Chapter 1

REVIEW OF LITERATURE

Cormier-Salem (1999) reports that though scientific interest on

mangrove ecosystems began with botanists, latter in collaboration with

botanists, it was extended to ecologists. Studies on world's mangrove

ecosystems are surplus. Reports on almost all types (fringing, dwarf, basin,

tidal, riverine , overwash etc.) of mangrove ecosystems and their integral

functions have been extensive (FAO, 1994). However many emerging or

recently developed mangrove ecosystems are yet to be identified and

documented. Studies on such newly colonized mangrove ecosystem and their

functions would reveal many unanswered facts on their origin, functional

integrity and development. Studies on nutrient dynamics, vegetation structure,

biodiversity, biomass would be able to add information on their sustainability.

Th term "dynamics" points to "changes in structure and composition".

The term 'dynamics' has been applied in an environmental, faunal or

in a floral context. In an environmental context it is applied to nutrient

dynamics (Tam et al, 1990; Cohen et al., 2004). sediment or detritus dynamics

and hydro-dynamics (Wolanski, 1992). In a faunal context dynamics is rcfemd

to as community dynamics and spatio-temporal dynamics. In vegetation context

spatial and temporal dynamics has been used equally to litter dynamics,

biomass dynamics, canopy dynamics and population dynamics (Clarke, 1995).

Nutrient Dynamics

Nutrient dynamics is an important function of mangrove ecosystem

in terms of biogeochemical cycling of elements in the coastal zone

(Jennerjahn and Ittekkot, 2002). Twilley, (1988) elucidates how nutrient

recycling is an important process that determines whether a mangrove

system functions as a nutrient sink or a nutrient source to adjacent aquatic

13

systems like estuarine or coastal ecosystems. McKee and Faulkner,

(2000) pointed out that assessment of biogeochemical functions in a

mangrove ecosystem should involve the evaluation of complex processes

that control soil condition, carbon movement, recycling of nutrients including

other primary interactions. Presence of carbon and other nutrients in soils

emulate several ecosystem processes like primary production, decomposition

of organic matter, abiotic conditions like temperature, moisture, oxidation

status, soil texture in addition to the biotic funtions like microbial and

faunal activities. According to Sherman et al. (1998) mangrove ecosystem

is not only an important source of organic matter but also a primary sink

for accumulation of sediment over a period of time.

Mangrove sediments are mainly anaerobic in nature with only a

thin aerobic sediment layer overlying it. Often the organic matter is available in

dissolved form and the nutrients gets recycled both within the mangrove

as well as in adjoining habitats (Kathiresan and Bingham, 2001).

Degradation of organic matter in the aerobic zone occurs predominantly

through aerobic respiration whereas in the anaerobic layer decomposition

occurs mainly through sulphate reduction (Nedwell et al., 1994; Sherman

et al., 1998). However studies on large number of coastal ecosystem

indicate that much of the energy flow through these ecosystems is mediated

through anaerobic microbial metabolism, especially by the sulphur cycle

(Day et al., 1989). Most of the studies on mangrove sediments in America

have been those of Robertson et al. (1992), Davis et al. (2001), Wasserman

et al. (2001) and in Australia similar studies have been those of Alongi

et al. (1992). Reports related to mangrove sediments of Southeast Asia

have been those of Kristensen et al. (1995). Tam and Wong (1999)

and Kathiresan (2002).

Alongi et al. (1989) and Moran and Hodson (1989) reported that

microorganisms are mainly responsible for the degradation of lignietllulosic

components which form the major constituents of mangrove leaves and

wood. Alongi et al. (1 993) and Holgiun et al. (1 999) also report that microbial

activity is responsible for a large part of nutrient transformation within a

mangrove ecosystem. Quality of litter also influences nutrient recycling

through its impact on the rate of microbial decomposition (Homer et al.,

1988) and macrofaunal utilization (Camilleri. 1989; Giddiw et al., 1986).

The bacterial communities of soil provide a cumulative effect like

reduction, oxidation, solubilization in recycling nutrients to mangrove

sediments (Anderson, 1995). Holguin et al. (2001) explain the functions of

diverse microbial and faunal activities that transform, reduce, oxidise, fixes

and recycle nutrients in the ecosystem. The decomposition of organic

matter in mangrove sediments has been widely studied by Nedwell et al.

