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BIOTROPIA NO. 23, 2004 : 13 - 39

FISHERIES ASSOCIATED WITH MANGROVE ECOSYSTEM IN
INDONESIA: A View from a Mangrove Ecologist

SUKRISTIJONO SUKARDJO

The Centre for Oceanological Research and Development, Indonesian Institute of Sciences,
Jl.Pasir Putih 1 Ancol Timur, P.O.Box 4801 JKTF Jakarta 11048, Indonesia. E-mail:

s_sukardjo@telkom. net and s_sukardjo@yahoo. com

ABSTRACT

Blessed with mangrove area of some 9.6 million ha in extent, Indonesia represents an important country with
fishery resources being a source of food and nutrients. The fishery resources utilized by man, such as fishes, crustaceans
and mollusks that are found in the mangrove ecosystem/swamp area arc enormous. There is a range of species caught in the
mangrove and surrounding areas with over 70 species. However, commercially valued species are limited to a few such as
rabbit fish, snapper, grouper, marline catfish, fringe-scale sardine, and anchovy. Leaf detritus from mangroves contribute a
major energy input into fisheries. But information about the study on the relationship between fishery species and mangroves,
ecologically and biologically, arc scanty. The mangrove is a physiographic unit, the principal components of which arc
organisms. Therefore, the problems are predominantly of a biological nature (e.g., mangroves - fishery relationship).
Positive correlation between the mangrove area and penaeid shrimp catch found in Indonesia, the Philippines, Australia
and Mexico. Finally, the most important part of the variance of the MSY (Maximum Sustainable Yield) of penaieds (53% of
the variance) could be explained by a combination of area of mangrove habitats and latitude.

Keywords : Indonesia/Mangrove/Ecosystem/Fisheries/Ecology/Coastal areas/Fishes/Molluscans/ Crustaceans.

INTRODUCTION

Indonesia (6° N - 10° S and 95° E - 142° E) is an archipelagic state in the tropical area
with 18,110 islands and almost more than 108,000 km of coastlines (Sukardjo 1997; Anonim
2003). These areas form an important and valuable natural resource with potential economic value,
and a potentially important production area for food. People have long relied on coastal waters as a
source of food. The coastal zone of the Indonesian waters includes a number of bays and gulfs into
which large and small rivers empty, creating estuarine conditions in the inshore areas. The extent of
the estuarine zone in the sea varies according to the size of the river and the volume of its
freshwater discharge, the steepness of the gradient, and the tidal range. Also, these coastal zones
contain diverse productive ecosystems that include mangroves, sand beaches, several river-
basins and freshwater bodies. Each of these ecosystems has components that are exploited in a
wide variety and used with different intensities because of socio-economic and socio-cultural
demands. Therefore, Indonesia, is considered as one of the largest maritime country in the world.

BIOTROPIA NO. 23, 2004

With almost more than 75% of Indonesian territories being seas, marine fishery is one of the
important renewable resources for the nation. For instance, 1,450,000 tons of pelagic fish had been
caught for whole Indonesia (EPS 1995). Ironically, depletion of the marine resources is starting to
become evident in Indonesia. The fishery resources utilized by man, such as fishes, crustaceans and
mollusks (oyster, mussel, cockle), that are found in the mangrove swamp area are enormous.
Indigenous people in Indonesia have exploited the biota of mangrove waters for centuries, and fish
and shrimp are still one of the major products harvested from this mangrove swamp (Schuster
1952). Thus, aquatic resources play a vital role in the social, economic and ecological well-being
of coastal communities in Indonesia. Furthermore, the value of the mangrove ecosystems is not just
of academic interest, it also relates to their cultural and commercial value. The full economic value
should be determined in order to make intelligent decisions about their future use. Thus the
understanding of both the roles and the functions of mangrove ecosystem in terms of fishery in
Indonesia is also of considerable importance. The following paper is, therefore, an effort to review
and methodize existing information on the mangrove-fishery association subject in Indonesia.

THE INDONESIAN MANGROVES: A Fishery Feature

Situated at the two continents, Asia and Australia, and two oceans, Pacific and Indian, the
Indonesia archipelago, has an ecologically and economically strategic position with distinct culture
that took shape on these 18,110 islands. The climate of Indonesia is tropical and generally governed
by the monsoonal situation, resulting in fairly regular climate variations. During the winter, the
northern part of the earth has air pressure around Asia higher than that of Australia. North of the
equator, the wind blows from North and East - the NE monsoon, at and near the equator, it
becomes more North and North - NW monsoon. South of the equator the winds turns from NW
via W to SW - the West monsoon. Consequently, Indonesia is blessed with high annual rainfall
(>1500 mm/year) and comfortable tropical temperatures. Moreover, Indonesia's waters are
homogeneous to an unusual degree. The country lies entirely within the tropics, straddling the
equator from roughly 5°N to 10°S latitude. Oceanographic conditions are uniform in this
equatorial zone, characterized by lack of seasonal changes and consistently warm waters. The
Indonesian waters are ideal monsoon region. These are very favorable for mangroves
development. Consequently, large areas of the mangrove ecosystem in Indonesia are to be found
and estimated at about the range of 4.25 million ha (1982) to 9.6 million ha (2002). Therefore,
mangrove forests are a major feature of the coastline in many islands of Indonesia. However, this
figure and its distributional extent is still in debates for further clarifications. This type of forest
vegetation is common in the Malesia (comprising the political states of Indonesia, Malaysia,
Singapore, Brunei Darussalam, the Philippines and PNG) and has stimulated the interest of various
systematics and ecologists as can be learned from comprehensive

Fisheries associated with mangrove ecosystem in Indonesia — Sukristijono Sukardjo

studies by Watson (1928) in Malay Peninsula, and by Brown and Fisher (1918) in the Philippines,
and by Becking et al. (1922) in Indonesia. A substantial body of information exists on the
biology, ecology and other aspects of mangroves or mangrove ecosystem or mangrove forests
or mangals (Macnae 1968). The bibliography lists of mangrove forests in Indonesia can be
found in e.g., Rollets (1997). However, recent records of mangrove literatures can be learned
through a series of the Proceedings of the National Seminar on Mangrove Ecosystem (I-VI) and
others. But our knowledge of the mangrove fish fauna in contrast, is limited to a handful of papers
that deal with inventory. A similar state of knowledge exists on the association between
mangroves and fisheries (See: Macnae 1974 for general information); and the economic value of
the fisheries function of mangroves in the Bintuni Bay, Irian Jaya, has been discussed by
Ruitenbeek (1991). Commercial fisheries in Indonesia or Indonesia's artisanal commercial
fisheries are largely dependent upon coastal and estuarine fishes.

