Long-term effects of a trophic cascade in a large lake ecosystem

Abstract

Introductions or invasions of nonnative organisms can mediate major changes in the trophic structure of aquatic ecosystems. Here we document multitrophic level impacts in a spatially extensive system that played out over more than a century. Positive interactions among exotic vertebrate and invertebrate predators caused a substantial and abrupt shift in community composition resulting in a trophic cascade that extended to primary producers and to a nonaquatic species, the bald eagle. The opossum shrimp, Mysis diluviana, invaded Flathead Lake, Montana, the largest freshwater lake in the western United States. Lake trout had been introduced 80 y prior but remained at low densities until nonnative Mysis became established. The bottom-dwelling mysids eliminated a recruitment bottleneck for lake trout by providing a deep water source of food where little was available previously. Lake trout subsequently flourished on mysids and this voracious piscivore now dominates the lake fishery; formerly abundant kokanee were extirpated, and native bull and westslope cutthroat trout are imperiled. Predation by Mysis shifted zooplankton and phytoplankton community size structure. Bayesian change point analysis of primary productivity (27-y time series) showed a significant step increase of 55 mg C m −2 d −1 (i.e., 21% rise) concurrent with the mysid invasion, but little trend before or after despite increasing nutrient loading. Mysis facilitated predation by lake trout and indirectly caused the collapse of kokanee, redirecting energy flow through the ecosystem that would otherwise have been available to other top predators (bald eagles).

Developing a broader scientific foundation for river restoration: Columbia River food webs

“…Within that context, sizedependent survival, density-dependent growth, and dependence of growth on the interplay between temperature and food availability as well as other important life history parameters could be viewed as consequences of trophic processes. Habitat and food web approaches are compatible, and if better integrated, they could improve restoration effectiveness and possibly avoid unanticipated consequences of management actions for target species, such as habitat actions that inadvertently facilitate invasion by nonnative predators or competitors and cause unanticipated, often destructive and unwanted, changes in food webs (28,44,45). Despite the long history of research on the Columbia River and many thousands of restoration actions, there is still little information on how food webs (Fig.…”

“…At the same time, ill-advised manipulations have resulted in serious environmental problems [the introduction of opossum shrimp (Mysis diluviana) into freshwater lakes being a particularly pernicious example (28)]. Food webs are often considered to depend on habitat, but habitat alone does not determine the food web; many other factors shape its internal organization, linkages, productivity, and resilience.…”

“…In the Columbia, linked trophic and population models have been essential in understanding the scope of predation by northern pikeminnow (Ptychocheilus oregonensis) and nonnative predators in the mainstem river reservoirs (59)(60)(61)(62), impacts of predation by gulls (Larus spp.) and Caspian terns (Hydroprogne caspia) on migrating juvenile salmon (63)(64)(65)(66), impacts of nonnative mysids and lake trout on kokanee and native salmonids in lakes (28,67), complex species interactions (68), and stage-specific growth and survival of some juvenile salmon populations during freshwater and early marine rearing (69,70). General statistical and population models have been used to explore density dependence and carrying capacities in lakeand stream-rearing populations (71)(72)(73)(74).…”

Angling baits and invasive crayfish as important trophic subsidies for a large cyprinid fish

“…These invasive species, when present in sufficient abundance, can act as novel autochthonous resources for native species, resulting in shifts in food web structure (Coulas et al 1998;Vander Zanden et al 1999;Ellis et al 2011). Moreover, invasive species often create novel trophic pathways, acting as both consumers and resources with, for example, invasive crayfish consuming both plant and animal material (Jackson et al 2014) and providing an abundant food resource for many taxa (e.g.…”

A Fine-scale Assessment of Using Barriers to Conserve Native Stream Salmonids: A Case Study in Akokala Creek, Glacier National Park, USA

“…However, these populations of high conservation value are at risk of invasion by proximate sources of nonnative salmonids (i.e., lake trout and rainbow trout). In addition, the lower portion of the drainage supports a spawning run of migratory westslope cutthroat trout from downstream Flathead Lake, where pressures from various nonnative species have resulted in reductions in abundance of these native salmonids [30]. Managers are, therefore, considering various alternatives to protect this unique native species stronghold through construction of an upstream fish passage barrier, while also seeking to minimize potential impacts to life history diversity and long-term persistence of native salmonid populations.…”