Ph.D Thesis

Ph.D StudentMakler-Pick Vardit
SubjectA Lake Ecosystem Model as a Research Tool for Exploring
Fish Impacts on Food Web Dynamics with Emphasis on
Intraguild Predation
DepartmentDepartment of Civil and Environmental Engineering
Supervisors PROF. Yohay Carmel
PROF. Gideon Gal
Full Thesis textFull thesis text - English Version


The aim of the research was to improve the usefulness of complex ecosystem models in exploring food web interactions and water quality in aquatic ecosystems. Specifically, the coupled 1D hydrodynamic-ecological model DYRESM-CAEDYM (DYRESM -Dynamic Reservoir Simulation Model, CAEDYM - Computational Aquatic Ecosystem Dynamics Model) was employed for studying the trophic dynamics and impact of fish on water quality in the study site of Lake Kinneret (Israel).

In the first chapter a new approach for global sensitivity analysis of a multi-parameter ecosystem model was developed and applied to DYRESM-CAEDYM. In addition to a prioritized list of sensitive parameters the results highlighted the ecological implications derived from the analysis results and enhanced our understanding of key ecosystem dynamics.

The focus of the second chapter was on the development, calibration and validation of an individual-based fish population model and the dynamic coupling of the fish model with DYRESM-CAEDYM. The aim was to elucidate fish impacts on the ecosystem by employing a complex model that incorporates all trophic levels from nutrients to fish. Specifically the model was used to study the impact of the dominant fish in Lake Kinneret, Acanthobrama terraesanctae (Lavnun), on the food-web and water quality of the lake. Model results suggest that the Lavnun has a significant impact (p < 0.05) on output variables such as its prey food - the predatory and micro-zooplankton, major chemical components like ammonium (NH4) and phosphate (PO4), and on Peridinium gatunense, Aulacoseira granulate, Aphanizomenon sp. and Microcystis sp.

In the third chapter I used the model to reveal the dynamics of the intraguild predation, and in particular, to study these dynamics when the number of fish is significantly higher than the multiannual average. The results indicate that in Lake Kinneret the predation of the predatory zooplankton on herbivorous zooplankton varies widely with season, exerting predation pressure of 10-20 times more than fish predation pressure at the time of its annual peak. When the number of the fish is significantly higher than the multiannual average the zooplankton groups turn to be controlled by the fish.

Together, the three sections of this research work contribute to the development of ecosystem models and enhance the understanding of the role of planktivorous fish in aquatic ecosystems.