survey of mangroves of cochin -...
TRANSCRIPT
SURVEY OF MANGROVES OF COCHIN
u Introduction
Brief History of Cochin
Geography of Cochin
u Materials and Methods
Sampling Stations Selected
Procedure of Survey
u Observation
u Discussion
SCJRVEY OF MANGROVES OF COCHlN
INTRODUCTION
Kerala lies towards the South - West coast of India, a segment barred by
the Westerrl Ghats It extends between the latitudes 8" 18' and 12' 48' north and
longitudes 71" 53' and 77" 24' east with an area of about 38863 sq. kms (Ganeadharan,
1999). Length of Kerala coast is approximately 580 km with a northern limit at
Manchesuaram and Southern limit at Pozhiyar. Temperature varies between 25' to 35' C
during summer. and 20" to 30" C during winter. The area under wetland in Kerala
estimated using satellite remote sensiny data is 127930.07 ha, out of which inland
uetlands cover 31199 57 ha (Anonymous, 2000~). hlastaller (1996) reported that some
70,000 ha of rliangroves of Kerala were cleared at the turn of this centuary. hlangrove
forest area of'the Eranakulam district is estimated to be 250 kmz (Anonymous; 1999a)
Biological diversity is now increasingly recoynised as a vital parameter to
assess global ar~d local envirorimental changes and sustainability of developmental
activities (Lovejoy. 1995). M)el-s (1990) identified areas of exceptional species richness
and endemicity on the global scale and referred them as 'hot spots' of diversity. A broad
scale classification of different types of landscapes i:r a use&] step towards the
biodiversir) assessnient (Nagendra and Gadgil, 1998). A survey is necessary to
understarid thc diversity of species in a vegetation. Diff'erent methods such as direct
countiny. quadrat ar~d transect can be employed to study the vegetation of an area. Line
transect methods were employed by Kunte el crl (1999) for the biodiversity study in
Western (illalr
Mangrove vegetation in Cochin area are seen along with the back water
channels and along the banks of estuarine water bodies, in the form of patches or
narrow continuous belt. Very little is known about the diversity and distribution patterns
of mangroves of Cochin area. An intensive survey programme was conducted in the
Cochin area for inventorying and monitoring the species diversity of mangroves of
Cochin Data were collected by field observations, ac,tual measurements, personnel
interviews, photography and through chemical analysis of plant, water and soil,
General information regarding the Cochirl area are given below (after
Naseer, 1996)
District - Ernakulam
Area - 87.341 sq. km.
Population - 11,39,543 (1996 census)
Latitudes and Longitudes - 9' 58' North, 76' 17" East.
Altitude
Rains
- Sea level
- South West monsoon (heavy rainfall) : June -
August, North East monsoon (light rainfall):
September - November
Annual rainfall - 310cm.
Climate - Moderate through the year
Temperature
Minimum : 2 2 . 5 ' ~
- Summer < Maximum : 35'C
Minimum : 20' C
- Winter < Maximum : 3 2 ' ~
A Brief History of Cochin
Coch~n came into existence as an important port in 1341 A D when the
flooded Periyar river destroyed what up to then had been a world renowned port,
Kodungallur. just north of Cochin. It is believed that the formation of a cluster of islets at
the end of the river Periyar, whic,h is emptying into Cochin backwaters, is the result of the
deposit of silt due to the catastrophic deluge which occurred in 1341 AD (Gopalan,
1992). The massive uncontrolled flood eventually lead to the accumulation of large
amount of silt giving birth to the various islets in the Cochin backwater region of
Vembanadu lake. The Vembanadu lake that we see now was also shaped at that time. The
new Cochin port found its echo in the neighbouring villages of Vytilla, Edapally,
Mamangalam, Palarivattom, Ernakulam, Vypeen, Vallarpadom, Thopumpady,
Kannamali. Edakochi and Palluruthy, which began their integration into Cochin from
then. The ideal location of its natural harbour helped Cochin emerge as a bustling centre
of commercial activity. After independence, the corporation of Cochin was formed in
1967 and the city took its present shape.
Geography of ('ochin
('ochin has one of the best natural harbour!; in the world. The Cochin back
water extends along the western side of the Cochin area which in turn is the northern part
of the Vembanad lake. The Ve~nbanad lake is the biggest and most extensive one in
Kerala I t extends between 9":s' and 10' 10' N and longitudes 76' 13' and 76' 31' E. The
lake covers an area of 7503 8 ha and Cochin backwater covers 2257.89 ha. Near the
nor their^ end of this lake is situated the port of Cochin where the lake is permanently
connected to the sea by a narrow channel. During flood tides the sea water (Lakshadweep
sea) enters the Cochin estuary via Cochin barmouth (12 m depth) and the flow reverses
during the ebb tides. In Cochin backwaters there exists many thickly populated islands.
