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Оглавление5.5. Inland Water Ecosystems in Papua: Classification, Biota, and Threats
DAN A. POLHEMUS AND GERALD R. ALLEN
DUE TO ITS LARGE SIZE, broad elevational range, and great topographic complexity, the island of New Guinea supports a diverse array of inland water ecosystems. All of the major aquatic ecosystem types are represented in Papua, ranging from obvious features such as the Mamberamo and Digul rivers and major lakes such as Paniai and Yamur, to thousands of smaller streams and rivers, a variety of other lakes occupying both lowland and upland basins, innumerable small seeps and springs, and vast coastal wetlands. This extensive array of aquatic ecosystems has in turn developed a rich and highly endemic biota.
Aquatic Ecosystem Classification
Aquatic ecosystems are in many ways more amenable to classification than terrestrial ecosystems because they possess discrete boundaries and can be unambiguously defined by the presence of water. Even so, terminology has presented a persistent problem in aquatic ecosystem classification schemes, since different authors have often employed ecological terms such as ‘‘habitat’’ and ‘‘ecosystem’’ in different contexts and then discussed these terms without providing the necessary definitions. As defined by Polhemus et al. (1992), individual aquatic ecosystems consist of a watermass with relatively sharp, delineable boundaries, enclosing resident organisms, and possessing discrete physiochemical features. Commonly encountered examples of such ecosystems include lakes, marshes, streams, and estuaries. Two basic components of such ecosystems are the biota, or totality of living matter, and the environment, which represents the nonliving physiochemical components of the ecosystem, including spatial dimensions. Although the term ‘‘habitat’’ has often been used more or less interchangeably with ‘‘ecosystem,’’ it is more properly applicable in an autecological sense to designate all ecosystem requirements of a resident species, including space. Habitats are thus not spatially exclusive subdivisions of an ecosystem, in contrast to divisions such as zones, strata, and reaches.
The various types of aquatic ecosystems present in Papua may be assigned to major divisions or classes, for example lotic (flowing) versus lentic (standing). Such classes are based on descriptions of both broad-scale environmental features, such as hydrological regime, water depth, salinity, and so on, and characteristic major taxa of the biota (with the fauna being generally more distinctive and useful in this regard than the flora). Within these broad classes, discrete ecosystem types may be defined by criteria that include altitude, topography, water character (e.g., temperature, turbidity), cultural influences (environmental and biological), and the presence of individual genera or species. In general, oxygen content and pH are usually not adequate descriptors at the ecosystem level because in many waters, particularly those of low ionic content and abundant flora, strong photosynthesis and respiration can diurnally change the levels of such characteristics significantly (pH sometimes by more than two units).
Utilizing the system outlined above and further explained in Polhemus et al. (1992), at least 15 types of inland aquatic ecosystems may be recognized in Papua, occurring across a wide range of elevations. These ecosystems may be split into two major divisions: surface and subterranean. The latter ecosystem types are poorly investigated in Papua, and are not dealt with in great detail here. Surface water ecosystems, by contrast, have received considerable attention, and may in turn be divided into two major ecosystem classes, lotic and lentic, within which there are many individual ecosystem types, discussed in greater detail below. See Definitions of Limnological Terms and Units, on the next page, for specific terms employed in discussion of these ecosystem types.
Lotic Ecosystems
Lotic ecosystems may be technically defined as limnetic surface waters flowing unidirectionally down altitudinal gradients, and may be divided into four types (Polhemus et al. 1992): perennial streams, intermittent streams, rheocrenes, and artificial ditches and flumes.
New Guinea lotic ecosystems are distinguished biologically by a flora consisting mainly of mosses, filamentous algae, and epilithic diatoms, a diverse and largely endemic aquatic insect biota including numerous species of Diptera, Trichoptera (Neboiss 1986a,b,c, 1987, 1989, 1994; Wells 1990, 1991), Ephemeroptera (Demoulin 1954; Grant, 1985; Edmunds and Polhemus 1990), Odonata (Lieftinck 1932, 1933, 1935, 1937, 1938, 1949a,b, 1955a,b, 1956a,b, 1957, 1958, 1959a,b, 1960, 1963), Coleoptera (Ochs 1925, 1955, 1960; Brinck 1976, 1981, 1983, 1984; Gentili 1980, 1981, 1989; Balke 1995, 1999, 2001; Balke and Hendrich 1992a,b; Balke et al. 1992, 1997, 2000; Bistrom et al. 1993), and Heteroptera (Andersen 1975; Baehr 1990; Brooks 1951; Hungerford and Matsuda 1958; Kormilev 1971; Lansbury 1962, 1963, 1965, 1966, 1968a,b,c, 1969, 1972, 1973, 1974, 1975, 1993, 1996; D. Polhemus 2002; D. Polhemus and J. Polhemus 1985, 1986a,b, 1989a,b, 1997, 1998, 2000a,b,c,d, 2001; J. Polhemus and Lansbury 1997; J. Polhemus and D. Polhemus 1987, 1990, 1991, 1993, 1994a,b, 1995, 2000, 2001, 2002; Todd 1955, 1959), but with very limited representation of Plecoptera and Megaloptera. In addition, such streams support a rich non-insect macrofauna of fishes (Allen 1991, 1996a, 2003a,b; Allen et al. 2000; Chapter 4.8), crustaceans (Bott 1974; Holthuis 1939, 1950, 1956, 1958, 1982, 1986), and mollusks (Haynes 2001), many of which are diadromous, with marine larval development.
Comprehensive faunal surveys have been undertaken for only a few of the major river basins in Papua, notably the Ajkwa River and portions of immediately adjacent systems (the Minajerwi and Iweka) draining the southern flank of the central ranges in the Timika region (D. Polhemus and J. Polhemus 2000d; Allen et al. 2000); the Wapoga River draining the western section of the central mountain ranges (D. Polhemus 1998; Allen and Renyaan 2000); and the lower reaches of the Idenburg (Taritatu) River (the major eastern branch of the Mamberamo River system) plus various tributaries (the Furu, Doorman, and Tiri) in the vicinity of Dabra (Polhemus 2002; Allen et al. 2002).
DEFINITIONS OF LIMNOLOGICAL TERMS AND UNITS
Physiochemical Measurements
o/oo: parts per thousand, a measure of salinity
% gradient: relative slope measured as the unit of elevational change per 100 horizontal units (as in m/100 m)
µmhos: reciprocal megohms, a measure of water conductivity
Water Regime
Lacustrine (lake-like): deeper open standing waters occupying distinct basins; lakes and ponds
Lentic (standing): water not subject to direct gravitational movement, although internal currents may occur
Limnocrene (spring pool): a pond or pool having a noticeable, discrete, subterranean water source (cf. rheocrene)
Lotic (flowing): water moving unidirectionally in response to substrate altitudinal (elevational) gradient; excludes waters moving in response to wind currents, waves, and tides
Palustrine (marsh-like): shallow standing water visually dominated by emergent vegetation such as mosses, sedges, rushes, trees, etc.
Rheocrene (flowing spring): lotic water from a subterranean source but not in a well-developed channel, and flowing in relatively low and constant volume
Dissolved Minerals
Qualitative aspects
Haline (halinity): brackish or salty water condition wherein dissolved ions are derived from seawater
Saline (salinity): general term for water with noticeable salt content
Quantitative aspects
Limnetic: freshwater, salt content < 0.5 o/oo
Mixohaline: brackish water, salt content 0.5–30 o/oo
Euhaline: seawater, salt content 30–40 o/oo
Hyperhaline: brine-like water, salt content > 40 o/oo
Concentration vs. time
Homiohaline: salt concentration stable or fluctuating only over a narrow range
Poikilohaline: salt concentration fluctuating widely
Ecological Qualifiers
Migration and movement
Amphidromous: type of diadromous animal (see below) that migrates between fresh and marine waters but not for breeding (e.g., sicydiine gobies)
Catadromous: type of diadromous animal that inhabits freshwater but breeds in the ocean (e.g., anguillid eels)
Diadromous: broadly referring to animals (e.g., certain fishes) that obligately migrate between fresh and marine waters during their life cycle
Itinerant: refers to animals that may irregularly or opportunistically migrate between fresh and marine waters (e.g., haline marine fishes sometimes found in streams)
Salt tolerance of biota
Euryhaline/saline: occurs over a wide range of total dissolved solids
Stenohaline/saline: occurs in a narrower range of total dissolved solids
Substrate relationship
Benthic: living on or in the bottom of a water body
Epigeal: living on or above the earth’s surface
Hypogeal: living beneath the earth’s surface (subterranean)
PERENNIAL STREAMS
Perennial streams (Figures 5.5.1–5.5.5) support continuous year-round flow and form the most widely distributed type of lotic ecosystem in Papua. Although the majority are continuous, discharging steadily to the ocean in their natural state, there are certain karst areas, particularly in the central mountain ranges and on the Vogelkop and Bomberai peninsulas, where such streams may be naturally interrupted, with their flow becoming subsurface in their middle or lower sections, although occasionally appearing as scattered pools in areas of bedrock exposure. In larger towns or near industrial developments, streams may also be artificially interrupted via partial or total diversion. Such human-made diversions are generally accompanied by channel alterations that in many instances modify or eliminate the native ecosystem character, particularly in urban areas. Altered streams of this type in lowland areas are often favored habitats for invasive aquatic species.
