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The mangrove ecosystem of the northern coast of west Java

Sukristijono Sukardjo

Introduction

The role of the mangrove ecosystem as a natural resource in Indonesia is increasing in importance. In Java, this is reflected in the rapid depletion of the mangrove forest through its conversion into agricultural land, tambak (fish ponds), and other uses which have been reviewed by Sukardjo (1978). Unfortunately, the natural regeneration of desired species such as Rhizopbora spp. and Bruguiera spp. in the mangrove forest in Java is generally poor.

It is sad, however, to note that the remaining virgin mangrove forests of the northern coast of West Java e.g., Ujung Karawang, are now subject to exploitation for firewood and other uses. This eventually paves the way for their further conversion into tambak as seen in the areas around Sukamandi, Bolongan, and Marunda. Owing to the importance of mangrove resources on the northern coast of West Java it is urgent to record more accurately the extent of mangrove forests, which are one of the primary features on the coastal zone.

The main objective of this paper is to provide information on the present status of the mangrove ecosystem of the northern coast of West Java which can be used as basic data for its development, especially in connection with the coastal resources management programme.

Environment of the Northern Coast of West Java

The whole area is mostly flat with an elevation of less than 10 m. It is extensively dissected by rivers running to the Java Sea. The main rivers are the Cimanuk, Cipunegara, Citarum, Bekasi, Ciliwung, Cisadane, and Cilontar (Fig.1).

The soil consists of alluvial material, a complex of yellow-red prodsolic soil, latosol, and lithosol that originated from igneous rocks and sedimentary materials (Soepraptohardjo 1972). Few studies concerning the properties of mangrove soils on the northern coast of West Java have been made, except on the Ujung Karawang area, which was investigated by Soerianagara (1971). Alrasjid (1971b) and Sukardjo (1979a) reported data on soils up to 20 cm deep from both mangrove forests in Ujung Karawang and the Cimanuk Delta (Table 1).

The mangrove forest on the northern coast of West Java has developed under the over-wet to (mid-year) dry climate (Kartawinata 1977). According to Schmidt and Ferguson (1951) the area belongs to the D (Mauk, Indramayu, and Ujung Karawang) and the C (Jakarta and Pamanukan) types, with the mean number of dry months (less than 60 mm) from 4.0 to 4.7 and the mean number of wet months (more than 100 mm) from 4.8 to 6.7; the ratio between dry and wet months is 0 - 79.9 per cent. The area has an annual rainfall of about 1,446 to 1,793 mm (Berlage 1949). The rainy season occurs mostly from November to March or April. During this period the rainfall is plentiful and regular, with very small variability, although the maximum rainfall occurs in January. Throughout the coastal area the duration of the dry season is less than 7 months. The seasonal temperature variations are very small, i.e., 0.9°C. The mean monthly temperature during the dry season rarely exceeds 27.5°C, and during the rainy season rarely drops below 25.1°C, mostly remaining at 26.8°C. The average relative humidity also remains fairly constant at about 65 per cent and rarely drops below 50 per cent. The climate diagrams for the meteorological stations at Indramayu, Pamanukan Cabang Bungin and Batujaya (Ujung Karawang), Jakarta, and Mauk are presented in Figure 1.

Extent and Distribution of Mangroves

Occurrence

The mangrove forest of West Java covers an area of approximately 21,642 ha, of which about 200 ha are designated as nature reserve (e.g, Ujung Kulon, Muara Angke, Rambut Island, and Dua Island). Mangroves are found mainly in Jakarta Bay and from Ujung Karawang to Indramayu (Table 2, Fig. 1). The forest is concentrated along the coastline and estuaries of the Citarum and Bekasi rivers. The mangrove forest is confined to certain coastal stretches. The coastal region including the estuaries, backwaters, and creeks is fringed with mangrove vegetation. Some of the areas like Rambut Island and Dua Island, and the Ujung Karawang region show a luxuriant growth of mangrove forests, while other areas, such as the Cimanuk Delta and Sukamandi regions have been degraded because of destruction by human activities. Human pressure in the mangrove area is strong everywhere.