In Indonesia, mangrove forests reach their greater structural and floristic diversity in all
biggest islands e.g., Sumatra, Kalimantan, and Irian Jaya, and tropical forests generally have higher
rates of litter production than temperate forests (Bray and Gorham 1964). Mangrove forests in
Indonesia are floristically rich with at least 94 species represented (Sukardjo 1994), and produce
large quantities of litterfall e.g., in East Kalimantan estimated to be about 21.10 to 29.35 dry
weight t/ha/year (Sukardjo 1995). They produce a large amount of fixed carbon which is used
by man for timber, firewood and charcoal. It is hypothesized that this carbon may also support
detritus-based food webs both in the swamp and in surrounding coastal waters. In a global
context, mangrove swamps have been recognized as extremely productive ecosystems, which not
only have a high rate of primary productivity, but also export organic matter and support a variety
of aquatic organisms (Odum and Heald 1972); and most of the aquatic organisms are valuable
economically for man. It is generally supposed that mangroves play an important role in supporting
a wide range of marine life in near-shore waters and in sustaining coastal fisheries. These highly
productive mangrove forests provide critical habitat and food for many organisms, including
important fisheries species. However, human population concentrates in the coastal zones,
imposing enormous pressure on these mangrove forests. In Indonesia moreover, mangrove
swamp communities or mangals (After Macnae 1968) occupy warm coastal areas where land is
becoming increasingly valuable for farming, mariculture, and recreation. Thus men's use of
mangrove areas in Indonesia for the establishment of ponds for the culture offish and prawns, and
other fishery activities, and for timber etc., is practically common.

In Indonesia, mangrove ecosystems or mangroves are found in tidal wetlands under varying
conditions of salinity, water-logging, anaerobic substrate, often hyper-saline (>33 %) and acidic.
Many of the largest mangrove areas of Indonesia occupy a significant portion of the deltas of
rivers, large and small. Here, mangrove ecosystems are delicate and complex, intensely
dynamic and fragile; and their principal components are the physical and chemical
environments, the biotic elements (flora and fauna), and human interferences. Each
component of the

BIOTROPIA NO. 23,2004

environment namely, climate, salinity, freshwater supply, siltation, erosion, substrate and nutrients,
act on flora and fauna, and, in-turn, these influence the environment. For instance, reduced
freshwater flow through a mangrove forest probably not only reduces the nutrient input from
surrounding terrestrial areas, but also results in higher soil salinities. Thus, it becomes a stress
for mangroves itself and their associated meiofauna.

Mangrove ecosystems are open systems and the cycles of material transport in mangrove
forests are driven by physical and biological factors that control the rate of input and output of
inorganic and organic components. Changes in the quality of water entering and leaving the
mangroves are particularly important in determining natural cycles. In addition, they support a
characteristic fauna which includes crabs, shrimps and molluscs. The waterways support a varied
fauna of fish, shrimp and plankters. The general acceptance is prawn fisheries are important
commercial fisheries in many developing countries and developed countries.

AN ECOLOGICAL IMPORTANCE OF THE MANGROVE ECOSYSTEM - Fishery Aspects

1. Ecological Features of Mangroves as Fish Habitat

Mangrove forests are a common type of pan-tropical coastal vegetation. In Indonesia,
characteristics of mangrove sites varied provincially and locally, but it does have the same serve
as fish habitats and refuges for a large number of species of conservation concern. For instance, in
the estuary of the Rokan River in Sumatra, Hardenberg (1950) has reported the occurrence of
some 175 species, including occasional migrants. The number of individuals is, however, high.
In Indonesia, there are large marine mangal areas in an environment characterized by tidal ranges of
2-5 m, fluctuating salinities of 28-33%o, high atmospheric humidity and constant subequatorial
temperatures; and mangrove forests of embankments, lagoons, and harbors are less dominated by
hydrological factors. For instance, the coast of Java experiences strong semi-diurnal tides, with a
range of 5 m and above during extreme spring tide. The coast may be classified as a high meso-
tidal environment. The waters are well mixed vertically, and salinities range from 20 to 32
%o. Major dilution occurs from the discharge of freshwater by 11 rivers. Also, wind blowing over
the sea surface can cause the disturbance of hydrodynamic sea stability. This condition,
furthermore, will result in a rising of sea water towards the surface from the below regions and
oceanographically known as upwelling; and it is very beneficial for fishery. In Sumatra and
Java, the color of estuarine water may be tea-brown or blackish, due to outflow from enormous
peat forests (Hardenberg 1950). The pH of this water is reported to be as low as 5 or less. There is a
marked increase in the number of planktonic organisms as a result of increase in nutrient salts.
Copepods diminish to be replaced by an increased amount of diatoms and Noctiluca. Finally,
mangrove ecosystems by their nature include an aquatic element; and

Fisheries associated with mangrove ecosystem in Indonesia — Sukristijono Sukardjo

marine species are replaced by coastal forms. For instance, the position of burrowing animals within
the substrate is most closely linked to the state of the tide. This may be merely the temporary
intrusion of seawater along open coasts at high tide, or it may be the waters of tidal creeks or
estuaries surrounded by mangroves. Thus, the unique association of animals and plants, for
instance, that dwell upon the roots of mangroves in Indonesian seas are interesting and has long
been attracting the attention of naturalists and ecologists.

