Ecological Indicators (Jul 2021)
Anthropogenic-induced environmental changes in the Nile-delta and their consequences on molluscan biodiversity and community structure
Abstract
Global climate changes and anthropogenic pressures have altered many coastal ecosystems worldwide. To understand the consequences of these perturbations on the community structure of the benthic communities, the fauna and the sediments retrieved from a short core in the Manzala Lagoon, which is largest in the Nile Delta, were quantitatively analyzed. The 120 cm long-core represents 170 years. A significant ecosystem shift took place in the upper 41 cm of the lagoon sediments were attributed to hydrodynamic changes, associated with the construction of Aswan High-Dam, where heavy metals concentrations, Pollution Load Index (PLI), and fine-grain sediments were increased. Consequently, the community structure of the benthic fauna was dramatically changed. Currently, the benthic community is dominated by brackish and opportunistic taxa (e.g., Fulvia fragilis, Pirenella conica, Corbicula fluminalis, and Melanoides tuberculata). In contrast, the pre-impact community contains equilibrium freshwater species. These salinity-controlled communities were better characterized on both Bray-Curtis -based Constrained Clustering (CC) and non-Metric Multidimensional Scaling (nMDS). The faunal density and Dominance Index are higher in the top samples, which point either to anthropogenic disturbance or taphonomic (mechanical or chemical) distortion with depths. However, higher species richness in lower samples suggested that the mechanical distortion has not altered the original communities and point to anthropogenic drivers of the diversity loss. Further declining or even extinction of the equilibrium species in the future is expected if no restoration programs implemented soon. Furthermore, nMDS and RMA regression models showed that the distribution of benthic fauna is governed by abiotic factors (e.g., water salinity, metal concentrations, and sediment grain-size). The latter indicates that biotic traits of benthic fauna such as feeding-mode and life-habit are highly sensitive to minor environmental changes and thus can be used as a robust indicator in paleoenvironmental reconstructions.
