Direct counts by epifluorescence microscopy demonstrated that cpilithic bacteria were numerically more important than fret-floating bacteria in unpolluted mountain streams. Concentrations of sessile bacteria associated with the upper surfaces of submerged rocks coincided with fluctuations in epilithic algal biomass. Electron microscopy of thin-section prcparations of natural samples showed that the attached algae provided a surface for bacterial colonization.This close physical relationship between the bacteria and algae was mediated by a network of fibers which, in mass, appeared as a layer of slime covering the streambed. The relationship between sessile bacterial conccntratons and epilithic algal biomass in one tributary suggested that, in some cases, factors other than epilithic primary production govcrncd the attached microbial population.

Average reaction norms relating number of day-degrees required to complete egg development to temperature are described for 95 species (1 15 populations) of Plecoptera, Odonata, Ephemeroptera, and Diptera (mainly Culicidae, with some Tipulidae and Sciomyzidae). The slope of the average reaction norm is used as an index of adaptation, with positive slopes indicating cold-adapted species, negative slopes indicating warm-adapted species, and slopes around zero indicating generalist species; 57% of the between-taxon variation in slope is associated with differences between orders, 14% among families, 7% among genera, 14% among species, and 8% among populations. Significant differences between congeneric species are found in only 4 of 92 possible comparisons. Only Plecoptera show much coldadaptation, with 40% of the species having significantly positive slope. However, 26% of the species (mainly in the Systellognatha) have significantly negative slope, suggesting adaptation to warmer waters than those in which the order is believed to have originated. The other orders probably originated in warm water and have generally maintained this adaptation. All Odonata, 7 1 O h of the Diptera and 81 % of the Ephemeroptera have significantly negative slopes. Diapause is a common alternative to metabolic adaptation to deal with unfavourable thermal environments. We suggest that it occurs widely in eggs of Plecoptera and in the mayfly Rhihgcna h y o b , cold-adapted species that may use diapause to survive periods of high temperature.

Nylon bags of 3.5 mm and 0.25 mm mesh were used lo investigate the processing of Salix drummondiana Barratt leaves in two second order Alberta Rocky Mountain Creeks, Twin Creek and Cabin Creek. Micro‐organism processing and macroinvertebrate shredding of the leaves were significantly greater in Twin Creek where it was estimated that macroinvertebrate shredding was responsible for 45% of the weight loss. The decay coefficient (k = 0.0209) for the leaves in Twin Creek, the more typical Rocky Mountain stream, was similar to that reported for the fastest decaying leaves in warmer streams. The predominant shredder among the leaves in the mesh bags, Zapada columbiana (Classen) (Plecoptera, Nemouridae) was also the most abundant macroinvertebrate in the benthos of Twin Creek. In Cabin Creek the predominant organism in the benthos, Oreogeton sp. was poorly represented in the leaves. Low orthophosphate concentration of the water and precipitation of calcium carbonate onto the leaves may have inhibited the biotic processing of leaves in Cabin Creek.

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Adults of the autumn-emerging capniid stonefiy, Mesocapnia oenone (Neave), were collected from the Bow River in the Canadian Rocky Mountains. After oviposition their eggs were incubated in the laboratory. Successful hatching occurred in the range 2°–15 °C; higher temperatures, except for a short period, were lethal. Eggs subjected to sub-zero temperatures, up to 17 days at −12 °C, also hatched successfully. Within the range 2°–15 °C there was a relationship, linear on logarithmic scales, between water temperature (T °C) and the egg incubation period (Y days), expressed by the equation: Y = 197T−0.59 (r2 = 0.99, P < 0.001). The number of degree-days required for hatching (Z degree-days) increased with increasing temperature (T °C) and also showed a relationship, linear on logarithmic scales, expressed by the equation: Z = 197T0.41 (r2 = 0.97, P < 0.001). In contrast to most other Capniidae, the winter is spent in the egg stage in M. oenone. Our data demonstrate that a combination of a low number of degree-days required for hatching at low temperatures and reduced sensitivity to higher temperatures ensures that egg hatching occurs in the spring. The characteristics of egg development in the autumn-emerging M. oenone are compared with the spring-emerging Capnia atra.