Because of the relatively intact nature of Papuan forests, the water clarity of undisturbed streams, at least in the smaller order streams of a given network, is generally high except during spates, and dissolved oxygen is normally near saturation throughout most watercourses.
Papuan perennial streams exhibit prominent altitudinal zonation of environmental conditions and biota (Allen et al. 2000; D. Polhemus and J. Polhemus 2000d). This longitudinal continuum may be divided into three broad zones: the headwater, mid-, and terminal reaches, described in greater detail below. Naturally interrupted streams also exhibit a similar zonation, except that the amount of available habitat in their mid- and terminal reaches is often significantly reduced. As such, their diadromous macrofauna, although similar to that of continuous perennial streams, is generally less diverse. Despite this, such streams may contain certain genera of diadromous gobioid fishes that access the upper reaches during intermittent spates that provide temporarily continuous water connections to the sea, and then hold over in the upper reaches until the next flood.
Headwater Reach
Headwater streams (Figure 5.5.1) drain first and second order catchments lying at elevations above 800 m or possessing gradients in excess of 30%; streams of this type in montane regions possess both such attributes. The substratum is usually bedrock or coarse alluvium such as large rocks and boulders; current speeds are generally high; water temperature is less than 18 C (most typically 12–15); conductivity is less than 50 µmhos (with dissolved solids less than 40 mg/l); and pH is often slightly acidic. The fauna of such small, steeply dropping streams is dominated by insects, particularly Ephemeroptera in the family Baetidae, Trichoptera in the families Glossosomatidae, Hydrobiosidae (Apsilochorema), Hydropsychidae (Hydropsyche), Hydroptilidae (Hydroptila), and Leptoceridae (Mystacides, Triae-nodes), Diptera in the families Dolichopodidae and Ephydridae, Odonata in the families Platystictidae (Drepanosticta), Megapodagrionidae (Argiolestes), and Platycnemididae (Idiocnemis), Coleoptera in the families Dytiscidae (Platynectes), Hydrophilidae (Enochrus), and Gyrinidae (Merodineutes, Macrogyrus), and Heteroptera in the families Naucoridae (Nesocricos, Tanycricos), Gelastocoridae (Nerthra), and Veliidae (Rhagovelia, Papuavelia, Tarsovelia), with crustaceans scarce, and fishes generally absent above 2,000 m (Allen 1991). Alpine streams, lying at elevations above 3,000 m, lack most of these biotic elements except for a very limited and specialized assemblage of Trichoptera in the families Hydrobiosidae (Apsilochorema), Hydropsychidae, and Hydroptilidae and Diptera in the family Chironomidae.
Fig. 5.5.1. This cascading tributary of the Kikori River, on Mt Bosavi in south-central New Guinea, is a typical high gradient headwater reach of a perennial stream, with extensive bedrock exposures in the stream channel.
Photo: D. A. Polhemus.
Midreach
The midreach zone (Figures 5.5.2 and 5.5.3) is intermediate in environmental conditions between the headwater and terminal reaches (for discussion of terminal reaches, see below). Depending on the length and gradient of an individual stream catchment, this can either be a brief and highly foreshortened zone, or conversely may comprise the majority of a stream’s length. The substratum is usually mixed alluvium consisting of boulders, rocks, and gravel, with occasional sand or cobble bars developing on the inner margins of bends, and water temperatures typically range between 18 and 24 C. The fauna of such streams in New Guinea is diverse, including plotosid catfishes, rainbowfishes (Melanotaenidae), grunters (Terapontidae), and gobioid fishes (Gobiidae and Eleotridae), Crustacea in the family Parastacidae (Charax), Ephemeroptera in the families Baetidae, Leptophlebiidae (Thraulus), and Prosopistomatidae (Prosopistoma), Trichoptera in the family Hydropsychidae (Cheumatopsyche, Hydropsyche, Macrostemum), Zygoptera in the families Calopterygidae (Neurobasis), Chlorocyphidae (Rhinocypha), Coenagrionidae (Palaiagria, Pseudagrion, Teinobasis), Platycnemididae (Idiocnemis), and Protoneuridae (Nososticta, Selysioneura), Anisoptera in the family Libellulidae (Huonia), Lepidoptera in the family Pyralidae, Diptera in the family Chironomidae, Coleoptera in the family Gyrinidae (Rhombodineutes), and Heteroptera in the families Gerridae (Ptilomera, Tenagogonus, Limnometra, Stygiobates, Metrobatoides), Veliidae (Rhagovelia, Strongylovelia, and numerous genera of Microveliinae), Mesoveliidae (certain Mesovelia), Ochteridae (Ochterus), Leptopodidae (Valleriola), Hebridae (Hebrus), Nepidae (Cercotmetus), and Naucoridae (Sagocoris, Aptinoocoris, Cavocoris, Idiocarus).
Figure 5.5.2. The upper midreach zones of perennial stream networks on New Guinea are composed of clear, rocky creeks, such as this tributary to the Ziwa River in the central mountains of the island. Such streams are numerous in forested upland terrain, and support extremely diverse biotas of native aquatic insects but only a limited array of native fishes.
Photo: D. A. Polhemus.
Terminal Reach
The terminal reach (Figures 5.5.4 and 5.5.5) is the section of a watercourse below the first sharp gradient that bars upstream migration of itinerant marine fishes, such as flagtails (Kuhlia). The elevation is generally less than 50 m (although though this may not be reached until far inland on large systems such as the Digul, Wapoga, and Mamberamo), and gradient is less than 5%. The substratum in larger streams and rivers is primarily fine sediment, intermixed to varying degrees with sand, gravel, and rocks. The water temperature is greater than 24 C (generally 25–27); conductivity exceeds 80 µmhos (mainly 100–150 µmhos); dissolved solids are 60–100 mg/l; and pH is neutral to slightly basic, ranging from 6.5–7.8. Large lowland rivers such as the Digul and Mamberamo fall within this division, as do the lower courses of many rivers draining from the southern face of the central mountain ranges to the Arafura Sea. Characteristic fauna includes Barramundi (Lates calcarifer), ariid catfishes, numerous gobioid fishes (Gobiidae and Eleotridae), Ephemeroptera in the family Palingeniidae (Plethogenesia), Odonata in the families Coenagrionidae (Agriocnemis, Argiocnemis, Pseudagrion, Xiphiagrion) and Libellulidae (Agrionoptera, Huonia, Neurothemis, Orthetrum, Rhyothemis, Tetrathemis), Coleoptera in the family Gyrinidae (Spinosodineutes), Heteroptera in the families Gerridae (Rhagdotarsus, Limnometra, Limnogonus, Ciliometra), Veliidae (Microvelia), Mesoveliidae (certain Mesovelia), Notonectidae (Nychia) and Corixidae (Micronecta). The terminal reaches of the larger lowland rivers in Papua experience periodic mass hatches of large-sized palingeniid mayflies, with body lengths exceeding 3 cm, which create an impressive sight on the water and represent an important food source for native fishes.
Figure 5.5.3. The midreach of the Minajerwi River as it exits the southern foothills of the Papuan Central Ranges north of Timika is indicative of the high velocity and base flow exhibited by many rivers in the mountains of New Guinea. The coarse alluvial character of the bed is in marked contrast to the fine sediments of the terminal reach channel occupied by this same river just a few kilometers downstream.