Table 1. The Chemical and Physical Properties of the Soil in Some Areas of the Northern Coast of West Java (After Alrasjid 1971b and Sukardjo 1979b)

Key to table: PS = Pancar Song
PB = Pancar Balok

FIG.1. A map showing the locations and the climate diagrams of the mangrove forest areas on the northern coast of West Java

However, much variation exists in estimates of the extent of the mangrove, and it is not clear whether this is because of the fast rate of reclamation, the result of natural destruction, or due to errors in the surveys. It is also not clear whether the estimated area includes only the wooded area or the total mangrove environment including salt marshes. Therefore, there is a need to have more accurate surveys.

Structure and species composition

The mangrove communities on the northern coast of West Java are structurally and floristically varied, from the relative simple community (e.g., Muara Angke) to the more complex and luxuriant community (e.g., Rambut Island and Ujung Karawang). However, in some areas, such as Sukamandi, Indramayu, and Pamanukan, the mangrove is declining (Sukardjo 1979a, b).

Few studies on the ecology of the mangrove community of this area have as yet been carried out. The forest on the Cimanok Delta has been recently investigated by Sukardjo (1979a), that on Rambut Island by Kartawinata and Waluyo (1977), and that on Dua Island by Buadi (1978). The silvicultural investigation in the Ujung Karawang mangrove was undertaken by Alrasjid (1969). The study of flora and fauna found in the mangrove forests of various places on the northern coast of West Java has received greater attention (Burhanuddin and Martosewojo 1978; De la Cruz 1978; Hutomo and Djamali 1978; Munaf 1978; Soemodihardjo and Kastoro 1977; Sukardjo 1978; Toro 1978).

Table 2. Mangrove Forests in West Java

Source: Direktorat Bina Program and PPA (Directorate General of Forestry, Bogor)

The species composition of the mangrove forest on the northern coast of West Java differs from one area to another. The forest consists of up to 29 species of mangrove trees, along with various shrubs and herbs. The most common and typical mangrove species occurring in the area are shown in Table 3. It is evident that Avicennia marina and A. alba are dominant and have a large number of individuals in all sites.

Human Impact on the Mangrove Ecosystem

Very little work has been done on human aspects of West Java mangrove resources (Arwati 1977; Kunstadter 1978; Kunstadter and Tiwari 1977).

A survey of the mangrove ecosystems on the northern coast of West Java has been done by Soemodihardjo et al. (1977), particularly those found in Jakarta Bay and adjacent areas. Sukardjo (1978, 1979b) and De la Cruz (1978) studied the human uses of the mangrove environment and the traditional use of mangrove species, and the Direktorat Bina Program (Directorate of Forest Planning) study (1977) was concerned with the stand density.

Effect of mangrove modification on human populations

On the northern coast of West Java, many mangrove forests have been cleared for various purposes such as tambak and agricultural land (Schuster 1949, 1952; Sukardjo 1979b). Poor coastal zone management has induced land erosion. Large-scale agricultural land reformation is resulting in stress to the mangrove ecosystem. The erosion of coastal areas seems to occur at several places annually. Further cutting of the mangrove forests and development of the tambak accelerate the erosion process, although these aspects have so far not been studied in detail (Hehanussa, personal communication).

Because of pollution, the productivity of the mangrove environment decreases constantly. The mangrove ecosystem, which is also considered the best nursery grounds for fish species, is adversely affected by pollutants.

Quantitative and qualitative appraisal of humaninduced stresses

Natural and human-induced stresses disturb the mangrove in various ways. There are different types of humaninduced stresses on mangrove environment, such as indiscriminate cutting, reclamation of mangrove areas, pollution of the wetland, and grazing on dryland. These stresses should be investigated further.

Table 3. The Distribution of Typical Mangrove Species in Terms of Their Relative Dominance in the Northern Coast of West Java

Key to table:
Rare : o 0.1% Very common: o 5 - 50%
Less common: o 0.1 - 0.5% Dominant : o 50%
Common : o 0 5 - 5%
Data collected by Mr. Buadi (Dua Island), Mr. Aliasrid (Ujung Karawang), and Mr. Victor Toro (Part Groups Isdand).

