Fig:
Pichavaram Mangroves
Mangrove
Ecosystem:
Mangrove
is the very most important ecosystem in the Pichavaram area .Totally the mangrove
covers an area of 12.05kmē. The mangroves of Pichavaram can explain in six zones
viz.
Zones:
Zone I
Zone II
Zone
III
Zone IV
Zone V
Zone
VI
Zone
I:
Avicennia
marina is dominant and shrubby in this region,
where the soil is principally sandy mud. But the sandy area of this is dominated
by the Halophtes, Salicoma
brachiata, Suaeda maritime, Sesuvium
portulascsturm, Arthrocnemum indicum
and Excoecaria
agallocha are
some other plants, which are sporadically distributed here. Sand heaped areas
are of frequent occurrence in this region and these heaps are do not get flooded.
The soil in the heaps is loose as Boearhavia
diffusa, Clerodendron inermae, Croton sp., Eragrosis sp., Geniosporum tenuiflorum,
Lpmoea pascaprae, Mollugo pentaphyilla, Oldenlandia umbellate, Opuntia sp., Phylla
nodiflora, Spinifix littoreus, Thespesia populanea and Vernonia cinerea.
All the plants represented in this zone do not exceed 0.5 m in height.
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Zone
II:
This
zone includes the banks of three creeks lying parallel to the sea shore. The banks
of these creeks show gradation of floristic components from shoreline inwards.
The eastern bank of the first creek shows three belts. The fringe of the shore
ward belt is almost barren, the middle belt is dominated by Salicornia
brachiata and the inward belt is occupied
by Avicennia
marina. The eastern bank of the second
creek also present three belts. The shoreward belt is colonized by Salicornia
brachiata and scrubby Avicennia
marina. The middle one is occupied by pure Salicornia
brachiata vegetation and the inward belt is colonized by Salicornia
brachiata and Avicenia
marina. The middle one is occupied by pure Salicornia
brachiata vegetation and the inward belt
possesses Rhizophora
apiculata and Rhizophora
stylosa,
and the middle belt shows Avicennia
marina whereas
the inner belt is found to have a mixed community of Excoecaria
agallocha and Salicornia
brachiata. The western bank of the third creek presents barren
sand are leading to terrestrial vegetation island. Arthrocnenum indicum occurs
in patches in this zone, which might probably colonize the 'Blanks'.
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Zone III:
Luxuriant mangrove vegetation
exists in this zone with maximum number of species of mangrove plants. The fringing
of theses channels are bordered by
Rhizopora apiculata
and Rhizopora
stylosa. Rhizopora apiculata is dominant along the main channels with
more fresh water. Rhizopora
apiculata and Rhizopora
mucronata are co-dominants along the fringes
of the other waterways. Immediately behind the Rhizopora communities, Bruguiera
cylindrical and Ceriops
decandra are common in shrubby habit. Excoecaria
agallocha also occurs. Just behind the fringe communities of Rhizophora
and other plants, three types of communities can be observed as 1) exclusively
consisting of Suaeda maritime community, 2) mixed communities of Suaeda maritime
and Avicennia marina and 3) exclusively consisting of Avicennia marina community.
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Zone IV:
This
fresh water zone is generally dominated by Acanthus
ilicifolius. The vegetation on the two banks of the Thiruvasaladai
freshwater channel varies considerably. The northern bank is dominated by Acanthus
ilicfolius along with a few representatives of Dalbargia
spinosa, Deris heterophila, climbing
on Acanthus ilicifolius,
Excoecaria agallocha and Sonneratia
apetala. On the southern bank, there is sporadic occurrence of high
Avicennia
officinalis
trees with mixed communities of Arthrocnemum
indicum, Excoearia agallocha, Lumnitzera racemosa, Salicornia brachiata
and Suaeda
maritime.
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Zone
V:
The
western bank of the channel is rich with Suaeda
maritime which occupies nearly 3 kmē giving the salt-marsh appearance
along with Salicorina
beachiata. This area is elevated with a vast intertidal area
and with lesser number of gullies. Suaeda
maritime community is noticed here. The soil texture, here, is more
towards silty mud. On the eastern side of the channel towards the sea shore Casurina
equisitifolia is under large cultivation.