(1994), Lacerda et al. (1995) and Alongi et al. (1999 and 2000). Sherman

et al. (1998) report that the availability of iron and phosphorus in

mangrove sediments is dependent upon the activity of sulfate-reducing

bacteria. Several available evidences (Gotto akd Taylor, 1976: Zuberer and . U

Silver, 1978: van der'valk and Attiwill, 1984; Hicks and Silvester, 1985;

D'Croz et al., 1989; Robertson and Daniel, 1989; Mann and Steinke. 1992)

report that the concentration of nutrients like the nitrogen is being

increased during decomposition and energy rich microbial biomass,

proteins and humic substances are entering into the ecosystem in dissolved

form (Odum and Heald, 1975). According to Kristensen et al. (1998), the

nitrogen-poor sediments act as sinks for nitrogen and that high rates

of denitrification takes place in mangrove ecosystems.

The physical and chemical characteristics of the Inanmove stdimcats

have been influenced by the decomposition of organic matter in the form of

shed leaves, stems and roots of mangrove plants (McKee and Faulkner, 2000).

Azariah and Govidasamy (1998) stated that the decomposition of

litter helps in remineralizing the ecosystem with organic and inorganic

nutrients that get ultimately sedimented in the mangrove. In addition

mangrove sediments are said (Wong et al., 1997) to retain essential nutrients

derived from wastewater. The retention mechanism of the sediments to

conserve nutrients is an adaptive response similar to that found in tropical

rain forests (Ball, 1996). Lacerda et al. (1995) have detailed the mechanism of

trapping sediments by different mangroves roots systems.

Vtgetrtioa Structure

Dynamics of mangrove vegetation structure in a particular area

constitute the base in the conservation and management strategies of the same

ecosystem. A clear understanding of the nature and dynamics of local mangrove

ecosystem is vital to any restoration or reafforestation programs (Field, 1996).

Satyanarayana et a?!, 12001) computed the relationship between the

vegetation indices, such as basal area and density using spectral indices

extracted from satellite data for Coringa mangroves of Godavari estuary, in

Andhra Pradesh. Selvam et al., (2003) reported that studies on community

structure of Pichavaram mangrove shows that Avicennia marina is mono-

specifically dominant and the other species of mangroves were rCptes~ted

by limited numbers. Similarly they also reported two ditkrent mation exiting,

- Rhizophora and Avicennia u ~ e , and that the latter trees form pure stands.

Guidelines to compute complexity index in mengroves from 13 localities

in Central Pacific coast of Columbia have been provided by Bloaco et d. (2001).

Different stand structures like as young, mature and desd mangrove in relation

to their biomass prediction have been well reported by Fromard et d(1998)

from Frmch Guiana.

According to Tomlinson (1986), mangrove stands generally have no

strata or understorey and characterized as even-aged and species-poor

than the other tropical forests. The floristics and structural features of

terrestrial forests when integrated with the numbers of species, stand

density, basal area and height of the trees reflects their course of development

(Holdridge, 1967). Impact of factors like species association, stand

development and forest turnover have been presented by Smith (1992).

Brokaw and Thompson (2000). discussed about the measurement of bre

girth at the height of 130 cm above the surface and its application in

computing the vegetation structural attributes. Quantifying the dynamics of

the early stages In the life cycle of mangrove is essential to predict the

distributton, specles composition and structure of mangrove

forests. Knowledge of the population dynamics of mangrove is essential

to forecast their dynamics and eventual recovery from perturbation

(Hoang et al.. 2003).

In addition to remote sensing, analysis of the mangrove vegetation at

the field level is essential to monitor the qualitative changes. Such vegetation

monitoring helps to identify the potential of that mangrove stand to regenerate

and develop or has there been any unsuitable conditions thrwgb rnt&ropo&enic

pressure that hinders the regeneration and sustainability of that mangrove

stand. This small input in identifying my unsuitable utilization or exploitation

of particular resources or succession patterns that is altering the vegetation

stand, should provide solutions imperative to be integrated with the data

generated through remote sensing and GIS in restontion programs (Mdouh-

Guebas, 2001). Monitoring changes in vegetation structure over the years

under different complexities like exploitation, pollution, global changes help

to focus on future changes and define steps to be taken under conservation

strategies.

Biomass

Litter in the form of fallen leaves, branches and debris contributes to

the addition of organic matter after decomposition (Holguin et al., 2001).

