6 litter fall loss-rate,
since there may be removal by the tide was calculated as the ratio of annual litter-fall mass L to litter-layer or standing crop X
ss
, k = L X
ss
. Turnover rate, the rate of the amount of a substance released by or entering into a compartment in a given time
was defined as the inverse form of decomposition rate 1k. Half-lives t
0.5
assuming an exponential model applies, were calculated as 0.693k Olson, 1963.
2. Litter-fall and litter-layer
The total small litter-fall was 18.65 thay for upper plants and 4.23 thay for lower plants, giving a total number of 22.88 thay. For upper plants leaf-litter was by far the
biggest contributor 65.16, followed by reproductive parts 15.48, wood 12.26, trash 3.23 and stipules 2.58. In contrast wood litter productivity 70.81 was by far the
highest for lower plants, followed by Derris 16.44 and Acanthus leaves 10.90. September to December was the most productive months for upper plant litter-fall but in
contrast the least for the lower plant. The lowest litter-fall for upper plants was in July- August. The total number of litter-fall in Segara Anakan was amazingly much higher than the
range reported for any other mangrove sites in South-East Asia such as Matupore Island, Papua New Guinea with total production of 14.30 Leach and Burgin, 1985, Bintuni Bay,
Papua 11.1 thay Pribadi, 1998, Kuala Selangor, Malaysia 15.8 thay Sasekumar and Loi, 1983, Matang Mangrove Reserve, Malaysia 11.4 thay Gong et al., 1984 and Ranong
Mangrove Forest, Thailand 10.88 thay Aksornkoae et al., 1991. There are several factors which influence litter-fall in mangroves: latitude Saenger and Snedaker, 1993; freshwater
input Pool et al., 1975, Flores-Verdugo et al., 1987; salinity Clough et al., 1982; Clough 1984; the ratio of precipitation to evaporation Clough et al., 1982; Clough, 1984; soil
nutrients Boto and Wellington, 1983; and the age or state of maturity of the forest Clough, 1985. The mangroves of Segara Anakan were not extreme as far as the above factors are
concerned and but surprisingly produced a very high litter-fall. It should be noted, however, that there might be overriding factors that can influence litter-fall in Segara Anakan in the
short term. As it was mentioned above the lagoon presently has a serious threat by a rapid accelerated sedimentation and infilling from the inlet rivers which of course influence water
salinity, and possibly other physical and chemical factors.
The amounts of nutrient returned through small litter-fall were estimated to be kg ha yr: N 255.5, P 41.0 and K 145.5. These values are higher than those reported by Pribadi
1998 for Bintuni Bay i.e. N 240.4, P 6.1 and K 43.2 and Gong et al. 1984 for Matang mangrove forest, Malaysia i.e. N 46.6, P 4.7, K 25.6. The lower values for both forests must
be viewed in the light of their lower annual litter-fall of Bintuni Bay 11.1 tha and Matang 7.8 tha than in Segara Anakan 22.88 tha.
3. Leaf-litter decomposition The
decomposition rate k values of 6.38 leaves, 2.51 wood, 8.89 fruit and
flower, and 14.84 stipule were much higher than the values for truly terrestrial tropical rain forests Olson, 1963; Anderson and Swift, 1983 because of the removal of litter by seawater.
The removal by seawater will differ with the tides and will be offset to some extent by an inflow as well as the outflow. The high value of decomposition rate k indicates the high ratio
of litter-fall and litter-layer. However, this finding is a common phenomenon in the mangrove forest since high tide normally removes most of the litter-fall from the forest floor. Leach
Burgin 1985 found that k was high 28.6 for Rhizophora stylosa-dominated forest in Matupore Island, Papua New Guinea. Robertson 1986, Robertson Daniel 1989 and
Robertson 1991 reported that in tropical Australia the k values varied from 6.19 for
7 Avicennia in a high intertidal area to 280 for Rhizophora in the mid-intertidal area. In Bintuni
Bay, Papua, Pribadi 1998 found the values was ranged between 26.0 fruit and flower and 158.4 stipules. The maximum tidal amplitude in Segara Anakan of 2.2 m c might explain
why the values were much lower than in Bintuni Bay with maximum tidal amplitude of 5.6 m.