1. Pollution

Pollution on the northern coast of West Java is constantly increasing due to the lack of regulations dealing with the disposal of industrial and other wastes from various cities. For different types of pollution, such as industrial, oil, sediment, and sewage (Hehanussa, personal communication; Soegiarto 1973,1975a, 1975b; Wisaksono 1974), the common outlet of pollutants is the estuary, where mangroves are invariably present (e.g., Ujung Karawang, Marunda, and Cimanuk). Although a considerable amount of work has been done on different aspects of pollution, none of it has been concerned with the toxic effects of pollutants on the mangrove flora and fauna or on the mangrove ecosystem. There is no doubt that some pollutants are capable of destroying the mangrove ecosystem on the northern coast of West Java. Recently, l observed that industrial wastes and petroleum products appear to be harmful to the growth and the survival of the mangrove seedlings. A one-year observation of the remaining mangrove forest at Sukamandi through Tegal and of the virgin forest on Rambut Island indicates that the mortality of Rhizophora mucronata seedlings is 10 to 15 per cent.

Sewage and industrial wastes from the cities, as well as miscellaneous household wastes, accumulate a great amount of organic materials and have an influence on the mangrove. My preliminary observations on the establishment of mangroves in polluted areas indicate that a remarkable change in the faunal communities on the mud surface is taking place. A heavily polluted area does not support as great a variety of animals.

2. Indiscriminate cutting

Mangrove forests on the northern coast of West Java have been adversely affected by illegal cutting at the Cimanak Delta, Sukamandi, Muara Gembong, and Marunda. During one year of observation, especially on the dry period, it was found that about two pikul (+ 40 kg) of wood/day/ha were removed from these areas. This includes trees and saplings. The illegal cutting is mostly attributed to the difficulties in obtaining firewood in the village and to the poverty of the villagers,

3. Reclamation of mangrove areas

According to the Direktorat Bina Program, the total area of forest in West Java is estimated to be 991,340.32 ha (22.23 per cent of the total land area). This includes 476,474 ha of protected forest (including nature and game reserves) and 514,867 ha of production forest (Direktorat Bina Program 1977; Haeruman et al. 1977; Wiroatmodjo and Judi 1978). Table 2 indicates that most mangrove in West Java is classified as unproductive, consisting mainly of abandoned cut-over forest. Due to this situation, the destruction of mangrove areas by the villagers and other local inhabitants is still going on. Unfortunately, the mangrove forests of the northern coast of West Java show many examples of areas where reclamation of the forests or marshy areas has been undertaken on a small scale by local inhabitants.

In the last decade, the illegal destruction of mangrove areas by local people has become a great problem in terms of coastal resources management. Studies to find remedies have not yet been undertaken. In the Cimanuk and Sukamandi regions, for example, approximately 500 ha have been converted into agricultural land and tambak by local inhabitants since 1950.

A few years ago there was a continuous belt of mangrove vegetation from Mauk to Muara Angke. Today, due to the population pressure, all of these areas have become tambak areas (e.g., Marunda).

Based on field observations from 1977 to 1979, I estimate that more than 1,500 ha of the mangrove forest land on the northern coast of West Java have been converted into tambak and agricultural land.

There is no data available on the total loss and decline of mangrove areas in Indonesia as a whole. However, from the information given above, some estimate can be made.

Economic Importance of the Mangroves of the Northern Coast of West Java

Sound management leads to the optimal use of the mangrove ecosystem for long-term benefits to human communities. This ecosystem is viewed as a valuable natural resource that provides free services and goods for human needs, and it functions without subsidies. People have the option to manage this ecosystem in its natural state or to subject it to limited or complete modification for other uses. Management must be in such a form that yields direct benefit to the local community (Soemodihardjo and Nontji 1978). The scope of the management scheme must be based on regional ,features of geomorphology, hydrology, labour, skills, and the social and economic structure of the community. Rational management schemes require decision-making criteria based on calculating the net value (total cost and benefits) of the existing mangrove ecosystem, and of the alternative uses for it.

It is well known that the mangrove ecosystem on the northern coast of West Java provides fishermen and inhabitants with valuable raw materials like firewood and tannin, although on a small scale (Alrasjid 1971b; De la Cruz 1978; Sukardjo 1978, 1979b). Also, a number of mangrove areas provide a good breeding ground for fish (e.g., Ujung Karawang, Muara Angke). It should be emphasized that the mangrove is little exploited industrially.

