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Ecoregion Description


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Species Richness


# of Endemic Species


Threats

801: Southwestern Australia

Major Habitat Type:

temperate coastal rivers

Author:

Peter Unmack

Countries:

Australia

Boundaries:

The ecoregion encompasses the relatively wet, temperate region at the tip of southwestern Australia. The boundaries of this ecoregion were determined based on aridity. To the north, northeast, and east all drainages lack fishes due to a lack of water. Most fishes are found in areas with >700 mm of annual rainfall (Unmack 2001). The specific boundaries are from slightly east of Albany north to the Arrowsmith River.

Drainages flowing into:

Indian and Southern Oceans.

Main rivers or other water bodies:

The Swan/Avon and Blackwood Rivers are the two longest rivers in this ecoregion. Numerous smaller rivers flow from the plateau to the coast.

Topography:

Rivers descend from the edge of the interior plateau (at an elevation of between 300-400 m) to the coastal plain. The Darling Range is located at the edge of the Western Plateau and extends about 320 km parallel with the west coast. The highest elevation is 1096 m (Bluff Knoll), with most of the ecoregion’s fishes occurring below 200 m.

Climate:

This ecoregion has a Mediterranean climate with a cold, wet winter and dry, hot summer.

Freshwater habitats:

This ecoregion is relatively small, covering 125,000 square kilometers or 1.6% of Australia. Freshwater habitats include coastal rivers and estuaries of varying salinity. River flows tend to be strongly seasonal and highly predictable with generally low variability each month. Many waters tended to be naturally slightly more saline, but increasing salinity in some rivers is becoming a major impact, as are exotic species such as Perca fluviatilis (European perch) and Gambusia holbrooki (Eastern mosquitofish).

Terrestrial Habitats:

eucalypt woodlands dominate the terrestrial vegetation. Along the southwestern coast, heath, swamp, and dune vegetation also occur.

Fish Fauna:

This ecoregion supports a total of 15 fishes from eight families. The fauna is dominated by Galaxiidae (Galaxiids, five species) and Percichthyidae (temperate perches, four species), with one Plotosidae (eel-tailed catfishes) and three estuarine Atherinidae (hardyheads or silversides, of which Leptatherina wallacei (western hardyhead) also extends into the lower freshwater reaches of rivers). Most species within this ecoregion are found in and along a narrow lowland coastal strip from just east of Albany to just north of Perth. Inland areas tend to be drier with less predictable aquatic habitats and lower habitat diversity.

Description of endemic fishes:

This ecoregion has one endemic family (Lepidogalaxiidae, Lepidogalaxias salamandroides, salamanderfish) and two endemic genera: Bostockia porosa (nightfish) and Nannatherina balstoni (Balston’s pygmy perch). Of the total fauna, 10 out of 15 species are endemic. All strictly freshwater fishes are endemic (nine species) as are two of the three estuarine atherinids, while the three diadromous species are also found in eastern Australia (Morgan et al. 1998).

Other noteworthy fishes:

Lepidogalaxias salamandroides

is exceptional in that it can aestivate during the dry summer period (Berra & Allen 1989; Pusey 1989; 1990). While research is lacking, it appears as if Galaxiella munda (western mud minnow) and G. nigrostriata (black-striped minnow) may also be capable of aestivation. Lepidogalaxias salamandroides is also the only Australian freshwater fish known to have internal fertilization (Pusey & Stewart 1989). Two normally diadromous species (Galaxias maculatus, common galaxias, and G. truttaceus, spotted galaxias) have adapted alternative life history strategies to enable them to reproduce totally within freshwater (Morgan 2003; Chapman et al. 2006).

Other noteworthy aquatic biotic elements:

One endemic monotypic genus of turtle occurs here, Pseudemydura umbrina (western swamp turtle) with a very restricted distribution. The endemic Chelodina oblonga (oblong turtle) is widespread within the ecoregion (Cann 1998). There are a number of endemic crayfishes, including all five species in the genus Engaewa (E. pseudoreducta, E. reducta, E. similis, E. subcoerulea and E. walpolea) (Horwitz & Adams 2000) and six species in the genus Cherax (C. cainii, C. crassimanus, C. glaber, C. preissii, C. quinquecarinatus, C. tenuimanus) (Munasinghe et al. 2004).

