Anthropogenic Influences on Phytoplankton Distribution, Abundance, and Diversity in the Calabar River System, Cross River State, Nigeria

Phytoplankton constitute a diverse assemblage of photosynthetic, predominantly eukaryotic organisms that inhabit the illuminated zones of aquatic ecosystems, including rivers, lakes, estuaries, and oceans. As primary producers, they are responsible for over 95% of photosynthetic activity in marine environments, contributing substantially to global primary production and atmospheric oxygen supply. Despite their ecological importance, phytoplankton communities are highly sensitive to environmental perturbations, particularly those arising from anthropogenic activities. Structural modifications such as the construction of bridges, dams, and barriers, as well as dredging operations, can significantly alter hydrological regimes, nutrient dynamics, and light penetration, thereby influencing phytoplankton distribution, abundance, and species composition. This study investigates the impact of human activities on the distribution, abundance, and diversity of phytoplankton in the Calabar River System, Nigeria. Water samples were collected from selected stations representing varying degrees of anthropogenic disturbance. Phytoplankton species were identified and enumerated using standard microscopic techniques, while diversity indices were computed to assess community structure. The results revealed spatial variations in phytoplankton composition and abundance across sampling stations. Areas exposed to intense human activities exhibited reduced species diversity and shifts in community structure, characterized by the dominance of a few tolerant taxa and the decline of sensitive species. Conversely, less disturbed stations showed relatively higher species richness and more balanced community assemblages. The findings demonstrate that anthropogenic modifications to river systems can significantly influence phytoplankton dynamics, potentially disrupting ecological balance and affecting overall aquatic productivity. Given the central role of phytoplankton in energy transfer and biogeochemical cycling, sustained disturbances may have cascading effects on higher trophic levels within the river ecosystem. This study provides baseline data on phytoplankton ecology in the Calabar River System and underscores the need for effective environmental management and monitoring strategies to mitigate the impacts of human activities on aquatic biodiversity.