Biodiversity publications archive

Australia's biodiversity: an overview of selected significant components

Biodiversity series, Paper no. 2
Biodiversity Unit
Department of the Environment, Sport and Territories
, 1994

4. Biodiversity in wetlands

Although Australia has a variety of wetlands including montane wetlands, permanent lakes and some large rivers, climatic factors have resulted in a relative scarcity of aquatic habitats, particularly in the arid and semi-arid regions 137 175. Australia is regarded as being more arid than any other continent apart from Antarctica. Rainfall in much of Australia is unpredictable and varies markedly with the seasons. This, combined with a low mean annual runoff, leads to a very high variability of flow which produces a large number of intermittent water bodies (both streams and lakes) in arid and semi-arid areas. These factors, along with high seasonal variation in evaporation, have resulted in seasonal variation of aquatic habitats, high levels of salinity and various patterns of temperature layering 177. As stated earlier, in contrast with most other countries, the area of saline wetlands in Australia far exceeds that occupied by fresh water. In addition, permanent lakes in Australia are few and running waters (temporary and perennial) are the dominant water-body type in number but not in surface area.

The general importance of inland aquatic areas to Australian biological diversity is worth noting. As areas of moisture in a generally arid continent, they are vital to many groups, notably birds, and many communities of floral and faunal species are specifically associated with them.

4.1 Significant features

The distinctive characteristics of Australian wetlands have in turn allowed the evolution of some unusual species and communities. The unusual composition of the Australian aquatic biota is discussed below and examples of groups significant for their endemism, ancient lineage and distinctive adaptations are provided.

Significant features of biodiversity in wetlands – summary

Australia's wetlands are characterised by unpredictable rainfall and seasonal variation in evaporation rates. Many also have high levels of salinity. The water level in lakes and streams is very variable and overall there is a scarcity of aquatic habitats, particularly in the arid and semi-arid areas. Despite these overall features, Australia has a variety of wetlands, which have allowed the evolution of a variety of aquatic biota, particularly fauna.

The aquatic flora is not distinctive and although some endemic species are found, most species are widely distributed. The fauna, however, is more diverse and includes the well-known Australian inhabitant, the platypus, which is one of only three species of primitive egg-laying mammals (monotremes) in the world. Other famous vertebrate inhabitants are two species of crocodiles: the endemic freshwater crocodile; and the more widely distributed saltwater crocodile. The waterways support a diverse fauna much of which is endemic, including freshwater sponges, snails, shrimps, isopods and a variety of insects. Southern trouts, which occur all over the southern hemisphere, are most abundant and diverse in Australia; while insect families such as caddis flies and mayflies are composed of different species groups in Australia than elsewhere.

The salt-lake communities, although restricted in species numbers, are noted for some distinctive and endemic shrimps and gastropods. Only a limited number of organisms in the world have adapted to life in salt lakes and many notable examples are in Australia. Many organisms have also evolved adaptations to cope with periods of drought, for example drought-resistant eggs or larvae; burrowing; and life-cycle adaptations including opportunist breeding after flooding.

'Living fossils'

There are many examples of Australian aquatic fauna with ancient origins. Crocodiles have fossil ancestors dating back over 200 million years. The Queensland lungfish is among the most ancient of living bony fishes with a fossil ancestry dating back for over 400 million years. A number of fish families, including the barramundi and salamanderfish, have Gondwanan or Pangaean ancestry as do numerous invertebrate groups. One small green damselfly species may be the most ancient species of the primitive insect order Odonata and has probably been on the Australian landmass for at least 280 million years.

4.1.1 Australia's endemic wetland communities

Many faunal species and genera inhabiting Australia's wetlands are endemic. Of the vertebrates, undoubtedly the best known is the platypus (family Ornithorhynchidae). The platypus is considered to be so completely different from other mammals that it has been placed in a separate mammalian subclass Prototheria, along with the echidnas. The platypus locates its living prey by 'electroreception' with the aid of special glands in the bill, which perceive the minute electric currents generated by the prey. Small families of fish that are endemic to Australian wetlands include the Ceratodontidae (lungfish), Gadopsidae (blackfish) and Lepidogalaxiidae (scaled galaxias) 114.

