Restoration of the food web of an alpine lake following fish stocking

Abstract

Trout stocking in the mid-1960s eliminated the calanoid copepod Hesperodiaptomus arcticus and other largebodied crustaceans such as Gammarus lacustris, Daphnia middendorffiana, and Daphnia pulex from many alpine lakes in the Rocky Mountain Parks of Canada. H. arcticus frequently dominates the plankton communities of fishless lakes, preying on rotifers and nauplius larvae. Following the extirpation of H. arcticus, rotifers and small-bodied cyclopoid copepods dominate the zooplankton assemblages of alpine lakes.We studied the zooplankton community of Snowflake Lake, Banff National Park, from 1966 to 1995. H. arcticus was eliminated following stocking of the lake with trout in the 1960s. It failed to become reestablished after the disappearance of the fish population in the mid-1980s. Several species of rotifers and small-bodied crustaceans, species originally rare or absent from the plankton, became abundant following fish stocking and remained so after the fish population declined.In 1992, we reintroduced H. arcticus to Snowflake Lake. The H. arcticus population grew exponentially for 4 yr, but had not reached stable densities typical of unmanipulated alpine lakes by 1995. By 1994, however, even the small population of Hesperodiaptomus was beginning to suppress populations of rotifers, copepod nauplii, and large diatoms. Because H. arcticus is omnivorous, a simple model of cascading trophic interactions did not predict the outcome of trophic manipulations in this alpine lake.

Recent climate extremes alter alpine lake ecosystems

“…6 and supporting information (SI) Table S1]. Cladoceran and copepod biomass, which were strongly affected by our experimental manipulations (14,15), were significant but weaker correlates of taxonomic change. Thus climate-related variables exerted strong bottom-up control over the community composition of primary producers in these high-elevation lakes, whereas direct manipulations of lake trophic structure played a lesser role.…”

“…1), part of the larger United Nations Educational, Scientific and Cultural Organization Canadian Rocky Mountains World Heritage Site. We measured the physical, chemical, and biological attributes of two reference lakes (Harrison and Pipit lakes) and two experimentally restored alpine lakes [Snowflake Lake, zooplankton reintroduction (14), Bighorn Lake, nonnative salmonid removal and zooplankton reintroduction (15); Table 1] between 1991 and 2003. Regional climate has substantially warmed since the Dalton solar minimum in the early 1800s (16).…”

Long-term changes in the littoral benthos of a Norwegian subalpine lake following the introduction of the European minnow (Phoxinus phoxinus)

“…Gammarus lacustris is omnivorous (Kortelainen 1990;MacNeil et al 1997;McNaught et al 1999;Wilhelm & Schindler 1999), and Gammarus species can be an important structuring factor in benthic communities (Conlan 1994). However, if G. lacustris was an important structuring factor of the benthic community in Øvre Heimdalsvatn one might expect greater differences in the benthic fauna between sampling stations, since densities of G. lacustris vary considerably around the lake.…”

“…Gilinsky (1984) reported an increase of a herbivorous chironomid after predation from bluegill on a carnivorous chironomid. A shift towards smaller invertebrates has been reported from several studies following fish introduction or from comparative studies of lakes with and without fish (Broooks & Dodson 1965;Conlan 1994;Crowder & Cooper 1982;McNaught et al 1999;Tate & Hershey 2003). In 1971-72 the large invertebrate carnivore, Diura bicaudata, was the most abundant plecopteran in the littoral of Øvre Heimdalsvatn (Lillehammer 1978a) and 20 % in weight of the trichopteran fauna were carnivorous/omnivorous (Lillehammer 1978b).…”

“…Fish are recognized as an important part of nutrient cycling in lakes. Several studies report an increase in primary production in lakes after fish stocking (Leavitt et al 1994;McNaught et al 1999;Parker et al 2001;Zimmer et al 2001). This is explained by the fact that fish make nutrients from terrestrial and benthic sources available for the pelagic community (Brabrand et al 1990;Tatrai 1987).…”