Vembanadu lake and connected Cochin backwaters are considered to be
an example for mangrove estuary. The rich particulate organic matter derived primarily
from the decomposed mangrove foliage is nutritionally very rich and hence forms an
important source of food for juvenile fishes and shrimps, Formerly, a highly productive
lagoon system bordered by lush mangrove forsets were present in the Cochin area, but
now the bay 1s secluded. On land Cochin area is midway between Alapuzha and Trichur
districts on south and north sides respectively. The main occupation of the people apart
from trading is fishing; but it has prosperous agncultural hinter- land which benefits from
the rich alluv~al soil of the region.
MATERIALS AND METHODS
The Sampling Stations Selected for the Present Study
After conducting a preliminary survey in and around Cochin, eleven
mangrove growing sites were identified (Figure 5) where coastal fishery and traditional
aquaculture are in vogue. All these sites had a mangrove distributional area of two
hectare and above The sampling sites were widely separated, had dissimilar sediment
character~st~cs, and u'ere influenced highly by monsoon These stations were selected so
as to have a M ~ d e representation of the prevailing complex environmental conditions.
Station No. I Katlnamali
The first station selected was at Kannamali, a typical mangrove area near
Chellanuni This station is directly under the influence of 1,akshdweep sea. Mangroves of
this area protect the coastline by acting as wave break. They stabilise coastline, promote
coastal accretion and serve as natural barriers against torrential storms. In this way they
preserve the coastline and prevent shoreline erosion.
Station No. 2 Kumbalangi
The station 2 is Kumbalangi island, a typical coastal area, lying parallel to
the Perumbadapu, coastal village. Kumbalangi is thickly populated island, where due to
encroachment to the estuarine domain not only the mangrove vegetation and its habitat is
reduced but also the ecological niche of its coastal belt is changed.
Station No. 3 Kumbalam
Station three is Kumbalam near Thripuriithura which is more or less
completely surrounded by Cochin backwaters. This is a thickly populated area and
mangrove ecosystem of this region is subject to population pressure. Extensive land
filling has affected the mangrove vegetation. This station is extended upto Panangad.
Station No. 4 Nettoor
Fourth station is Nettoor near Thirunettoor Railway station. A number of
creeks and canals are found to traverse the area fringed with mangrove plants.
Eranakulani - Alapuzha railway line and National highway 47 are also passing the
through th~s area. Extensive land filling has been made in this station through very thick
mangrove forests
Station No. 5 Rlangnlavanam
Mangalavanam mangrove forest is located i n the heart of the Cochin city
on Dr Salini Ali Road near the Hish Court of Kerala This is declared as a bird sanctuary
by the Governnient of Kerala This area is considered to be hnctioning as the lungs of
the city Large scale storage tanks for petroleum products of Indian Oil Corporation is
situated verv close to this station
Station No. 6 Panambukad
Station six selected for this investigation is a small island in Vypeen block
Panambukad. This island is surrounded by the estuarine waters of Cochin backwater. The
island has an area of 9.27 sq, km. Except for the human dwellings, the island is occupied
by traditional prawn cum fish farms fringed by mangroves. This station is coming under
the purview of Goshree project proposal of district administration. The project involves
the land filling of several hectares of estuarine habitat for the construction of a network of
bridges
Station No. 7 Puthuvypu
This station is situated half kilometer away from lighthouse of Vypeen
island An extend of 101 ha of land supporting mangroves in patches exist at Puthuvypu
There are several tidal channels. sand pits and creeks which support good mangrove
vegetatiotr
Statiou No. 8 Pallipuram
Station number 8 is a Pallipuram which is situated towards the northern
end of Vypeen island near Munambam. This area is lying parallel to the Lakshadweep
sea with a direct tidal influence Lying on two sides of the Pallipuram are backwater.
There are many channels and creeks fringed with luxuriant mangrove vegetation. Isolated
species could also be seen in detached water bodies and reclaimed lands along the coastal
tract.
Station No. 9 Karumallor
Station number 9 is Karumalloor situated near Aluva. This area is directly
connected by backwater system, which is highly influenced by tidal incursion. Most of
the mangrove area of this site has been converted into coconut plantation, paddy fields
and used for human settlement
Station No. 10 Pattanam
The area ofthis station is more or less completely land filled. A long canal
is traversing through this station. Patches of mangrove species are growing along the
banks ofthis canal
Station No. I I Moothakunnam
Station number I I is at Moothakunnam, which is also a land filled area
surrounded b!; creeks on one side and backwater on the other side. Patches of mangroves
are yrowing here and there. Hiyhly restricted occurrence of the mangroves of this area is
directly attributed to the gross interference of man's activities.
Procedure of Survey
In the present investigation the distribution and density of the mangrove
vegetation and the varying hydrological conditions of the estuary were studied for 3 years
from Januaq 1996 to January 1999. In the first phase of the study a detailed survey of
mangrove tlora was conducted during the year 1996. Documents regarding the number of
species, total number of specles, area occupied, nature of spread, morphological
peculiarities, special adaptations and other details connected to the mangrove and
associated tlora were collected from each station during the survey. Further changes in
the community area of mangrove spread and depletion were noted time to time and
updated till January IO99.
