EFFECTS OF INTRODUCED FISH ON MOUNTAIN LAKE ZOOPLANKTON COMMUNITIES

Abstract

Decades of fish introductions into mountain lakes have altered invertebrate communities. I assessed the current status of fish populations and their effects on crustacean zooplankton communities by sampling 37 lakes in the mountain parks, where stocking practices had been halted over 25 years ago. I discovered that introduced fish were more likely to persist in colder alpine lakes than in montane sites. However, their effects on total zooplankton biomass and species diversity increased with rising lake temperatures. Persistence of introduced fish in warmer lakes favored small-bodied zooplankton species, whereas larger-bodied communities in colder, larger alpine lakes were relatively unaffected. Greater resistance and resilience (i.e. recovery rate) of alpine zooplankton (e.g. Hesperodiaptomus arcticus) in deeper, fish-stocked lakes was likely attributable to a greater availability of refuge from predators and more abundant diapausing egg banks. Fish residence time and the species of stocked fish were key factors of taxonomic stability in perturbed zooplankton communities.