The structural-functional diversity of the true-mangrove species complex is probably best
expressed in the remarkably high diversity of animals for which the ecosystem provides a variety
of physical habitats and food sources. For example, the Rhizophora mangroves that predominate the
fringe habitat have a well-developed prop-root system that is flooded semi-diurnally by tides and
may provide habitat to fishes. Also, some structurally heterogeneous habitats in tidal waters have
been shown to provide fish with protection from predators and enhanced feeding opportunities
(Rozas and Odum 1988) as can be learned that a large proportion of fish found in mangroves are
considered juveniles and species of a small size at maturity (Bell et al. 1984). Thus, the
mangroves-fisheries connection may, therefore, lie in the nursery function through provision of
food and shelter from predation (Hatcher et al. 1989); and protection from predation is offered by
physical structure (e.g., mangrove roots, substratum, and turbidity), in combination with for
example, shrimp behavior such as hiding and burying (Dall et al. 1990). Moreover, the estuaries of
the Indonesian coastal zone support a varied fish fauna, but it is rather poor in species. The fish
fauna consists of species that spend all or a major part of their life in the estuaries, and marine or
freshwater species which migrate seasonally into or through the estuaries (Table 1). Consequently,
the fish or ichthyoids fauna occurring in and/or within mangroves and/or mangrove environment,
have been placed in various ecological groups: as permanent residents, temporary residents or rare
species.

Table 1. Types of fish species recorded from Apar mangrove bay areas, East Kalimantan, and from Banyuasin
mangrove estuary areas, South Sumatra .

Type Estuarine Species Marine Species Riverine Species Total *)
Adults 73 69 25 145

Juveniles**) 45 31 15 68
Total 73 75 26 151

Notes : * As some species can be classified under several headings, totals given arc not the sums of
Columns.

** As the specific identification of juvenile fish is frequently difficult the numbers of species given mere
approximations.

BIOTROPIA NO. 23, 2004

The mangrove forest and aquatic ecosystems are independent, with biological production
processes different from those of purely terrestrial forest ecosystems. Due to their characteristic
location, the mangroves play an important role in the ecology of the coastal zone area and in
support of the marine species that utilizes the mangrove environment during part or all of their life
cycles. For instance, some prawn species may breed and complete their life cycle in shallow
coastal mangrove waters. Many species require the more saline deep offshore waters to spawn.
The larvae then migrate back to the food rich and protective coastal mangrove waters to mature.
Adults of the commercially important penaeid prawns usually spawn at sea and after a short larval
life (2 to 3 weeks), the post-larval stage settles in the near inshore areas and estuaries (Dall et al.
1990).

Roles of the mangrove forests in interactions with neighboring coastal and marine
ecosystems in Indonesia are summarized in Table 2. There are features in common, including
physical, chemical characters and effects of seasonality, of the mangrove areas as habitats for fish
and other aquatic animals. For certain species of fishes, areas of higher salinities may provide
suitable habitat for developing juvenile fishes. Also, the fish of muddy estuaries show affinities to
deep-sea fauna in some of their features. Some genera of clupeids and polynemids have prolonged
fin-rays, and others have small-diminutive eyes. Hardenberg (1950) has recorded even a species of
blind sole from the Rokan estuary. The organic nitrogen compounds of the falling leaves of
mangroves are either incorporated into the sediment or converted into peat for detritus - feeding
shellfish, or broken up to become food for bacteria, fungi and finfish. The importance of bacteria
both as a food source in marine and estuarine sediments and as mineralizing agents has been
widely commented upon. Thus exported detritus also provides an important habitat for juvenile
prawns in near-shore sub-tidal mudflats (Daniel and Robertson 1990). Johannes (1978) pointed out
that many fish in tropical marine environments move inshore to spawn. In this context, he
mentioned the Gerridae, Sparidae, Engraulidae, Pomadasydae and Sciaenidae, all of which are
demersal coastal forms and spawn in estuaries. For example, in the Palau (8° N, 135° E) spawning
migrations, only Herklotsichthys sp. migrated from its usual seagrass and/or lagoon habitat to spawn
in mangrove creeks (Johannes 1978). One common mangrove-deniser, Lutjanus argentimaculatus,
migrated to the lagoon and reef slope to spawn. Lethrinus sp and Siganus lineatus were the only
other fish which occasionally inhabit mangroves that migrated to spawn on reef slopes.

Estuaries play a role in energy transfer between a river and the sea, which is especially
important for many commercial coastal fishes whose fish larvae and juveniles are dependent on
the estuary as a nursery and feeding grounds. As discussed by Hambrey (1996a, b), the nursery
function of mangrove ecosystem is likely to be highly variable, with some areas being of far greater
value, and others of far lower value than the global estimates would suggest. For example,
mangrove swamps of reef flats are generally important as nurseries for mullet (Mugilidae) and
baitfish (Clupeidae and others), and, together with inland mangroves, are a source of crab (for
instance Scylla serrata and Sesarma spp.). The dominant mullet in all

Fisheries associated with mangrove ecosystem in Indonesia - Sukristijono Sukardjo

mangrove creeks is Liza subviridis. Large mullet, Valamugil sp and L. argentea appear to be more
abundant in the open main channels of Indonesian mangrove system. Ambassis gymnocephalus is
the dominant zoo-planktivore in mangrove creeks. Thus, mangroves are often considered to be
important to coastal fisheries both in terms of their role as breeding and nursery grounds for
various fish and prawn species, and as a source of food.

Table 2. Roles of the mangrove forest in Indonesia: an experience with the mangrove forests in South China Sea, East
Kalimantan, South Sumatra and Segara Anakan Cilacap.

Physical Interactions

Nutrient Interactions

Biotic Interactions

1.1. Filtering terrestrially
derived sediment, and
1 .2. Reduction in sediment
load reaching the sea.

1. Export of dissolved and
paniculate organic matters
(DOM, POM).

1 . Export of mero-planktonic larvae to marine food
chains.

2.1. Buffering salinity
changes.
2.2. Reduction in volume of
freshwater reaching the sea.

2. Sinks for paniculate
organic matters (POM).

2.1. Provision of feeding habitat (PFH) -marine
invertebrates and fin fish (diurnal and seasonal migration).
2.2. PFH - seabirds, shorebirds, marine mammals.

