Thermal tolerances of two stream invertebrates exposed to diurnally varying temperature

• Published in: New Zealand journal of marine and freshwater research 2000-06, Vol.34 (2), p.203-208
• Main Authors: Cox, T J, Rutherford, J C
• Format: Article
• Language: English
• Subjects: Deleatidium autumnale; Ephemeroptera; Freshwater; New Zealand; Potamopyrgus antipodarum
• ISSN: 0028-8330
• DOI: 10.1080/00288330.2000.9516926

For two key New Zealand freshwater invertebrates (the mayfly Deleatidium autumnale and the snail Potamopyrgus antipodarum) the upper thermal tolerances were measured in the laboratory under both constant and diurnally varying temperatures. At constant temperature 50% mortality in 96 h ( sub(const)LT sub(50)) occurred at 24.2 plus or minus 0.9 degree C for mayflies and 31.0 plus or minus 0.6 degree C for snails: values similar to previously published estimates (Quinn et al. 1994). For diurnally varying temperatures (daily amplitude 10 degree C) 50% mortality occurred when the daily mean temperature was 21.9 plus or minus 0.7 degree C (mayflies) and 28.6 plus or minus 0.4 degree C (snails) which is c. 10% (2.5 plus or minus 1.3 degree C) lower than the sub(const)LT sub(50). Conversely, 50% mortality occurred when the daily maximum temperature was 26.9 plus or minus 0.7 degree C (mayflies) and 33.6 plus or minus 0.4 degree C (snails) which is c. 10% (2.5 plus or minus 1.3 degree C) higher than the sub(const)LT sub(50). Many published temperature limits for stream organisms are derived from constant temperature experiments. Our results indicate that such limits should be applied to a temperature midway between the daily average and the daily maximum of a diurnal profile.