Xeric Basins
In many cases, flowing and still water habitats of the Xeric Basins MHT are oases in the desert. Highly variable water temperatures, water chemistry, and flows often characterize aquatic habitats in arid systems. These wide fluctuations support a very specialized biota, often comprised of large numbers of endemic species. The role of springs and subterranean flows in these areas may be of critical importance for the maintenance of these habitats.
Australasia
C
entral Australian Freshwater [193] - Australia
Geographic Location: Central Australia
Biodiversity Features: Characterized by the some of the most unpredictable flow patterns of any continent, freshwater systems in arid Australia support species with amazing adaptations to environmental variability. This ecoregion is defined primarily by the interior-draining Lake Eyre and Bulloo-Bancannia drainage basins, though it also overlays a portion of the Great Artesian Basin, one of the world’s largest artesian basins. Around the artesian basin occur numerous mound springs and spring-fed complexes, such as Dalhousie Springs. This ecoregion has high levels of ecoregional and local endemism, as well as several relict taxa. Taxa exhibiting exceptional levels of endemism include fish, wetland-dependent plants, amphipods, ostracods, isopods, and hydrobiid snails (greater than 20 species in at least 2 endemic genera). HIGH LEVELS OF ENDEMISM AND RELICT TAXA, PARTICULARLY AMONG AQUATIC INVERTEBRATES
Selected Species: A large portion of this ecoregions’ freshwater species exhibit highly restricted ranges, though a few, such as spanged perch (Leiopotherapon unicolor), are more widespread. The Dalhousie Springs fauna is notable for its extremely high endemicity. Endemic fish include Dalhousie catfish (Neosilurus sp.), Dalhousie hardyhead (Craterocephalus dalhousiensis), Dalhousie mogurnda (Mogurnda sp.), and Dalhousie goby (Chlamydogobius gloveri). Other endemics found at Dalhousie Springs are at least six hydrobiid snails, a blind amphipod crustacean, and possibly one crayfish and one frog species. Endemic plants to the mound springs in general include Halosarcia fontinalis and Eriocaulon carsonii.
General Threats: In this arid ecoregion, any water withdrawals or other modifications to the flow regime pose serious threats to aquatic species. Exotics, including Australian natives occurring outside this ecoregion, pose a threat to indigenous taxa primarily through predation and hybridization. Illegal fishing for local consumption and commercial trade is a serious problem. Overgrazing of surrounding lands by introduced rabbits and livestock has led to sedimentation of these fragile aquatic ecosystems. Large populations of feral and domesticated grazing animals also pollute waters with their wastes. Proposed dams and water diversions pose a future threat, as do commercial fisheries.
Nearctic
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hihuahuan Freshwater [194] – Mexico, United States
Geographic Location: Southern North America
Biodiversity Features: The river basins of this xeric ecoregion are remarkably different from one another, each containing unique species that evolved following a series of tectonic events and resulting geographic isolation. Within Cuatro Ciénegas, an interior basin containing hundreds of spring-fed pools in a desert environment, about half of the 20 species of fish are endemic. Twenty-three of the 34 species of freshwater molluscs in Cuatro Ciénegas are also endemic. Some of these fish and mollusc species are restricted to individual pools of only a few square meters in size. Other taxa have not diverged appreciably from ancestral forms and are important relict species. THESE AQUATIC HABITATS SUPPORT A diverse subtropical desert basin fauna with a high degree of local endemism. globally outstanding evolutionary radiations and adaptations of Cuatro CiÉnegas biota
Selected Species: Species here include the aquatic box turtle (Terrapene coahuila), the endemic black softshell turtle (Trionyx ater), pond slider (Pseudemys scripta), plain-bellied water snake (Nerodia erythrogaster), and Cuatro Ciénegas cichlid (Cichlasoma minckleyi). Three endangered endemic fishes are Cuatro Ciénegas shiner (Notropis xanthicara), Cuatro Ciénegas darter (Xiphophorus gordoni), and sardinilla (Lucania interioris). Other endemic fishes are Cuatro Ciénegas gambusia (Gambusia longispinis), robust gambusia (G. marshi), yellowfin gambusia (G. alvarezi), Conchos pupfish (Cyprinodon eximius), Comanche Springs pupfish (C. elegans), bighead pupfish (C. pachycephalus), Devil’s River minnow (Dionda diaboli), and roundnose minnow (D. episcopa). Among the endemic invertebrates, which are found predominantly in spring-fed habitats, are a number of aquatic snails and amphipods: Pecos assiminea (Assiminea sp.), Phantom Spring cochliopa (Cochliopa texana), Phantom Lake tryonia (Tryonia cheatumi), Phantom Spring amphipod (Gammarus hyalelloides), San Solomon amphipod (G. sp.), and Noel’s amphipod (G. desperatus).
General Threats: The largest threat to freshwater diversity may be water withdrawals associated with population growth and agricultural activities. The construction of irrigation canals and the resultant lowering of water levels leads to the loss of critical habitat in this water-poor environment. Overgrazing, introduced species, potential large-scale tourism, mining, and pollution also threaten many freshwater communities. In addition, a number of exotic species have been introduced, such as the cichlid Hemichromis guttatus and the crayfish Procambarus clarkii.
Palearctic
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natolian Freshwater [195] – Syria, Turkey
Geographic Location: Western Asia on the Eastern Mediterranean
Biodiversity Features: This ecoregion has diverse freshwater habitats, particularly compared to surrounding drier areas. These include both running-water and lake environments. This ecoregion historically supported about twenty species and ten subspecies of endemic fish, many with very local distributions. Lakes are abundant in this ecoregion and are important habitat for migrating waterbirds. THE AQUATIC HABITATS OF THIS ECOREGION SUPPPORT A LEVEL OF ENDEMISM AMONG FISHES THAT IS HIGH FOR THE PALEARCTIC
Selected Species: A number of endemic fish species within the ecoregion that are of conservation concern include Alburnus akili, two subspecies of Capoeta capoeta, Chondrostoma holmwoodii, Leucalburnus kosswigi, Phoxinellus anatolicus, Phoxinellus egridiri, and Aphanius burduricus. Waterbirds that occur in abundance include great bustard (Otis tarda), ruddy shellduck (Tadorna ferrugininea), and common crane (Grus grus).
General Threats: Habitat loss, excessive water diversions, and pollution are the principle threats to the fish fauna of this ecoregion. In particular, pollution from industry, agriculture, and domestic sources has been blamed for declines in several imperiled species. Introduced species, particularly zander (Stizostedion lucioperca), threaten natives through predation, and overfishing is a problem for some lake species. Draining of wetlands for malarial control and conversion to agriculture is also reducing the amount of available habitat for aquatic organisms. At least one dam has adversely affected an endemic species of fish.
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