls of seedling protrudes and expands from the fruits when it is on the (parent) tree.
2. Cryptoviviparous seeds
Avicennia (bean-like fruits), Aegiceras (cylindrical fruits) and Nypa form cryptoviviparous fruits of which the seeds germinate but are covered with their pericarp (fruits skin) before detaching from their (parent) tree.
3. Normal seeds
Sonneratia and Xylocarpus form ball-shaped fruits with normal seeds. The fruits of most other species are capsular in shape, just like fruits containing normal seeds. The fruits should undergo a system that enable them to break and scatter their seeds when reaching the water.
6. How do mangrove species grow? (Physiological Characteristics)
The major and minor components of mangrove species grow well unaffectedly by salty water. However, if the water is too salty, the tree does not grow very high. It should be noted that mangrove species grow faster in fresh water than in salty water.
Through their salt glands, several mangrove species develop a system enabling them to grow in high salinity water condition. Avicennia, Aegiceras, Acanthus and Aegialitis control salt balance by secreting salt from the glands (Tomlinson, 1986). There are a large number of salt glands on leaf surfaces which may be crystallized and easily observable.
Other species, Rhizophora, Bruguiera, Ceriops, Sonneratia, and Lumnitzera control the salt balance in a different way such as by losing old leaves containing accumulated salt, or by applying osmotic pressure in the roots. However, detailed explanation regarding this issue is not convincingly supported by any studies.
7. What does the mangrove produce? (Utilization)
Timbers produced from mangrove forest can be used for housing materials, furniture, ships or boats and chips for pulp or paper. The logs of Rhizopora or Bruguiera are used as pillars as they contain a good amount of tannin, and strong astringent substance.
Mangrove firewood and charcoal are widely used as a good fuel for cooking in tropical countries. Mangrove charcoal is exported to many different countries including Japan where it is locally named as “Nan-yo Bincho-tan” (Southern good charcoal).
In arid region where there are little grass and trees, mangrove, which has abundant leaves all year round, is an important source of food for cattles, donkeys, camels and goats.
Mangrove hah also many other uses such as: (i) tannin, pesticide, dyes and chemical are extracted from their bark; (ii) the fruit of some species are used for food; and (iii) the sap produces sugar and alcohol.
8. What roles does mangrove play? (Function and benefit for public)
Mangrove forests play many important roles and serve many different functions for public benefits, such as protection against high waves, strong winds, sea breezes and coastal erosion.
Mangrove forests on the coastline break waters to protect people’s lives and houses from high waves caused by typhoons. They also protect the crops from damages caused by sea breezes blown in by strong winds.
Old mangrove leaves and branches falling into the soil will be decomposed by micro-organism which will later function as a food source for planktons. The planktons are a food source for young shrimps, crabs and fish, which in turn, a food source for bigger living organism such as fish, birds, and mammals. This is called the food chain, in which mangrove plays a vital and essential role in key resources supply.
During a high tide, mangrove forests become part of the ocean. This is a paradise where fish gathers due to abundant food supply. The thick mass of mangrove trunks and stilt root are also a safe heaven to hide especially for young fish and shrimps.
Mangrove forests are also the paradise for birds where they easily search food and raise their offspring safely.
It can now be stated that mangrove forests provide a much better living conditions for fauna as well as contribute significantly to not only direct products but also stable yields of fish, shrimp and crabs.