111 order to study the distribution pattern of mangrove and associated
species, quadrat analysis were done in all the stations (Michael, 1984). After conducting a
preliminary survey size of the quadrat was determined as 10 x 10 m. the number and
position of all species at each station were accurately marked on a chart. To confirm the
precision of the data quadrats were taken in each station at different locations.
Phytosociological analysis such as density, abundance and diversity were calculated from
the quadrat data (Trivedy et a]., 1'187; Krebs, 1999). Diversity Index was calculated using
the following Shannon-Wiener fUriction
S HI = c (pi) log 2 pi)
1 = 1
Where H' Information content of sample (bitsfindividual)
or
Diversity Index of the species
s - Number of species
pi = Proportion of total sample belonging to i th species.
Theoretical maximum diversity was calculat.ed using the equation
L,og10 s H ,,, = log 2 S =
-
120g,o 2
S = Number of species
Ratio of observed diversity to the theoretical maximum diversity was also
computed
where E = equitability (range 0 - 1:)
D~stribution and succession pattern of mangrove and associated flora were
assessed from the data collected
Flowering twigs of mangroves and associated species were collected form
all the eleven stations. Analysis of habit, vegetative characters, morphological features
and adaptations were done. The species of mangroves and associated flora were
identified based on its vegetative and floral morphologica.l characteristics with reference
to the published flora (Gamble, 1967; Dewit, 1967; Matthew, 1983) and by comparing
with the herbarium specimens The distribution map of the mangroves in all the selected
stations of [ochin area were prepared.
OBSERVATION
In Cochin area ten true mangrove species belonging to seven genera were
enumerated through the survey (Table 1). Table I1 a, Table I1 b and Table 111 show the
mangrove spread area, total number of species, density and diversity at each station. In
the Cochin area Acattthrrs i1icrJol;zr.s L. was found in maximum number followed by
A~licettt~ia offiotra1i.c L. Rhizophora carzdelaria DC. and Kattdelia candal L. were found
in minimum Maximum diversitv was noticed at Kumbalam station. Different mangrove
species of Cochin area are known in different local names based on their colour and
special features Accordingly red mangrove (Rhizophora species), orange mangrove
(Hrr~gzriercr species), black mangrove (Aiicetutia species) and milky mangrove
(Excoecuntr species) are recognized. Acarlthrrs i/ic~fo/;lrs L. was found distributed in all
stations except Karun~allor. In Karumallor, Excoecaria itzdica Willd. was observed. This
species was found endemic to this region. Other species of Excoecaria was represented in
other stations A~Vceta~icr c?Cficirrtrlis L. was surveyed in almost all stations except in
Pattanam and Kammalloor. At Pattanam only are species such as Acattfhlcs ilicfotizrs L.
was present. Maxinl~nn number of mangrove species were observed at Panambukad
where seven species of mangrove plants were seen. Katid~lia cartdel L. and Riti:ophora
cc~t~delcrrrcr DC. were obsewed at Nettoor and Panarnbukad stations respectively.
H ~ I I ~ I I I L ~ ~ . I I fi).n~t~orhizl~ Lamk was observed in Puthuvypu and Panambukad. However
this plant was also scarcely distributed at Mangalavanam. It was noticed that mangroves
of Mangalavanan] station is terribly affected by the urbanization and oil spill form the
nearly located storage tanks of Indian Oil Corporation. Panambukad, Karumalloor and
Nettoor stations showed the presence of Sotrtlerafia cuseolcrri.s L. A depletion of
Table 1 The mallgrove plant species at different sampling stations observed during the survey
I i 1 ~~ ~ - - L . i~ ~ - I
t~ 1 + - - + ~ - - + + ; i 1 . 4 ~ , 1 ~ c ~ / f t l t ~ / o/~lclrirr/i.c L. Aviceniaceae - + i~ I ,~ ~
+ 1 J 1 . . + j _
I I ! I . I / / / I ~ / . \ t / i f / . I. .\cantllaceae + + + 1 q - + ! +
1 . 1 , . I I i<hizo!jhor.o mrrr~!.o!itr!rr + i + i ~ - - : + i
L a n k
I ilhiropho/.n cntr~Jc/trr.;n
!
cylitrdric~r m
i Rhizophoraceae + - + + - -
WA -
6 Rrrrgr~iercr gymtlorhyzn Rhizophoraceae - - - + + + - - - Lamk.
-
7 Kntidrlin catidel L. Rhizophoraceae - + - - - - - 8 .\i)nr~erntic~ co.seo/aris L. Sonneratiaceae - - - + - + - - + - . 9 Excoecnrin npllocha L. Euphorbiaceae + - - - - + + - - - 10 Excoecnrin it~dicn Willd. Euphorbjaceae - - - - - - - + - -
+Present, - Absent.
