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Indian Journal of Geo Marine Sciences
Vol. 46 (10), October 2017, pp. 2046-2053
Survival rate of mangroves: A proxy to assess ecosystem health
Abhijit Mitra1*
, Nabonita Pal2, Arpita Saha
3, Tanmay Ray Chaudhuri
2, Pardis Fazli
4 & Sufia Zaman
2
1Department of Marine Science, University of Calcutta, 35 B.C. Road, Kolkata 700019, India 2Department of Oceanography, Techno India University West Bengal, Salt Lake Campus, Kolkata 700091, India
3Indian Institute of Bio-Social Research and Development, Prafulla Kanan, V.I.P. Road, Kestopur, Kolkata 700101, India 4Department of Biological and Agricultural Engineering, University Putra, Selangor, Malaysia
*E-mail:[email protected]
Received 05 April 2017 ; revised 21 April 2017
Survival rate of mangroves is highly species-specific, which significantly varies between sites. It is observed that
survival rate of Sonneratia apetala, Aegiceros corniculatum, Bruguiera gymnorrhiza, Xylocarpus granatum, Nypa fruticans,
Heritiera fomes and Derris trifoliate is more in the western sector compared to the central sector of Indian Sundarbans.
However, a completely reverse picture with higher survival percentage in the hypersaline central sector is observed for
species like Avicennia marina, Avicennia alba, Avicennia officinalis, Acanthus ilicifolius, Excoecaria agallocha, Phoenix
paludosa, Ceriops decandra, Rhizophora mucronata and Aegialitis rotundifolia. Salinity seems to be the major driver for
mangrove survival. Survival percentages of mangroves seedlings and their transformation into adult forms can be a potential
indicator of ambient environment particularly in context to salinity. Such approach can be of importance in the ecosystem
health monitoring programme preferably for regions like Indian Sundarbans, where significant spatial variation of salinity
exists.
[Keywords: Mangrove, survival rate, Indian Sundarbans]
Introduction
The ecosystem health approach
considers the functionality of a system and
distinguishes between functional and
dysfunctional system states1. The health of any
ecosystem is a function of the behavior and
dynamics of all its components in stressed and
unstressed conditions. An ecosystem can be
regarded as healthy if it can maintain its
structure and function under extreme stress
condition (resilience). The health of an ideal
ecosystem can be judged from various points
of view e.g., socio economic status of the
people dependent on mangrove ecosystem,
species richness, floral biomass, primary and
secondary production rates, ecosystem
services etc. In most cases, ecosystem health is
considered from the perspective of abiotic
component of ecosystem, as an unhealthy
ecosystem poses an adverse impact on the
socio-economic profile of the local
inhabitants. The example of Indian
Sundarbans can be cited in this context. The
western sector of Indian Sundarbans has a
relatively good health compared to the central
part of the mangrove dominated deltaic
complex. In western Indian Sundarbans, the
species richness and the mangrove floral
biomass are more compared to the central
Indian Sundarbans, which may be the effect of
significant variation of salinity2,3,4,5,6,7,8,9,10
. In
addition to this, anthropogenic activities have
resulted in pollution in and around the
mangrove ecosystem of Indian Sundarbans,
which is the World Heritage Site. In order to
sustain functioning and integrity of this unique
ecosystem, we require more potential
indicators to monitor the ecosystem health, so
INDIAN J. MAR. SCI., VOL. 46, NO. 10, OCTOBER 2017
that an effective management action plan can
be adopted to save guard this valuable
ecosystem, which is also the homeland of
Royal Bengal tiger (Panthera tigris tigris).
Materials and Methods
The entire network of the present study
consists of three phases.