The principal product is firewood. The forests are quite often used as grazing grounds for buffalo, cattle, goats, and sheep, and as an important source of forage, for which the sprouts and young leaves of Avicennia spp. are preferred (e.g., Cimanuk Delta, Tiris-lndramayu, Sukamandi [Sukardjo 1979b] ).

Exploitation of the mangrove forest

it was mentioned earlier that remaining mangrove forests on the northern coast of West Java are now subject to exploitation for firewood (e.g., Indramayu, Purwakarta, and Bogor) and other local uses, and later are clear-cut to make tambak. Some areas are already leased for the latter purpose#, e.g., Sukamandi, Balongan, and Cirebon.

In West Java the productive mangrove forest covers an area of about 7,066.69 ha (see Table 2). The Rhizophoraceae are now so small in number that they cannot be exploited for tannin. Most of the trees are used only as firewood. The average production is about 19.8 m³/ha/year, consisting of trees of cutting-age classes IV through Vll. They mostly come from Indramayu (Haeruman et al. 1977). The acreage of mangroves in West Java according to age class is presented in Table 4.

In the remaining mangrove areas, Sukardjo (1979a) estimated that Avicennia alba and A. marina make up nearly 90 per cent of the saplings (diameter: 2 - 9.99 cm), especially those in the Cimanuk Delta. Both species occur gregariously throughout the Indramayu and Sukamandi areas. Their natural regeneration rate is good, and seed is efficiently dispersed by tidal waters. For full growth the young plants need direct sunlight. In the case of Sonneratia alba and S. caseolaris, which occur together in the Avicennia belt, seedling regeneration is very poor.

Unfortunately, firewood is in great demand, especially in coastal districts where mangroves are easily accessible. The villagers prefer firewood collected from the mangrove trees for home consumption. As yet there is no data available on the exploitation of mangrove trees by villagers.

Some local uses of the principal mangrove species

This is based on field work conducted from 1977 to 1979. The villagers possess the art of effectively utilizing the mangrove forest products, including those of herbaceous plants and halophytes. The use of each species is much the same from one region to another. It is generally the fishermen who make the best use of the plants.

Avicennia spp.
All species of Avicennia are heavily exploited for their wood, which is considered to make the best firewood for home consumption, especially at Marunda, Muara Gembong, Sukamandi, the Cimanak Delta, and Pamanukan. The sprouts and young leaves are used as fodder and vegetables in Sukamandi and the Cimanuk region. Avicennia is good for reforestation. It produces large quantities of fertile seed that is able to withstand transport by sea water for several weeks. It also coppices well (Alrasjid 1971a). Sometimes Avicennia is used as green manure, especially in the tambak region which is managed through the tumpangsari (multiple crop) system (e.g., Sukamandi and Pamanukan).

Nypa fruticans
This plant is not very common on the northern coast of West Java, except in Marunda, Ujung Karawang, Tiris, and Balongan. The leaves of Nypa are quite costly since they are highly valued as a roofing material. Planting of Nypa fruticans in some areas in Ujung Karawang or Pamanukan is recommended to supply local needs.

Ceriops Spp.
There are two species of Ceriops which are collected by local people for firewood. Ceriops decandra is the most important species and it is also used for the construction of small houses and huts. The fishermen also extract a reddish liquid from the bark and use it to protect fishing nets.

Table 4. The Hectarage of the Productive Forest by Age Classes in West Java (after Haeruman 1977)

Lumnitzera racemosa
This is a small tree with a dense, hard, and resistant wood. It is used mostly for construction of small buildings and also for firewood.

Sonneratia alba
This species has been over-exploited for firewood. In the Cimanuk Delta and on the eastern coast of Jakarta it has almost completely disappeared.

Aegiceras corniculatum
This is a bushy or shrubby species found on all parts of the northern coast of West Java. The wood is used as firewood and for the framework of huts. The fishermen, e.g., in Tiris-Indramayu, use the bark as a fish poison.

Excoecaria agallocha
This species, along with Avicennia, is one of the common species in Ujung Karawang. It offers a very good plant cover because of its rapid growth. Its wood is soft and light, and is used for making fishing floats, crates, and boxes, and as firewood. Preparations of the latex from the leaves and bark are used in the treatment of many ailments in the countryside.