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Zone
VI:
This
zone exists nearly to the coleroon estuary. The channel on the landward side is
reacted with Salicornia
branchiate, whereas the channel on the seaward side is occupied by
small shrubby Avicennia
marina. Sand heaps are also noticed with Pandanus
species. Before the joining of the two channels nearer coleroo, the
intermediate region is occupied by Avicennia
marina, Suaeda marina and Salicornia
brachiata.
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IUCN
Status:
Extinct
and Rare species:
Two
mangrove plants such as Kandelia
candel and Bruguiera
gymnorrhiza recorded from this area have become extinct in 19th century
and Xylocarpus
granatum face
now extinction. One rare species, Rhizophora
lamarckii are
reported to be near extinction.
Endangered and Vulnerable species:
Among the 14 species of mangroves
recorded, the IUCN have categorized 10 species of Endangered (EN), 3 Vulnerable
(VU) and 1 Lower risk near threatened (LRnt) (Table 8).
The mudspipper fish, Boleophthalmus boddarti,
belonging to the Family Gobiidae are reported as vulnerable species.
Table 8.
IUCN categorized mangroves of Pichavaram
| Sl.No |
Species
name | Family |
IUCN
status |
| 1 |
Acanthus ilicifolius | Acanthaceae |
*EN |
| 2 |
Aegiceras corniculatum | Myrsinaceae |
EN |
| 3 |
Avicennia marina | Avicennniaceae |
EN |
| 4 |
Avicennia officinalis | Avicennniaceae |
EN |
| 5 |
Bruguiera cylindrica | Rhizophoraceae |
EN |
| 6 |
Ceriops decandra | Rhizophoraceae |
EN |
| 7 |
Lumnitzera racemosa | Combretaceae |
EN |
| 8 |
Rhizophora apiculata | Rhizophoraceae |
EN |
| 9 |
Suaeda maritime | Polypodiaceae |
EN |
| 10 |
Suaeda monoica | Polypodiaceae |
EN |
| 11 |
Arthrocnemum indicum | Chenopodiaceae |
*VU |
| 12 |
Excoecaria agallocha | Euphorbiaceae |
VU |
| 13 |
Rhizophora mucronata | Rhizophoraceae |
VU |
| 14 |
Salicornia brachiata | Polypodiaceae |
*LR.nt |
*EN-Endangered:
* VU-Vulnerable and *LRnt- Lower risk near threatened
Biodiversity:
Pichavaram
forms a great wealth of biological diversity in mangrove ecosystem. The aquatic
floral community such as seaweeds
(Enteromorpha,Cladophora, Chaetomorpha, Padina, Gracilaria
and Hypnea) and seagrasses
(Halophila and Halophila) occur in this ecosystem.
The
mangroves are distributed in varying degree of abundance, in which Avicennia
marina is the most common species followed by Rhizphora
apiculata, Rhizophora mucronata, Bruguiera cylindrica and Aegiceras
corniculatum.
The
mangroves support an abundant growth of oysters namely Crassostrea
madrasensis, Crassostrea
gyrphoides, Crassostrea discoidea and Saccostrea cucullata.
Commercially important crustaceans
like Macrobrachium malcomsonii, Penaeus indicus, Pmonodon
and Scylla
serrata are commonly available species. Similarly the important fishes
include Mugil
cephalus, Lates calcarifer and Liza
species. Only one species of marine
turtle, the Olive ridley lepidochelys olivacea has been reported.
Pichavaram is an important habitat for a variety
of resident and migratory waterfowls and other birds. About 200 species of birds
have been recorded; among those Egretta
garzetta, Egretta intermedia, Nycticorax
nycticorax, himantopus himantopus, Anatomus oscitans, etc. are
notable. The mammals known to occur in this region include the common Otter
Lutra lutra and the jackal Canis
aureus.
Fishery Resource:
Pichavaram
mangrove is very good potential fishery source. Prawns constitute the bulk (81.1%)
of total fisheries, of these,
Metapenaeus monoceros(29.5%), Penaeus
indicus (17.6%)
and Metapenaeus
dobsoni (17.4%)
are worth mentioning. The crab fishery is dominated by Scylla
serrata and Portunus
pelagicus contributing 4.1% of the total catch. Fishes contribute
with 7.1% of the total annual landing by mullets (Mugil
cephalus, Liza dussumieri, Liza macrolepis,
Liza tade and Osteomugil
speigleri).