Phase 1: Site selection
Mangroves are influenced by many
environmental functions, which shape the
abundance, diversity and productivity of each
mangrove fores11
. In Indian Sundarbans, the
abundance, diversity and biomass are
regulated primarily by salinity4,10
and therefore
the entire study area was divided into two
major sectors (on the basis of salinity as the
primary criterion) namely western and central
Indian Sundarbans. A total of 10 stations were
selected in these sectors with five in each
sector (Table 1, Fig.1). Stations 1 to 5 and 6 to
10 are located in the western and central
sectors respectively, which have different
profiles of salinity. Earlier studies indicate that
the western sector is freshening, whereas
salinification is occurring in the central Indian
Sundarbans owing to complete blockage of
fresh water due to Bidyadhari siltation12
.
Fig.1- Sampling stations in Indian Sundarbans
Table 1- Sampling stations with coordinates in Indian
Sundarbans
Station Longitude & Latitude
Harinbari (Stn. 1) 88004/22.88// E
21046/53.07// N
Chemaguri (Stn. 2) 88008/49.01// E
21039/42.88// N
Sagar South (Stn. 3) 88004/ 0.51// E
21037/49.90// N
Lothian island (Stn. 4) 88019/8.47// E
21039/08.04// N
Prentice island (Stn. 5) 88017/3.62// E
21042/43.31// N
Canning (Stn. 6) 88041/04.43// E
22019/03.20// N
Sajnekhali (Stn. 7) 88048/15.78// E
22006/34.19// N
Chotomollakhali (Stn. 8) 88054/26.71// E
22010/40.00// N
Satjelia (Stn. 9) 88052/49.51// E
22005/17.86// N
Pakhiralaya (Stn. 10) 88048/29.00// E
22007/07.23// N
Phase 2: Monitoring the Relative abundance
of seedlings
The relative abundance (RA) of a
species is expressed as
RA = ×100
The RA of seedlings was monitored from the
average values of 10 quadrats (10m × 10m) for
each station during 2012, when the seedlings
were ~ 5-6 months old. After 4 years, during
2016 the RA of the trees were calculated in the
same plots. This approach is adopted to
identify the dominant species in Indian
Sunadarbans, which is the template of the
present study.
Phase 3: Evaluation of survival rate
The population density of each species
(considering both the seedling and adult stage)
2047
MITRA et al.: SURVIVAL RATE OF MANGROVES: A PROXY TO ASSESS ECOSYSTEM HEALTH
is used to estimate the survival percentage as
per the expression
Survival percentage =
×100
Result
Mangroves are unique vegetation at the
land-sea interface that can withstand tidal
actions with variations in salinity. They can
tolerate deterioration of ambient water and
soil, and the reflection can be evaluated
through several indicators like above ground
biomass values, growth rate, survival rate etc.
This paper aims to study the ecosystem health
of Indian Sundarban mangroves in 10 selected
stations using survival rate of the true
mangrove species as proxy. For this we
estimated the population density of the
mangrove flora for the seedling and adult
stages in the same quadrates and computed the
survival percentage as per the standard
expression. It is interesting to note that
survival rate of the mangrove species are
strikingly site-specific or in other words
sites/location/environment have regulatory
influence on the survival of mangroves and
such influence varies with species. It is
observed that survival rate of Sonneratia
apetala, Aegiceros corniculatum, Bruguiera
gymnorrhiza, Xylocarpus granatum, Nypa
fruticans, Heritiera fomes and Derris trifoliate
is more in the western sector compared to the
central sector of Indian Sundarbans. However,
a completely reverse picture is observed for
species like Avicennia marina, Avicennia alba,
Avicennia officinalis, Acanthus ilicifolius,
Excoecaria agallocha, Phoenix paludosa,
Ceriops decandra, Rhizophora mucronata and
Aegialitis rotundifolia. These species exhibit
more survival percentage in the central sector
compared to the western Indian Sundarbans
(Fig.2).
