INDONESIAN CORAL REEFS
Indonesia is the largest archipelagic nation in the world comprising an estimated 17,508 islands. Coastal length has been variously estimated at between 80,791km (
Moosa, 1994) and 204,000km (
Tomascik et al, 1997). The official estimate for the area of coral reefs is 7500km² (
KLH 1992). A re-estimate by Tomascik et al (
1997) based on the longer figure for coastline length is 85,707km² which represents about 14% of the world total.
The area covered by this review is loosely termed as Eastern Indonesia. It includes the eastern shores of the island of Kalimantan, Sulawesi, Halmahera, The Moluccas, West Papua and the islands of Bali, Flores, Sawu, Timor and Banda Seas. It thus covers the provinces of Bali, West Papua, East and South Kalimantan, Maluku, West and East Nusa Tenggara and North, Central, South and South-east Sulawesi. This area probably contains more than 50% of Indonesian coral reefs. It also corresponds closely to the areas of East and Central Indonesia as defined by Tomascik et al (
1997) and shown by reef type in
table 1.1.
Indonesia straddles the equator and it is not surprising that it has such an area of coral reefs. As Tomascik et al (
1997) note the “complex interplay of atmospheric, oceanographic and geologic processes has resulted in one of the most dynamic marine environments on the planet”. Although seasonal fluctuations do occur, variations in temperature and salinity are probably less than anywhere else in the world and disruptions from meteorological phenomena such as hurricanes are almost unknown. As disturbance is one factor which is responsible for the maintenance of high diversity and overall stability of coral reef ecosystems (
Connell 1978), it is therefore somewhat enigmatic to find that Eastern Indonesia is the world centre of diversity for coral reefs and associated flora and fauna (
Moosa, 1999).
A major influence on this diversity relates to the geological history of the region. The modern scleractinian corals evolved in the ancient Tethys Sea in the Trassic, (
Veron, 1995). This body of water lay between the northern continents of Eurasia and the Southern African and Indo-Australian land masses. These have drifted together, closing the Tethys Sea from the west, the collision forming the massive fold mountains stretching from the Pyrennees and the Alps to the Himalayas. The main centre of coral reef evolution has thus been pushed eastwards to what is now archipelagic Southeast Asia. This region, centred on Indonesia is the direct descendant of the Tethys Sea and is a modern collision zone with all the same characteristics of complex archipelagoes and island chains in which earthquakes and volcanic action provide the required degree of disturbances for the high diversity.
Highly favourable biological, ecological and geological conditions of Eastern Indonesia have thus provided the richest and most diverse region of modern coral reefs. Unfortunately within Indonesia as a whole these are under increasing anthropogenic pressure from a population which is largely coastal and utilises coral reef resources extensively. Indonesia’s population is currently about 195 million, though the 11 provinces which make up Eastern Indonesia, as defined above, are home to a proportionally lower population of 35 million people. Many areas of reefs may still be in good condition and could benefit from sustainable management based on integrated coastal zone management principles.
LOCATION AND TYPES OF EASTERN INDONESIAN CORAL REEFS
This section describes the coral reefs of Eastern Indonesia from north and west to south and east. It relies extensively on the descriptions in Tomascik et al (
1997).
East and South Kalimantan
A major influence on reef distribution in eastern Kalimantan is the Mahakam River which drains almost one third of East Kalimantan with a discharge of 1500m3/sec a suspended sediment load of 80mg/l and a sediment yield of up to 10 x 106 tonnes annually. The plume may extend 400km to the south-east of the Mahakam Delta and is responsible for a general paucity of coral reefs along the coastline to the south. Only occasional fringing reefs are found with some offshore patch reefs, for example in front of Balikpapan Bay.
Immediately to the north of the Mahakam, however, well developed fringing reefs are found from Tanjung (Cape) Setan to Tg. Samuntai (140km). A further 180km of fringing reefs are found around the Mangkalihat Peninsula but are then disrupted by the Berau River discharge. However, because of the southward coastal current, fringing reefs are again found immediately to the north for a further 60km to Tg. Karangitigau. Northwards to the border with Sabah the coastline is reefless, dominated by major river deltas.
The southwestern coast of South Kalimantan is also largely deltaic and devoid of reefs. Conditions for reef development improve considerably east and north of Tg. Selatan and significant fringing reef development occurs along the southeast and southwest coasts of the island of Pulau Laut.