Many wetland invertebrates are also endemic to Australia and this is seen at both the species and genus levels. For example: half of the 24 known species of freshwater sponges; 15 per cent of the 600 known species of Rotifera (freshwater zooplankton); many of the genera and species of gastropods (snails); 19 of the 20 species of the Conchostraca (clam shrimps); all the described genera of isopods; approximately 75 per cent of genera and a higher proportion of species of Ephemeroptera (mayflies); most of the genera and species of Trichoptera (caddis flies); and 44 per cent of the genera and 74 per cent of the species of Odonata (dragonflies and damselflies), are endemic 177. In addition, all 196 species of stoneflies (Plecoptera) – including 24 of the 26 Australian genera – are endemic 154. Freshwater crayfish of the family Parastacidae have a very high level of endemism with eight of nine genera endemic and only two of 98 species found elsewhere (in Papua New Guinea) 68.

Although invertebrate endemism is not so high at taxonomic levels above species and genera, there are some families found only in Australia. These include Anaspididae, Koonungidae and Psammaspididae, which are all syncarids (crustaceans) 177. Other endemic invertebrate superfamilies and families include the dragonflies Hemiphlebioidea and Lestoideidae, the caddis flies Plectrotarsidae and the cnidarian Australomedusidae 177.

Australia's salt lake communities are noted for a high percentage of endemic species rather than a wide variety of species. The eight described brine shrimps of the genus Parartemia, for example, are endemic 54, as are the nine Australian species of the gastropod genus Coxiella 146.

The Australian aquatic flora is less distinctive than the fauna. Algal species, for example, are usually cosmopolitan, although some species are distinctive, such as the endemic desmid Micrasterias hardyi 173. Levels of endemism among the approximately 600 species of macrophytes that can be considered native are also low, with many cosmopolitan genera and species. This is probably a reflection of the role played by birds in aquatic plant dissemination 198 218.

Australia's endemic aquatic flora includes several species in the family Menyanthaceae, including some species of Nymphoides (marshworts) found in northern Australia and ten species of Villarsia endemic to southwest Western Australia. Ondinea is an endemic genus of plants related to water lilies, and Maidenia, Caldesia and Nymphaea (water lillies) contain endemic species that grow in northern Australia. Limnophyton, Aponogeton and Nymphaea include species endemic to Cape York north of the Atherton Tablelands 198.

4.1.2 Unusual composition of inland aquatic communities

The higher order composition of the wetland fauna of Australia is not grossly different from that of inland waters elsewhere – standing or flowing, fresh or saline. For example, copepods, cladocerans and rotifers dominate lake plankton; insects are important in fast streams; notostracans, shrimps, mussels and snails are important in large rivers, and anostracans and conchostracans characterise the fauna of many temporary water-bodies.

At the same time, there are so many particular differences, involving both endemism at several taxonomic levels (as discussed in the previous section), and, in some cases at least, profound changes in the balance of faunal groups present in a given ecosystem, that almost all animal groups present in Australian wetlands possess a distinctive regional complexion. The only exceptions appear to be provided by the Nematoda and Polyzoa (Bryozoa).

Many faunal groups are much more diverse in Australian waters than in aquatic systems elsewhere. Notable examples are provided by the freshwater mussels of the family Hyriidae; crayfish (Parastacidae, Decapoda); Phreatoicidae (Isopoda, many of which have limited distributions); the southern frogs (Myobatrachidae), and galaxiid fish (Galaxiidae). The Galaxiidae or southern trouts, a group confined to the southern hemisphere, is most abundant and diverse in Australia. Some groups adapted to highly saline conditions, such as the brine shrimp genus Parartemia mentioned above, are notably diverse in Australia 177.

The composition of some invertebrate components of the fauna of Australia's inland aquatic habitats is distinctive, including groups such as the mayflies and caddis flies. An unusual feature of mayflies is the strong dominance of Leptophlebiidae, which contrasts with the situation elsewhere. A significant feature of the Australian caddis fly fauna is that the family Limnephilidae comprises less than one per cent of Australian species: in other continents this family comprises about 25 per cent of the caddis fly species 177.