Photo: D. A. Polhemus.
The above three stream divisions may each be further segregated into two zones, erosional and depositional. Erosional zones include waterfalls, rapids, riffles, and other areas where there is a net loss of substrate or organic material due to the action of flowing water. Depositional zones include pools, the inner margins of stream bends, and other areas where such material is deposited. Since these two types of zones alternate and intergrade along the length of any given reach, they are not considered as discrete ecosystems per se, but they are often important habitat determinants for individual taxa. For example, the goby genus Stenogobius is generally restricted to depositional zones.
Figure 5.5.4. Terminal reach streams in lowland areas, such as this rainforest creek in the Wapoga River basin, typically occupy low gradient beds of fine alluvium, and are among the faunally richest aquatic ecosystems in New Guinea in terms of both fishes and insects.
Photo: D. A. Polhemus.
INTERMITTENT STREAMS
Intermittent streams (Figure 5.5.6) comprise seasonally flowing waters in discrete channels, with flow decreasing in volume to slow-exchanging pools prior to desiccation. Examples of such ecosystems include small creek beds in lowland alluvial forests, such as those seen near Kuala Kencana in the Timika area, and periodically flooded overflow channels adjoining larger rivers (Figure 5.5.6), which carry water briefly during spates, or for more prolonged periods during the rainy season. Pools in such systems generally persist for at least a few weeks to a few months, usually as discontinuous surface manifestations of diminishing hyporheic (subsurface) flow. Ecosystems of this type most frequently develop in porous, sandy channels where flow can readily retreat subsurface, and although water quality is variable along such reaches, in some cases becoming stagnant, it is often high due to some slight degree of flow coupled with natural sand filtration.
Because intermittent streams differ environmentally from perennial streams in terms of flow regime and water continuity, they are biologically distinct in lacking many diadromous species (those that migrate between fresh and salt water), but by contrast often contain abundant insects and other small invertebrates that may be rare elsewhere. Such ecosystems generally support an impoverished fish biota except in the largest and most persistent pools, where fishes such as blue-eyes (Pseudomugil), hardyheads (Craterocephalus), rainbowfishes (Melanotaenia), and glassfishes (Ambassis) may be present. The fish-free pools of these systems serve as important breeding refugia for a variety of aquatic insect species, however, including the Zygoptera in the families Protoneuridae (Nososticta), Platycnemididae (Idiocnemis), and Coenagrionidae (Teinobasis), Heteroptera in the families Gerridae (Tenagogonus, Limnometra), Hydrometridae (Hydrometra), Veliidae (Microvelia), Notonectidae (Enithares, Anisops), Corixidae (Micronecta), and various aquatic Coleoptera in the families Dytiscidae, Hydrophilidae, and Gyrinidae (Macrogyrus).
Figure 5.5.5. The Tirawiwa River upstream from its confluence with the Wapoga River, in north-central New Guinea, is typical of a low gradient, terminal reach river flowing across alluvial lowland terrane.
Photo: D. A. Polhemus.
Figure 5.5.6. Overflow channels, such as this one along a tributary to the Doorman River near Dabra, in north-central Papua, function as intermittent streams, carrying surface flow during the wet season and then receding to scattered pools fed by hyporheic flow during the drier months of the year.
Photo: D. A. Polhemus.
RHEOCRENES
Rheocrenes, literally ‘‘flowing springs,’’ are perennial seeps and springs flowing short distances over rock surfaces (Figure 5.5.7) or in indistinct channels. These numerous, ubiquitous small seepages (which represent ‘‘leaks’’ from elevated aquifers) are typically found as natural occurrences on bedrock faces or banks of deeply incised streams (particularly adjacent to waterfalls), as well as artificially along road cuts. Water quality of such ecosystems is variable, with their waters sometimes iron-rich as evidenced by bacterial precipitation of orange ferric hydroxide. Two divisions can be recognized: thermal, with average water temperature noticeably (at least 10 C) above the mean annual temperature of the air at the same locality, and non-thermal, with water temperature near or below the mean annual air temperature.
Figure 5.5.7. Rheocrenes, such as this seeping bedrock face and outflow pool near Etna Bay, are common in the mountains of New Guinea and support a highly specialized insect biota rich in endemic Coleoptera, Heteroptera, and Odonata.
Photo: D. A. Polhemus.
Non-thermal rheocrenes, by far the most common type, have a distinctive and often highly endemic biota consisting of a flora of algae, mosses, ferns, Diptera in the family Dolichopodidae, Odonata in the families Megapodagrionidae (Argiolestes) and Corduliidae (Hemicordulia), Coleoptera in the families Dytiscidae and Hydrophilidae, and Heteroptera in the families Gelastocoridae (Nerthra), Ochteridae (Ochterus), Hebridae (Hebrus), Saldidae (Saldula), and Microveliinae (Aegilipsicola, Rheovelia, Brechyvelia). Although they may support distinct algal communities, thermal rheocrenes in general tend to have a highly impoverished fauna, as is typical of thermal waters in general throughout Papua.
ARTIFICIAL DITCHES AND FLUMES
Ditches and flumes are artificial streams constructed by humans to convey water to areas where it would otherwise not naturally flow. Such conduits often pass over or through ridges, and thus transgress natural drainage divides. Although some ditches were built by prehistoric Papuans for crop irrigation, particularly in the Baliem Valley, most were constructed during the past century for municipal water supplies or to provide drainage in urban and industrial areas. At higher elevations, such systems are generally associated with mining developments, such as the Grasberg mine above Timika, while at middle elevations they include a wide array of local water supplies ranging from rudimentary split bamboo flumes to joined plastic pipes many kilometers long.
The environmental character and biota of ditches and flumes differs with their location and degree of use, but in upland Papua they often contain high-quality water comparable to midreach stream water. In general, a lack of shelter and slack water results in low faunal diversity, with the most prominent biotic elements being certain aquatic mollusks, Diptera, Heteroptera, Odonata, and occasionally atyid shrimps, with fishes generally scarce. In lowland areas, particularly in or near larger towns, effluent ditches are commonly constructed to remove water from small reservoirs, agricultural sites, and use facilities. Water quality in such effluent ditches is moderate to low, and the macrofauna, when present, consists mainly of introduced fishes and hardy invertebrates.
Lentic Ecosystems
Lentic ecosystems are defined as standing or still waters, generally in definite basins. They may be divided into two types, lacustrine and palustrine, depending on the type of basin they occupy.
LACUSTRINE SYSTEMS (LAKES AND PONDS)
Lacustrine ecosystems are standing waters occupying definite basins with discrete shorelines, and have predominantly open water with depth generally exceeding 2 m. Such ecosystems are numerous in Papua, and vary greatly in size, from small montane ponds to large lowland lakes, and even flooded World War II bomb craters.
Natural Lakes and Ponds
This ecosystem class comprises natural freshwater lacustrine ecosystems (Figures 5.5.8–5.5.12) with salinities less than 0.5 o/oo, including limnocrenes (pond-like springs with subterranean limnetic water sources). Although relatively uncommon in the tropical Pacific as a whole, such ecosystems are well represented in Papua due to its young, rugged topography and extensive karst exposures. These factors have combined to create many areas with blind or poorly integrated drainages, particularly in the Lengguru Fold Belt of the Vogelkop region (Figure 5.5.10), and to a smaller extent in the strike valleys along the crest of the central mountains (Figure 5.5.9). The lake systems of Papua are extensive, and each individual lake is distinctive in terms of its location, environmental features, and native biota (for a list of major lakes in Papua and their endemic biota (see Table 5.5.1). The natural biotas of such systems in the lowlands include many fishes, especially melanotaeniids and gudgeons, as well as Zygoptera in the families Lestidae (Lestes) and Coenagrionidae (Agriocnemis, Ischnura) and Heteroptera in the families Gerridae (Limnogonus), Mesoveliidae (Mesovelia), and Veliidae (Microvelia), in addition to a diverse waterfowl assemblage (Erftemeijer and Allen, 1989). These systems are frequently degraded by introduction of exotic food fishes, particularly carp and tilapia (see further discussion later in this chapter). By contrast, alpine lakes, such as Lake Andersen near the Grasberg mine (Figure 5.5.9), support a limited and specialized insect biota of Diptera in the family Chironomidae, and Coleoptera in the family Dytiscidae (tribe Bidessini), and also represent important habitats for native waterfowl such as Salvadori’s Teal.
