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Young Mary river turtles (Elusor macrurus) that were incubated at temperatures predicted under climate change showed reduced mobility and preference for shallow water. Photo Credit: Mariana A. Micheli-Campbell.
The Mary river turtle (Elusor macrurus), is one of the rarest chelonians in the world, which remained unrecognized right up until 1994. It is restricted to only one river system in Australia, where plans by Queensland's state government to build a dam on the river aroused fierce opposition, because of the threat to this and the other endangered species occurring in these waters.
Furthermore, new research suggests that the Mary river turtle will suffer multiple problems if the temperatures predicted as a result of climate change are reached, according to researchers from the University of Queensland.
The scientists, who presented their findings at the recent Society for Experimental Biology Annual conference in Glasgow, Scotland, incubated eggs of this species at 79, 84, and 90 degrees Farenheit (26, 29, and 32 degrees Celsius). This resulted in distinct behavioral differences amongst the hatchlings.
Those young turtles which developed at the highest temperature showed a reduced swimming ability and a preference for shallower waters, compared with those hatched at the bottom end of this temperature scale, which is more representative of how they normally hatch given the current climate.
The combination of physiological and behavioral effects would have a significant impact on their survival chances in the wild. "Deeper water not only provides the young turtles with protection from predators but is also where their food supply is found," explains Ph.D researcher, Mariana Micheli-Campbell. "Young turtles with poor swimming abilities which linger near the surface are unable to feed properly and are very likely to get picked off by birds. These results are worrying as climate change predictions for the area suggest that nest temperatures of 90 degrees Farenheit (32 degrees Celsius) are likely to be reached in the coming decades."
The Mary river turtle is already listed as endangered, and is featured on the IUCN Red List. The population has suffered a large decline over the past decades. Some factors known to have affected their numbers include collection of eggs for the local pet trade in the past, and the impact of predators such as foxes and dogs. "Whether climate change has already contributed to the decline is not clear," says Ms. Micheli-Campbell. "But these results show it may be a danger to this species in the future."
These findings could also apply to other species of turtle, but the outcome is likely to be more extreme in the case of the Mary river turtle. This is because climatic warming is likely to be particularly pronounced in the area of Australia where the turtle is found.
Furthermore, the relatively shallow nests of freshwater turtles are more susceptible to changes in ambient temperature than the deeper nests of sea turtles. Additional research is clearly needed to understand the effects of climate change on incubation patterns and hatchling behavior in other freshwater species, but these findings are worrying.
The situation for the Mary river turtle is also potentially worsened by the fact that it takes an exceptionally long time for these turtles to attain maturity. Other research suggests it may well take at least 25 years for females, and possibly as long as three decades for males, before they are likely to start breeding.