Crustaceans occupying drying waterholes in seasonal tropical rivers can access terrestrial areas to regulate hyperthermia. An experiment tank filled with water and containing a mesh ramp and dry platform was designed to determine the terrestrial locomotion response of the tropical inland freshwater crab Australothelphusa transversa (von Martens, 1868) when exposed to increasing water temperatures. A thermoline controller increased water temperature (acclimation 25 °C, ± 0.5) at two rates, 18 °C h–1 (commonly employed in other studies) and 3 °C h–1 (reflecting measured regional river conditions) to determine the acute effects temperature (AET50) threshold for the crab. Random movement was minimal in the 18 °C h–1 experiment, with crabs accessing and remaining on the platform until the experiment ended (AET50 = 40.2; maximum = 41.69 °C). Crabs exhibited more random movement in the 3 °C h–1 experiment, visiting the platform for 3–21 min before returning for 3–131 min (AET50 = 34.2, maximum = 37.25 °C). Crabs collected from a second, more arid, geographical location in northern Australia had a similar AET using 3 °C h–1 increase (AET50 = 35.3; maximum 37.60 °C) and a similar AET using 18 °C h–1 increase (AET50 = 39.3; maximum 41.7 °C) to the coastal crab results (ANCOVA interaction location and ramp rate F = 1.88, P > 0.15). A temperature rate altering AET estimates by several degrees (regardless of where crab population was collected: ANCOVA location, F = 0.668, P > 0.4; rate increase factor, F = 4.31, P < 0.001) highlights the need for laboratory experiments to be underpinned by relevant field data. These data outline that crab avoidance responses could include accessing river banks, as a response necessary to regulate temperature during critical periods.
Keywords: climate change; freshwater crabs; ramp rates; thermal emergence; tropical ecology
Journal Article. 5668 words. Illustrated.
Subjects: Biological Sciences ; Aquatic Biology ; Evolutionary Biology ; Zoology and Animal Sciences ; Invertebrates
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