Offshore in eastern Kalimantan, the better water quality has allowed the development of three barrier reef systems (
Table 1.2) where substrate is suitable. The longest barrier reef in Indonesia runs inside the 200m isobath at the margin of the Sunda shelf. Lying 60km offshore, the Great Sunda Barrier Reef has a length of 630km but little work appears to have been carried out on this system. Smaller barrier reefs are found north of the Mahakam delta. The Berau system is found immediately north of the Berau Delta, in places only 10km offshore, and has a length of 25km. Parts of the Mangkalihat Peninsula are also bordered by a barrier reef. North of the Mangkalihat Peninsula are three major reefs which Tomascik et al (
1997) term atolls, though they are more likely large lagoonal shelf reefs rather than fulfilling the strict geological criteria for oceanic atolls with volcanic foundations. These reefs lie about 90km offshore, in front of the Berau barrier reef (note their location as given in table 16.1 of Tomascik et al (
1997) is in error). They are of considerable size: Muaras (288km²), Maratua (690km²) and Kakaban (21km²), the latter two having raised limestone rims up to 120m above sea level. Open water coral reefs are also probably associated with the islands of the Java Sea in the south (Pulau Keramian, P. Matasiri, P. Kadapongan, P. Kalamban).
Sulawesi
The island of Sulawesi, with a coastline of 4750km, probably has the largest coral reef area in Indonesia. A very high proportion of its coastline is fringed with reefs, as are the offshore islands. Although a systematic geographic description is not available, most references to Sulawesi describe almost continuous fringing reefs up to 200m wide.
Even more impressive are the almost undescribed barrier reefs of Sulawesi. Tomascik et al (
1997) describe 34 individual barrier reefs around the islands with a total length of 2084km, i.e. bordering 43% of Sulawesi’s coastline (
Table 1.3). No less than 8 are more than 100km long and whilst the majority are only a few kilometres offshore, the most studied, that of the Spermonde Archipelago, lies 60km offshore from the coastline of south-west Sulawesi. The longest is in the Gulf of Tomini 165km long, running eastwards from the volcanic Togian Islands. The most unique barrier system in Indonesia is the Banggai Barrier Reef running 175km along the southern margins of the Banggai Islands. Part of this barrier consists of lagoonal faro reefs very similar to those found in the Maldives.
Tomascik et al (
1997) describe 27 atolls in the waters around Sulawesi. However, whilst many may have the superficial resemblance to open ocean atolls, with annular rims, with or without islands, and various types of lagoonal patch reefs, it is doubtful whether many have developed from volcanic foundations in the relatively simple tectonic setting of a mid oceanic location. Thus these reefs are considered with the further 27 oceanic or
platform reefs as identified by these authors around Sulawesi. They also include open water reefs with continental (not always volcanic) islands and a number of submerged reefs.
These open water reefs occur in clusters around Sulawesi:
- extending to the southwest of Makassar (Ujung Pandang) including Kepulauan (Archipelago) Liukang Tenggaya, K. Tengah
- extending to the west of Makassar, P. Marasende, P. Dewakang-lompo, P. Doandoangan-besar, P. Kalukalukuang
- within and to the south of Teluk Bone, including K. Bone Rate. The best known and best studies of the Indonesian “atolls”, Taka Bone Rate is found here
- to the southeast, including Kepulauan Tukangbesi
- in Teluk (Bay) Tolo, including K. Bowokan
- within Teluk Tomini
Very few of these offshore reefs have been the subject of scientific study.
Although not coral reefs, a closely related habitat which requires similar management and conservation approaches is the area of
Halimeda bioherms found at the southern end of the Makassar Strait off southeastern Sulawesi. (
Roberts and Phipps, 1988;
Phipps and Roberts, 1988). Associated with the Kalukalukuang Bank in particular, these algal reefs may also be found around the margin of the Sunda Shelf towards Kalimantan. Here algal growth is favoured over reef growth as nutrient rich deep Pacific water floods southwards through the Makassar Strait and upwells around the banks and shelf margin.
Bali and Nusa Tenggara
These islands are all part of one of the worlds most active volcanic island arcs, formed at a tectonic plate subduction zone. Many of Indonesia’s active volcanoes are found here.
Fringing reefs are again ubiquitous, their morphologies depending on the geomorphology of the coastline and the tectonic history of the islands. Many are narrow structures 30 to100m wide with an intertidal reef flat and very sharp seaward drop-off. However, much wider reefs are present. For example around Bali, van Woesik (
1997a, in Tomascik et al pp 689-894) indicates the fringing reefs extend 500m from the shoreline.
