Isotopic Analysis of Trophic Structure and Food Web Dynamics in the Lower Niger River, Niger Delta Zone

Understanding trophic structure and energy flow in large tropical rivers is essential for fisheries management and predicting ecosystem responses to environmental change. This study used stable isotope analysis of carbon-13 and nitrogen-15 to characterise trophic structure and food web dynamics in the lower Niger River in the Niger Delta zone. Muscle tissue samples were collected from fourteen fish species spanning benthic, pelagic, and demersal feeding guilds, alongside samples of primary producers, zooplankton, macroinvertebrates, and riparian leaf litter. Bayesian stable isotope mixing models were used to estimate dietary contributions of primary production sources to each consumer group. Trophic positions were calculated from nitrogen-15 enrichment relative to baseline consumers. Results revealed a food web spanning 3.8 trophic levels, with demersal catfish occupying the highest trophic positions. Carbon isotope analysis indicated that benthic algae and phytoplankton were the dominant carbon sources for most fish species, with riparian leaf litter contributing substantially only to benthic macroinvertebrate consumers. Seasonal variation in carbon source contributions reflected flood pulse dynamics, with higher reliance on flood-derived allochthonous carbon during peak inundation periods. Isotopic niche analysis showed moderate niche overlap among co-occurring predatory fish, suggesting resource partitioning. These findings contribute novel trophic baseline data for the lower Niger River and provide a framework for isotope-based food web monitoring in response to hydropower operations and climate-driven flow changes. Keywords: stable isotopes, trophic structure, Niger River, food web, Niger Delta.