3.1. Provision of juvenile (nursery) habitat (PJH) -
crustaceans (shrimp, lobster) and mollusks.
3.2. PJH - fin fish (reef fish, sea-grass bed fish, pelagic).
3.3. PJH — seabirds and shorebirds nesting (also roosting).
3.4. PJH - marine mammals (dolphins).

2. Aquatic Ecology

The ecological importance of mangrove forests (e.g., Thayer et al. 1987; Robertson and
Duke 1987; 1990) in estuarine and coastal ecosystems throughout the world is well established.
Estuaries in Indonesia contain diverse habitats, including mangrove forests, sea-grass beds, mud-
flats and open water channels, all of which may differ in depth, structural heterogeneity, substratum
type and tidal exposure.

It is widely accepted that mangrove communities are important components of estuarine
ecosystems (Odum 1961; Odum and de la Cruz 1967). Elsewhere in Indonesia, mangroves are
associated with estuaries; and most estuaries in Indonesia are mangrove-lined for much of their
lengths. Thus, mangrove forests contribute a great amount of structural heterogeneity to these
estuaries. Mangroves in the estuaries are able to absorb inorganic compounds from fresh water
runoff for photosynthesis and thus play an important role as primary producers. Mangroves are

BIOTROPIA NO. 23, 2004

a source of primary productivity for food webs that serve as a base for the production of marine
and estuarine organisms such as lobsters, finfish and shellfish. Mangrove estuaries and creeks
usually have significant salinity fluctuations. The great changes in salinity occurring during rainy
seasons may cause periodic mass mortality of marine organisms. On the other hand, changes in
salinity will also result in soil salinity of root zones in the mangrove forests.

The mangrove forests and/or association in Indonesia may be considered of great
importance too, for example, the South China sea, including the estuaries, adjacent coastal
waters and the offshore waters, as its high productivity probably makes it the major source of
organic matter. These communities act as nurseries for many organisms and produce large
quantities of organic matter (e.g., litter-fall) which forms the base of estuarine food chains.
Moreover, their detritus and nutrients are exported out of the ecosystem through tidal flushing and
these form a food base for marine micro-organisms which in turn support the valuable estuarine and
near-shore fisheries.

The vast mangrove system in Indonesia may be considered as very important in terms of high
productivity and as a major source of nutrients to the ecosystem of the estuaries, the adjacent waters
and the offshore waters. In Apar Bay East Kalimantan, Sukardjo (1995) found that the total flux of
organic matters (woody detritus and other mangrove litter components) estimated to be about
21.11 to 29.34 dry weight t/ha/year. This is exported to adjacent waters in the form of fine
suspended materials. In Florida, Ray (1974) found that 90% of water-borne debris within the
mangrove zone is derived from mangrove vegetation. About half of this is exported to adjacent
waters in the form of fine suspended material so that about 35-60% of all suspended matter on the
off-shore olithic banks is of mangrove origin.

The waters in the deltas, as well as those inshore, carry a large amount of suspended, as
well as large plant materials, such as leaves, branches and trunks. Teredinid mollusks play an
important role in many mangrove swamps by rapidly breaking down wood and releasing
nutrients into the food chain. Since teredinids use wood as a substratum for burrowing and, in many
species, as food (Turner 1966, Rayner 1977), the numbers of teredinids may be directly related to
the amount of wood available. On the other hand, the major food of sesarmid crabs in mangrove
forests is leaf litter (e.g., Malley 1978). These crabs carry leaves down their burrows as well as
consuming them on the sediment surface, and Macnae (1968) suggested that feeding by sesarmid
crabs may account for the scarcity of leaves on the floors of mangrove forests. It is interesting than
that in inland mangroves most of the detritus must be broken down in situ. The high productivity
of associated estuaries and banks is due to such suspended matter. In Indonesia, my field
observations have shown that fish in the mangrove environment utilize virtually all sources of
food available, as follows :

1. Insects and fruits from mangroves and from terrestrial sources (e.g., Toxotes and some
catfish).

Fisheries associated with mangrove ecosystem in Indonesia - Sukristijono Sukardjo

2. Detrital mud (e.g., Scatophagus, mullets, some catfish).
3. Small invertebrates (e.g., gudgeons, gobies, ambassids, anchovies, etc.).
4. Prawns and crabs (e.g., Polydactylus, Johnius, Pristia, Lates calcarifer, Kurtus,

Scutengraulis, some catfish).
5. Mollusc (e.g., Cinetodus,Acanthopagrus, Tokifugu).
6. Fish (e.g., Carcharhinus, Lates, Johnius, Polydactylus, some catfish).

Some fish are primarily estuarine, with the major portions of their population residing in the
mangrove areas. Others appear to enter the estuaries from either the sea or rivers mainly to forage,
while others again pass through the area on breeding migrations or breed within the area or in
adjacent coastal waters. Those forms which breed within the mangrove belt or in the adjacent sea
frequently utilize the area as nursery grounds for juveniles during various stages of development.
Marine and riverine forms penetrate the mangrove zones to varying degrees either as small
peripheral populations or occasional individual stragglers. Table 2 summarizes the data available
in the reports. It gives some idea of the inter-linking of the mangrove community with the adjacent
marine and riverine communities and the presence of juveniles indicates which species utilize the
mangrove area for breeding or nursery grounds. Thus, the productivity of the mangrove ecosystem
is not measured simply by the productivity of plant material by mangroves, but must include the
production of fisheries that are dependent on the mangrove detritus.

3. Ecological Productivity of Mangroves as Habitat and Fisheries

In Indonesia, mangroves represent the dominant soft bottom plant communities of the marine-
terrestrial transition in the coastal zone; and considered to be areas of high primary productivity
which support economically important detrital-based marine food webs. As a consequence of the
range of spatial and temporal variation in physical and chemical factors found in such
environments, the biological communities display remarkable adaptations which permit them to
survive under such harsh environmental condition. For instance, the extreme ranges of pH, DO,
temperature and salinity are caused by freshwater influx or conversely, by the shallowness of
mangrove waters and high incident radiations are common features.

