Document: WIL-3-99-155

Winterkill cascade: Top-down effects of fish on littoral fauna in boreal lakes.

LANGLOIS, P.W.*, W.M.TONN, E.E.PREPAS and C.A.PASZKOWSKI

University of Alberta, Edmonton, AB T6G 2E9 Canada ¹

Abstract:
Top-down effects of fish predation on freshwater invertebrates are well established in pelagic zones of lakes. However, studies of fish impacts on littoral macroinvertebrates are less clear-cut, often focus only on specialists and their prey, or involve experiments of limited spatial scale or habitat complexity. We employed a whole- and multi-lake natural experiment to investigate the strength and selectivity of interactions between fish and littoral macroinvertebrates in northern Alberta lakes. In this region, climatic, edaphic, and landscape features conspire to make fish winterkills a frequent natural disturbance. We sampled littoral macroinvertebrates in a lake before, immediately after, and 1 year following a severe winterkill of fish. If predation by fish is an important mechanism structuring the littoral fauna, winterkill should result in increased densities of invertebrates eaten by fish. Indeed, densities of amphipods and chironomids, common prey of the fishes that dominated the local assemblage (northern pike and yellow perch), increased 8-10 times following winterkill, and subsequently returned to pre-disturbance levels when fish populations began to recover. A dramatic increase in the recruitment of metamorphs emerging from the lake was also noted in amphibians. Fish densities increased in a second lake during the same time period, and densities of invertebrate prey correspondingly decreased. Dynamics of other, less common prey were not consistently related to changes in fish densities. Despite high productivity and a depauperate fish fauna dominated by generalist species, we suggest that effects of winterkill in these lakes can cascade down to littoral communities.

Keywords: winterkill

This abstract is being presented at: 8:45 AM in session:
Oral Session #54: Lake Ecology.