THERMAL CONSTRAINTS AND PREDATION RISK SHAPE SPATIO-TEMPORAL DYNAMICS OF ZOOPLANKTON TAXA IN STRATIFIED LAKES

Predation risk and thermal structure jointly shape the spatio-temporal dynamics of fish and zooplankton in stratified lakes. Using in situ imagery (Underwater Vision Profiler) and acoustic telemetry of brook charr, we examined how 3D fine scale habitat variability, thermal barriers, and behavioral differences modulate predator prey relationships. During summer, zooplankton communities exhibited pronounced within lake heterogeneity, both in terms of contrasting species dominance and of strong variation in size spectra that matched differences typically observed among distinct lakes. As the lake cooled, fish redistributed across depths, initiating shifts in zooplankton size structure and composition that pointed to a cascading effect of predator movements. Thermal constraints restricted fish access to epilimnetic zones in summer, limiting overlap with large cladocerans except for a subset of individuals that consistently selected resource rich areas. When the thermal barrier weakened, fish entered littoral and upper layers, increasing spatial overlap with their prey. Zooplankton diel vertical migration also responded to these seasonal changes in predation risk, with large cladocerans remaining in the epilimnion during summer while avoiding the metalimnion where fish aggregated. Together, these patterns illustrate how thermal fragmentation and selective predation determine the spatio- temporal overlap between fish and zooplankton, but ultimately among zooplankton taxa, shaping their resource use across vertical and horizontal gradients in temperate lakes.

Presentation Preference: Standard Oral (12 Minutes)

Primary Presenter: Andrea Bertolo, Université du Québec �  Trois-Rivières (andrea.bertolo@uqtr.ca)

Authors:

Riwan Leroux, Université du Québec à Trois-Rivières (Québec, Canada)  (riwan.leroux@uqtr.ca)

Marc Pépino, Ministère de l’Environnement, de la lutte contre les changements climatiques, de la Faune et des Parcs (Québec, Canada)  (marc.pepino@environnement.gouv.qc.ca)

Alan Fritsch, University of South Bohemia in České Budějovice (Czechia)  (afritsch@frov.jcu.cz)

Pierre Magnan, Université du Québec à Trois-Rivières (Québec, Canada)  (pierre.magnan@uqtr.ca)