Clough ( 1992) reports that the amount of litter produced in the murgrove is

negat~vely correlated with latitude because the local fluctuations of litterfall

are related to stress which is habitat specific. In general, litter fall is heavier

during dry seasons when thinning of the canopy results in reduced

transp~ratlon (Roy, 1997). Reports of varying ranges on litter production are

hab~tat dependent Saenger and Snedaker (1993) fCp0I-t litter production to be

largely related to local conditions and species composition besides

Individual mangrove productivity However production of heavy litter varies

from specles to species. L~tter production in Avrcennra marina in India is

reported to be high In post-monsoon period and low in pre-monsoon

period (Ghosh et a]., 1990)

Mangrove leaves are useful contributors of nutrient mass in a mangrove

environment. It has been reported by Bandaranayake (2002) that mangrove

leaves contain sufficient amounts of minerals, vitamins and aminorcids.

which are essential for the growth and nourishment of marine organisms md

livestock. Microbial degradation of the litter added to kaching process is

mainly responsible for the recycling of nutrients (h et a]., 1990).

Globally, aboveground biomass of mangrove forests have been

%ported to range between 6.8 - 436.4 t ha-' (Saenger and Snedaker, 1993),

'and the litter fall to range from 1.3 - 18.7 t ha-' yr'. Twilley et al. (1992)

report the estimation of total global mangrove biomass to be approximately

8.7 gigaton dry weight (4 gigatons of Carbon). According to Clough (1992).

mangrove forest biomass may reach 700 t ha-l yr ' elsewhere. Sukardjo and

Yamada (1992) report that the aboveground biomass in an lndones~an mangrove

measures to 93 7 t ha-'. In a mixed forest, the aboveground biomass was

estimated to be 94.4 t ha-' that is in Mgeni estuarine mangrove of South

Africa. Litter production has been variously reported as of 0.01 1 t ha-'ya-'

in the mangroves of Kenya, of 9.4 t ha-' ya' in the mangroves of Bermuda and of

23.69 t ha-' ya-' in the mangroves of Australia (Kathiresan and Bingharn, 2001).

Twilley et al (1986) estimated the leaf fall in basin mangroves in Florida to

be 0.4-1.4g/m2/d and according to Day et al., (1996) in Mexico it is 0.6-

1 Sg/m2/d Steinke and Ward ( 1 990) reported the estimated litter production

for Gazi Bay of Kenya to be 4.50 t ha-' yr-I. However the litter production

from Avrcennra marrna in Australia was estimated by Clarke (1994) as

3.10 t ha" yr-' and by Bunt (1995) to be 15.98 t ha-' yr ' . In India, the

litter product~on from a m~xed forest of Andaman Islands is 7.10 to

8.50 t ha-' yr-' (Mallet al., 1991).

Biodiversity

In many geographical areas the biodiversity of mangroves is

decreasing with time as a result of destruction of mangrove forests besides other

various anthropogenic stresses (Hamilton and Snedaker. 1984). Alongi and

Sasekumar (1992) explain that the abundance and species diversity of

infauna are generally low compared with other benthic habitats. They also

explain that the low species diversity cab be interpreted with the presence

19

of polyphenolic acid in these environments, which has deterant property to

many of the organisms. Ravi and Kathiresan (1990) report the presence of

polyphenolics compounds in mangrove leaves. The well being of mangrove

is dependent on diverse, and largely unexplored, microbial and faunal activities

that transform and recycle nutrients in the ecosystem (Holguin et al., 2001).

The diverse plant and animal life associated with mangrove

ecosystems are best suited for nature education, tourism and scientific

study, thereby enhancing further social and economical values (Ashton

and Macintosh, 2002).

Sediments of mangroves support a variety of epibenthic, infaunal

and meiofaunal invertebrates and the sediment characteristics of the

individual mangrove determines the diversity of these fauna which varies

from habitat to habitat (Kathiresan and Bingham, 2001 ). About 300 benthic

taxa have been ~dentified from Southern Florida by Sheridan, (1997) who

also reported that annelids and tanaids are the dominant species. Gurreiro

et al. (1996) reported that polycheates to be the dominant macrobenthos

distributed in a Mozambique mangrove. Diaz and Erseus (1994). found an

oligochaete, belonging to the family Limnodriloidinae is entirely restricted to

mangrove sediments.

Mangrove habitats and prawnlshrimp populations an tightly linked

in many regions. Analysis of the relation between the commercial prawn

production and abundance of the same spread in the surrounding mangrove area

has indicated a strong correlation (Sasekumar et al. 1992; Kathiresan

et al. 1994; Vance et al. 1996). Kathiresan and Bingharn (2001) reported

eight penaeid prawn species to be abundant in Pichavaram mangroves.