Several other aquatic groups common elsewhere are naturally absent or have only minor occurrence in Australia. These include the mayfly family Heptageniidae, the isopod Asellidae, the cladoceran Holopedidae, the frog family Ranidae, and the bird family Phoenicopteridae (flamingos) and order Gaviiformes (loons) 177. While all four fish classes are represented in Australia, the total number of native fish species (which show a high degree of endemism) in Australia is low, at less than 200 species 205, compared to the total number of fish elsewhere. Several families that are significant elsewhere are absent in Australia (except as recent introductions), such as the salmonids (trouts and salmon), and the cyprinids (carps).

Australia's aquatic flora not only has a lower percentage of species endemic to Australia than its fauna, but the composition of its flora is less characteristic than that of its fauna. This relatively low degree of endemism and diversity in Australia's inland aquatic flora is probably because of the cosmopolitan nature of many aquatic plant species. As is the case in other continents, monocotyledons generally dominate inland aquatic ecosystems198.

4.1.3 Ancient and relict components of Pangaean and Gondwanan origin

Several of Australia's aquatic animals are of great antiquity, apparently having Pangaean or Gondwanan origins. These taxa are highly valued since, through them, scientists can better understand how existing groups have evolved.

Perhaps the best known of Australia's 'living fossils' is the Queensland lungfish (Neoceratodus forsteri), which is one of only three extant choanichthyid fish. Lungfishes are among the most ancient of living bony fishes and their fossils date back more than 400 million years 1. The family Ceratodontidae contained seven species, but only one, N. forsteri, still exists. Fossils from northern New South Wales from the early Cretaceous (100 million years ago) are virtually identical with the Queensland lungfish, making Neoceratodus one of the oldest living vertebrate genera 1. Other fish of ancient lineage include the barramundis, one of which, Scleropages leichardti (the spotted barramundi), is endemic to Australia. The salamanderfish, Lepidogalaxias salamandroides, also appears to have Gondwanan or Pangaean ancestry 176. At least five other families of fish have a possible Gondwanan ancestry: Retropiniidae, Prototroctidae, Galaxiidae, Aplochitonidae and Percicthyidae 176.

Also of ancient lineage are the crocodiles, of which Australia has two species, the endemic freshwater crocodile (Crocodylus johnstoni), and the saltwater crocodile (C. porosus). Crocodilian fossils extend back to the Triassic period, 220 to 250 million years ago 47.

Invertebrate groups also have strong links with this time. The crustacean superorder Syncarida is interesting from an evolutionary point of view, as one of its orders, the Anaspidacea, contains fossil and extant forms that are morphologically similar to the ancestors of the malacostracans (e.g. crabs, lobsters, shrimps) 177. Extant Tasmanian syncarid shrimps of the family Anaspididae (order Anaspidacea) resemble primitive forms about 200 million years old 68. One of these, the mountain shrimp Anaspides tasmaniae, is found in mountain streams and tarns in Tasmania. Most members of the Anaspidacea are confined to southern Australia. The syncarids are known from fossils dated from the Carboniferous and Permian periods, 215 to 350 million years ago 102. Australia is also a major evolutionary centre and refuge for freshwater shrimps (order Amphipoda). At least six families have been delimited for Australian freshwater species, and crangonyctoids and the corophiids may have descended from Gondwanan forms 177.

Conspicuous among Gondwanan freshwater animals are crayfish of the family Parastacidae (superorder Eucarida), with representatives in Australia (Tasmania), New Guinea, New Zealand, Madagascar and South America. This group is thought to have had its centre of origin in the southeast Australian region of Gondwana 129.

Some orders of insects also have Gondwanan links: some 40 per cent of dragonflies and damselflies (order Odonata) are possible Gondwanan relicts, and southern Australia harbours several examples, such as members of the families Neopetaliidae and Petaluridae (which also extends to north Queensland) 167. Other ancient aquatic insects include water beetles of the genera Hygrobius and Microsporus. Both are worldwide genera of presumably great antiquity, with three of the five species of Hygrobius, and two of the eleven Microsporus species found in Australia 90 69.

