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Ecoregion Description


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Species Richness


# of Endemic Species


Threats

808: Murray - Darling

Major Habitat Type:

temperate floodplain rivers and wetlands

Author:

Peter Unmack

Reviewers:

Michael Hammer, Evolutionary Biology Unit, South Australian Museum, Australia

Countries:

Australia

Boundaries:

This ecoregion largely follows the boundaries of the Murray-Darling Basin, but also includes a small piece of land on the Gulf of St. Vincent immediately to the west of the basin (the South Australian Gulf region). The northern boundary in the Gulf of St. Vincent is the Wakefield River.

Drainages flowing into:

Southern Ocean

Main rivers or other water bodies:

The Murray, Darling, and Murrumbidgee rivers are the three main rivers of this ecoregion at about 2,530, 2,740, and 1,690 km long, respectively (Murray-Darling Basin Commission 2005).

Topography:

This ecoregion is flanked by the Great Dividing Range in the south, east, and north with maximum elevations typically greater than 500 m, but up to 2,228 m (Mt Kosciuszko), while the western boundary primarily consists of low hills mostly below 200 m. The majority of the basin is of low elevation (< 200 m asl) and consists of extensive plains and low undulating areas.

Climate:

The ecoregion experiences a range of climatic conditions and there is high variability in rainfall due to the impact of the El Nino - Southern Oscillation (ENSO) on southeastern Australia. The vast plains and low elevations experience semi-arid conditions whereas cool humid conditions occur in the eastern uplands, and sub-tropical conditions occur in the northeast (Global Energy and Water Cycle Experiment 2005).

Freshwater habitats:

The majority of this ecoregion consists of one massive interconnected river system covering over 1,132,000 square kilometers, or 14% of Australia (Lintermans 2007). The western section contains a series of independent small coastal streams. There is a large variety of habitat types throughout the ecoregion, including saline lakes, alpine to intermittent streams, sub-alpine bogs, vast floodplains, lowland rivers, swamps, and lakes. The Murray-Darling Basin Commission estimates that there are greater than 30,000 wetlands found within the basin (Murray-Darling Basin Commission 2005). Floods and droughts are crucial components relative to the health of lower portion of the province, especially floodplain habitats. Most rivers are now dammed and river flow is highly regulated.

Terrestrial Habitats:

Dry forest and eucalypt woodlands dominate the vegetation in this ecoregion, although alpine and sub-alpine communities occur on the flanks of the Great Dividing Range (World Wildlife Fund 2001).

Fish Fauna:

Fourteen freshwater fish families are known from this ecoregion, which has a mix of northern and southern faunas due to its broad latitudinal expanse. Many northern groups have their southernmost occurrences here, being absent from surrounding southern coastal drainages. The ecoregion is notable for its richness of Percichthyidae (temperate perches) species, as well as Eleotridae (gudgeons or sleepers) and Galaxiidae (galaxiids) with five species. The remaining eleven families all have three of fewer representatives. Numerous species are threatened to various degrees with recent major surveys detecting few or no representatives from several species across a large portion of the ecoregion (Harris & Gehrke 1997).

Due to the lack of significant elevation differentiation most species tend to be widespread. Upland faunas in the north have a larger number of species and are quite different from those in the south, as conditions are warmer and elevation and stream gradients are lower in the north. In the higher elevation, cooler portion of the ecoregion there is a distinctive upland fauna consisting of Galaxias olidus (mountain galaxias), G. fucus (barred galaxias), and Gadopsis bispinosus (two-spined galaxias), with the latter two species being restricted to upland areas in the southeast, and the first being found in all upland areas and to a lesser extent in lowland areas as well. As elevation decreases, species such as Retropinna semoni(Australian smelt), Gadopsis marmoratus (river blackfish), Maccullochella macquariensis (trout cod), Macquaria australasica (Macquarie perch), Nannoperca australis (southern pygmy perch), and Hypseleotris spp. (carp gudgeons) begin to become more common. Once drainages cross the plains, these species mix with most of the remainder of the ecoregion’s fishes. Species with life histories tied to the oceans are only found in the lower-most portion of the ecoregion. Nannoperca obscura ( Yarra pygmy perch) is also restricted to the lowermost portion of the drainage. A few southern species are absent from the Darling River in the northern portion of the province (Galaxias fuscus, Craterocephalus fluviatilis, Gadopsis bispinosus, Nannoperca australis), or they are only found in the Macquarie River (the southern-most Darling River tributary) in addition to southern drainages (i.e., Galaxias rostratus, Maccullochella macquariensis, Macquaria australasica), while Philypnodon grandiceps (flathead gudgeon) and P. macrostomus (dwarf flathead gudgeon) are also found in the Condamine River in addition to the Macquarie River. Three species are restricted to the north: Craterocephalus amniculus (Darling hardyhead), Melanotaenia splendida (rainbowfish), and Neosilurus hyrtlii (Hyrtl’s catfish), while Leiopotherapon unicolor (spangled perch) is only rarely found in southern drainages and does not establish permanent populations there.

Description of endemic fishes:

No genera are endemic, but a number of species are: Galaxias fuscus, G. rostratus, Craterocephalus amniculus, C. fluviatilis, Melanotaenia fluviatilis, Gadopsis bispinosus, Maccullochella macquariensis, M. peelii (Murray cod), Macquaria australasica, Bidyanus bidyanus, and Hypseleotris sp. (Murray-Darling carp gudgeon).