Table 11 a
The density of mangrove species of the various sampling stations found during the survey
! Station (1) Kannaniali Station (4) Nettoor 1 - - - - - - -- -. ~ ~
Sps. : 7-- i
i - No. + 1 - - M~lngrove -. s ~ i e s present , I Density1 - ~~ ha .+ i - No + Mrl~lgrove speciegresent -~ 1 Density1 ha I I 'I l 1 1 1 1 1 1 1 c 1 1 1 1 1 I 8 ( ~
-- . .- ~
ilicifo1111.r L -----
3 rRhizophorn ~nrrcrot~nttr Lamk.
4 I Rr~rg~riern cy/irrdr.icn W A .
- I I 1 I
-- Station (2) Kumbalangi Station (5) Mangalavanam - Sps. Sps.
Station (3) Kumbalam 40 1
No. 1
2 Acn~r/hlis i1icifolirr.s L Acarrfhrrs i1icifolin.s L
Mangrove species present Avicrrrr~io qfficirmli.~ L
1760
Mangrove species present A~licer~rlia oflcilialis L
3 Rhizophorn mrrcroiratn Lamk. HR I I
Density1 ha 2500
No 1
Mangrove species present A~~icernria qflcirra1i.s L
Density1 ha 2600
1 S P ~ . I ! i No. Mangrove ~~ ~ speries - . present p~~~~-~- -~ ---- ~- M x t ' o v e - 1 i 1 , ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ l ~ ~ ( ~ ~ L . ~ I I ~ I I ~ . s I . ! A I, IL.~II I I ILI O/~~~L~III~ZI;.V . . L
Table 11 b The density of mangrove species of the various sampling s t a t i o ~ ~ s found during the survey
. -- / ~ / ~ i z o ~ h % m~rcror~rrtrr Lamk +-- 1 3 6 0 j ~ ! , h o r . ~ ~ ~ c r / ~ r ~ a m k :-- 1 -- &--++ ---* Rhizophora cn~rdelorirr DC. 4 I L3xcoecnri~~ ogizl loc/~~~ L. 3620 1
2:: Rrlig~iiern cylirldricn \NA. Station (9) Karumallor
/ Station (6) Panambukad Station (8) Pallipuram 1
A- ...+ - - -7 k Rrl~g~~ierrr ,gyn~rrorh~ztr 1,arnk. 100 Sps.
g 7 Sor~ricrofiir crrseo/nri.s L. 160 --
Station (7) Puthuvypu
No 1
2
Mnngrove species present Sorn~ercrficr ct1.seo1~1ri.s L
E:xcoeccrrin irldicn Willd.
Density1 ha 400
1140
720 --
1940
60
40
Sps. No. 1
2
3
4
5
6
Mangrove species present Ai:icer~r~in ofJici11n1i.r L
Ae~urthu.~ i l i c ~ f u l i ~ ~ ~ L pppp--
Rhizophom 1~711cro11nltr 1,amk .-
Hrrlg~~iern cylitldricn WA.
Rrrrgtiern gyn~r~orhyzn Lamk
Excoecnrin ngnflocha L.
Station (10) Pattanam
Sps. No Mangrove species present -~ - Density1 ha 1 1 Acnr1~1~11s i / i c i j L K ~ 2400
Stnlioe (I I ) M o o t h a k u ~ ~ a a m
Sps. No 1
2
--
M a n g r - s p e c i e s present Avicern~in t?ff ici~~al is L
Acnt~thr~.~ i l ic i fol i r~.~ L
Density1 ha 920
3040
Table In
The dominant species and nomberlha of mangroves sampling stations ohsewed during the Suwey. - ~p ---
I-- . - . Station ! Name of Station ! Dominant Species 7 N u m h e r / h a ;
Mangalavanam A i~icrro~in c?fficirmli.s L 2600 2
. ~. . --
Panambukad Rhitcy~horn mi~cronnta Lam k . 1360 I 1
Puthuvypu Hrriprrem cyli~idrica WA
9
10
I 1
Karumallor ppp
Pananam
Moothakunnam
Excorcnrin irrdicn Willd.
A C O I I ~ ~ I I S ilicijbli~is L
Acar~thrrs ilicifoliri.~ L
760
2400
3040 -
mangrove area of Nettoor site was noticed due to the newly constructed Eranakulam
Alapuzha railway line and Eranakulam Thiruvananthapuram bypass road (Plate 1 to
Plate 25).
Different plant species growing in different statior~s follows difference in
their growth and distribulion pattern In the present study frequency of Aco~ithrrs
ilicrfolir~.~ L. was maximum. Km~delia cniidel L, and Rhizophorn catidelorin DC. was
minimum in the Cochin area Whenever Khizophoro species were present at stations they
,.,ere seen along the banks of'water logged areas such as ditches and ponds.