Figure 5.5.8. High alpine lakes, such as these formed at the base of melting glaciers near the summit of Mt Jaya, are numerous along the crest of the highest mountains in western New Guinea, but relatively poor in aquatic biota.
Photo: D. A. Polhemus.
Figure 5.5.9. Lake Andersen, near the Grasberg mine, is typical of alpine lakes formed in strike valleys amid the tilted limestone layers of the central mountains of Papua. Note the series of lakes that occupy basins of progressively lower elevation along the westward strike of the valley. Such ecosystems contain specialized suites of aquatic insects such as Coleoptera and Trichoptera, and also serve as important habitat for waterfowl such as Salvadori’s Teal. They are devoid of native fishes.
Photo: D. A. Polhemus.
Figure 5.5.10. Lake Laamora in the Bird’s Neck region of Papua, shown here in the dry season, is trapped amid a parallel series of limestone anticlines upthrust in the Miocene, and has a seasonally fluctuating water level. It supports an endemic rainbowfish species.
Photo: G. Allen.
Artificial Reservoirs
Reservoirs consist of lacustrine waters occupying artificial basins or human-made impoundments. In contrast to other parts of the world, Papua lacks large-scale reservoirs created by high dams, although many smaller artificial basins and impoundments built for various purposes are scattered throughout the province, intermixed in a few areas along the north coast with small artificial basins created by warfare, in the form of water-filled bomb craters. In addition, the construction of logging roads often inadvertently creates unplanned reservoirs of varying size and duration due to the obstruction of streams by culverts and other temporary crossings.
The environmental quality of such reservoirs and their resulting biotic assemblages vary with reservoir type. Primary storage reservoirs, built primarily for agricultural and domestic water supplies, frequently lie on or near source streams in remote upland sites, and have relatively stable surface levels and good water quality. As such, they often support submerged and floating water flora, which in turn provides excellent habitat for aquatic insects and mollusks. Distributional reservoirs, by contrast, lie mainly on agricultural lands or in populated areas, and are used mostly for temporary water storage and redistribution. As a result, they have fluctuating surface levels and moderate to poor water quality, with their waters often turbid. Accidental reservoirs created by warfare or road construction vary widely in environmental quality and may exhibit any of the above characteristics.
Figure 5.5.11. Lake Sentani, near Jayapura, is formed in a basin lying between the accreted terrane of the Cyclops Mountains to the north (right side of picture), and the foothills of the Foja Mountains to the south (left side of picture). It contains at least three species of endemic fishes.
Photo: D. A. Polhemus.
Although they are artificial ecosystems in terms of basin origin and structure, such ecosystems are often colonized by dispersive native lowland aquatic insect species, particularly wide-ranging Anisoptera in the families Libellulidae (Pantala, Diplacodes) and Aeschnidae (Anax), and Heteroptera in the families Belostomatidae (Appasus), Nepidae (Ranatra), Notonectidae (Anisops), Veliidae (Microvelia), and Mesoveliidae (Mesovelia). They may harbor rainbowfishes and a few other native fish species, but are also frequently stocked with livebearers and rivulines (for mosquito control) as well as food fishes such as tilapia.
Saline Lakes
Although present as shoreline features or closed lagoons on other islands in the region with seasonally drier climates, particularly Timor and the Lesser Sunda Islands, saline lakes have not been documented in Papua. The shores of such lakes, which have waters with salinities exceeding 0.5 o/oo (and in some cases exceeding 100 o/oo), typically support a limited but extremely distinctive halophytic (salt-adapted) biota, particularly among certain insect groups such as Diptera in the family Ephydridae and Heteroptera in the family Saldidae (Pentacora, Micracanthia, Saldula).
PALUSTRINE SYSTEMS
Palustrine ecosystems, more commonly referred to as ‘‘wetlands,’’ comprise various types of swamps and marshes with lentic waters less than 2 m deep (usually <1 m), occupying irregular or poorly-defined basins (Figures 5.5.12–5.5.15). This category encompasses a broad array of individual ecosystems that tend to form a continuum, and creating an unambiguous classification to accommodate the full range of variation involved has proven problematic, but as a general rule forested wetlands are considered to be swamps, while open, non-forested wetlands are classified as marshes.
Figure 5.5.12. The vast wetlands bordering the Mamberamo River in the Meervlakte basin form a complex mosaic of lotic and lentic ecosystems, the latter including both lacustrine and palustrine components.
Photo: D. A. Polhemus.
Palustrine ecosystems include wetlands at both high and low elevations, each with several types. Elevated wetlands, located in remote areas, are primarily natural systems in which native biota dominates, good examples being the marshes that are frequently encountered in the upland valleys of the central mountain ranges. Low elevation wetlands have in most parts of the Asia-Pacific region been severely modified by humans (IUCN, 1991), but in Papua they retain a largely natural character (Figure 5.5.13), due to a general absence of rice cultivation and consequent channelization. This situation is changing, however, in the Merauke and Jayapura regions, where physical alteration of wetland structure and introduction of invasive fishes is rapidly transforming such ecosystems.
Upland Bogs
Upland bogs comprise small bodies of acidic open water on flat, elevated topography at elevations generally above 2,000 m in areas of high persistent rainfall (> 300 cm year). The soil substratum beneath such bogs tends to be primarily organic, producing clear, cool (< 16° C) waters that are very low in dissolved minerals (conductivity <30 µmhos), stained yellow to brownish with humic solutes, and acidic (pH < 5.5). Such bogs are widely distributed in the Papuan uplands, and are distinguished by their strongly acidic water chemistry and impoverished invertebrate faunas, which include aquatic Diptera in the families Ephydridae and Dolichopodidae. Due to their elevation, these bogs uniformly lack fishes.
Upland Swamps and Marshes
Upland marshes are perennial to seasonally intermittent, non-forested wetlands in upland areas (100–1,200 m) of moderate to high rainfall, but with better drainage than boglands. Their waters are clear and sometimes yellowish, with low to moderate dissolved mineral content (conductivity 30–80 µmhos), and circumneutral (pH 5.5–7.5). Emergent aquatic plants (sedges and grasses) are often abundant, including Drosera, Gentiana, Utricularia, Brachyposium, Carex, and Scirpus. Their fauna is similar to that of bogs described above, but more abundant and diverse.
Figure 5.5.13. The diversity of juxtaposed lotic and lentic aquatic ecosystems in lowland New Guinea is well illustrated in this satellite image from the Kikori River basin of Papua New Guinea. Aquatic ecosystems visible in this image include lowland rivers and their tributary creeks, mixohaline mangrove swamps, freshwater swamps, and freshwater marshes.
Photo: D. A. Polhemus.
Upland swamps are perennial to seasonally intermittent forested wetlands in upland areas (100–1,200 m) of moderate to high rainfall. Their waters are non-acidic, with characteristics similar to those of upland marshes. By comparison to marshes, however, their fauna is more diverse and often endemic, including a few fishes (often gudgeons of the genus Mogurnda), specialized Odonata in the family Coenagrionidae (Ischnura), and Heteroptera in the family Veliidae (Microvelia, Neusterensifer).
Overall, upland marshes and swamps appear to be more productive than bogs, and support a greater faunal diversity. Such ecosystems tend to be localized and of relatively limited extent, forming either in natural depressions, or in areas where streams are impounded by either natural barriers or by the construction of road crossings.
Freshwater Lowland Swamps and Marshes
These ecosystems comprise naturally occurring, shallow, standing, perennial limnetic waters in lowland areas at elevations < 100 m, which may occupy either definite or indistinct basins not immediately adjacent to the coastline, with emergent flora predominant. They are maintained by either stream inflow, or by exposure of the natural water table. Water quality in such systems may be variable, but salinity is always < 0.5 o/oo (conductivity 100–300 µmhos), with nearly neutral pH values of 6.0–7.5.
Figure 5.5.14. Lowland freshwater swamps, as seen here on Gam Island in the Raja Ampat group, intergrade along their seaward margins into mixohaline and saline mangrove swamps. Such ecosystems formerly covered extensive areas in Papua, but have been heavily degraded by logging. They are the favored habitat of certain fishes such as blue-eyes and gudgeons.
