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Implications of climate change on the aestivating Salamanderfish, Lepidogalaxias salamandroides Mees and the Black-stripe Minnow, Galaxiella nigrostriata Shipway

Ogston, Garry (2015) Implications of climate change on the aestivating Salamanderfish, Lepidogalaxias salamandroides Mees and the Black-stripe Minnow, Galaxiella nigrostriata Shipway. Honours thesis, Murdoch University.

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Aestivating aquatic fauna are able to survive periods of drying using various unique behavioural, morphological and physiological adaptations. The Salamanderfish, Lepidogalaxias salamandroides, and Black-stripe Minnow, Galaxiella nigrostriata, are aestivating fishes restricted to the south-western most corner of Australia. The region has experienced a drying climate since the 1970’s and this trend is projected to continue due to climate change. The associated reductions in surface flows and groundwater is placing pressure on many of the highly endemic freshwater fishes of the region that are known to have been severely impacted by other anthropogenic stressors. Several of the region’s freshwater fishes are listed as threatened, however, the current conservation status of the two aestivating species is in need of updating and threats to both are largely unknown. This study aimed to assess the current conservation status of these species and determine the key physicochemical and hydrological variables associated with their distributions to help project future population viabilities under hydrological change scenarios.

A total of 53 sites were sampled throughout the historical range of L. salamandroides and G. nigrostriata and a suite of physicochemical and habitat variables measured. Of the sites surveyed, 39 and 28 historically contained L. salamandroides and G. nigrostriata, respectively. Concerningly, the study revealed that only 26 currently contained L. salamandroides (66.67% of their historical distribution) and 20 contained G. nigrostriata (71.43% of their historical distribution). Both L. salamandroides and G. nigrostriata were absent from the four eastern-most sites sampled representing approximate reductions in extent of occurrence (EOO) of 79% and 12% for the two species, respectively. Area of occupancy (AOO) of L. salamandroides and G. nigrostriata has declined by approximately 71% and 56% for each species, respectively. Both species qualify as Endangered (IUCN Red List Threatened Category) under A2c), A4 c); population size reductions (past and projected based on AOO and EOO).

Historical sites were predominantly ephemeral wetlands that were acidic (mean pH = 4.77 (±0.12 SE)), had low salinity (mean 0.23 mg/L (±0.01 SE)) and a shallow (<1m) depth to groundwater during the dry period. Species distribution modelling was undertaken to determine those environmental variables that best explained the presence and absence of the species and revealed that sites with greater depth in winter and length of the annual non-wetted period were the variables of highest importance for L. salamandroides, with higher connectivity to surrounding wetlands a key variable of importance for G. nigrostriata.

Both species exhibited depleted lipid content after aestivation. The change in lipid content across seasons was more pronounced in L. salamandroides; however there was also a significant difference between G. nigrostriata and the non-aestivating Galaxiella munda suggesting that G. nigrostriata may also utilise lipid storage as part of its aestivation strategy. Increases in the annual dry period of wetlands may push the limits of such physiological strategies.

Analysis of seasonal stable isotope composition (δ2H and δ18O) of surface, ground and rain water identified that the wetlands are reliant on winter rainfall for recharge, with high rates of evaporation occurring during summer.

The results of the study suggest that climate change is likely to have been a key factor in the recent decline of these species. It is likely that the viability of populations will continue to be challenged given groundwater models project that the water table within much of this region will decrease by up to 4 m by 2030 and therefore further population losses may be expected. This research has considerable implications for future management of these aquatic ecosystems, including the management of groundwater levels in the region, reducing anthropogenic modifications and maintaining existing habitats. To help ensure survival of these enigmatic species in light of projected climatic and hydrological change, novel approaches such as creation of artificial wetlands and breeding programs may be necessary to help ensure their survival.

Item Type: Thesis (Honours)
Murdoch Affiliation(s): School of Veterinary and Life Sciences
Supervisor(s): Beatty, Stephen, Morgan, David and Pusey, Bradley
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