Fig. 2(a)- Survival rate of S. apetala Fig. 2(b)- Survival rate of A. marina
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INDIAN J. MAR. SCI., VOL. 46, NO. 10, OCTOBER 2017
Fig. 2(c)- Survival rate of E. agallocha Fig. 2(d)- Survival rate of A. alba
Fig. 2(e)- Survival rate of A. officinalis Fig. 2(f)- Survival rate of A.ilicifolius
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MITRA et al.: SURVIVAL RATE OF MANGROVES: A PROXY TO ASSESS ECOSYSTEM HEALTH
Fig. 2(g)- Survival rate of A. corniculatum Fig. 2(h)- Survival rate of B. gymnorrhiza
Fig. 2(i)- Survival rate of X. granatum Fig. 2(j)- Survival rate of N. fruticans
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INDIAN J. MAR. SCI., VOL. 46, NO. 10, OCTOBER 2017
Fig. 2(k)- Survival rate of P. paludosa Fig. 2(l)- Survival rate of C. decandra
Fig. 2(m)- Survival rate of R. mucronata Fig. 2(n)- Survival rate of H. fomes
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MITRA et al.: SURVIVAL RATE OF MANGROVES: A PROXY TO ASSESS ECOSYSTEM HEALTH
Fig. 2(o)- Survival rate of A. rotundifolia Fig 2 (p)- Survival rate of D. trifoliate
Discussion
Survival rate is a signature of the
degree of the environmental stress on a
particular/group of species. More the stress
posed by environmental variables, less is the
chance of survival. Depending on the adaptive
capacity of species, the percentage of survival
varies greatly among different sites.
The western Indian Sundarbans has a different
set of environmental parameters compared to
the central sector, particularly with respect to
salinity2,3,4,510,13,14
. This variation in salinity is
attributed to complete blockage of the fresh
water in the central sector of Indian
Sundarbans due to Bidhyadhari siltation since
the late 15th century
4,12,15, which has made the
region hyper-saline compared to the western
sector. The western Indian Sundabans, on
contrary receives fresh water through Farakka
barrage discharge. Such a variation of salinity
is the major driving force on survival
percentage in the present geographical local as
mangrove flora are capable of adjusting in
different salinity gradient depending on their
salt regulating capacity.
The overall results thus point out very clearly
the different degree of adaptation of the
species to ambient salinity and suggests for an
interlinking of the Hooghly River (in the
western Indian Sundarbans) with Matla River
(in the central sector of Indian Sundarban) for
a better homogeneous salinity throughout the
deltaic lobe. Apart from flood control in the
western sector, the benefits of interlinking may
be perceived through eco-restoration of the
central sector in terms of salinity, which may
be a smart approach for increment of
mangrove diversity in this world heritage site.
Species like Sonneratia apetala, Aegiceros
corniculatum, Bruguiera gymnorrhiza,
Xylocarpus granatum, Nypa fruticans,
Heritiera fomes and Derris trifoliate.can
survive under this scenario in the central
Indian Sundarbans and thus can be a road map
for eco-restoration of mangrove ecosystem
health.
Conclusion
The entire study leads us to conclude that
survival rate of mangroves can serve as
potential indicator of ambient environment,
particularly in terms of salinity. It is also
extremely salinity – specific, due to which
contrasting variation is observed in the
survival rate of the studied species thriving in
the western and central sectors of Indian
Sundarbans. The two sectors are strikingly
different in terms of salinity which caused
variation in the survival pattern of mangroves.
It seems from the study that the mangrove
species that survived better in the central
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INDIAN J. MAR. SCI., VOL. 46, NO. 10, OCTOBER 2017
sector are resilient to climate change and
subsequent sea level rise in the present
geographical locale.
Acknowledgement The authors acknowledge the support of
the project entitled “…Vulnerability
Assessment and development of adaptation
strategies for Climate Change impacts with
special reference to coasts and island
ecosystems of India (VACCIN)….” funded by
CSIR for undertaking the experimental works
on the seedling samples collected from the
islands of Indian Sundarbans.
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