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:abhijit_mitra@hotmail.com

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)

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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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