Unique groups of ancient lineage

The insect order Odonata is an ancient one, and it appears that Australia may have its most archaic member. This is the small green damselfly species Hemiphlebia mirabilis (see page 39), a rare insect that has been given its own superfamily (Hemiphlebioidea) and has probably been on the Australian landmass for at least 280 million years. It possesses a mixture of primitive and apparently reduced morphological features and is thought to be the sister taxon to the whole of the rest of the Odonata 157 167.

4.1.4 Distinctive adaptations

Australian wetlands harbour many biota that possess unusual adaptations to their environment, notably to salinity and to hydrological variability.

Salinity

A number of Australian aquatic species have adapted to the saline conditions of many of our wetlands (salt lakes are classified as highly saline if salinity is greater than 50 parts per thousand). Adaptations to assist survival in such harsh conditions vary: some species avoid periods of high salinity by having short life cycles that are completed when the wetlands are full of water and salinities are lowest; some plants excrete salt on to leaf surfaces; and other animals and plants use osmoregulatory mechanisms to concentrate salts in their cells to osmotically match concentrations in the external solution.

Osmoregulation is employed by the endemic brine shrimp Parartemia zietziana, which coexists with salt-tolerant plants in Australia's saline waters. This shrimp can be found in waters with over 300 parts per thousand salt and feeds on Dunaliella, a genus of algae that is extremely tolerant to saline conditions 102.

Other salt-tolerant plants include the genera Ruppia and Lepilaena. These can be found in lakes with up to 100 parts per thousand salt, and some species can survive at more than 200 parts per thousand, as dormant seeds or bulb-like turions. Lamprothamnium papulosum is also of note as the most salt and drought-tolerant macroalga, tolerating salinities up to 210 parts per thousand and habitats which may be dry for up to ten months of the year.

In Australia, as indeed globally, only a limited number of animals have adapted to life in salt lakes. Almost all the species found in Australia are endemic and several are noteworthy. In addition to P. zietziana (mentioned above), Haloniscus searlei is the only oniscoid isopod unequivocally known to have adapted to saline waters and Coxiella striata is the most salt-tolerant of all known gastropods 176. Table 5 gives examples of the maximum salinity levels recorded for some salt-tolerant species.

Table 5: Maximum salinity levels recorded in the field for significant halobionts
Order Species Maximum salinity level
(parts per thousand)
Anostraca Parartemia zietziana 353
Ostracoda Diacypris whitei 180
Copepoda Calamoecia salina 131
Isopoda Hasloniscus searlei 192
Mollusca Coxiella striata 112
Insecta Tanytarsus barbitarsis 95
Pisces Taeniomembras microstomum 70

Source: Williams and Allen 1987

Species in Australian salt lakes are generally eurytopic, that is, tolerant of a wide range of ecological conditions, as the salinity in their habitats often rises considerably with evaporation. For example, the endemic isopod Haloniscus searlei has been found over the salinity range of 3.6 to 192 parts per thousand 174.

Ephemeral water

The 70 per cent of Australia that is arid and semi-arid is characterised by often unpredictable rainfall and ephemeral water bodies. These latter include temporary watercourses, floodplain wetlands, rockpools and temporary salt lakes. Three main types of adaptations are used by aquatic animals in these environments: adaptations to resist desiccation, life-cycle adaptations, and adaptations to enable dispersal 176.

Many crustaceans produce eggs resistant to desiccation. Daphniopsis pusilla, for example, is found in mildly saline lakes, and produces large numbers of non-resistant eggs in favourable conditions. However, with the onset of unfavourable conditions, this cladoceran produces a smaller number of resistant eggs 176. Chironomids (midges) are noted for their desiccation-resistant larvae, and an Australian example is provided by Allotrissocladius amphibius which produces a protective larval capsule which can resist drying for considerable periods. Adults of the snail Coxiella striata avoid desiccation by tightly fastening their opercula to their shells. The isopod Haloniscus searlei, which like C. striata inhabits mildly saline lakes, survives dry periods by sheltering in refuges such as under stones 176.