In general, the results showed leaf-litter decomposition in Segara Anakan are varied among species. Sonneratia alba, Excoecaria agalocha, Avicennia alba and Finlaysonia
decomposed very fast with only less than 25 of the initial mass remaining in litterbags after 32 days. Derris trifoliata, Acanthus ilicifolius, Ceriops tagal, Bruguiera gymnorrhiza and
Xylocarpus granatum
were slower with mass remaining ranged between 25 – 75, while Scyphiphora hydrophylacea, Aegiceras corniculatum and Rhizophora apiculata
showing a way much slowly decomposition rate leaving more than 75 after 32 days of experiment.
Steinke et al. 1983, 1990, 1993 attributed differences in decomposition rates to differences in leaf morphology, anatomy and chemistry. B. gymnorrhiza, for example, has glabrous leaf
surfaces which are covered with a thick cuticle which would impede the entry of water and degradative organisms. In contrast, only the adaxial surface of A. marina leaves has a thick
cuticle; the lower abaxial surface is covered with numerous fine, non-glandular hairs. Fahn and Shimony 1977 have shown that the non-glandular hairs are covered by a very thin
cuticle that may be absent in parts. It is suggested that water and microbes may enter readily through the leaf underside. Benoit and Starkey 1968 and Swift 1976 had pointed out that
the presence of tannins in mangrove leaves can also delay the colonisation by fungi and bacteria. Ceriops tagal, Bruguiera gymnorrhiza and Rhizophora apiculata are among
member of family Rhizophoraceae that well known with high tannin and lignin concentration on its tissues. Choong et al. 1992 reported that Sonneratia alba has a relatively a high ratio
of protein N to fibre, which they believed to be a good predictor of leaf palatability and digestibility.
The decomposition process pretty similar: faster in the first week then slower in the following weeks. Some species showing a mass increment after two days in the field but then
consistently decreased at the rest of the time. Hodgkiss Leung 1986 discovered that the highest fungal cellulolytic enzyme activity was found during the first six weeks of
decomposition, indicating that microbial cellulolytic activity is likely to reach a peak at this time. They also noticed that time was also required for the leaching of tannins and the build
up of microbial biomass. This assumption corresponds well with the knowledge and understanding of the biology of litter decomposition. As decomposition proceeds, soluble
components and relatively easily degraded compounds such as sugars, starches, and protein will be rapidly utilised by decomposers such as fungi and bacteria, while more recalcitrant
material such as cellulose, fats, waxes, tannins, and lignins will be lost at slower rates. Thus, with time, the relative proportion of these recalcitrant materials will increase and the absolute
decomposition rate will decrease Wieder and Lang 1982. Benoit and Starkey 1968 and Swift 1976 had pointed out that the presence of tannins in mangrove leaves could probably
delay the colonisation by fungi and bacteria.
8
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11
SPATIAL AND TEMPORAL DYNAMICS OF MANGROVE CONVERSION AT THE SEGARA ANAKAN CILACAP, JAVA, INDONESIA
by
Erwin Riyanto Ardli
Faculty of Biology, University of Jenderal Soedirman, Purwokerto, Indonesia eriantooyahoo.com
Introduction
The term “mangrove” is used to designate a group of floristically diverse tropical trees and shrubs belonging to unrelated families that share physiological characteristics and
special adaptations, which allow them to persist on waterlogged, saline, oxygen depleted silty and unconsolidated substrates. Mangrove forests or ecosystems are referred to as tidal
forests, mangrove forests, mangrove swamps or mangal Novelli et al., 2000. Mangroves are found along sheltered coastlines in the tropics and subtropics. Where they fulfill
important ecological and economic functions in conserving biological diversity and providing wood and non-wood forest products FAO, 2003. They protect coastline from
erosion, storm damage and wave action by acting as buffers and catching alluvial materials. They protect reefs and sea grass beds from siltation and pollution William,
2005. They provide a protective habitat for spawning, and represent nursery and feeding grounds for a variety of fish, crustacea and shellfish, including many commercial species
Primavera, 1998; Adeel and Pomeroy, 2002. Mangroves are critical for sustaining the production of coastal fisheries Primavera, 1998; Alongi et al., 2005; Manson et al., 2005,
and are important indicators of coastal changes Blasco et al., 1996.