Conclusions and Recommendations

The economic importance of the mangrove forest both as an ecological niche and a source of firewood cannot be ignored. Every effort should be made to try to maintain it in perpetuity. Even if a large-scale regeneration of this forest fails, the smaller areas that can regenerate successfully should be maintained as a habitat for marine life and as a perpetual source of firewood for domestic consumption.

I believe that we must underscore the urgency of two factors. First, the physical destruction of estuarine mangrove (e.g., Cimanuk areas-Indramayu, Muara Angke areas-Jakarta) must be halted and their biological fitness restored through pollution abatement. Second, it must be widely recognized that estuarine farming is based on entirely different principles than dryland farming. Consideration must always be given to other uses, too. The mangrove forests on the northern coast of West Java are rapidly diminishing. Measures must now be taken before we totally lose the mangrove forests, and the many tangible and intangible benefits derived therefrom that play a vital role in stabilizing the socio-economic life of fishermen (e.g., Ujung Karawang, Cimanuk Delta, Muara Angke).

Regarding tambak development in Java and Bali, I recommend detailed studies on the carrying capacity of the mangrove areas before permitting them to be used for tambak culture and other aquaculture projects. The Directorate General of Fishery, in cooperation with the Directorate General of Forestry, is seeking conservation of the mangrove forests in Jakarta Bay at Ujung Karawang.

Encouragement should be given also to increase the yield per hectare through the introduction of new technology to improve the production of fish, instead of increasing the acreage (extensification system).

In coastal resource management cases involving the structural, dynamic, and economic values of the mangrove system on the northern coast of West Java, while taking into consideration the importance of the mangrove forest and the surrounding environment, I suggest that:

1. Mangrove areas should be surveyed using aerial photographs supplemented with ground data.
2. Critical areas, e.g. Marunda, Muara Gembong, Ujung Karawang, the Cimanuk Delta, where immediate attention is required, should be given priority in future studies.
3. Inventory and distribution of mangrove flora and fauna should be studied in detail, with particular reference to economically important species.
4. Forest law should be clearly defined and published separately for wide circulation. If possible, local languages (Sundanese and Cirebonese) should be used so that laws are easily understood by the villagers and the poachers.
5. Sufficient funds should be released for research and development work on mangroves.
6. Rules and regulations framed by the Directorate General of Forestry should be implemented properly. Also, better working plans should be prepared.
7. Rehabilitation of mangrove areas should be done judiciously.
8. Utilization of mangrove trees or areas should be undertaken without disturbing the ecological balance of nature.
9. Strict measures should be taken against polluting the mangrove environment.
10. More studies on the effect of external factors on mangrove ecosystems, including the input of fresh water, nutrients, and silt from upstream, and tidal input from the Java Sea, should be undertaken.
11. Future studies should include the determination of the net primary production of the plant community in the mangrove ecosystem in relation to the environmental variables within a single area and between different areas. Studies should also cover such aspects as the effects of aeration and drainage of the soil by mud burrowers, the magnitude of litter decomposition, and the transport of debris to nearby waters.
12. It is desirable to study the waters within and adjacent to the mangrove ecosystems along the following three lines of research:

1. Geomorphology, bathymetry, water volume, and sedimentation dynamics.
2. Hydrology, including water budgets and water turnover rates.
3. Seasonal shifts in the physiochemical and biological dynamics including budgets of organic constituents and patterns of population movements. Budget studies should include inputs, outputs, and internal accounting of recycling. Ail studies should consider the horizontal, vertical, and seasonal variations of physical and biological parameters.

13. Studies to determine the significance of litter production, particulate detritus, and soluble organic compounds to consumers within mangrove forests, to consumers downstream, and to the fauna of nearby marine areas should be encouraged.
14. Identification and quantitative analysis of the eggs and larvae of commercially important fishes, prawns, crabs, and shellfish within mangrove areas and determination of the nature and availability of their food requirements and their seasonal succession should be undertaken.
15. The direct values of mangroves and the products derived from them, and an estimate of the extent and value of the coastal fisheries (shellfish, prawns, crabs, and fish) that are dependent on mangroves at some stage of their existence should be determined.
16. Studies should also include the determination of the indirect values of mangroves through their contributions to neighbouring ecosystems and coastal stability.