Figure b shows the variation in number of mangrove plants growing in
different station s studied Species variation observed during the survey is also given in
the figure 6 . Maximum denljity of mangrove plants was observed at Kumbalam station
the Aviceti~~io ( ~ f f i c ~ ~ ~ ~ r l r s L represented in 3800lha. Marked variation in the density of
different Mangrove species was noticed in all the stations (Table IIa and Table Ilb).
There was a difference in the dominant species of mangrove plants in different stations
(Table 111). Ac~u1lhli.t 111c1folirr.s L. was dominated at 4 stations, Excoecnrin at 3 stations
and A~~icerrtrirr at 2 stations. lfiizophorcr and Hrrrgrriern were dominant at one station
each. In the community structure mangrove plants resembled climax species. Occurrence
of competition was limited and if at all present was intraspecific.
Maximum number of mangrove plants were noticed at Panambukad, the
value of Shannon Wiener index was 2.02 bitslindividuals. Diversity value was zero at
Pattanam were the station represent onlv one species. At Kumbalam eventhough only two
species were represented they showed maximum possible natural diversity (Table IV).
Table IV
The diversity index of mangrove sampling stations found out during the survey
Shanon Wiener Diversity index bitslindividual . T
~-
H m u x I E I 1 + ~ -- -4 r ' - 232 I
0 76 I +--159--1 -
I t 076 -1 I
- _ _ i 1.00
4 ' Nettoor 2.32 0.68 i ~~
O g 6 ._I -
G, +- 2.00
2.81
2.59
2.00
100
0.00
l .OO
5
6
7
8
9
10
11
4
10
0.63
0.72
0.75
0.78
0.17
0.00
0.79
Manyalavanam
Panambukad
Puthuvypu
Pallipuram
Karumallor
Pattanam
Moothakunnam
4
7
1.25
2.02
10 1.93
- 5
3
3
5
4
2
1 ,
2
- 1.55
0.17
0.00
0.79
Distribution of mangroves in different sampling stations of Cochin area is given in Figure
6A to F i ~ u r e 6 K
In the present study 4 species of semi mangroves and 6 species of
mangrove associated plants were identified at different stations (Table V and Table VI).
Acro.sfichtrnt urn-ermr L was seen in the most of the stations however, Manglavanm,
Puthuvypu and Pallipuram lack this plant. Plants such as Dolichartdrort spaiheceae L. and
('oesa//)~)ttnu trtrgu I.. were observed only at Kammallor. UerrIs r~l~gtosa Benth. was
noticed in all stations except Kammallor and Pananam. None of the semi mangrove plant
species was observed in common to all stations. Moreover in all stations semi mangrove
plants were seen along with the true mangrove species. Kammalloor station showed
maximum number of semi mangroves in present survey (Plate 24 to Plate 27).
.Amon$ the mangrove associated species C~olophyllrrm ittophyllzlnn L. was
observed only at Panambukad, an island station. Ipon~oen,prscaprrne Sweet. was seen in
Puthuvypu and Pallipuram stations situated in Vypeen island. Thespe.~iapoptrIttea L. was
observed in all stations except in Mangalavanam and Ka~umallor. Clerodetrdr-ort itrernti
L was observed commonly in Kannamali, Nettoor, Panambukad, Puthuvypu, Pallipuram
and Pattanam .\ijlttrc.r nttth~is irrdictrs L. was observed in all stations except in Kannamali,
Kumbalam. I'uthuvypu, Kammallor and Pattanam. Maximum mangrove associated plant
species were seen at Panambukad and minimum at Karurna.llor (Plate 28 to Plate 33).
Table V
Semimangrove p l a n t species a t d i f ferent sampl iog stations observed during the survey , . . ~~~ 7..-.-.p-- ~-~ --
S1 Scmin~;~nero!c sllecics F;~rnil? riGi-rXtYn11~1 I K e r n n N r t t ~ ~ l n x l i l 1 panam 1 ~ u t h u v j ~ a l l i ~ Karu I ~ a t t r !'Tithali7 I , 'VIP I I iu~ei ' i n I \;III;I~ : bukatl 1 )IIII ; warn , m a l l , I un~lilrn 1
I 2 / : 4 5 6 7 8 , 9 1 0 11
/ 3 / Derrix iilipii?oso Ucntl~. ) Fahaceac + i 1 I I + - 1 - 1 + i i i i + + + I
Tab le VI
Mangrove associated species a t d i f ferent sampl ing stations observed during the survey
1 I Cerrhero oifollnnr Gaertn Apocyanaceae + + + + 2 C ' I e r ~ ~ ~ l c ~ i ~ ~ I r ~ i n ttirrtttt L / VC~~~IIWCC~C + + + + + I -
+ Present. - Absent.
