Mangroves are salt-tolerant forest ecosystems found mainly in tropical and sub-tropical inter-tidal regions of the world. They are trees or shrubs that have the common trait of growing in shallow and muddy salt water or brackish waters, especially along quiet shorelines and in estuaries. They exhibit remarkable capacity for salt water tolerance. Typically they produce tangled masses of arching roots that are exposed during low tides. Some mangrove roots extend above the water in the form of specialized vertical branches, called pneumatophores, which act as aerating organs and therefore are also known as respiratory roots. Among mangroves, there are some that prefers a daily tidal wash while others find their optimum conditions in shallow areas subject to occasional high tides. This process governs their distribution. Mangroves do not appear on sandy beaches and rocky shores. A muddy substratum of varying depth and consistency is necessary for their growth. They are rarely found near the open sea or mouth of an estuary, but abundantly found in sheltered places like creeks and estuaries. The eco-system is highly fragile, subjected to long duration of intrusion as well as incessant physiological and morphological stresses, salinity effect, aeration and onslaught of wave action.

Salient features of mangroves

• Mangroves are practically evergreen with thick leathery leaves designed to minimize transpiration.
• Root system is adapted to the peculiar conditions found in the mangrove forests such as still root in Rhizophora and knee roots in Bruguiera. Pneumatophores (breathing roots) are sent in profusion in Sonneratia and Avicennia.
• Viviparous germination where the seed germinates while still on the tree and falls down in the germinating condition with a long radicle- characteristic of Rhizophoraceae.

 Status of Mangroves of Andaman & Nicobar Islands

            Total area under mangrove vegetation in India is 4827 sq.km. as per the latest estimate of the Forest Survey of India (1999 ). Out of this, 966 sq.kms. area of mangrove vegetation occur in Andaman & Nicobar Islands which means that one fifth of the country’s total mangroves occur in these islands. In Andaman district, area under mangroves is 929 sq.kms., while in Nicobar district mangroves occupy 37 sq.kms. Area wise A & N islands are third in the country after W. Bengal and Gujarat, but as far as density and growth are concerned, mangroves of these islands are probably the best in the country. The mangrove vegetation of these islands constitutes 9.4% of the land area or 10.85% of the total forest area. Mangroves occurring in these islands are mostly fringing the creeks, backwater and muddy shores. Along the creeks the width ranges from 0.5 km. To 1 km.at places this salt tolerant community is found on rock shores subjected to tidal action and regular deposits of mud. Luxurient mangroves can be seen in Shoal Bay (South Andaman), Yerrata Jetty in Rangat (Middle Andamans) and in Austrin Creek (Mayabunder).

 IMPORTANT MANGROVE SPECIES OF A & N ISLANDS

           About 60 species of mangrove occur through out the world. Asia is the richest region of mangrove species diversity with 44 species reported to occur. As per available information from various sources 27 tree species, 5 shrubs, 1 climber and 2 species of palms and ferns each belonging to 17 genera are reported to occur in the mangrove ecosystem of these islands. Important mangrove species found in these islands include- Rhizophora mucronata, R. apiculata, Bruguiera gymnorrhiza, B. parviflora, Avicennia officinalis, A. marina, Ceriops tagal, Heritiera littoralis, Sonneratia caseolaris, S. alba, Exoecaria agallocha, Xylocarpus granatum, Aegiceras corniculatum, Scyphiphora hydrophyllacea, Nypa fruticans etc.

Acanthus ebracteatus A shrub glowing upto 2 m height, has stout, stiff, cylindrical branches; spinulous leaves and white flowers. Commonly found in Oral Katchal, Baratang, South Andamans and in Nicobar Islands also.

A.ilicifolius   Similar to A.ebracteatus in morphology. Flowers in spikes, bright blue with bared anthers. Found in South Andaman, Ritchie’s Archipelago and Baratang.

A.volubilis  A slender unarmed climber with entire oblong-oborate leaves and white flowers. Rare in distribution, found in Oral Katchal, Baratang, Burmanala and Rutland.

Aegialitis rotundifolia   A soft wooded shrub with a club shaped stem; leaves simple and alternate; Flowers white or pale yellow. Very rare, reported to found in Andaman.

Aegiceras corniculatum  A small shrubby tree, stem smooth, bark brown with reddish tinge; flowers white in umbels, terminal or in axillary branchlets, fruit cylindrical, acute, 3 cm long, germination viviparous. Not very common, found in North and South Andaman.

Avicennia marina  Known as ‘white mangrove’ because of its distinctive smooth white bark. Leaves glaucous, flowers yellow or white Germination viviparous. Not found in Nicobar islands.

A.officinalis A tree with smooth yellowish grey bark. Leaves not glaucous, flowers yellow or sessile. Commonly found in Andamans forming pure patches along sea-shores or muddy flats.

Bruguiera cylindrica A medium sized to tall buttressed tree with smooth, grey bark. Leaves 7 to 10 cm. Long. Flowers white, km. long with very small caylxtube, Viviparous germination. Rare, found in Middle Andaman end at Sipighat in South Andman.

B.gymnorrhiza A straight stemmed, butteressed, tall tree with a dark coloured cracked bark. Leaves 10-16 cm long, crowded at the ends of branchlets; flowers solitary. Knee roots are prominent. Most common mangrove found through out A & N Islands.