Sukardjo (1979b) also suggested that the plans concerning management and research, especially in Java and Bali, should be laid down as follows:

1. Effectively assess the exploitation of mangrove by dividing the mangrove forest into a reservation zone and an exploitation zone.
2. Fishery-study the relationship between the mangrove ecosystem and coastal fishing, and investigate ways to increase the yield of coastal aquaculture in order to fix a suitable area for coastal culture.
3. Forest-study forest management, including reforestation and methods for increasing productivity.
4. Mining-studY the ecological impact resulting from mining in the mangrove area.

In order to achieve these goals, the First National Symposium on the Mangrove Ecosystem held in Jakarta in 1978 strongly recommended that research in various fields be accelerated and that the government promote this research and intensify enforcement of existing laws and regulations.

Acknowledgement

I wish very much to thank Prof. Dr. Purukawa Hisao (The Centre for Southeast Asian Studies, Kyoto University, Japan) for his financial support for my field work in Java and Bali in 1979, and the Director of Lembaga Biologi Nasional-LIPI, for allowing me to leave my duties during the trip.

References

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Discussion

Hehanussa: What about the effects of pollutants on the mortality of Rhizophora?

Sukardjo: The effect is not known, except that there is mortality at some polluted areas, such as Tegal, Cirebon, and Indramayu.

Hehanussa: The mortality of mangrove at some areas has been pointed out; in this case, what is the cause of the mortality, the oil pollution or any other factor? What species are mostly affected?

Sukardjo: Oil is one of the factors, but the species disturbed have not been studied extensively.

Bird: Do you have any control area for comparison?

Sukardjo: We do have, at Ujung Krawang.

Koesoebiono: I suggest that not only carrying capacities but also economic feasibility has to be considered in doing research.

Sukardjo: I mentioned the connection between "destruction" of mangrove forests and the depletion of fishery problem; to produce fish from the area without mangrove forests seems to be impossible, because of the imbalance of nature.

Bird: About eight mangrove species have economic value. Is it possible to develop artificial cultivation of these mangroves?

Sukardjo: Many species belonging to Rhizophora have been destroyed widely. To use only certain kinds of mangrove is difficult, and not easily accepted by the local people.

Bird: Are the reserve areas adequate to maintain the species?

Sukardjo: Rhizophora species are not being maintained.

Siregar: Can the mortality of the seedlings (10 - 15 per cent) be used as an indication of the existence of any pollutant? Other methods should be applied for monitoring pollutants.

Sukardjo: I agree with your suggestion.

Siregar: Do you observe the mortality of other species?

Sukardjo: Yes,Avicennia sp. and Rhizophora sp.

Ongkosongo: Is Bruguiera sp. a pollutant indicator?

Sukardjo: It prefers to grow on sites with low salinity and hard soil, usually on land, and is less useful as an indicator.

Muluk: Mangrove seedlings can die naturally without any pollutant.

Sutamihardja: What is the dominant cause of pollutant?

Sukardjo: I think oil is dominant.

Soegiarto: Some of the previous questions were not completely answered.

1. Is there any proof that 10 - 15 per cent of mortalities of mangrove seedlings were caused by oil or is this conclusion not yet proven?
2. What is the origin of the oil, is it from oil wells, harbours, or ships?
3. Is it possible to use Rhizophora seedlings as a species indicator for pollution, especially oil pollution? One of the reasons is that they are very sensitive to pollutants.
4. is the present system adequate for conservation purposes of economically important species? Or for ecologically important species?

Sukardjo:

1. It is important to determine the pollutant. My observation is limited to the knowledge that the pollutant has negative effects on the growth and existence of Rhizophora mucronata seedlings, but from observations, it seems that the oil originates from oil discharge.
2. The origin of the pollutant might be discharged from harbours and ships.
3. At the moment I am not able to state that Rhizophora seedling is an indicator species for pollution. First I want to know whether there is negative affect for the growth and existence of Rhizophora mucrata. After that I want to know the growth rate of the seedling in a polluted area. Finally, lethal doses I LD) can be determined, and this is my final goal.
4. Traditionally the fishermen and people living near the coast know the basic principles of conservation of several species which have economic values. The system in management which is presently used by the Directorate General of Forestry is adequate, but the execution is not good and is not based on ecological data on the mangrove forest. As we all know, much of the mangrove forest of the northern coast of West Java has been destroyed, and reforestation is badly needed. For certain sensitive areas the conservation of ecologically important species is useless.

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