Plasticity of upper thermal limits of Australian Paratya spp. (Decapoda, Atyidae) and considerations of climate-change adaptation

Context. The ability of ectothermic stream invertebrates to adapt to the predicted increases in mean and extreme stream temperatures is crucial to ensuring they continue to exist. Aims. To examine the plasticity of thermal limits of Australian Paratya spp. (Decapoda, Atyidae) from streams in eastern New South Wales (NSW). We hypothesised that the upper lethal temperature (ULT, as indicated by the median lethal temperature, LT50) would be higher for warm water-acclimated shrimp individuals than for winter-acclimatised shrimp individuals because of the importance of acclimatisation temperature. Methods. Controlled experiments were undertaken to determine the ULT by using ramping assays for winter field-acclimatised and warm water laboratory-acclimated Paratya spp. Key results. Warm water-acclimated shrimp individuals demonstrated a significantly higher LT50 of 36.1 degrees C than did winter-acclimatised shrimp individuals at 34 degrees C. Paratya spp. exhibited a limited plasticity for acclimation to warmer temperatures. Conclusions. Results demonstrated the potential vulnerability of ectothermic stream invertebrates to climate change if stream temperatures increase as predicted and thermal thresholds are exceeded. Implications. Understanding the ULT of stream invertebrates helps predict their ability to respond to temperature variability and response to climate change. Increasing resilience through target management of resorting riparian vegetation for shade and securing environmental flows may reduce the impacts of stream warming.