The Influence of Temperature on Nymphal Growth Rates in Mountain Stoneflies (Plecoptera)

Growth of stonefly nymphs was investigated in Ovre Heimdalsvatn, a subalpine lake a 1090 m above sea level in the Jotunheimen Mountains of central southern Norway. The lake is ice covered from mid—October until early June. Four species, Nemoura cinerea, Nemoura avicularis, Capnia atra, and Diura bicaudata, were studied at regular intervals over a 2—yr period. Nymphal growth curves were divided into periods during which exponential growth was constant. Specific growth rates were measured in terms of both length (GL) and dry mass (GM). The following respective ranges of GL and GM were recorded: N. cinerea, 0.3—1.5 and 0.8—3.6%/d; N. avicularis, 0.2—0.7 and 0.3—1.1%/d; C. atra 0.1—1.3 and 0.3—3.6%d; bicaudata, 0.2—1.7 and 0.8—5.9%/d. While most species had low specific growth rates (GM = 0.3—0.9%/d) during ice cover, C. atra had a growth rate (GM) of 1.6%/d when the mean water temperature was only 0.6°C. There were no significant differences between the growth rates in the 2 yr for each particular period of constant growth. However, there was considerable variation in growth rate throughout the year, there being a strong positive correlation (P < .001) and a monotonically increasing relationship between specific growth rate and mean water temperature.