EFFECTS OF FISH DENSITY AND RIVER FERTILIZATION ON ALGAL STANDING STOCKS, INVERTEBRATE COMMUNITIES, AND FISH PRODUCTION IN AN ARCTIC RIVER

This study examined the relative importance of bottom-up and top-down controls of an arctic stream food web by simultaneous manipulation of the top predator and nutrient availability. We created a two-step trop hic system (algae to insects) by removal of the top predator (Arctic g rayling, Thymallus arcticus) in fertilized and control stream reaches. Fish abundance was also increased 10 times to examine the effect of h igh fish density on stream ecosystem dynamics and fish. We measured th e response of epilithic algae, benthic and drifting insects, and fish to nutrient enrichment and to changes in fish density. Insect grazers had little effect on algae and fish had little effect on insects. In b oth the control and fertilized reaches, fish growth; energy storage, a nd reproductive response of females declined with increased fish densi ty. Fish growth and energy storage were more closely correlated with p er capita insect availability than with per capita algal standing stoc k.