The plant species are members of terrestrial families which have adaptations to survive under
conditions of high salinity, low oxygen and nutrient availability in the soil, wind and wave action,
and substrate instability. The animals are, like the plants, representatives of largely terrestrial groups.
In contrast the aquatic animal community is dominated by members of essentially marine families
which are adapted to viable salinity, turbid conditions and to feeding directly or indirectly on
materials from the dominant primary producers.

In a global context, mangroves are one of the more productive ecosystems in the world in
terms of both primary productivity and the productivity of marine animals. The primary
productivity is manifested in terms of the accumulation of

BIOTROPIA NO. 23, 2004

biomass (wood, root etc.) and the production of leaves. In Indonesia, Sukardjo < Yamada (1992)
reported that the biomass of R. mucronata amounted to be 93.73 dry weight/ha and mangroves
produce a large quantity of organic debris in the fo of leaf litter, viz 7.56-10.82 dry ton/ha/year
(Sukardjo 1995). Generally, the tc biomass, height, litterfall, decomposition, and fresh water
turnover increase fn dwarf to riverine mangrove forests (Pool et al. 1975, 1977; Brown and Lugo
198 The significance of this detritus in the food web has been recently focused upon some workers
(Leh and Sasekumar 1980; Thong and Sasekumar 1980). Mullet a some juvenile fishes, and penaeid
shrimps utilize this material in mangrove estuar almost exclusively. Leaves which are continually
being shed by mangroves under decomposition and result in POM (Particulate Organic
Matters) and DO (Dissolved Organic Matters) that enter into the near-shore estuarine or mari
environment. The POM, which consists of small particles, is consumed by larval a; juvenile marine
organisms that utilize the mangrove habitat as a nursery and feedii ground. The DOM, which consists
of a wide range of soluble organic compounds, consumed by filter feeders (e.g., clams, oysters,
mussels, etc.) that are common the near-shore environment, and who retain the phyto-nano-and
micro-plankton th is vastly composed of primary producers who need DOM to synthesize organ
matter. The production of bacterial biomass from DOM is an important step carbon and energy
flow through marine environments and potentially serves as tl mechanism by which dilute
dissolved organics become available to metazoc trophic levels (Azam et al. 1983). In
addition, any organic material that transported seaward is flocculated by the increasing salinity.
The flocculated organ matter (FOM) becomes a substrate for benthic feeders and scavengers.
Therefor mangroves are known to be very productive in terms of primary organic mated! and
recycling of mineral nutrient (Lugo and Snedaker 1974). Also, the richness c mangroves in organic
materials provides a wide variety of food at different levels c the food web for organisms that will ,
in turn, serve as fish food (Beumer 1978 Mugil cephalus and Cyprinodon variegatus are
mentioned as such. Also, mud crat Scylla serrata occupies a niche between the primary
producers and tertiar producers and is thus, an important organism in the energy-flow of the
mangrov ecosystem.

Sukardjo (1995) reported that the canopy closure by mangrove trees range 87.70-99.00%.
Macnae and Kalk (1962) considered that shading by mangrove tree protects animals, particularly
juvenile and larval forms, in shallow water (e.g. mangrove creeks) from direct sun. In addition,
the complex and entangled mangrovi roots and stems offer refuge and protection from predators.
Thus, the importance o mangroves as habitat for fish and prawns continues to be a topic of debate
amonj marine ecologists (Macnae 1974; Robertson and Duke 1987). The detritus is eithei
refractory and sinks to the bottom, presumably never enters the food chain, or is dispersed over
a large area without any local impact (e.g., magnification of benthic secondary production).
However, it should note that marine ecologists generall} agree that inshore areas constitute a
crucial part of the life support systems oi offshore populations by providing nursery and feeding
areas (Jansson et al. 1988).

Fisheries associated with mangrove ecosystem in Indonesia - Sukristijono Sukardjo

Therefore, biologists have recently paid much attention to the mangrove areas as nursery areas for
shrimp and fish, such as certain species of penaeids that are dependent on mangrove forests during
their juvenile stages. These species include Penaeus monodon, P. indicus, P. merguiensis and most
species of Metapenaeus, P. semisulcatus and P. latisulcatus spend larval and juvenile stages. The
life cycle of these prawns and environmental factors influencing it, are summarized in Figure 1. It
has been shown that the mangroves and the environment they create is vital to the continuation of
many commercial penaeid prawn fisheries. Also, many commercially important fishes such as
Chanos sp., Mtigil sp., Hilsa sp., and Pomadasys sp. use mangrove water ways as nursery grounds.
Moreover, mangrove communities function as a solar-powered, tidal subsidized and pulse
stabilized ecosystem (Odum 1974). There is a large energy surplus in mangroves in the form of
detritus. The detritus forms the basic component in the marine primary consumers diet, and thus, a
basic support for many commercial fisheries. Therefore, the role of mangroves as a habitat for fish
and prawn is interesting, even today.

P. merguiensis is an important component of the commercial catches of penaeid prawns
throughout Indonesia. The population dynamics of juvenile P. merguiensis in estuarine systems in
Indonesia have been studied intensively by Toro and Sukardjo (1990), and mangrove-lined mud
banks have been shown to be the main nursery area for this species. However, until recently, little
research had been carried out on the behavior of juvenile P. merguiensis or the degree to which
they utilize the mangroves. From the inventory of various sources, hundreds species of fish and
prawn belonging to residents and non-residents will be found in the mangrove environment in
Indonesia (Table 2). But not all non-resident fish found in mangroves inhabit them as fry or juveniles.