T Z n T
Nett oor 4
Puthu \ )pu
7
Palli lu ram
8
Mootha kunnam
11
Mangla vanam
5
Kalv mallor
9
Panam bukad
6
Pat1a nam 10
Fig - 6.A
Fig - 6.B
EJq
Fig - 6.C
Fig - 6.F
LEGEND
Rhizophora mucronata Larnk. - - E3nib.u iera cylindrica WA.
Fig - 6.G
LEGEND m I
49
Fig - 6.H
LEGENB WATER -u
LAND - STUDY AREA -0
U N T S Acanthus ilicifolius L. - I
TATION - 11, MOOTHAKUNNAM
DISCUSSION
The mangrove vegetation possesses marly structural and physiological
peculiarities, and is composed of species with strongly marked characteristics grouped
under 'true mangroves'. There are also plants with less strongly marked characteristics
which are known as semimangroves (Tansley and Fritsch, 1905). There is yet another
group of plants which grow adjoining the mangrove areas but thrive on the land which
does not yet submerged by brackish water even during the high tides but with saline soil. . .
They can withstand some amount of brackish water stagnation for a very short period.
These can be grouped as mangrove associated species (Basha, 1992). In the present study
10 species of true mangroves, 4 species of semimangroves and 6 species of mangrove
associated plants were identified. The pattern of distribution in all the eleven stations
were discontinuous and in patches of varying extent.
I n the Cochin area Acatt/hrr.s i/icifo/ius L,, was found distributed in all . .
stations except one followed by Avice~n~in oflcitra/is L. The later was absent From 2
locations Act~~li711.s i1ictfOlit1~ L. has been reported to occur in varied habitates in the east
and west coasts (Mudaliarr~rd hntm4954). According to them, it was forming large
formation at the edge of back waters of Chirakkal, Tellicherry, Kasaragod and Udupi of
Kerala and tiarnataka states, which is similar to the distribution in the Puthuvypu station
of the present study Other places where Acntttl7tr.s i/ic~fi)i'itts L. formed large formations
in Chiplun uhere it dominated (Joshi and Jamale, 1975) and Bombay (Navalkar, 1973)
where i t existed alor~g with A ~ ~ i c ~ t n ~ i n . Acattlhtrs ilic~fo;folirrs L. is conspicuously absent
from Karumallor This station shows only 17% of possible diversity and can be
considered as the n~aximum affected area in the present investigation. Eventhough back
water zone is surrounding the station expected diversity is absent. The reason may be the
anthropological intervention of the mangrove habitat. Rao and Sasthry (1972) reported
that Acnr~~hri.s i1rc;folius L. is occupying the third zone from estuarine water along with
Excoecnrm agalltxha L., similar to the Pallipuram station of the present investigation.
Kannamali, Pallipuram and Ka~mal lo r stations were dominated by the
genus l<xc~oectrrrtr. ?'his is an indication of the presence of more or less similar
environmental factors prevailing over these stations. According to Joshi and Jamale
(1975) the limits of migration in mangroves are possibly due to their capacity to increase
uptake of potassium and calcium and to reduce the uptake of sodium and chloride ions.
They pointed out that Acatrthzr.~. Excoecnria and Kai~delia are less efficient in these
characters 11 appears that potassium and calcium are responsible for developing salt
tolerance in mangroves. &corcrnin ngallocha L. and Ai~ice~raia rnarirra were the main
species of south coastal Andhra pradesh (Jayasundramma, 1987). At Muthupet mangrove
forests AI~ IL .~ ,~ I I I IU I)KII.IIIU. was the most common and abundant species followed by
Excorcari~r trgi~llocha I,. and Acc~r~/hrr.r. ilic~jolitrs (Kannan el' nl., 1998)
Mukherjee (1975) described Acntithus ilicrfolir~s L as occupying reclaimed
areas, alons embankments and edges of creeks, which resembled the distribution pattern
of Puthuvq-pu, Pattanam and Nettoor. All these areas are developed by reclamations.
Acnr~fh~ts rl t<.~fi) l i~~s L is less efficient in competing with Ai~iceirnia in regions of lesser
inundation 'The stunted growth of Accrr~ll?~~s ilicifolirrs L. in Moothakunnam, and
Pallipurarn are indicative of this factor. in Panambukad and Kannamali the luxuriant
growth of AL.CIII~/III.Y mav be due to the higher inundation rate
In a11 earlier investigation Suma (1995) found that Vypeen block of
Cochin was composed of Ac~zrrfhrrs ilicrfolius L. along with Rhirophora mzrcronata and
A~?crrrtotr oficirm1i.s .. L. At Puthuvypu area Avicerzrria seems to be the early colonizer
followed bv i<hihizoyhora, Derris and Acatzthus respectively (Mohanan, 1997). Hence
Acar1fhrr.s has no pioneer role in the migration of a mangrove community to an area. This
seems to be an evidence of the fast changes in the mangrove vegetation of Cochin area.