Temporary pools and streams have a rapid succession of species and surprisingly harbour a relatively high density of invertebrates, especially insects 86 16. In addition, some Australian temporary streams have an unusually diverse range of species, often as diverse as that of permanent streams with which they share many species 16. When temporary streams dry up, many animals seek refuge in water below the stream bed and in crayfish burrows, or as drought-resistant stages in dried sediment and leaf litter on the stream bed. Elsewhere in the world, for example Arizona, such in-stream refuges are not as well used 17.

Life-cycle adaptations (some of which involve the production of resistant phases) include rapid growth rates, the capacity to synchronise life cycles with water availability, and dispersal abilities. Several major strategies are employed by fauna inhabiting temporary water: most saline water invertebrates are dormant during dry periods; and freshwater insects inhabiting temporary water sources often have a dormant phase and employ an active dispersal strategy. Dispersal without a dormant phase is characteristic of aquatic birds and some insects 176.

Variable hydrology in permanent waters

Although little information on adaptations to the variability of Australian aquatic systems is available, some clear examples are known. The golden perch (Macquaria ambigua) and the silver perch (Bidyanus bidyanus) are two examples of fish, found in the Murray River, which spawn only after flooding. One obvious advantage of this strategy is that young fish develop at a time when nutrients released from flooded sediments stimulate the growth of food organisms. Such fish resorb eggs if flooding does not occur 176. The ubiquitous grey teal (Anas gibberifrons) is an example of a bird in which reproduction starts only when water levels begin to rise. If conditions become unfavourable, adults disperse. This opportunistic breeding cycle is in marked contrast to most northern hemisphere water fowl 176.

Some invertebrates also show adaptations to variability. The atyid prawn Paratya australiensis, which occurs typically in lowland streams and rivers in southeastern Australia, produces planktonic larvae, unlike most freshwater invertebrates. The larvae avoid being swept downstream because the prawn's breeding cycle begins in summer just before inhabited watercourses dry to pools. By the time the water flow is strong, the prawns have grown large enough to resist being washed downstream 176. Another invertebrate that relies on changes in water levels is the freshwater snail Notopala hanleyi, which was found extensively on the River Murray before its flow was regulated. Like many other snails, N. hanleyi is a detritivore, eating both algae and bacteria on the substrate where it occurs, but requiring a high proportion of microbes in its diet to obtain sufficient nutrients. Before the Murray River was dammed, water flow varied markedly and there was limited algal growth . Since regulation, however, the more constant water flow and level has increased algal growth and most submerged surfaces are now coated with mats of filamentous algae. N. hanleyi is no longer found in the river itself, but has colonised irrigation pipes. It is thought that the change in food resources resulting from human changes to hydrology may have been a key factor in N. hanleyi 's disappearance from its normal habitat 143.

Figure 4: Variability in stream flow for some Australian rivers.

Figure 4: Variability in stream flow for some Australian rivers.

Solid histogram indicates average flows, and open histogram indicates flows likely to be equalled or exceeded one year in ten.

Source: adapted from Williams and Allen (1987)

4.2 Some special wetland areas

Special wetland areas – summary

There are a number of unique wetland areas in Australia that deserve special consideration because they provide areas of moisture and a variety of habitats in an otherwise arid continent.

The Kakadu area includes a mosaic of wetlands and during the annual wet-dry cycle, some areas can be flooded for up to nine months of the year. Species diversity and abundance is great with 60 species of waterbirds which congregate in their millions on the floodplains. The freshwater crocodile inhabits permanent watercourses with several species of freshwater turtles including the pig-nosed turtle. There are 59 species of fish, 25 species of frogs and 10-100 000 species of insects, many of which are endemic to the area and of considerable scientific interest.

The lower Cooper wetlands, including the Coongie Lakes of central Australia form another important wetland area with a complex system of claypans, channels, fresh and saline lakes, internal deltas, swamps and flooded meadows, occurring over the floodplains. The diverse aquatic flora and fauna of this area is characterised by spectacular fluctuations in abundance and for its adaptation to an 'opportunistic' lifestyle. The Coongie Lakes are of particular interest with a mosaic of lakes, intersecting dunes and a maze of channels. The lakes support a diverse and often extremely abundant bird population, including 24 species classified as rare or endangered (for example the freckled duck – one of the ten rarest waterfowl in the world). The lakes also support an exceptional number of zooplankton species as well as rich frog and fish faunas.