In Indonesia, six habitat groups can be identified in the mangrove environment. Not all of the
species will be found in any one of the habitat group. Different resident species occupy different
habitat in the mangrove ecosystem (Table 3). For instance, in Indonesia generally, the mudflat fish
community consisted of mainly Ambassids, Ariids, Clupeids, Cynoglossids, Engraulids, Mugilids
and Sciaenids. Five residents species found only on the mudflats were the catshark Hemiscyllium
indicum, the grey mullet Liza argentea, the silver pennah croaker Pennalia argentata, the spotted
croaker Protonibea diacanthus and the anchovy Stolephorus macroleptus. Also, the mangrove
inlets and creeks were dominated by schooling fish species belonging to the families Ambassidae,
Eleotridae, Engraulidae, Clupeidae, Leiognathidae and Mugilidae. Among those, the dominant
species in terms of weight were Arius sagor, Ambassis gymnocephalus, Liza subviridis,
Toxotesjaculator, Sphyraena barracuda and Lates carcarifer. By using gillnet, 70% of the total
catches consisted of Sardinella melanura, Thryssa kammalesis, T. hamiltonii and Stolephorus
indicus. Also, several demersal fish species reportedly inhabit the creeks. Thus, only 29 species
are recorded to be commonly found in all of the habitat groups (Table 4).

Figure 1. summary of the Factors Afecting Penaeid prawn in the Mangrove Ecosystem

BIOTROPIA NO. 23, 2004

Table 4. (Continued)

Species

Family

Mangrove
creeks &
inlets

Mudflat

Near
inshore
waters

Far inshore
waters

14. Saurida tumbil Synodontiidae + + + +

15. Sccutor insidiator Leiognathidac + + + +
16. Sctipinna taty Clupcidae + + + +
17. Sillago sihama Sillaginidac + + + +
18. Stigmatogobius
sadanundio

Gobiidac

19. Stolcphorus tri Engraulidae + + + +
20. Tcnulosa sinensis Clupeidac + + + +
21. Thcrapon jarbua Theraponidae + + + +
22. Thryssa hamiltonii Engraulidae + + + +
23. T. kammalcnsis Engraulidae + + + +
24. Trichiurus savala Trichiuridac + + + +
25. Trypauchcn vagina Gobiidae + + + +
26. Mctapenacus affinis Penaeidac + + + +
27. M. brevicornis Pcnacidae + + + +
28. Parapcnacopsis sculptilis Penaeidac + + + +
29. Pcnacus merguiensis Penaeidac + + + +

DISCUSSIONS AND CONCLUDING REMARKS: An Indonesian Perspective

A positive correlation between near-shore catches of shrimp or fish and mangrove area
has been documented for Indonesia (Martosubroto and Naamin 1977), Malaysia (Gedney et al.
1982), Australia (Staples et al. 1985), the Philippines (Camacho and Bagarinoa 1987) and
elsewhere (cf. Table 5). Also, there exists an obvious link between the fishery in the immature
mangrove system and the one in the adjacent marine system. Fish populations in both estuaries
and mangrove ecosystems can be abundant with a wide diversity of species. It is well known to
fishermen that many species of fishes occur in mangrove estuaries and creeks, and it has been
observed many times that these systems act as nursery areas for larval and juvenile fishes. A
comprehensive listing of fish species that actually spend their juvenile years in mangrove
environments has yet to be made. Nor is it known to what degree the relationship is obligate or
facultative for particular species. Much of the evidence is circumstantial. Moreover, the structural
heterogeneity of habitats in tidal waters has been shown to provide fish with protection from
predators and

Fisheries associated with mangrove ecosystem in Indonesia - Sukristijono Sukardjo

Table 5. Quantified relationships between mangroves and coastal resources.

No.

Study Site

Formula

References

Remarks

Indonesia

Y = 0.1 128 X + 5.473
(r2 = 0.79, n = NA)

Martosubroto and
Naamin 1977

Y = Shrimp production
(x 1000 tons)
X = Mangrove area
(x 10,000 ha)

Philippines

Y = 0,8648X + 0.0991
(1^ = 0.66^= 17)

Paw and Chua
1989

Y = Log 10 of penacid
shrimp catch (tons)
X = Log 1 0 of mangrove
area

38 regions of
the world

Log 10MSY = 0.4875
LogAM-0.0212L + 2.41

Pauly and Ingles
1986

MSY = Maximum
Sustainablc Yield of
pcnacids
AM = Area of mangroves
L = Degrees of latitude

Australia

Y= 1.074X + 218.3
(r2 = 0.58, n = 6)

Staples et al. 1985

Y = Banana prawn catch
(tons)
X = Mangrove shoreline
(Km)

NortheastGulf
of Mexico and
in Lousiana

Y= 1.96X-4.39
(r2 = 0.92, n = 7)

Turner 1 977

Y = Percentage of brown
shrimps
X = % of saline vegetation
in an hydrological unit

27 locations in
Asia, America
and Africa

No equation given
(r2 = 0.69, n = 5; 8)

In: Turner 1977

Y = Annual shrimp yield
X = Hectare of vegetated
estuary

Gulf of Mexico

Ln Y = 0.496LnX + 6.070
(r2 = 0.48,n= 10)

Yancz-Arancibia et
al. 1985

Y = Fish capture (tons)
X = Coastal marshes in km2

enhanced feeding opportunities (Rozas and Odum 1988). Indeed, the supposed connection
between mangroves and juvenile nekton is often advanced as one of the key arguments for the
conservation of mangrove forests in Indonesia. Unfortunately, the use of fringing mangrove
habitats by commercial and recreational fishery in Indonesia has not been well documented.
Also, no reliable catch statistics are available for both commercial and recreational fish
production from mangroves. Moreover, in Indonesia, very little and/or no listing is made of
various teleost families, such as the Apogonidae, Bothidae, Chandidae, Chanidae, Dorosomidae,
Elopidae, Engraulidae, Gerridae, Latidae, Leiognathidae, Megalopidae, Platy-cephalidae,
Pseudomugilidae, Soleidae, Syngnathidae and Toxotidae, all of which

BIOTROPIA NO. 23, 2004

contain species occurring in mangrove systems. While the ichthyo fauna occurring within
mangrove environment may be broadly categorized into those fishes that exist there permanently,
those that intermittently enter them as adults, and those that seasonally occur there as eggs, larvae,
or juveniles. Thus, one of the principal reasons for rehabilitating mangrove ecosystem in Indonesia
is to increase biodiversity and conserve the ecosystem.