Photo: D. A. Polhemus.
Such freshwater lowland swamps and marshes represent a complex series of ecosystem types ranging from flooded taro and rice fields to natural marsh basins and riverine swamp forests. Included in this category are the vast lowland swamp forests of the Meervlakte, the huge palustrine basin along the central course of the Mamberamo River and its tributaries (Figure 5.5.12). Anthropogenically-altered ecosystems of this type are often favorable for the establishment and spread of invasive fishes, including snakeheads and tilapia (see discussion later in this chapter).
Lowland freshwater marshes are perennial lowland wetlands lacking trees but with abundant emergent vegetation of other types. Natural systems of this type in Papua are exemplified by the extensive wetlands of the southern lowlands in the Digul and Trans-Fly regions; artificial systems are increasingly numerous and often agricultural, dominated by monocultural taro or rice. The characteristic fauna of both natural and artificial systems includes numerous fishes (especially blue-eyes, rainbows, glassfishes, and gudgeons), a diverse array of Odonata, particularly in the families Coenagrionidae (Agriocnemis, Pseudagrion) and Libellulidae (Agrionoptera, Neurothemis, Orthetrum, Rhyothemis, Tetrathemis), and various Heteroptera in the families Belostomatidae (Lethocerus), Nepidae (Ranatra), Gerridae (Limnogonus), Mesoveliidae (Mesovelia), and Veliidae (Microvelia).
Figure 5.5.15. Mangrove swamps, such as this one on Batanta Island, are extensive along the coasts of New Guinea, and intergrade into freshwater swamps along their inland margins. They support a rich fish biota, and a distinct and diverse assemblage of aquatic insects, particularly surface-dwelling waterstriders.
Photo: D. A. Polhemus photo.
Lowland freshwater swamps, in contrast to marshes, are forested perennial lowland wetlands (Figure 5.5.14), with their water depth often fluctuating on a seasonal basis due to influxes of limnetic water from perennial streams. This ecosystem category includes a range of botanically diverse coastal plain and riparian forested wetlands, including sago swamps, pandanus swamps, and peat swamp forests, all of which are extensively represented in Papua, particularly along the southern coast bordering the Arafura Sea. Peat swamp forests could potentially be segregated as a separate ecosystem on the basis of acidic water chemistry, similar to the case with upland bogs. Distinguishing flora includes Metadina, Barringtonia, sago (Metroxylon sagu), various Pandanus species (for list see Stone, 1982), and Campnosperma brevipetiolata in very wet areas. Also assignable here are the ‘‘freshwater mangrove’’ forests, florally dominated by Myristica, Callophyllum, Syzygium, Campnosperma, Palaquium, Intsia and Diospyros, and similar riparian forests of Sonneratia caseolaris (for additional discussion see Johns 1982 and Chapter 5.7). This is prime habitat for certain fishes such as blue-eyes (Pseudomugil), and gudgeons (Oxyeleotris and Mogurnda). Typical insect fauna includes Odonata in the families Protoneuridae (Nososticta) and Libellulidae (Agrionoptera, Orthetrum), and Heteroptera in the families Gerridae (Limnometra, Rhagdotarsus), Veliidae (Microvelia, Strongylovelia), Hydrometridae (Hydrometra), Veliidae (Microvelia), Belostomatidae (Appasus), and Nepidae (Ranatra).
Saline Lowland Wetlands
Lowland saline marshes, more commonly known as salt marshes, are non-forested lowland saline wetlands dominated by emergent vegetation, most characteristically Pickleweed (Batis maritima). Lowland saline swamps, by contrast, are forested lowland or riparian saline wetlands dominated by a diverse array of mangrove species (Figure 5.5.15), and often intergrade into true euhaline mangrove estuaries. Such mixohaline swamps support mixed floral assemblages of Avicennia, Nypa, Rhizophora, Bruguiera, and Sonneratia (for further discussion see Johnstone and Frodin, 1982), and a characteristic surface insect fauna (J. Polhemus and D. Polhemus 1996; Andersen 1992; Andersen and Weir 1999) of trepobatine Gerridae (Stenobates, Rheumatometroides) and haloveliine Veliidae (Xenobates). Salt marshes and mangrove swamps of these types are common along the coasts of Papua, with the latter extensively developed bordering the Arafura Sea, along the margins of Bintuni Bay, and at certain river mouths along the north coast. They are discussed more extensively in Chapter 5.4.
Also falling within this ecosystem class are various intermittent lowland wet-lands, consisting of lentic waters occurring seasonally in shallow basins. Their waters are generally warm (20–30 C), mixohaline or poikilohaline (although evaporation may cause such waters to become hyperhaline as drying progresses), and basic, with pH values of 6.5–8.0. Characteristic biota includes certain littoral halophilic insects, including Diptera in the family Ephydridae (Ochthera) and Heteroptera in the family Saldidae (Pentacora, Saldula). Fishes may also be present, especially blue-eyes and various gudgeons. Examples of such ecosystems in Papua include certain seasonally dry lake basins formed between limestone anticlines east of Kaimana in the Vogelkop region, and salt pans that border the back margins of mangrove estuaries along the southern New Guinea coast.
Anchialine Pools
An additional type of saline lowland wetland ecosystem found to a limited degree in Papua consists of anchialine pools. The name (from Greek anchialos, ‘‘near the sea’’) was suggested by Holthuis (1973) to define ‘‘pools with no surface connection to the sea, containing salt or brackish water, which fluctuates with the tides.’’ Such pools contain a distinctive biota consisting most typically of invertebrates of marine origin that have invaded through subterranean interstices, and often support unusual taxa not found elsewhere, particularly red shrimps, with fishes being rare or absent. These pools are generally small, with the majority being less than 100 m2 in area. Their surfaces are usually inland extensions of the oceanic water table, although mixohalinity, usually less than 10 percent, often results from dilution by seaward percolating groundwater. Ecosystems of this type, sometimes referred to as ‘‘marine lakes’’ are known to occur on the Raja Ampat Islands of Mansuar and Misool. The pool on Mansuar is surrounded by mangrove and rain-forest, has a soft silty bottom, a narrow band of algae and sponge along the perimeter. Five fish species are present in this ecosystem, including Kalyptatherina helodes, the only member of the family Telmatherinidae known outside of Sulawesi. This same fish species is also found in clear waters of sheltered mangrove-coral reef inlets throughout the Raja Ampat Islands.
On the islands adjacent to the Papuan region (e.g., Timor), anchialine pools occur primarily in elevated fossil reef rock, and are variable in depth depending on tidal stage, with certain very shallow pools appearing only at high tide. Their surface waters are generally mixohaline, ranging from 1–10 o/oo, but occasionally approach euhaline levels, and are usually clear and circumneutral, with temperatures ranging from 22–30 C. Waters within individual pools are usually homioha-line, but with sharp, stable, vertical salinity stratification evident in deeper pools. Although there are no direct surface connections with ocean, tidal fluctuations are also usually still evident, because the water surface level is merely an inland extension of the marine water table, with the mixohalinity resulting from dilution of intruding ocean water with seaward-percolating groundwater. Such pools may occur singly, but are more typically found in groups with subsurface interconnections, and thus represent surface manifestations of otherwise subterranean ecosystems.
The biota of anchialine pools is unique and distinctive, with some faunal species, particularly red shrimps, not found elsewhere. Introduction of alien fishes quickly degrades or eliminates such crustacean communities, a process well documented elsewhere in the Pacific, particularly Hawai’i.
Subterranean Aquatic Ecosystems
The anchialine pools discussed in the preceding section are localized surface exposures of larger and more extensive subterranean aquatic ecosystems that occur in all areas of tropical karst terrain. Such ecosystems may be lotic, such as the ‘‘Baliem Swallet,’’ where the Baliem River disappears underground for a considerable distance near Mt Trikora, or lentic, in the form of standing pools within cave systems. Despite the known existence of such ecosystems in Papua, their faunal exploration has been extremely limited. Cursory collections have been made from pools in a few accessible cave systems in the Baliem Valley, revealing that certain insect species occurring above the surface in surrounding areas, particularly the genus Microvelia in the Heteroptera, will colonize pools in the twilight zones of such caves. To date, no blind cave fishes, crustaceans, or insects have been recorded from Papua, although such taxa are known from adjacent Papua New Guinea (Allen 1996; Holthuis 1980; Chapter 5.13).