Two specialised wetland areas are worthy of special mention. The first is the granite outcrops of the southwest of the continent, which allow the development of transient pools and marshes during winter and spring. These are inhabited by a variety of unusual plants such as the pin-cushion plant which can remain alive in a dry state for up to four years. Carnivorous plants are also common. Second are the mound springs of the Great Artesian Basin where pools of springwater form, and which are refuges for a variety of fish, invertebrates and plants (water and land), some of which are dependent on mound springs for their survival.

4.2.1 Kakadu wetlands

Kakadu National Park

Kakadu National Park

The Kakadu area, while not limited to wetlands, encompasses a mosaic of contiguous wetlands including seasonal creeks, extensive freshwater floodplains, permanent lagoons, paperbark swamps and semipermanent billabongs. The large Mary and Alligator river systems also have much of their catchments in Kakadu. Up to 15 per cent of the 1.3 million hectares encompassed by Stages 1 and 2 of the Kakadu National Park is inundated annually, in some areas for up to nine months.

This has given rise to an almost continual change in the composition of plant communities during the wet-dry cycle in seasonal floodplains. The vegetation varies from grasslands dominated by annuals or perennials, to sedgelands and herbfields, and Melaleuca forest. Eucalyptus woodland, dominated particularly by E. papuana and E. polycarpa, are associated with the margins of alluvial plains or the levees of the larger rivers. In more permanently wet areas, remarkable 'floating mats' of species (for example, the grasses Hymenachne acutigluma and Pseudoraphis spinescens) not rooted to the substrate can be found. These rafts are often sufficiently stable to walk on and are a favoured crocodile nesting habitat 5.

There is considerable species diversity associated with the Kakadu wetlands. The wetland environments support more than 60 species of waterbirds, including herons, egrets and bittern (ten species), ibis, spoonbill, ducks, geese, darters and cormorants. Waterbirds congregate in huge numbers on the floodplains, reaching maximum numbers, some 2 500 000 birds, in the dry season 5. The freshwater crocodile inhabits permanent freshwater habitats, particularly the upper reaches of streams that persist during the dry season as discontinuous chains of billabongs. Seven species of freshwater turtle can be found in Kakadu, and the pig-nosed turtle (Carettochelys insculpta) is particularly significant scientifically. This turtle is the sole surviving member of a family that has undergone some 40 million years of independent evolution and adaptation. Twenty-five species of frogs, the majority of which occur in seasonally inundated wetlands and wooded margins, can also be found in Kakadu. Of the 10 000 to possibly 100 000 insect species in Kakadu, it is the aquatic ones that are the most endemic and significant for conservation 5. Two noteworthy stream-dwelling dragonflies with Gondwanan affinities, Hemigomphus magela and Austrocordulia territoria, are recorded only from the Arnhem Land escarpment and 105 species of caddis-fly are known from Kakadu's freshwater streams, among them 11 new species 5.

The fish fauna of Kakadu is also significant, being richer than in similarly-sized drainage systems in tropical areas of the world and in southern Australia. Fifty-nine fish species, 12 of them essentially marine, have been recorded from freshwater locations in Kakadu. This represents about one-third of all fish species found in Australian freshwater habitats. Five species, the exquisite rainbowfish (Melanotaenia exquisita), Mariana's or the Magela hardyhead (Craterocephalus marianae), the sharp-nosed grunter (Syncomistes butleri), Midgley's grunter (Pingalla midgleyi) and a new species of gudgeon (Hypseleotris species) have been recorded only from the northern part of the Northern Territory, and Kakadu contains a significant portion of the total range of the first four of these species 5.

4.2.2 Lower Cooper wetlands

Coongie Lakes, part of the Lower Cooper wetlands

Coongie Lakes, part of the Lower Cooper wetlands<

The flow regimes of Cooper Creek, as with other large rivers of central Australia, is among the most variable in the world 122, and unlike the Kakadu rivers, its variations are highly irregular in time. Rivers like Cooper Creek also have a complex morphology extending over vast floodplains. This unpredictable and spatially complex environment creates a distinctive ecology, based on opportunistic use of pulses of resources, which are scattered in space and time 122.