In the present investigation Acarrthlis ilicifolius L. and .Avicennia ofJicir~alis L. were
found most frequent in the Cochin coast. It was observed that species diversity gradually
tapers from the Mahanadi and Sunderbans delta of the East mast to the Andaman and
Nicobar islands and Southwards to the Godavari - Krishna and Cauveri delta of the East
coast and is much less along the West coast regions including Kerala coast (Banerjee and
Gosh, 1998) I'his may be due to the large physical forces of saline tide water and lack of
stable substrate At Pattanam onlv one species of mangrove was present i.e., Acarrlh~is
i/ic!fi,liri.\ L According to Venu (1999) land fills, industrial estates and housing estates
for human habitation destroyed mangroves of India.
I t Mas seen that i(/ri:ophorn rnrmotrnta Lanlk. and Hrrrg~riera cylirrdrica
WA. form the dominant vegetation with highest spread over the areas in Panambukad.
While A L . ~ N ~ I / ~ I I . Y i/ic!fi)/lr~s L. together with Hnr~rreru cylirrdricn dominated in Puthuvypu
and A~~icerriritr (?fficirr~~/i.c. together with Fkcoecaria agrrllocha dominated over the
Pallipuram statioris. ilctrtrthri.\ ~I~c!fi~Ii~rs together with Al~icetrnin c~ f i c i r~ l i s were
dominated in stations like hlan~alavanam, Kumbalam, Kumbalangi, Nettoor and
hloothakunuam 'l'his may be due to the effect of same type of environmental factors
prevailing over. these stations. .A riel* association was noticed in Kammallor. They were
mangrove species lixi:ot,caria it~dica Willd. and semi mangrove species Dolicha~~dro~~e
spathac~,tr I..
Maximum diversity of species in the present study was observed at
Kumbalam, where theoretical species diversity was calculated as 1 bitlindividual and
actual computed diversity was .96 bitslindividual. 96% of the possible species diversity
was present at t h ~ s station. It is clear that the maximum possible diversity will occur when
all the species show equal probabilities to occur with exactly equal dominances in the
ecosystem Such type of ecosystem will be more complex, stable and less predictable in
terms of species (Trivedy el a / . , 1987).
Panambukad station is an island which is surrounded by Cochin estuary
and may be least affected by external interference. At Panambukad two species
Xhizophorcr tnr~crontrutn Lamk and Rrzrg~iera cyl~t~drrc~!~ WA, more or less dominate
together as in Kumarakam estuary. Ramachandran and Mohanan (1987) studied about the
mangroves of Kumarakam estuary and observed the presence of a mixed population of
Rhirophoru cr/)rcrrlu/tr~ atld Hrrrgttiera ~).n~tiorhiza bordering the estuary. The mangroves
of the station Panambukad is threatened by the construction of a network of bridges
connecting ('ochin and Kodungallore. If necessary steps 1:o protect the highly diversified
mangroves of this station is not done,devastating effect of bridge construction will result
in col ossal damage of mangroves of that area.
Lotdrlin cattdc.1 L is only noticed in the estuarine margins of Nettoor
station as described hy Ramachandran and Mohanan (1987). This plant shows very fast
disappearance from the mangrove locations of Cochin Nettoor station is drastically
affected by the land filling for house constructions, road and rail expansion. There are no
attempts of conservation of mangroves and as result backwater connection channels and
creaks to the mangrove habitat are now more or less totally hindered by the land filling
activity and water bodies are completely dried off.
.4 f eu species like Excoecaria itidica and Bniguiera parv~jlora are very
rare in Kerala and show restricted distribution in both the coasts (Malabar and
Travancore) indicating fast disappearance of the species due to speedy conversion of land
for alternate land use (Basha, 1992). In the present study the unique species Excoecaria
itldica was frequently observed in station 9, Karumallor. Uolochandrorie spnthacea L.
were reported bv Gamble (1967) in the Malabar coast but now they are not seen near
mangrove locations (Basha, 1992). But in this study i3olichatdrone spathacea L. is
found to be associated with b;xcoecarin itidicn Willd. in some of the areas of Karumallor.
According to Basha (1992), mangrove vegetation along the coastline is
generally the association of KhIzophora species and Hniguiera species, where soil in this
zone gets inundated by the sea water twice in a day. Typical example of this pattern of
associat~on was observed in Panambukad station of the present study and they were
dominant in that station. The mangrove exhibited zonation depending on the soil, salinity
and tidal inundation. Waisel ( 1972) have included Rhizophorn mucrotlata Lamk. in
inundation class 1 i.e., the mangrove floor reached by all tides. MacNae (1968) has
opined that complete zonation would be found only in the areas having considerable
intertidal range So tidal inundation is the most significant factor controlling the
distribut~on of i(hizo/)horn rnric,r~trnln Lamk. In Panambukad and Puthuvypu where the
tidal inundation of all tides occur Khizoph~rn ntricrotmttr Lamk. was found in excess in
the current investigation. Maximum mangrove species were represented in these stations.
