Fish diets and dynamics across diverse habitats: lake characteristics and restoration implications for ecosystem management

TY - BOOK

T1 - Fish diets and dynamics across diverse habitats

T2 - lake characteristics and restoration implications for ecosystem management

AU - Berthelsen, Andreas Severin

PY - 2024/1

Y1 - 2024/1

N2 - Fish diets, and the processes resulting from their interactions with the broader foodweb, are central to lake structuring. These interactions are both influenced by andinfluence the surrounding environment. Typically, fish diets derive primarily fromthe pelagic or littoral/benthic trophic pathways. Understanding the balance betweenthese pathways is ecologically significant as they form the foundation forseveral management applications, notably fish removal.Arctic char (Salvelinus alpinus) is a key species in Greenland, given its dominantrole in the predator-prey dynamics of Arctic lake food webs. This thesis investigatedhow habitat type and lake morphology shape the trophic positioning of Arcticchar. By employing stomach content and stable isotope analyses, the dietarytrends of char in two Greenlandic lakes of varying size were analyzed. Generally,fish from the smaller of the study lakes displayed a marked preference for littoralmacroinvertebrates. The cause of this was the relatively larger littoral habitat ofthe slightly smaller, elongated, and shallower, though still 10 m deep, of the studylakes. Further, there was increased reliance on zooplankton by small char in thelarger of the two study lakes during the study period from 2008 to 2019. Theseobservations show the interconnectedness of lake morphology and fish feedingbehavior.Large-scale fish biomass reductions, both intentional via biomanipulation andnatural fish kills, significantly impact lake ecosystems. We analyzed the diets ofroach (Rutilus rutilus) and European perch (Perca fluviatilis) in a eutrophic shallowlake over 18 months, before and after a major fish removal. The results revealed ashift towards increased zoobenthivory across all fish sizes post-removal. Additionally,a temporary surge in zooplankton biomass saw both species predominantlyfeeding on daphnids, likely causing their number to drop. This suggests that afterlake restorations involving fish removal, intermittent zooplanktivory could lead tounexpected top-down effects.Further, we examined the collective impact of fish removal and Phoslock® treatmentin a shallow lake. The intervention led to lower nutrient levels, clearer water,and expanded macrophyte coverage. Post-restoration, fish notably shifted fromdetritus feeding to macrophyte foraging and a general move towards a more pelagicdiet, which contrasts with the findings presented in paper 2.This thesis highlights how fish diets depend on their environment, and how fishadaptively change diets based on changes in the environment. Further, it presentsspecific restoration cases where fish play a more pronounced role in the top-downcontrol than previously thought.

AB - Fish diets, and the processes resulting from their interactions with the broader foodweb, are central to lake structuring. These interactions are both influenced by andinfluence the surrounding environment. Typically, fish diets derive primarily fromthe pelagic or littoral/benthic trophic pathways. Understanding the balance betweenthese pathways is ecologically significant as they form the foundation forseveral management applications, notably fish removal.Arctic char (Salvelinus alpinus) is a key species in Greenland, given its dominantrole in the predator-prey dynamics of Arctic lake food webs. This thesis investigatedhow habitat type and lake morphology shape the trophic positioning of Arcticchar. By employing stomach content and stable isotope analyses, the dietarytrends of char in two Greenlandic lakes of varying size were analyzed. Generally,fish from the smaller of the study lakes displayed a marked preference for littoralmacroinvertebrates. The cause of this was the relatively larger littoral habitat ofthe slightly smaller, elongated, and shallower, though still 10 m deep, of the studylakes. Further, there was increased reliance on zooplankton by small char in thelarger of the two study lakes during the study period from 2008 to 2019. Theseobservations show the interconnectedness of lake morphology and fish feedingbehavior.Large-scale fish biomass reductions, both intentional via biomanipulation andnatural fish kills, significantly impact lake ecosystems. We analyzed the diets ofroach (Rutilus rutilus) and European perch (Perca fluviatilis) in a eutrophic shallowlake over 18 months, before and after a major fish removal. The results revealed ashift towards increased zoobenthivory across all fish sizes post-removal. Additionally,a temporary surge in zooplankton biomass saw both species predominantlyfeeding on daphnids, likely causing their number to drop. This suggests that afterlake restorations involving fish removal, intermittent zooplanktivory could lead tounexpected top-down effects.Further, we examined the collective impact of fish removal and Phoslock® treatmentin a shallow lake. The intervention led to lower nutrient levels, clearer water,and expanded macrophyte coverage. Post-restoration, fish notably shifted fromdetritus feeding to macrophyte foraging and a general move towards a more pelagicdiet, which contrasts with the findings presented in paper 2.This thesis highlights how fish diets depend on their environment, and how fishadaptively change diets based on changes in the environment. Further, it presentsspecific restoration cases where fish play a more pronounced role in the top-downcontrol than previously thought.

KW - Fish dietary trends

KW - Stable isotope analysis

KW - lake restoration effects

KW - fish management

KW - fish removal

KW - Greenland lakes

M3 - Ph.D. thesis

BT - Fish diets and dynamics across diverse habitats

PB - Aarhus University

ER -