Ecological and physiological impacts of salinisation on freshwater turtles of the lower Murray River

Abstract

Context The increasing intensity and extent of anthropogenically mediated salinisation in freshwater systems has the potential to affect freshwater species through physiological and ecological processes. Determining responses to salinisation is critical to predicting impacts on fauna. Aims We aimed to quantify the response of wild-caught turtles from freshwater lakes that had become saline in the lower Murray River catchment. Methods Plasma electrolytes of all three species of freshwater turtle from South Australia were compared among two freshwater sites (Horseshoe Lagoon and Swan Reach), a brackish lake (Lake Bonney) and a saline lake (Lake Alexandrina). Key results Chelodina longicollis, C. expansa and Emydura macquarii from a brackish lake had higher concentrations of plasma sodium and chloride than those from freshwater habitats. However, osmolytes known to increase under severe osmotic stress (urea and uric acid) were not elevated in brackish sites. Turtles from the highly saline lake were colonised by an invasive marine worm which encased the carapace and inhibited limb movement. Conclusions Freshwater turtles in brackish backwaters had little response to salinity, whereas the C. longicollis in a saline lake had a significant physiological response caused by salt and further impacts from colonisation of marine worms. Implications Short periods of high salinity are unlikely to adversely affect freshwater turtles. However, secondary ecological processes, such as immobilisation from a marine worm may cause unexpected impacts on freshwater fauna.

Salinity tolerances and use of saline environments by freshwater turtles: implications of sea level rise

“…Their lachrymal gland is similar in structure to those in other freshwater turtles (Cowan, ), but in M. terrapin these glands are much larger, function to minimize water loss, and, therefore, play a significant role in maintaining internal salt balance. Other species, such as C. longicollis , are suspected of having functional lachrymal glands (Chessman, ), given their relatively high tolerance to salinity among freshwater turtles (Bower, Death, & Georges, ; Bower, Hodges, & Georges, ), but evidence to date remains inconclusive.…”

Salinity tolerances of two Australian freshwater turtles,Chelodina expansaandEmydura macquarii(Testudinata: Chelidae)

“…Freshwater turtles are one taxa that can be very sensitive to salt ( Dunson, 1981 ). However, one study found that wild populations of three species of Australian freshwater turtles inhabiting a brackish lake showed only a mild change in osmolytes in response to brackish water, and this may have been behaviourally regulated, for instance by drinking freshwater, or physiologically regulated via salt excretion ( Bower et al ., 2012a ). Knowledge of species’ tolerance to salinity and mechanisms of persistence can assist with predicting the impacts of salinization.…”

Current conservation status of Australian freshwater turtles

“…Australian freshwater turtles are not immune from this trend, and 44% (11 of 25 taxa) are currently listed as vulnerable or worse at state or federal levels, and/or by the IUCN (Table 1). Recent studies are increasingly reporting declines in Australian turtle species, either as long-term trends (Chessman 2011) driven by a variety of factors including invasive species (Spencer et al 2016), drought (Bower et al 2012), and/or habitat modification (Ferronato et al 2016;Ocock et al 2018), or as rapid crashes caused by disease events that remain poorly understood (Spencer et al 2018). Accordingly, we convened a conference on freshwater turtle conservation in Canberra, ACT, in February 2017 to discuss the threats to Australian turtle populations.…”