SEAWARD INTERFACES
The inland water ecosystems described above intergrade into marine systems at several points, the most important being saline marshes and swamps, and the estuaries that form at the seaward ends of the terminal reaches of perennial streams. Recent classifications of marine environments in the insular tropical Pacific address such estuarine ecosystems in a manner similar to that used above for freshwater systems.
The estuarine transition zone between limnetic and euhaline waters is primarily one in which mixohaline waters in delineable basins exhibit continuous or periodic surface connection to the ocean, allowing the entry of a diverse euryhaline marine fauna, including certain snappers, glassfishes, cardinalfishes, damselfishes, gobies, and gudgeons (this definition excludes waters inhabited by stenohaline marine inshore fauna such as corals, urchins, etc.). The level of the water surface exhibits tidal fluctuations, which may also produce strong inflows and outflows, and there is generally a pronounced stratification of halinity (concentration of sodium chloride), temperature, and (usually) oxygen concentration. Two distinct subtypes of natural estuaries may be recognized based on freshwater inflows and diadromous fauna.
True Estuaries
These are drowned river and stream mouths fed by limnetic water from perennial stream runoff. Their inland extent is determined by measurable tidal fluctuation and topography, such that estuaries of this type tend to be much more extensive on the south coast of Papua than on the north. In Papua such estuaries also tend to be horizontally stratified, with relatively large freshwater inflows relative to channel or basin volumes, leading to pronounced differences in salinity from head to mouth as one progresses along the length of the estuary. Additionally, such estuaries usually have a degree of vertical stratification, resulting from the fact that freshwater has a lower density than salt water, and therefore tends to ‘‘float’’ on top of a salt water wedge as the stream discharges into the ocean. The predominance of horizontal or vertical stratification is dependent on a variety of factors, including the volume and velocity of freshwater inflow, the depth and size of the estuary basin, and the degree of mixing created by winds and currents. In general, estuaries at the mouths large rivers tend to be homiohaline along any particular reach, while those of smaller stream systems tend to exhibit poikilohalinity resulting from wide seasonal fluctuations in freshwater discharge. Along many coasts in Papua true estuaries are often dominated by mangroves, and serve as important migratory pathways for larval and juvenile diadromous fishes and other animals (Erftemeijer et al 1989). They also support unique assemblages of marine water striders in the family Gerridae (Halobates, Rheumatometroides, Stenobates) which partition such estuaries on the basis of horizontal salinity gradients (Herring, 1961; J. Polhemus and D. Polhemus 1996; Andersen and Cheng 2004).
Estuarine Limnocrenes
Estuaries of this type consist of nearshore basins with subterranean limnetic water sources (generally basal springs) and open connections to the sea. In contrast to true estuaries, their waters tend to be uniformly homiohaline, due to annually stable limnetic discharges. The biota is generally similar to that of true estuaries, but may also include submerged vascular plants, and lacks transient diadromous stream fauna.
Threats to Inland Water Ecosystems in Papua
Although the overall condition of freshwater ecosystems in the New Guinea region is excellent, there are still obvious threats to the biota, which tend to manifest themselves on local rather than regional scales. These threats may be grouped into three general categories: physical alteration of habitat, utilization of biotic resources, and invasive species. Each of these threat categories is discussed separately below.
PHYSICAL ALTERATION OF HABITAT
Logging
Large-scale industrial logging, particularly by international timber companies, is a clear threat to watershed integrity throughout the New Guinea region. The obvious and disastrous effects of clearcutting aside, even selective logging by such companies results in an extensive network of poorly-planned and constructed secondary roads that create widespread siltation and stream impoundment problems. Although treefalls are a natural element of the New Guinea rain forest and the small impoundments resulting from them are encountered on nearly every forest stream in the region, particularly in the lowlands, logging tends to greatly increase the number of such channel obstructions, increasing pool habitat and decreasing riffles. Logging roads also tend to employ rudimentary bridges that subsequently collapse, creating further impoundments. Opening the forest canopy also increases insolation (exposure to sunlight) and thereby increases water temperature. The overall effect, then, is to create a stream that is warmer, more slowly flowing, and traps more sediment.
Much of the large-scale logging in Papua is undertaken by foreign companies with poor environmental records, or their local Indonesian subsidiaries. In addition to large-scale operations by companies such as PT Inhutani II and PT Astra, local military garrisons often set up illegal logging operations to subsidize their pay, usually with no consideration of environmental effects.
By contrast, the advent of small-scale logging, utilizing ‘‘walkabout sawmills’’ appears to result in rather light and transient damage to streams and watersheds. Such operations leave a lighter environmental footprint because they usually target only particular tree species, such as rosewood, which are widely scattered in the forest; they do not operate in one area for a long period of time; and they do not require the creation of an extensive road network.
Shifting Cultivation
The impacts of shifting cultivation are similar to those of clearcut logging, but on a far more localized scale. In traditional village settings, the effects of shifting cultivation were mitigated over time by the fact that such garden patches were relatively small in size and widely dispersed. In many cases, if all available garden areas had been used at least once, entire villages simply relocated to alternative sites, allowing the old gardens to go back to forest. As population has increased in many highland areas, however, the number of gardens has proliferated while the number of years they are allowed to lay fallow has decreased, and local governments have discouraged villages from changing location.
In general, shifting cultivation tends to have disproportionate impacts on first order streams (the smallest streams in a given drainage network), which are characteristic of the ridge slopes on which gardens are usually established. Creeks passing through newly cleared garden areas are usually exposed to intense sunlight and high air temperatures, and obstructed by massive tangles of vines and tree branches that in many cases make them nearly impossible to traverse. These ecosystem impacts produce significant faunal changes, with deep forest species that require cooling shade, particularly certain genera of Odonata (Selysioneura, Tanymecosticta), being absent in such areas. Provided that a patchwork of forest and garden plots remains intact, however, such forest biota will eventually recolonize streams in former garden areas once a canopy of native trees is re-established.
Oil Palm
In common with clearcut logging, oil palm plantations result in wholesale ecosystem conversion that has broad impacts across entire stream catchments. The creation of a plantation requires initial land clearing equivalent to clearcut logging (which may in fact be the first step if the proposed plantation area is covered with primary forest), after which a new canopy structure of oil palms eventually becomes established. Nutrient inputs from such plantations into adjacent streams appear to be high, probably due to fertilizer and other agrochemical runoff, leading to a proliferation of algae and consequent impacts on the benthic biota. Because oil palm development is generally undertaken on relatively flat lowland sites, it disproportionately impacts the terminal reaches of streams via clearance and drainage channelization of alluvial and swamp forests, with consequent impacts on diadromous biota similar to those described subsequently for mining.
Mining
Large-scale mining operations have had obvious local impacts to certain river systems in Papua, most notably the Ajkwa, which lies downstream of the Freeport Grasberg gold and copper mine. Although large scale-mining produces dramatic local impacts that are highly visible, reasonable attempts to mitigate these impacts, which include siltation, chemical contamination, and catchment dewatering for pipeline slurries, have been undertaken at Grasberg. A more pernicious set of impacts often arises from small-scale gold mining efforts that are common throughout the New Guinea region. As noted by Susupu and Crispin (2001): ‘‘Environmental issues do not seem to be a strong concern for members of the smallscale artisanal mining community. Issues such as damage to river beds, solids in water and destruction of riverbanks are not addressed.’’
The most persistent impact to freshwater ecosystems from such small-scale mining arises not from physical disturbance to streambeds, however, but from the mercury used in the mining process. By way of example, some 4 tons of mercury per year is presently sold to alluvial miners in Papua New Guinea, based on wholesalers’ records (Susupu and Crispin 2001). This mercury is used to extract gold from black sand either in between the sluice-box compartments or via simple panning. In the Wau/Bulolo area, where dredge mining occurred from the late 1920s through the 1960s, bulldozers still occasionally uncover large puddles of mercury, and similar situations are reported from long-term mining sites on Bougainville (Susupu and Crispin 2001). In Papua, local mercury pollution is now also occurring in the Timika area due to illicit gold refining operations being conducted by military units using barrels of concentrate stolen from Grasberg mine. Being non-soluble, mercury remains in river sediments indefinitely, and may be difficult to detect, since it is possible for river water to flow clear of mercury even when high levels of mercury are present in the river bed. Such mercury contamination, however, frequently enters the riverine food chain, where it is amplified through successive trophic levels, eventually posing severe risks to local human populations who consume fish and crustaceans.