Tides help in washing away salt, mixing of nutrients, reducing water temperature and
distributing seedlines (Mohanan, 1997). Rhizophora carldelaria DC. is exclusively found
only in the 6'' station Panambukad. Khizophora was not at all found in station 3,9,10 and
11. This may be due: to low tidal action in all these stations. Ecological condition of
mangrove system and its associated coastal water is influenced by stratification caused by
slow currents and weak tidal mixing ( Anonymous, 1987; Suma 1995).
Some species like Sorrrleratia caseolaris L. shows abundance in
Travancore coast, but was seen rarely in restricted localities at Malabar (Blasco, 1975).
The plant Sororercr~io caseolaris L. was found frequently in Panambukad and rarely in
Nettoor and Karumallor and totally absent in the other eight stations. It shows that this
plant is rapidly disappearing from the region.
Heddome (1866) has described Hr~rgr~irra tzylitrdrica WA. as occuning in
Malabar and Travancore coasts and Brrrgrriera caryophyNoi& in Malabar coast. Hooker
(1972) has also described the above species and further enumerated yet another species,
Hrzrgrriertr n~trltrhto.~ca as found occurring in Malabar. Dn~ry (1864) and Ramarao (1914)
also mentioned Hrrr~:uiercr n~crlahcrriccr as occuring along the Malabar coast. From the
descriptions of the above authors, it is clear that once there existed all the three species in
Kerala coast H u t recent workers have described all the three species to be one and the
same, /.tJ . Nrrrgrrier.tr cylirrdr~cn WA a as ha, 1992).
Both .Yrr~g~~iertr tylir~dricn WA, and Hrrr&v~iera gyrnr~orlliza were present
in Panambukad, and Puthuvypu stations. Brrrgr~iera ,symrorhiza Lamk. was seen only at
Mangalavanam. and Hrrtguic,r~r cylirrdrico WA. at Kannitmali. In all other stations this
genus was not observed. This shows the gradual extinction of this plant from the Cochin
backwater belt Mangroves of Mangalavanam is considered to be a secondary growth
developed after the closing of a timber depot (Mohanan, 1997). This station is
represented by 4 mangrove species. Only 63% of the expected diversity has been
observed in this stati0.n. This reduction in the diversity may be due to the toxic effect of
spilled oil from the storage tanks of Indian oil corporation situated near the
Mangalavanam. Anonymous (2000a) has reported about the devastating effect of oil
pollution to the Nigerian mangroves. Mangroves of Mangalavanam are also often used as
open garhage dumps.
Successional Patterns of Mangroves
Uns~~ccessful natural regeneration because of biotic interference results
in complete loss of ~mangroves. in such conditions only Acroslicirni alireirni L. and
Acnrr/hri.c .s/)eotJ.\ invade the area and become dominant (Singh et al. , 1990). The very
same condition was observed in typical land filled area in Pattanam station. There the
mangrove species Acorrthrr.~ iliclfoliris L. was only found with A c rosficrrrn aureuni L. It
is believed that the succession of the mangrove vegetation is governed by the three
factors namely. natul-e of substrata, soil salinity and biotic disturbances. Due to biotic
interference the mangrove vegetation was fast disappearing. Only those species which are
more hardv and resistant can tolerate and are able to colonize in such environment. The
most important invader species of the environment i:i A~licernin oflcinalis L. and
A~~icerrtr~lr nr~u.~ir<r, being of hardy nature and its higher range of adaptability (Singh et nl..
1990). At Pichavaram Avi~~ctrtrln c?fficitmlis is represented by large trees mixed with
1~lri-o~~hor.tr at the borders of channels (Kannupandi and Kannan, 1998). The limit of
tolerance of each species is determined by its specific environmental requirements. Thus
at the sea front Avia;.rrrrin and Someratia are often the pioneers. Usually species with
large propagule size are sorted towards water front while those with smaller propagules
and ability to withstand less salinity to hinterlands (Mohanan, 1997).
4 common observation during this study is that the reclaimed lands are
first colonized by A~~icnirria ~flicirialis L. followed by A~:atrfhzrs ilicifoliz~s L. Mangrove
plants are not allowing any understory species and hence no stratification was observed.
Semimangroves and Mangrove Associated Plants.
In the present study Derris ulignosa Benth. the semimangrove, is found to
be closely associated with true mangrove species especially Avicetrnia oflcinalis L.
Derris t,li~vro.v~r Benth is found in all stations except in 9* and 1 0 ~ stations where
A~~/crt~tt/tr (?fliotta/is L. is totally absent.
Uone of the mansrove associated species is observed in common to all
stations But ('errhr(z tdollani Gaertn is noticed in 7 sttations out of 11 studied. No
speciality. specificity or relationship between the occurrence of mangrove associated
species and mangrovt: species were observed (Suma, 1995).