The lower Cooper wetlands, including the Coongie Lakes, constitute a complex system of aquatic habitats in the floodplain of the lower Cooper Creek. This floodplain extends for 20 000 square kilometres into the longitudinal sand dunes of the Strzelecki Desert, and encompasses ephemeral interdune claypans, permanent deep interconnecting channels, shallow braided channels, fresh and saline lakes, internal deltas, swamps and flooded meadows. The Coongie Lakes region is a mosaic of dozens of lakes, intersected by dunes and connected by a maze of channels. This diversity in space is multiplied in time by the enormous variations in flow, which give each lake a different and changing inundation pattern.

The diversity and changeability of habitat has resulted in a rich aquatic biota characterised by spectacular fluctuations in abundance, high dispersal and colonising capabilities, tolerance of extreme conditions, and flexible and opportunistic life histories.

The Coongie Lakes region supports a highly diverse and at times abundant bird population. With over 205 species reliably recorded, the region has a higher bird species diversity than any other truly arid region in Australia 127. These include some 24 species classified as rare, vulnerable or endangered in South Australia, such as the endangered bush thick-knee (Burhinus grallarius) and the vulnerable freckled duck (Stictonetta naevosa) which is listed as one of the ten rarest waterfowl in the world 127. For much of the year the concentration of birds can be spectacular with at least 20 000 waterbirds occupying the Coongie Lakes, but these numbers fluctuate continuously within each lake and between lakes. Breeding populations of pelicans, for example, may reach 80 000.

The Coongie Lakes system also exhibits an exceptional diversity of zooplankton (some 41 rotifers, 12 cladocerans and four copepods identified from December 1986 collections alone) attributable in part to an overlap of tropical and temperate faunas. With some eight species of frogs, including an undescribed species of water-holding frog (Cyclorana species), the Coongie region contains the richest frog fauna within central Australia 127. The fish fauna is unusual for a large river system in having only two exotics, the goldfish (Carassius auratus) and the mosquitofish (Gambusia affinis holbrooki), neither of which is dominant in the community. At least one fish species in the Coongie region, an eel-tailed catfish (Neosilurus sp.), is endemic to the Cooper 210.

Flooding is the most crucial factor in shaping the life-history patterns of aquatic biota in the region. Waterbirds move between the lakes to capitalise on habitats that suit their dietary needs, foraging methods or reproductive condition, which change as the lakes fill and recede 127. The fish populations of the system also respond to flooding in various ways. Juveniles undertake downstream colonising migrations, and adults of most species spawn during floods, some, such as the Lake Eyre Basin callop (a species of Macquaria awaiting formal description), after upstream migrations 128 210. The breeding behaviours of most species, however, are more flexible than their southern Australian counterparts.

The highly variable flooding regime also enables adaptations to drier conditions. Crustaceans such as the shield shrimp (Triops australiensis), the clam shrimps (Conchostraca) and the fairy shrimps (Branchinella) hatch from drought-resistant eggs and live through an accelerated life cycle. The inland crab Holthuisiana transversa survives long droughts by sealing itself in deep burrows 128.

Finally, the Coongie Lakes community essentially retains its original composition and ecological cycles and may serve as a benchmark by which to gauge the effects of alterations to other inland aquatic systems.

4.2.3 Wetlands of granite outcrops

In high places, notably outcrops of ancient granitic rock in the southwest of the continent, rainfall allows transient pools and marshes to develop during winter and spring and a variety of unusual plants populates these wetlands. An example is the genus Borya which comprises species capable of drying out in summer and then rehydrating and resuming photosynthesis within a day or so after the next wet season starts. One of its species, the pin-cushion plant Borya nitida, a lily that occurs in southern Western Australia, has leaves and stems that can remain alive in a dry state for up to four years 108.

Carnivorous plants are prominent in these high wetlands and include sundews (Drosera) and bladderworts (Lentibulariaceae). The ancient plant group Lycopsida, which flourished in the Carboniferous period, is represented by two genera, Phylloglossum and Isoètes. Isoètes is a worldwide genus with six species endemic to Western Australian rock pools. These temporary water sources are also home to a small but interesting fauna, such as the chironomid midges Paraborniella and Allotrissocladius, which are inactive in winter when water temperatures are low, but which mature rapidly in the higher temperatures of summer 102.