Other noteworthy fishes:

Maccullochella peelii is the largest Australian freshwater fish, reaching 113 kg and 1.8 m. Today, fish over 45 kg are rare.

Other noteworthy aquatic biotic elements:

Elseya bellii, Bell’s turtle, is endemic to the headwaters of some Darling River tributaries (Cann 1998). The most widespread species of the freshwater crayfish genus Euastacus, E. armatus, is endemic to the Murray-Darling ecoregion, and has an east-west range of around 800 km (Morgan 1986). A second endemic, E. crassus, has a highland distribution along the south-eastern margin of the province. Although details of the habitat were not recorded, the sole locality for Euastacus gamilaroi is a reservoir near Nundle, New South Wales (Morgan 1997). The crayfish species C. rotundus, as currently recognized, is endemic to the ecoregion (Austin et al. 2003).

Ecological phenomena:

Several species in this ecoregion are known to be highly migratory, with one of these, Macquaria ambigua (golden perch) having been recorded moving over 2,300 km completely within freshwater environments (Reynolds 1983). Macquaria ambigua and Bidyanus bidyanus (silver perch) are both unusual in that they have pelagic eggs, which is rare in freshwater fishes. This is thought to be an adaptation to floodwater dispersal away from spawning areas and into areas with more abundant food resources (Merrick & Schmida 1984). Craterocephalus fluviatilis frequently inhabits quite saline lakes, some of which have salinities significantly greater than sea water.

Evolutionary phenomena:

Of note is the recent determination that three of the Hypseleotris species are involved in a hybridogenic complex involving both female and male hemiclonal lineages (Bertozzi et al. 2000; M. Adams pers. comm.).

Justification for delineation:

The Murray-Darling ecoregion has a moderate level of endemism and complex relationships with surrounding regions. It has high similarity to parts of Eastern Coastal Australia [807], the Bass Strait Drainages [809], and the Great Artesian Basin [806]. Overall, the ecoregion appears to have experienced mixing of faunas from surrounding regions with distinctive faunas, while maintaining a high degree of endemism. With the possible exception of southwestern Victoria drainages in the adjacent Eastern Coastal Australia ecoregion, all faunal connections must have occurred across drainage divides (Unmack 2001).

Level of taxonomic exploration:

Overall, the taxonomic exploration of the fauna is good, with aspects of the fauna being relatively well known. A number of taxonomic problems remain, especially within Galaxias olidus (which probably represents 4-5 taxa) and morphological and molecular examinations of other components of the fauna will likely result in a number of species being separated into multiple taxa (e.g., Retropinna (Hammer et al. 2007), Gadopsis (Miller et al. 2004), and Hypseleotris (Thacker et al. 2007)).

References/sources:

Austin, C. M., Nguyen, T. T. T., et al. (2003). "The taxonomy and phylogeny of the 'Cherax destructor' complex (Decapoda: Parastacidae) examined using mitochondrial 16S sequences" Australian Journal of Zoology 51 99-110.

Bertozzi, T., Adams, M., et al. (2000). "Species boundaries in carp gudgeons (Eleotridae: Hypseleotris) from the River Murray, South Australia: evidence for multiple species and extensive hybridization" Marine and Freshwater Research 51 805–815.

Cann, J. (1998). "Australian freshwater turtles" Singapore: Beaumont Publishing.

Global Energy and Water Cycle, Experiment (2005). "Murray-Darling Basin Water Budget (MDB) Project" (2005; www.gewex.org/mdb.html).

Hammer, M., Unmack, P. J., et al. (). "Retropinna in retrospect: additional taxa and significant genetic sub-structure redefine conservation approaches for Australian smelts (Pisces: Retropinnidae)" Marine and Freshwater Research

Harris, J. H.,Gehrke, P. C. (Ed.) (1997). "Fish and Rivers in Stress. The NSW Rivers Survey" NSW Fisheries Office of Conservation, and Cooperative Research Centre for Freshwater Ecology.

Lintermans, M. (2007). "Fishes of the Murray-Darling Basin: an Introductory Guide" Canberra: Murray-Darling Basin Commission.

Merrick, J. R.,Schmida, G. E. (1984). "Australian freshwater fishes: biology and management" Netley: Griffith Press Ltd..

Miller, A. D., Waggy, G., et al. (2004). "Mitochondrial 12S rRNA sequences support the existence of a third species of freshwater blackfish (Percichthyidae: Gadopsis) from south-eastern Australia" Memoirs of Museum of Victoria 61 121-127.

Murray-Darling Basin, Commission (2005). "Murray-Darling Basin Statistics" (2005; www.mdbc.gov.au/naturalresources/basin_stats/statistics.htm).

Reynolds, L. F. (1983). "Migration patterns of five fish species in the Murray-Darling River system" Australian Journal of Freshwater and Marine Research 34 857–871.

Thacker, C., Unmack, P. J., et al. (2007). "Comparative phylogeography of five sympatric Hypseleotris species (Teleostei: Eleotridae) in southeastern Australia reveals a complex pattern of drainage basin exchanges with little congruence across species" Journal of Biogeography 34(9) 1518-1533.

Unmack, P. J. (2001). "Biogeography of Australian freshwater fishes" Journal of Biogeography 28(9) 1053-1089.

World Wildlife, Fund (2001). "Southeast Australia temperate forests (AA0409)" 2005 (2005; www.worldwildlife.org/wildworld/profiles/terrestrial/aa/aa0409_full.html).

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