New Zealand Journal of Marine and Freshwater Research abstracts
Thermal tolerances of two stream invertebrates exposed to diurnally varying
temperature
TIMOTHY J. COX
J. CHRISTOPHER RUTHERFORD
National Institute of Water & Atmospheric
Research Ltd
P. O. Box 11 115
Hamilton, New Zealand
email: k.rutherford@niwa.cri.nz
Abstract 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 (constLT50)
occurred at 24.2 +/- 0.9deg.C for mayflies and 31.0 +/- 0.6deg.C for snails:
values similar to previously published estimates (Quinn et al. 1994). For
diurnally varying temperatures (daily amplitude 10deg.C) 50% mortality occurred
when the daily mean temperature was 21.9 +/- 0.7deg.C (mayflies) and 28.6 +/-
0.4deg.C (snails) which is c. 10% (2.5 +/- 1.3deg.C) lower than the constLT50.
Conversely, 50% mortality occurred when the daily maximum temperature was 26.9
+/- 0.7deg.C (mayflies) and 33.6 +/- 0.4deg.C (snails) which is c. 10% (2.5 +/-
1.3deg.C) higher than the constLT50. 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.
Keywords freshwater invertebrates; temperature tolerance;
diurnal temperature variation
M99023
Received 29 April 1999; accepted 10 November 1999
PDF file of entire paper: medium quality (449K); (scanned from paper original: notes about this process)
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