In contrast to logging or oil palm plantations, which degrade entire catchments via wholesale landscape conversion, mining effluents generally impact only the main stem of any given catchment, leaving most tributaries undisturbed and available as potential reservoirs of biotic recolonization. The degradation of main stem rivers, however, particularly in the terminal reaches, can have serious impacts on certain diadromous faunal elements such as fish and prawns, preventing completion of the longitudinal migrations essential to their life cycles and thereby potentially extirpating them from certain river systems.
Petroleum
Petroleum development has relatively limited impact on inland waters, because the environmental disturbances associated with it tend to be small, scattered, and highly localized. Outside of the possibility of spills and pipeline leaks, which can obviously have serious short-term local impacts, the major threat from petroleum development results from forest degradation or clearance adjacent to the network of service roads, which provide conduits into previously undisturbed tracts of forest. In general, due to the scattered nature of the operations and shifting well sites, the overall ecosystem impacts of petroleum development are in some aspects similar to those of selective logging or shifting cultivation. In addition, because petroleum operations are restricted to a only a few particular areas in Papua such as the Vogelkop Peninsula, they do not appear to pose a broad-scale threat to freshwater ecosystems in Indonesian New Guinea on the same order as logging or even mining.
Dams
Dams and hydropower developments are sparse in the New Guinea region, and their impacts on freshwater systems are currently minimal. Larger scale projects, such as the proposed large dam on the main stem of the Mamberamo River in northern Papua, would clearly have significant basin-wide impacts were they to be constructed, but such plans are currently shelved due to economic constraints. By contrast, small mini-hydros, which are commonly used in the mountains of New Guinea to provide electricity for local mission stations, have minimal biotic impact.
Ungulates
The impacts of ungulates on New Guinea aquatic systems are underappreciated, but can be significant and extensive, in both upland and lowland areas. In the highlands, cattle grazing has been observed to create widespread slope terracing and converts valley bottoms into muddy marshes, increasing river siltation and water turbidity. Introduced Rusa Deer have similarly impacted savanna lowland habitats in southeastern Papua. Feral pigs, although widespread in New Guinea, have not had the same disastrous impacts to native forests as observed on smaller islands in Polynesia. Feral pigs are intensively hunted throughout the region, which probably serves to keep their numbers in check to some extent. It is unknown if they act as vectors of the water-borne disease leptospirosis, as they do in the Hawai’ian Islands, but this seems likely.
UTILIZATION OF BIOTIC RESOURCES
Live Aquarium Fish Trade
With a single exception, there appears to be little impact on the native fauna due to the live aquarium fish trade. As far as can be determined there is very little commercial harvesting of wild fishes for the aquarium trade with the exception of the illegal trade for Saratoga or Bony Tongue (Scleropages jardinii: family Osteoglossidae), which occurs in the southeastern border area of Papua. Saratoga is popular in the aquarium trade, probably because of its similar appearance to the Asian Arowana (S. formosus), which is a much sought-after ‘‘good-luck’’ fish in eastern Asia, particularly China and Japan, where they are known as Dragonfish. The huge popularity of the Dragonfish has apparently resulted in a demand for other species of bony tongues.
Saratoga is a popular aquarium and sports-fish native to southern New Guinea and northern Australia. It breeds annually just prior to the wet season (September to November). After external fertilization the female orally incubates a brood of about 30–130 eggs until they hatch 1–2 weeks later (Allen et al. 2002). The female then guards the newly hatched young, which remain close to her mouth for the next 4–5 weeks. The young fingerlings are particularly vulnerable at this stage of the life cycle and are easily harvested. The species is protected by law in Indonesia, and subject to various regulations in Australia.
Beginning in the 1990s villagers in the Torassi or Bensbach River area, in the Western Province of PNG immediately adjacent to the border with Papua, have been collecting and selling wild Saratoga fingerlings to merchants from across the border in nearby Merauke (Hitchcock, in press). These fish, as well as illegally captured fingerlings from Papua, are then exported to Asia, where they commanded considerable prices for several years. Australian fish breeders report that saturation of the market by Torassi Saratoga led to a collapse in prices and dramatic decline in demand for the species, which has negatively impacted upon the Australian export trade in wild-caught and captive-bred fingerlings. There is also evidence from local villagers living along the Bensbach River that seasonal harvesting of Saratoga over the past decade has resulted in a dramatic decline in population numbers. Therefore a critical need exists for more detailed study of this problem as well as a sound management plan that will insure the sustainability of the fishery. In addition, effective policing of the illegal trade is needed on the Papuan side of the border.
There is scant information on the harvest of other ornamental species. Rain-bowfishes of the family Melanotaeniidae are the only New Guinea group that is regularly seen in the international aquarium trade. Most of the species were introduced to the trade by various foreign collectors, often operating illegally. Rainbow-fishes spawn readily in captivity and there is now a large captive breeding pool that apparently satisfies most of the commercial demand, thus negating the need for wild-caught fish. However, there is probably limited capture of wild fish by Indonesian merchants in places such as Sorong and Jayapura, although reliable data are lacking.
At least one merchant was operating in Sorong as recently as six years ago. His trade revolved mainly around rainbowfishes, especially the brightly colored Boeseman’s Rainbow (Melanotaenia boesmani), which is endemic to the Ayamaru Lakes region of the central Vogelkop Peninsula. The species was introduced to the aquarium industry in 1983 by a German collector, and it has steadily increased in popularity. By 1989 Ayamaru villagers were catching so many live fish for the aquarium trade the species was on the brink of becoming endangered (Allen 1995). An estimated 60,000 male rainbows were captured each month for shipment to Jakarta exporters. Fortunately, the Indonesian government eventually placed controls on the industry.
Impact of Food Fish Harvesting on Native Fishes
There are virtually no data on the harvest of native fishes for human consumption or the possible impact of this activity on native fishes in general. Compared to the considerable harvest of marine fishes, the take of freshwater fishes seems relatively insignificant. Nevertheless, people living along the major river systems depend on freshwater fishes for a significant portion of their diet. Most of the larger villages have regular fish markets, which appear to be dominated by forktail catfishes, large gudgeons (Eleotris and Oxyeleotris), and various introduced fish, especially carp and tilapia. Forktail catfishes (family Ariidae) are represented in New Guinea fresh waters by 21 species and are probably the most important food fish in this habitat. Although they are heavily targeted by gill netting and traditional fishing methods their numbers do not appear to be declining, at least in major Papuan river systems such as the Digul and Mamberamo.
A variety of fishing methods are employed including hook and line from canoes, home-made traps, and various nets ranging from simple one-person hoop nets to large seines and gill nets. Streams, some of considerable size, are sometimes diverted and the former channel containing isolated pools with dense fish concentrations are then netted or speared. Some villages also employ Derris (Fabaceae) root to poison ponds, stagnant pools or slow flowing sections of creeks. In addition, local fishers are usually adept at catching by hand gudgeons and other fishes that hide in crevices.
Traditional fishing methods appear to have insignificant impact on the native fish fauna. After all, they have been used for centuries and continue to be sustainable. The problem lies with more modern techniques, especially when outboard motors have been introduced in combination with gill nets. It is our opinion that gill nets should be banned from areas of special biological significance in Papua, such as Lake Sentani and Lake Yamur. Gill netting has certainly played a major role in the demise of the Freshwater Shark (Carcharinus leucas) in Lake Yamur and the Giant Sawfish (Pristis microdon) in Lake Sentani.
INVASIVE SPECIES
In relation to its overall size, the New Guinea region exhibits a remarkably low incidence of invasive freshwater species. This fortuitous situation appears to result from the fact that the region is lightly inhabited, has not experienced extensive colonization and settlement by foreign peoples (although this situation is changing in Indonesian New Guinea with a continuing influx of western Indonesian settlers that were initiated through now-defunct government-sponsored transmigration programs), and is still not well integrated into the global economy. The result is that freshwater ecosystems in many parts of the island and its proximal archipelagoes remain among the most pristine on earth.
