Ziga Ogorelec

Research Project E2: Resilience of whitefish population dynamics in response to oligotrophication

Whitefish (Coregonus wartmanni) is the most important fish species for the local fishery in Lake Constance and presumably exerts a strong predation pressure on the zooplankton community.  Due to re-oligotrophication (phosphorus value dropped from 80 µg/L in 1970s to below 10 µg/L nowadays) there is lower primary production and the whitefish population is in decline. Additional threat is invasive three spined stickleback (Gasterosteus aculeatus), which firstly appeared in the pelagic zone just a few years ago. It has quickly outnumbered whitefish population and according to recent studies (LAC, 2016) it represents 96% of a number and 28% of biomass of all pelagic fish. Hence, re-oligotrophication as well as the recent invasion of sticklebacks are expected to strongly change fish-zooplankton interactions. Nevertheless, in the same years crucial changes appeared also on lower trophical levels: outbreak of Daphnia cucullata on level of zooplankton and Plantothrix rubescens on level of algae.

In my research project I am trying to better understand whitefish (Coregonus wartmanni) and invasive stickleback (Gasterosteus aculeatus) diet preferences and their effects on zooplankton community. To understand interactions on different complexity levels, I will combine aquaria experiments (functional response experiments with different prey species and prey selection experiments) and field observations (stomach content of both fish species, zooplankton sampling and using long term zooplankton data). Comparing with previous fish diet studies, I will define responses to (a)biotic changes and reversibility of Constance Lake pelagic ecosystem.

Key words

Whitefish (Coregonus wartmanni), three spined stickleback (Gasterosteus aculeatus), Bythotrephes longimanus, Leptodora kindtii, Daphnia spp., zooplankton fish interactions, prey selection, functional response, diurnal vertical migration, fish stomach content, reversibility

Educational background

Since 2017  PhD student – University of Constance

2012-2015  Master of Ecology and biodiversity – University of Ljubljana

2009-2012  Bachelor of Biology - University of Ljubljana