Veenakumari et al (1997) found 276 insect species in the mangroves of

Andaman and Nicobar islands of India. About 70 species of ants, spiders,

mites, moths, roaches, termites and scorpions have been reported from

mangroves of Belize of Central America by Feller and Mathis (1997).

Mosquitoes which are ubiquitous in mangrove habitats, are often dense

and 18 species are reported from Pichavaram mangroves by Thangam and

Kathiresan (1993). Though many of the insects are temporary visitors,

they provide linkages between the mangrove and other environments

(Ananda Rao et al., 1998). Mollusks found throughout most of the mangrove

habitats, occupy a number of niches and contribute to the ecology of

mangroves in many important ways. The molluscan fauna in mangrove is

mainly composed of bivalves and snails (Balasubrahmanyan, 1994). Jiang and

Li (1995) reported about 52 species of mollusks from the mangroves of

Jiulong river in China. Among the fishes, 197 species have been reported

from Embley River of Australia (Blaber et al., 1990 and Brewer et al.,

199 1 ), 1 17 species belong to 49 genera are reported from Matang mangroves

of Malaysia (Sasekumar et al., 1994 and Yap et al.. 1994) and 260 speices

from Mekong deltaic mangroves of Vietman (Hong and San (1993). About 35

, reptilian species and four genera of frog were reprted from Sunderbans

(Gopal and Krishnamoorthy, 1993 and Hussain and Acharya, 1994).

Mangrove ecosystem in India is rich in biodiversity. Out of the 1862

species reported, 420 are flora and 1442 are fauna (Kathiresan ,2000). True

mangrove flora comprises 35 species under 16 genera and belong to 13 families.

of which 31 species are reported along the East coast, 18 species reported

from west coast and 31 species reported on the coasts of Andaman and

Nicobar Islands. 48 species of mangrove associates belonging

to 39 genera in 13 families have been reported along the Indian coast.

Kathiresan (2000) reports I07 zooplankton, 48 prawnsJshrimps, 82 crabs,

136 molluscs, 341 finfishes, 378 birds, 42 reptiles, 22 amphibians, 56

mammals and 230 other benthos from the Indian mangroves

Mangrove Resource and Economics

Mangroves play an extremely important role in maintaining high

productivity and rich biotic diversity of coastal waters and are of interest

from economic, scientific as well as wildlife management point of view

(Kar and Satpathy, 1990). Mangroves are of interest not just to the

biologists but also to economics, social scientists and so on. Mangroves are

highly productive ecosystems with various important economic and

environmental functions (FAO, 1994). Their diversity and productivity makes

them the source, d~rectly and indirectly of many products of use to humans.

The uses of mangroves ofien fall into two categories.

Direct use of the mangrove ecosystem is in the form of vital ecological

functions such as control of costal erosion and protection of coastal lands,

stabilization of sediments, natural purification ofcoastal waters from

contaminants.

Indirect use is in the form of economic benefits which are many and

varied;

b Fishery (fishes, prawn, crab. oyster, lobsters ctc) production,

9 Charcoal, firewood, poles, timber, hrniture, boats, etc.,

> Production of tannins, honey, harvest.

b Eco-tourism and the like.

The other principal ecological functions of mangrove that can be listed are:

a breeding, spawning, hatching and nursery ground for many marine fauna,

play a major role in shoreline stability by protecting shoreline from

excessive erosion,

traps nutrients preventing them from entering into the sea,

supports the growth of the sea grasses and corals,

increases species richness or biodiversity in estuarine areas,

Significance of mangroves to humans though varies greatly horn region

to region, in the present study but attempts have been made to achieve an

overall economic valuation of the goods and services derived from these

mangroves. However all the services typically have no market price (Woodward

and Wui, 2001) and hence measures of their values could be obtained only

through non-market valuation techniques. There is a remarkable range of

estimates involved In many wetland valuation studies conducted. One recent

estimate ~ndicates that on an average the annual value of one hectare of

mangrove is approximately $10000, resulting in a worldwide total

contribution of $1648000000 per annum (Hogarth, 2001). However the

valuation by Costanza et al. (1998). hold the worth of mangrove to an estimated

$180,895,923,000 per annum. The mean monitory value of mangrove of

$9990 ha-lyrt; is second only to the value of estuaries and seagrass and is

greater than the economic value of coral reefs. Clough, (1993) explains that

generally mangrove related fisheries resources are valued at more than natunl

and agricultural goods. Alongi (2002) provides these resources to be

about $60 ha'lyr" for fisheries alone.