4.2.4 Mound springs of the Great Artesian Basin

The Great Artesian Basin

The Great Artesian Basin

Source: from Habermehl, M. A. 1980 BMR journal of Australian Geology and Geophysics Vol 5.

Mound springs, such as those found in large numbers on the fringes of the Great Artesian Basin, one of the largest artesian systems in the world, are of great significance as foci for plant and animal life – and as refuges in generally dry regions. The springs are associated with mounds, or accumulations, of sediments that may be up to eight metres high and tens of metres across, and the spring water emerges as seepages, as flowing springs, or forms pools of standing water. Depending on the rate of water flow and the morphology of the mounds, moderately large pools may form over the spring site, some feeding streams or tails several kilometres long. Mound springs often occur as groups, such as the approximately 80 active springs of the Dalhousie group, which is geologically unique as well as biologically valuable. This group, which is one of only two groups currently afforded protection, is a refuge for six species of fish (three of which are probably endemic to these springs) and 90 species of terrestrial and semi-aquatic vascular plants, including several species rare amongst mound springs 187 120. The ten springs of the Freelings group consist mainly of seeps sometimes forming small flows. The unusually firm substrate of bedrock and limestone provides a damage-resistant environment for three fish, some 18 plant and several invertebrate species, including five hydrobiid snails. These organisms include both relict and narrowly endemic species 103.

While many of the plants found in mound springs are relatively common and found in rivers and bores, a number seem to be dependent on mound springs for their survival. Halosarcia fontinalis and the button grass Eriocaulon carsonii are endemic to the mound springs of the Great Artesian Basin. Several other plants found in these springs are rare, such as Nicotiana burbidgeae and Goodenia anfracta. Some 14 species found in these mound springs have been identified as having very significant disjunct distributions, including the sedges Gahnia trifida (cutting grass) and Baumea juncea (bare twig-rush), which have their major populations confined to the high rainfall areas of southern Australia. The mound spring populations of such species may be relics of a wetter climatic period when the species had much wider distributions 103.

A variety of invertebrates is found in mound springs. Species endemic to the springs include amphipods, ostracods and hydrobiid snails, as well as an unusual flatworm (Platyhelminthes: Macrostomidae) 145, and the isopod Phreatomerus latipes, which is closely allied to fossil isopods and extant species found in New Zealand, India and Africa. The endemic amphipods probably belong to the genus Afrochiltonia and it is likely that there are several species, some of which may be restricted to certain springs 103. They include an eyeless, probably subterranean, species. The amphipods, in common with all endemic invertebrates of mound springs, generally appear to prefer continuously flowing water and are rarely found near the source or tail of a spring 209. The ostracod fauna is also poorly known, but includes at least one endemic genus and subfamily (Ngarawa dirga, of the Ngarawinae) 108 103.

Twenty species of hydrobiid snails in three genera have been described to date from Great Artesian Basin mound springs in Queensland, and the Lake Eyre Supergroup of South Australia 119, with at least three new species and one new genus to be described from the Dalhousie Springs 209. The distribution of several of these appears to be highly localised, and in some cases, restricted to single springs or small, tightly grouped springs 119 120. Up to five species of hydrobiids can be found in any one spring, sometimes in enormous numbers: more than one million snails and other invertebrates per square metre can be found in the most favoured areas 119.

While at least one of the fish inhabiting mound springs, the spangled grunter (Leiopotherapon unicolour) is widespread 197 204, as more information comes to light, more and more species of fish appear to be restricted to particular groups of springs. The desert goby (Chlamydogobius eremius), which was originally thought to be widespread, is now believed to be six species of Chlamydogobius, five of which occur in desert areas, including the Dalhousie goby (found in Dalhousie Springs), and a species restricted to Edgbaston Springs, Queensland 204. The Dalhousie hardyhead (Craterocephalus dalhousiensis) and the Dalhousie catfish (a new species of Neosilurus) also appear to be narrow endemics 197 209, as does Scaturiginichthys vermeilipinnis, which has only been found at Edgbaston Springs 197.