https://scholars.wlu.ca/etd/2560

Invertebrate drift is a key process that potentially affects multiple levels of food web organization within stream environments. However, our understanding of the mechanistic drivers of drift in high latitude streams and subsequent bottom-up control that drift may have on fish predators in these environments remains understudied. This project aimed to gain the baseline knowledge of how drift functions across two major high latitude ecozones, the boreal forest and tundra, and how those possible differences in drifting community characteristics may impact drift-feeding Arctic grayling (Thymallus arcticus). These objectives were accomplished by characterizing stream environments across both ecozones, sampling the benthic macroinvertebrate (BMI) community and drifting components of macroinvertebrate communities, and utilizing drift data in a drift feeding bioenergetics (DFBM) model to calculate potential tissue growth of Arctic grayling. Both benthic and drift compositions differed significantly based on ecozone. Abundances of BMI were 10 times greater in tundra streams. Nevertheless, drift densities between the two ecozones remained equal, suggesting drivers within boreal streams promoted active drift. Potential drivers of drift in boreal streams were higher benthic predator presence, and resource limitations due to significantly lower TDP and increased shading. Body size of drifting invertebrates did not differ between ecozones and, in combination with equal drift densities, produced no difference in potential growth of grayling. Potential growth of grayling differed by age-group, with grayling fry having higher growth potential than juveniles, suggesting the habitat of these smaller tributaries is not suitable for juveniles at this time of year (August 2021). Growth potential also differed significantly based on food resources. Benthic prey items provided the most growth potential across both ecozones. Potential growth derived from terrestrial and upstream lentic sources was significantly higher in boreal and tundra streams respectively, suggesting potential dietary differences between the grayling in boreal and tundra streams.

https://scholars.wlu.ca/etd/2560