B.parviflora A medium-sized columnar buttressed tree with preumatophores and dark orange coloured bark. Rare in distribution, found in Andaman and Car Nicobar.

B.sexangula  A medium to tall tree bearing knee-like pneumatophores and buttresses more like B.gymnorrhiza; bark dark-grey or pale brown. Less common, found in South Andaman and Nicobar islands.

Ceriops decandra A 2 to 3 m tall shrub forming small butteresses; branches thick, leaves simple and opposite; flowers di-to tri-chotomous in condensed axillary cymes; hypocotyle 9-15 cm long, sharply ridged, fruit one celled one seeded. Forms thin knee-like pneumatophorh. Very rare.

C.tagal A small 1 to 2 m glabrous shrub. Flowers white in axillary cyme, hypocotyle 15-25 cm long and terete or slightly ridged. Very common in Andamans but very rare in Nicobars.

Cynometra ramiflora A small or medium sized tree with dark coloured bark and paripinnate leaves; sepals not curved, style straight and fruit without a prominent lateral beak. Common in Andamans especially at Chidiyatappu and New Wandoor.

C.iripa  Very rare, differs from C.raniflora by distally curved sepals, bent style and fruits with a prominent lateral beak.

Excoecaria agallocha A commonly found small free with acrid milky juice; leaves 5 to 10 cm long, flowers yellowish green in catkin-like spikes; capsule deeply 3-lobed, Acrid milky juice is poisonous and blisters the skin.

Heritiera littoralis  A very common mangroves bordering other mangroves. A tree of moderate size with thin plank-shaped, often curving buttresses and grey coloured cracked bark. Leaves 10-25 cm long, flowers small creamy-pink and clustered. Fruit woody and compressed campsule. 

Kandelia candel A very rare small tree with smooth, reddish bark.

Lumnitzera littorea A tall tree with a dark coloured, rough, fissured bark. Flowers bright scarlet, in terminal recemes. Fruit bears knee-shaped roots. Common in Andamans particularly in Baratang, Ritchie’s Archipelago and Manjeri.

L.racimosa A small tree with similar leaves as in L.littorea, but flowers are white in axillary racemes. Less common, found at Wandoor, Ritchie’s Archepelago and Car Nicobar.

Nypa fruiticans A palm with underground stems; 5 to 7 m long pernate, leaves, fruit 6 to 15 cm long turbinate, fibrous with a large white seed. Found frequently in Kadamtala, Mayabunder, South Andamans and Galathea river basis.

Phoenix paludosa An erect palm upto 7 m height, with 1 to 2 m long leaves. Leaflets are arranged in pairs and folded inwards along the length. Flowers yellowish in compact spikes; Fruits 1 cm. in diameter, orange red but turns black when ripens. Palm bears thin knee-like pneumatophores.

            Not very common. Found in Middle Andaman and New Wandoor.  

Rhizophora apiculata  One of the most commonly found species and distributed in almost all islands. A moderate sized much branched and rough barked tree. Flowers sessile, petals glabrons, radical cylindrical upto 30 cm. long.

R. lamarckii  A moderate sized tree with grey to brown bark. Petals hairy and inflorescence in leaf axils; considered to be a hybrid of R. apiculata and R.stylosa.

R.mucronata One of the most commonly distributed mangrove species. A moderate sized tree with a very rough bark. Flowers yellowish-white; Inflorescence two to eight flowered.

 R. stylosa A columnar shrub or tree reaching a height upto 20 m., bark grey or brown black. Stem has forking still roots at base. Flowers in subterminal axillary cymes. Hypocotyle slender, upto 40 cm. long. Not very common, can seen at Chidiyatappu.

Scyphiphora hydrophyllacea A spreading glabrous shrub growing to 2 m height. Inflorence in dense many flowered cyme. Fruit a hard cylindrical drupe about 6 mm long, longitudinally eight ribbed and divided internally into four one seeded cells which eventually separate into four pyrenes. Commonly found as secondary association especially in South Andamans.

Sonneratia alba A not commonly found, much branched tree reaching upto 12 m. Negative geotropic stout conical pneumatophores are characteristic of this genus. Bark orange-brown, branches silvery-grey, smollen; leaves leatherly and glabrous. Fruit 3 cm. long with numerous small seeds. Found at Chidiyatapu, Bambooflat and Ritchie’s Archepelago.

S. apetala A moderate sized evergreen tree upto 15 m height with usual conical, slender prneumatophores. Flowers three large with four lobed calyx. Not commonly found. Can be seen in S.Andamans and Ritchie’s Archipelago.

S.caseolaris A moderate sized tree with a dark brown rough bark. Flowers terminal, solitary with red-tinged anther filaments. Very common from N.Andamans to Great Nicobar.

S.griffithii A very rare moderate to small sized tree. Flowers large with 6-8 lobed calyx. Fruit 2.5 to 5 cm in diameter, flashy.

Xylocarpus granatum Very common moderate sized tree with flat buttresses and smooth yellowish-grey bark. Flowers cream coloured. Fruit leathery and smooth, 18 to 25 cm in diameter.

X.mekongensis (=X-gangeticus) – A very rare (Baratang and New Wandoor only) moderate sized up to 20 cm high preumatophores.

X.moluccensis  Commonly seen in most places in Andamans. A moderate sized tree with plank-shaped buttresses and grey bark with longitudinal fissures. Flowers pinkish yellow and fruit is of the size of an orange.