Mangroves are often considered as an ecosystem per se, due to their strong specificities
(Twilley et al. 1996) but they belong to intermittently brackish tidal zone and can be seen as a part
of estuarine systems. Young fish utilize estuaries, near shores marine areas and mangrove
ecosystem in order to benefit from the availability of food and perhaps also to gain protection from
predators. In Indonesia, estuaries can be considered ecosystems because they are composed of
numerous subsystems or habitats. The term habitat refers to the place occupied by an entire
community of organisms. Thus estuaries are known to be important as feeding, nursery, or habitat
areas, in the life cycles of many fish species, while the role of estuaries, particularly mangrove, in
producing commercially important fishes is being recognized, their value for fishes of little or
indirect commercial or angling importance has not been accepted. It seems that estuaries, all over
the world are mainly nursery for many marine animals. As a matter of fact, the problem of exact
relationship existing between ichthyology and mangroves is far from being solved. Even in
temperate estuaries there are groups of important fishes which spend a part of their life either in the
estuary itself or in the ocean during their life cycles.

In recent years, the importance of the mangroves is well established (e.g., critical feeding,
rearing and nursery habitat for economically important marine species, providing a buffer against
storms, filtering pollutants from upstream sources, and preventing coastal erosion). Also,
quantitative relationships between fish yield and area of mangrove have been well established. For
instance, according to Turner (1977) who has analyzed the data for 27 locations in America, Asia
and Africa, the abundance of penaeid shrimp is directly related to the absolute area and type of
estuarine vegetation. However, in Indonesia, the degree of importance to commercial ecological
functions of the mangroves are often under pressure from economic uses of this coastal area. For
instance, conversion of mangrove forest which destroys the natural nursery grounds of fish and
shellfish aggravated by the conversion of inland freshwater swamp forests which diminished the
area of freshwater habitat and affects the supply of water and nutrient to the spawning and nursery
areas.

Studies in mangrove communities (e.g., Austin 1971; Odum and Heald 1972; Lasserre and
Taffort 1977; Janez-Aranbicia et al. 1980; Bell et al. 1984) have generally concluded that the fish
fauna has a low species diversity and high proportion of temporary residents occurring mainly as
juvenile. There is however, little evidence of fish spawning or breeding inside mangrove areas.
Recorded evidence refers only to gobiid fishes (Penridge 1971) including mudskippers
(Boleophthalmus, Periophthalmus, Periophthalmodon, Scartelaos). The abundance

Fisheries associated with mangrove ecosystem in Indonesia — Sukristijono Sukardjo

and species composition of fish and crustaceans in mangroves and their
adjacent near-shore habitats (sea-grass, sand-flats, mudflats etc.) at several sites
in particular islands of Indonesia are necessary to answer the questions
regarding mangroves-fishery relationship. For instance, the correlation between
offshore prawn catches and area extent of mangroves (Macnae 1974; Turner
1977; Martosubroto and Naamin 1977) has been suggested to be indication of
the dependence of juvenile prawns on mangroves rather than of a food chain link
(Hatcher et al. 1989). Though prawns offshore did not carry the mangrove carbon
signal, it was shown that several species of juveniles prawns collected from a
mangrove inlet consumed mangrove -derived carbon (Rodelli et al. 1984).
Another example is, the environmental conditions in the estuaries are not
conducive to the survival of the first-stage zoea of Scylla serrata and berried
females, therefore, migrate to sea to spawn. Thus, program aimed to test the
belief that mangroves as major nursery grounds for juvenile's fish and
crustaceans are needed.

In Indonesia, since mangrove forests sustain marine life in estuaries and
ponds and act as shelter belts against tropical cyclones, the fresh water needs of
mangrove forests should be evaluated in water management practices along
the coasts. Moreover, the estuarine is one of the common features in the
coastal mangrove belts, and represent an important zone for many marine
organisms to feeding, breeding, spawning, and other behavior. In addition, it is
essential to determine, for a given local fishery, the real dependency of fish
resources on estuarine environment by answering the following questions in
regard to the relation with fishery, as follows:

1. Is the estuarine zone essential for a given species?
2. Are there alternative areas for its development?
3. Which parameters are critical in its life-history?
4. What are its trophic relationships with other species?

In Indonesia, major fishing grounds are located in the coastal areas in
East Sumatra, South and East Kalimantan, and South Irian Jaya where there are
extensive virgin mangrove forests (Table 6) (Chong et al. 1990). Fortunately,
ecological information for fisheries fauna associated with mangroves in
Indonesia is scant. Fisheries resources in the mangrove environment have
usually been examined in terms of their economic potential, and thus only the
commercial species such as P. monodon has received only detailed bio-
ecological study (e.g., Toro and Sukardjo 1990, 1995). The prawn species of
creeks were represented by juvenile Penaeus penicillatus, P. merguiensis, P.
indicus, P. monodon, Metapenaeus brevicornis and M. ensis (affinisT). Also,
sediment type and organic carbon have been known to influence the
distribution of prawns (e.g., William 1958; Branford 1981; Toro and Sukardjo
1997), as do the effects of salinity (e.g., Gunter et al. 1964; Mair 1980 ; Dall
1981) and the presence of coastal vegetation (e.g. Young 1978; de Freitas
1986). i he fluctuations and success of prawn fisheries appears more dependent
on the juvenile stage, and the conditions in the mangroves which influence it
(e.g., salinity, water discharge, sediment type etc.), than any other part of its life
history.

BIOTROPIA NO. 23, 2004

Thus, the small number of prawn species as observed in mangrove habitats in Indonesia could be
due to the following three factors:

1. Niche occupation being limited to the epibenthic surface of the substrate.
2. The substrate being comparatively homogenous (in this case, a largely silt-clay one), and
3. A lack of euryhaline species.

