An Original Ecological Stoichiometry Framework for Understanding Nutrient Limitation in Nigerian Freshwater Zooplankton Communities Across Eutrophication Gradients

This dissertation develops and empirically validates an original ecological stoichiometry framework for analysing nutrient limitation and its consequences for zooplankton community structure across eutrophication gradients in Nigerian freshwater ecosystems, spanning the South West, South East, North Central, and North East geopolitical zones. Ecological stoichiometry provides a mechanistic basis for predicting how nutrient element ratios in primary producers constrain zooplankton growth, reproduction, and community composition, but its application to African tropical lakes and reservoirs is largely absent from the literature. The dissertation samples zooplankton communities and their phytoplankton food at 40 sites representing a designed eutrophication gradient from oligotrophic to hypertrophic conditions across eight water bodies. Body elemental composition (C:N:P ratios) of dominant zooplankton taxa is characterised by elemental analysis. Phytoplankton stoichiometry and the mismatch between consumer requirements and food quality are calculated. Controlled mesocosm experiments test the consequences of phytoplankton C:P enrichment on zooplankton growth efficiency and species composition. The original Nigerian Freshwater Stoichiometry Model (NFSM) is constructed by integrating field and experimental data, predicting zooplankton community shifts as a function of phytoplankton stoichiometric quality across the eutrophication gradient. Copepoda show the greatest sensitivity to phosphorus-depleted food at intermediate eutrophication, while Rotifera dominate stoichiometric composition at high eutrophication. The NFSM provides predictive benchmarks for water quality management at target reservoirs and an original stoichiometric baseline for tropical West African zooplankton ecology. Keywords: ecological stoichiometry, zooplankton, eutrophication, freshwater ecology, Nigeria.