Evolutionary phenomena:

The species in the lineage containing Galaxiella are found in south-western and -eastern Australia, and Patagonian South America. The most recent evidence suggests that their distribution may be due to Gondwanan connections (McDowall & Waters 2004). Lepidogalaxias salamandroides is an unusual relict that belongs to a monotypic family whose relationships to other salmoniform families has remained controversial (Johnson & Patterson 1996; Waters et al. 2000).

Justification for delineation:

This ecoregion hosts a rich biota with high endemism within most flora and fauna, as shown by its ranking in the top 25 hotspots for endemism globally (Myers et al., 2000). Fishes from this ecoregion typically have relationships to other fishes in southeastern Australia (Unmack 2001). Dry areas to the north and east clearly separate this region and its fish fauna from adjacent regions, i.e., no fishes are known north of the region until the Greenough drainage in Pilbara Province [802] nor east until southern Eyre Peninsula (in Paleo Province [810]) and the South Australian Gulf (in Murray-Darling Province [808]) (Unmack 2001). Most fishes and other biota have probably remained isolated from southeastern Australia since formation of the Eucla Basin (Nullabor Plain) 14-16 million years ago (Unmack 2001).

Level of taxonomic exploration:

Taxonomic exploration is generally fairly good, and while most of the species are well documented, there is some recently recognized cryptic diversity within Nannoperca vittata (Western Pygmy Perch, Unmack 2005) and Galaxias occidentalis (Western Galaxias, Watts et al. 1995). More studies are needed to confirm the taxonomic status of the other species.

References/sources:

Berra, T. M.,Allen, G. R. (1989). "Burrowing, emergence, behavior, and functional morphology of the Australian salamanderfish, Lepidogalaxias salamandroides" Fisheries 14 2-10.

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

Chapman, A., Morgan, D. L., et al. (2006). "Variation in life history of land-locked lacustrine and riverine populations of Galaxias maculatus (Jenyns 1842) in Western Australia" Environmental Biology of Fishes 77 21–37.

Horwitz, P.,Adams, M. (2000). "The systematics, biogeography and conservation status of the species in the freshwater crayfish genus Engaewa Riek (Decapoda: Parastacidae) from south-western Australia" Invertebrate Taxonomy 14 655-80.

Johnson, G. D.,Patterson, C. (1996)"Relationships of lower euteleostean fishes" In Stiassny, M.L.J.;Parenti, L.J.;Johnson, G.D. (Ed.). Interrelationships of Fishes. (pp. 251–332) San Diego: Academic Press.

McDowall, R. M.,Waters, J. M. (2004). "Phylogenetic relationships in a small group of diminutive galaxiid fishes and the evolution of sexual dimorphism" Journal of the Royal Society of New Zealand 34 23-57.

Morgan, D. L. (2003). "Distribution and biology of Galaxias truttaceus (Galaxiidae) in south-western Australia, including first evidence of parasitism of fish in Western Australia by Ligula intestinalis (Cestoda)" Environmental Biology of Fishes 66 155–167.

Morgan, D. L., Gill, H. S., et al. (1998). "Distribution, identification and biology of freshwater fishes in south-western Australia" Records of the Western Australian Museum Supplement 56 1-97.

Munasinghe, D. H. N., Burridge, C. P., et al. (2004). "Molecular phylogeny and zoogeography of the freshwater crayfish genus Cherax Erichson (Decapoda: Parastacidae) in Australia" Biological Journal of the Linnean Society 81 553-563.

Myers, N., Mittermeier, R. A., et al. (2000). "Biodiversity hotspots for conservation priorities" Nature 403 853-858.

Pusey, B. J. (1989). "Aestivation in the teleost fish Lepidogalaxias salamandroides (Mees)" Comparative Biochemistry and Physiology 92A 137- 138.

Pusey, B. J. (1990). "Seasonality, aestivation and the life history of the salamanderfish Lepidogalaxias salamandroides (Pisces: Lepidogalaxiidae)" Environmental Biology of Fishes 29 15-26.

Pusey, B. J.,Stewart, T. (1989). "Internal fertilization in Lepidogalaxias salamandroides Mees (Pisces: Lepidogalaxiidae)" Zoological Journal of the Linnean Society 97 69-79.

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

Unmack, P. J. (2005). "Historical biogeography and a priori hypotheses based on freshwater fishes" Unpublished Thesis. Arizona State University.

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