Traditionally mangrove ecosystems have provided some of the richest fishing grounds for
much of the islands in the country. Also, fishery activity within the mangroves is mainly at the
subsistence level (cf. Table 6). For instance, crabs belonging to different genera and species are
abundant along the estuarine shores and mangrove swamps, but those of economic importance
affording minor fisheries are the swimming crabs belonging to the genera Scylla and Neptumis. Scylla
serrata, Neptunus pelagicus and N. sanguinolentus are the most common forms. Therefore,
methods and sampling time, and type of nets will catch different species composition by weight
and diversity. Fishing gear utilized includes fixed traps (sero and kelong), hook and line, cast nets,
gillnets, beach seine, trammel net, stationary lift net and stationary tidal seine (logo), e.g. in Muna
(Table 7). The gill nets for instance, were not effective in catching the demersal fish and prawns.
Main demersal fish caught are Ariidae, Carangidae (excluding Megalaspis spp. and Decapterus
spp.), Leiognathidae, Lutjanidae, Polynemidae, Sciaenidae, Serranidae. Main pelagic fish caught
are Rastrellinger spp., Megalaspis cordyla, Decapterus spp., and Sardines (Clupeidae). Multiple
tidal nets are usually set up in the main river streams for catching shrimp.Trammel nets are used in
river mouths for catching coastal shrimp such as P. merguiensis, P. monodon and M. brevicornis.
Traps (sero) are placed at river mouths or at the edge of the mangrove forests. Crab nets are used at
the river edge or in small canals and streams for catching mangrove crabs. For instance crab nets
are very valuable and efficient economically for fishermen in Muna (Tables 7, 8). Thus, the people
who live within the mangrove ecosystems and exploit them have adapted their life-style and land-
use patterns in a variety of ways along the Indonesian coasts, e.g., in South Sumatra for general
illustration (Table 9).

The results of investigations of fisheries fauna associated with mangroves in Indonesia
enable some generalizations to be drawn regarding the structure and composition of mangrove
associated fish communities. Such communities appear to be characteristically composed of 13 to
14 families with only 10 families recorded being dominant (Tables 2-4). Some fish families,
whose taxonomy is still under review, such as Mugilidae (Thomson, In Lal et al. 1984),
Leiognathidae and Lutjanidae (Alien, In Lal et al. 1984) and Sphyrocnidae (Rose, In Lal et al.
1984). FAO (1994) reported that 64 fish species, 74 crustacean species and 71 mollusk species
were harvested from the mangrove area in Malay Peninsula.

The main facts that emerged from the discussions on the fisheries associated with mangroves
were as follows :

Fisheries associated with mangrove ecosystem in Indonesia - Sukristijono Sukardjo

1. The life cycles, reproduction cycle, food habits and growth rates of mangrove species are
poorly known and have only recently been the object of attention in relation to the mangrove
ecosystem. The species being investigated are those of economic importance, such as
Sesarmids crabs, penaeid prawn, fin fish and certain molluscs.

2. Research on food webs indicates complex pathways, which qualitative measurements of
conversion efficiency are available.

3. Migrations, behavior, eco-physiology and habitat requirements of species are partly known but
generally poorly understood.

4. Studies on the relationships with adjacent ecosystems such as sea-grass beds and coral reefs
are being studied, but only a few are described in any detail.

5. The question was addressed as to what extent forest structure has an effect on fauna
populations and trophic relationships, and it was re-emphasized that more studies are urgently
needed on this area.

6. The often quoted factors which influence fisheries potential and production in mangrove systems
are only described, seldom experimented upon and not quantified.

7. The level of assimilation efficiency has been measured for a few species of animals but
measurements are still crude. At this stage we are still looking at quantitative rather than
qualitative changes.

BIOTROPIA NO. 23, 2004

Table 6. Fishery regulations (applied to all of Indonesia): Gear and vessel restriction.

Zone (Distance from
shoreline)

Vessel size and power
maximum

Gear not allowed in zone

1 : 0-3 miles

5 gross tons, 10 HP Purse seines, nets > 120 m length

2: 3-7 miles

25 gross tons, 50 HP

Nets > 300 m length

3: 7-12 miles

1 00 gross tons, 200 HP

Nets > 600 m length

4:> 12 miles

No limit

Table 7. Fishery production in the mangrove forest in Muna project sites in 1996.

Fishing gear
(100% used in the
mangrove area)

Number of fishing
gear (unit)

Number of
fishermen
(H.Hold)

Production
(t/year)

Economic value (Rp/year)

1. Togo (Multiple
Tidal net)

87.70

500,976,000

2. Jala (Cast net)

0.52

2,254,000

3. Rokkang (Crab net)

1,300

260

135.20

540,800,000

Table 8. Fishery product from mangrove forest by species in Muna fish collector in 1996.

Species

Production (ton/year)

Prize (Rp/kg)

Economic Value (Rp/year)

1. Shrimps

7.30

5,500

40,150,000

2. Scylla scrrata

60.00

4,500

270,000,000

3. Portunus pclagicus

57.36

1,000

57,360,000

4. Sea cucumber
(Teripang)

8.50

25,000

212,500,000

Fisheries associated with mangrove ecosystem in Indonesia - Sukristijono Sukardjo

Table 9. Coastal zone resource use compatibility matrix: Compatibility of resource use options in South Sumatra (numbers
correspond to resource use). C = Complementary, H = Harmful, E = Exclusive

Sector

Item

Fisheries

1 . Coastal Fishery *

2. Inland Fishery - *
3. Aquaculturc H E *

Forestry

4. Large scale
forestry

5. Husbandry of
nipa

6. Husbandry of
nibung

7. Husbandry of
jelutung

8. Crocodile
hunting

9. Monitor lizard
trapping - -

- -

Agriculture

10. Transmigration
scheme

- -

1 1. Irrigation
scheme

- -

Transport

12. Port
construction

- -

Tourism

13. Small scale
tourism

- -

Conservation

14. Habitat &
endangered
species

15. Migratory
shore birds

- -

1 6. Breeding water
birds

C C E -

C C - - - H H - C

C *

ACKNOWLEDGMENTS

The author is very grateful to anonymous reviewers who read critically the manuscript.

BIOTROPIA NO. 23, 2004

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