Although very accessible few of these reefs have been described and there is no systematic description of their distribution. A few areas with more detailed studies or descriptions include:
- Southeastern Bali, where comparative surveys of 1992 and 1997 have been undertaken by van Woesik (1997a, 1997b). Contrasting structure and assemblages were noted on southern aspect reefs open to the high energy Indian Ocean swells and those more sheltered. Strong upwelling of cool oceanic water is also found along the southern side of the whole island arc and is believed to influence the diversity of flora and fauna including the presence of both deep water species and more poleward species, in the shallow coastal waters of the fringing reefs (Tomascik et al 1997, p 698).
- Komodo National Park, where The Nature Conservancy has produced a number of reports on the coastal reefs of Komodo (e. g. Djohani et al, 1999).
- Lembata Island, with 3 active volcanoes and described in detail by Tomascik et al (1997). Fringing reefs may be less continuous along the high energy southern shore of the island but are dominated by well constructed spur and groove systems. On the more sheltered western and northwestern sides facing the Flores Sea, the reefs are more continuous and up to 800m wide, with dense growth of sea grasses on the flats, which in the past may have been the habitat for dugongs.
Similar patterns of distribution may be found in other islands of Nusa Tenggara.
Some 9 barrier reefs are listed by Tomascik et al (
1997) in this region (
Table 1.4) though some are very close to shore and difficult to separate from fringing reefs. At least a third of the north coast of Flores is bordered by such a barrier with other significant barriers on both north and south coasts of Sumbawa, the north coast of Lombok and near Maumere Bay, P. Besar.
Probably because of the great depth of water away from the volcanic arc islands no open water reefs are found to the south and only two in the Flores/Banda Sea area off the northern shores of Flores (Karang Serbete and Gosong Boni).
Maluku
The coral reefs of Maluku are regarded as the most extensive and richest in the world but unfortunately detailed descriptions are largely lacking. However, indicative of both rapid growth and species diversity and richness is the report of Tomascik et al (
1996) on the rapid coral colonisation of a 1988 lava flow from the Gunung Api volcano in the Banda Islands. Within 5 years of the eruption the flow supported a diverse coral community of 124 species with a coral cover of more than 60%.
Tomascik et al (
1997) suggest that some of the most widespread fringing reefs in Indonesia are found even in the turbid waters of the Aru Islands, which consist of 6 main islands and 79 smaller islands separated by long narrow channels. Major fringing reef development is along the shallow east coast where the reef can be up to 15km wide, but narrower reefs are found along the remaining coastlines, except the southern part of the west coast.
15 barrier reefs are listed for Maluku (
Table 1.5) with a total length of 425km but so little of this area has been surveyed that this is probably an underestimate. They are associated with the islands of Morotai, Halmahera, Seram, Gorong, Kofiau, Obimayor, Batanme, Nila and K. Tanimbar. Open water reefs, very few if any of which are true atolls, are found in the Banda Sea (Kep. Lucipara and Kep. Penyu) and to the south and east of Halmahera.
West Papua
West Papua, with a coastline length of 4200km remains one of the least studied areas in Indonesia. Because of high run-off and sediment yield, fringing reefs are missing from significant sections of the coastline, notably from Sarmi to Napainwainrami in Cenderawasih Bay on the north coast and from the Papua-New Guinea border to the Omba river on the south coast. Elsewhere, fringing reefs appear to be very continuous. Tomascik et al (
1997) make particular mention of:
- the north coast from Jayapura to the border
- Jayapura to Tg. Kandara, where the reefs are 300-400m wide and westwards to Sarmi
- all the islands of Cenderawasih Bay, 50-100m wide
- on the south coast west of the Omba River
- the southern side of the “Bird’s Neck” between Lakahia Bay and Kamarau Bay and between Tg. Tongerai and Tg. Kirana
- the coastlines along the foothills of Kumafa and Fakfak Mountains
- the northern side of the “Bird’s Head” appears to be suitable for fringing reefs though not the south side which is largely low lying riverine plain.
Barrier reefs are reported in West Papua (
Table 1.6), mainly around the islands of Cenderawasih Bay (P. Numfoer, Biak and Supiori) and the islands off the western tip of West Papua (P. Waigeo, Bakanta and Boo). That off the north coast of Waigeo is reported as being 250km long though this seems excessive from the size of the island (c. 120km long).
Open water reefs are also found in close proximity outside the barrier reefs (Cenderawasih Bay and the western extremity of West Papua). Tomascik et al (
1997) also list some atolls further offshore in the Pacific Ocean (Bepondi, Ayawi and Mapia) all of substantial size (105-250km²) and possibly true atolls, though little is known about them.