Indonesia has one of the world’s largest mangrove areas, estimated of 2.93 million ha or 20 of the total mangrove area of the world FAO, 2003. However, they
continuously declined at an assumed rate of about 1.7 per year during 1990 – 2000. In 1997, the Segara Anakan mangrove forest covered about 13,577 ha Tomascik et al.,
1997. It
has been severely degraded and reduced by 192.96 ha per year Ardli and Widyastuti, 2001. Segara Anakan is subjected to
multiple resource use conflicts, overexploitation of coastal resources and environmental degradation. The coastal
communities traditionally exploit mangroves. Key management issues are the decreasing size of the lagoon due to heavy riverine sediment input from upland activities, water
quality problems, particularly pesticides runoff from upland agriculture and poor economic conditions of the coastal inhabitants Dudley, 2000; BPKSA, 2003; Yulastoro, 2003.
There were two large-scale Integrated Coastal Management ICM projects in Segara Anakan. The first was the Coastal Resources Management CRM Project 1984 –
1992 implemented by the Directorate General of Fisheries and supported by USAID. The objectives of this project were to establish a land use zoning scheme that satisfied the
different resources users, to preserve ecological important areas of coastal forest, estuarine and marine ecosystems; and to solve land use conflicts. The second project was the Segara
Anakan Conservation and Development Project, SACDP, from 1996 to 2004 implemented by the Directorate General of Regional Development and supported by an ADB loan.
Primary objectives were water resources management and sedimentation control, rehabilitation and management of mangroves through community participation, capacity
building and education White et al., 2005.
Remote sensing technologies provide useful information about coastal features including mangrove ecosystems Filho and Paradella, 2002. Many environmental and
12 ecological properties can be measured using remote sensing Mumby et al., 2004. Landsat
thematic mapper TM and SPOT Le Systeme Pour l’Observation de la Terre images are adequate for mapping marine and intertidal habitats Mumby et al., 1999; Donoghue and
Mironnet, 2002, as well as for mapping mangrove cover changes Long and Skewes, 1996; Ardli and Widyastuti, 2001; Vasconcelos et al., 2002; Wejers et al., 2004. Landsat
TM and SPOT multispectral XS are the data sets used in this study to determine coastal habitat changes, based on the available data, and the provided spectral and spatial
resolution Mumby et al., 1999; Wejers et al., 2004.
Mangrove conversion in Segara Anakan has been reported in many studies Purba, 1991; Soemodihardjo et al., 1991; Tomascik et al., 1997; Dudley, 2000; BPKSA, 2003;
Yulastoro, 2003; White et al., 2005, but there is limited information on the trends of mangrove conversion temporally and spatially in this area. The main purposes of this study
are to map and analyse mangrove converted of the Segara Anakan and to monitor and assess their temporal 1978 – 2003 and spatial changes by analyzing the satellite and
ground truth data.
Figure 1. Map of the Segara Anakan ecosystems, Cilacap Regency, Java.
Material and Methods 1. Study Area
The Segara Anakan coastal ecosystem is located in the south-western part of Central Java 108
o
46’ – 109
o
03’ E; 7
o
34’ – 7
o
47’ S, west of Cilacap city. This ecosystem is protected from the open ocean by a barrier island called Nusakambangan.
Segara Anakan Lagoon
Indian Ocean
Cilacap Nusa Kambangan Island
Cikonde River Cibereum River
Citanduy River
Indonesia
Java
Motean Klaces
Plawangan Barat
13 The climate at Segara Anakan is tropical and humid, with the southeast monsoon
dry season during the months April – October and the northwest monsoon rainy season November – March. Rainfall during the rainy season exceeds 300 mmmonth and falls to
100 mmmonth or less in the dry season Tomascik et al., 1997. Tides are semidiurnal with an amplitude within the lagoon is 1.48 m in average White et al., 1989. The area of
the present study included the Segara Anakan lagoon, the rivers Citanduy, Cibeureum and Cikonde in the northern part of lagoon, Motean in the eastern and Klaces in the southern
part of the lagoon Figure 1. 2. Data sets
Satellite images were used in this study is listed in Table 1.
Table 1. List of satellite images in this study.
Sensor Platform Spectral
coverage µm
Number of channels
Spatial resolution
m PathRow
scene Acquisition
date
MSS Landsat 5
0.50–12.6 4 G,R, 2 x
NIR 79 MS 240
TIR 129065 25.04.1978
HRV 2 SPOT 1
0.50–0.89 3
10 PAN 20 MS
289-3650 10.11.1987 HRV 2
SPOT 3 0.50–0.89
3 10 PAN 20
MS 289-3650 11.07.1995
TM Landsat 5
0.45–2.35 7 B, G, R,
NIR, 2 x MIR, thermal IR
30 MS 120 TIR
121065 19.01.2003
3. Data processing: 3.1. Pre-image processing