New Guinea’s general ecological integrity notwithstanding, the presence of exotic freshwater fishes is an increasing problem throughout the island. Allen (1991) reported the presence of 22 species representing 19 genera, 11 families, and all six continents. Since then at least six more introductions have been noted, and more can be expected, especially on the Indonesian side of the island. In the present chapter we provide details of the more recent introductions as well as a general overview of the invasive problem.
Most of the introductions have had a negative impact, either by competing for space and limited food resources, or by feeding on native species, including their eggs and fry. Tilapia (Oreochromis mossambica) has adversely affected the environment, creating turbid conditions in formerly clean lakes, and badly overcrowding the indigenous fauna due to its prolific breeding. Several species including tilapia, walking catfish, carp, and climbing perch appear to be undergoing rapid population increases and therefore pose a serious threat to native fishes.
The current distributional pattern of introduced fishes is closely tied to transmigration areas of Papua Province, particularly the larger population centers such as Jayapura and Timika. The transmigration program of the Indonesian government is no doubt responsible for many of the introductions. Newly arrived settlers often bring their pets and fish-pond stock from other parts of the archipelago. Thus, there is a major potential for further introductions.
Of primary concern is the relatively recent appearance of four invasive species (tilapia, snakehead, climbing perch, and walking catfish) in the Bensbach River system of southwestern Papua New Guinea (Hitchcock 2002). At least some of these possibly entered the river via drainage ditches associated with the building of the Trans-Irian Highway, which in 1982 crossed the international border in two locations on the Upper Bensbach. Tilapia and walking catfish are more recent introductions, having been first noticed in the area in about 1995.
Of equal concern is the appearance of two South American fishes, Prochilodus argenteus (Prochilodontidae) and Colossoma bidens (Characidae), and Barbonymus goniotus (Cyprindiae) from western Indonesia in the Ramu system of Papua New Guinea. The origin of these introductions remains a mystery, but they may have been species that were experimentally raised for potential introduction during an ill-conceived fish stock enhancement program sponsored by the Food and Agriculture Organization of the United Nations (FAO) in the 1980s.
Allen et al. (2002) noted that the Mamberamo River in Papua Province had the highest percentage (17.1) of introduced fishes of any major river system in New Guinea. The appearance of species such as tilapia, walking catfish, snakehead, and three species of cyprinids is particularly alarming, given the relative isolation of this system and lack of major population centers.
Another problem area is the Timika region of southern Papua Province. Prior to the opening of the Freeport gold and copper mine, there were no invasives in the region. But a huge influx of transmigrants has seen the introduction of tilapia, climbing perch, walking catfish, and snakehead (Allen et al 2000). In addition, the Blue Panchax (Aplocheilidae) from southeast Asia was introduced in the 1990s, apparently for mosquito control.
Across New Guinea as a whole, invasive species appear more concentrated in lakes and wetlands, although certain lowland streams and river systems, particularly in the Mamberamo and Sepik-Ramu basins, are badly contaminated. The amazingly intact character of New Guinea’s wetland systems in a physical sense may in fact be limiting the spread of invasives, due to a lack of canals and periodically flooded agricultural field systems, coupled with natural seasonal drying. By contrast, the introductions of invasive fish into lotic (i.e., flowing water) environments is of great concern, since this enables highly vagile invasives such as tilapia, mosquitofish, or snakeheads to penetrate repeatedly both riverine and ephemeral riparian wetland habitats after seasonal flooding. Particularly problematic in this regard has been the introduction and continuing spread of snakeheads (Channa spp.) because of their ability to survive buried in the mud of ephemeral wetlands for months utilizing their accessory breathing organ (Courtenay and Williams 2004). This predaceous invasive has the potential to spread throughout the entire coastal wetland zone of southern New Guinea, from Etna Bay eastward to at least the Lakekamu River.
Although the invasive fish species already present in New Guinea appear to be undergoing population expansions, thereby posing a grave threat to native species (Allen 1991), the specific impacts of such invasives on aquatic organisms endemic to New Guinea have for the most part not been determined. Similarly, little work has been undertaken regarding the identity or spread of other invasive freshwater animal species, particularly invertebrates.
The following section provides additional detail on many of the most significant invasive fishes documented from the New Guinea region, and their varying degrees of ecological impact as known to date.
Carp
Carp (Cyprinus carpio) are common in a few areas such as the upper Baliem River in Papua, Lake Kopiago, and the Lower and Middle Sepik and Ramu river systems of PNG (Allen 1991). Like many invasive fish species, carp modify their environment to conditions for which they are better suited to survive in than native fish species. World-wide, carp are regarded as a pest fish because of their tendency to uproot and destroy aquatic vegetation which results in increased turbidity and deterioration of habitats (Fuller et al. 1999). Carp have also been found to not only impact native fish species directly through egg predation, but also negatively impact waterfowl by increasing turbidity causing a reduction in food availability needed by both birds and native fish (Fuller et al. 1999).
Tilapia
Tilapia (Oreochromis or Sarotherodon spp.) are perhaps one of the most adaptable and widespread species of fish in existence, and have been stocked throughout the world. These highly invasive fish are now abundant in the Timika region of Papua (Allen et al. 2000), and in the lower Ramu and middle and lower Sepik rivers of Papua New Guinea, and have become the most important food fish in the Sepik area (Allen 1991). Tilapia have ecological impacts similar to carp in that they uproot aquatic plants, are known to feed on wetland taro, and reduce food supplies for native bird species (Englund and Eldredge 2001). In contrast to carp, tilapia are even more invasive in tropical areas because their ability to withstand saline and brackish-water environments (Englund and Eldredge 2001) allows them to spread along a coastline.
Snakeheads
Native to areas of Indonesia west of Weber’s Line, snakeheads (Channa striata) currently are found on Waigeo Island off western Papua (Allen et al. 2000); in streams near Bintuni on the Vogelkop Peninsula (Allen 1991); in the Timika region (Allen et al. 2000); and in the vicinity of Merauke (Hitchcock 2002). Because migrants prefer eating this fish, it is commonly first found near their settlements (Allen et al. 2000) and would be expected to be spread throughout Papua by migrant communities. Species in the genus Channa are voracious and highly effective predators, and further establishment in New Guinea would have highly detrimental impacts to all freshwater biota. Snakeheads have been implicated in the extinction of at least four species of fish in Madagascar, displacing the formerly common native Cichlid genus Paratilapia from the central plateau and Lake Aloatra (Courtney et al. 2004; Courtenay and Williams 2004). In New Guinea, snake-heads appear to have caused a general reduction of native fish numbers and diversity in areas where they are present (Allen et al. 2000).
Trout
Although Brown Trout (Salmo trutta) were introduced in 1949 to the highland regions of Papua New Guinea, and by 1952 had become established in this area (Werry 1998), there is no record of similar introduction into the upland streams of Indonesian New Guinea. In Papua New Guinea, the effect of trout on the native ichthyofauna appears to be minimal because they have survived in high elevation (> 2,000 m) areas lacking native fishes (Allen 1991), although they have been documented to prey upon two species of endemic waterbugs, Nesocricos mion and Tanycricos acumentum, the latter of which also occurs in the central ranges of Papua (Polhemus and Polhemus 1985, 1986). The impacts of this predation are unknown, however, and these insect species still remain common enough after the introduction of trout to be used as bait by highland tribesman (Polhemus and Polhemus 1985).
Livebearers (Poeciliids)
At least three poeciliid species have been recorded from New Guinea: Mosquito-fish (Gambusia affinis), Guppies (Poecilia reticulata), and Green Swordtails (Xiphophorus helleri). Although Mosquitofish and the other two species of poeciliids were introduced into New Guinea to control mosquitoes, their impact in this regard has been minimal, and they instead crowd out effective native predators of mosquitoes such as rainbowfishes (Allen 1991). Given their continuing popularity as supposed biocontrol agents, however, such fishes will likely continue to be introduced to Papua, particularly in streams near larger towns. The situation in Papua New Guinea provides a cautionary example: guppies are now common in the Goldie River and in streams around Port Moresby, and are often the only fish present. In 2004, surveys funded by Conservation International also found guppies in the lower Gumini River system of Milne Bay Province; these guppies were the only invasive fish species found in this otherwise faunally pristine stream. Green Swordtails, although unknown from the main body of Papua province, are present in at least one upland stream on Biak Island, and are highly invasive, having the ability to penetrate streams far inland (Englund and Eldredge 2001).
