Sensitivity of Submerged Aquatic Macrophytes and Their Epiphytic Microalgae to the Different Environmental Variables in River Nile, Egypt

This paper examines the difference in distribution, abundance and species composition of the submerged aquatic macrophytes and their epiphytic microalgae in relation to the environmental variables along the River Nile from Aswan High Dam to Al Kanater Al-El-Khayria during hot and cold seasons (summer and winter) 2017. A total of 200 epiphytic microalgal species related to 72 genera and 6 classes were identified on the recorded aquatic plants (Myriophyllum spicatum L., Ceratophyllum demersum L., Potamogeton crispus, Potamogeton perfoliatus L. and Potamogeton pectinatus L.). There were major differences in community structure between the two seasons, in addition to the highest diversity in hot season. Among the recorded macrophytes species Myriophyllum spicatum was the most frequent (observed in P =80% and 86.7% of the samples collected during the cold and hot seasons, respectively). It represented 62% of the total submerged macrophytes standing crop. The phytochemical screening revealed the presence of some biologically active substances in the macrophytes. Bacillariophyceae were the dominant algal group (92.3%) on all aquatic macrophytes, with 119 taxa related to 31 genera. The dominant epiphytic algal species of Cocconies placentula, Cyclotela occellata, Synedra ulna, Scenedesmus ecornis, S. quadricauda, Lyngbya limnetica and Microcystis aeruginosa were found on all types of the investigated aquatic plants in all habitats during the two seasons. PCA showed the selectivity between epiphytes and macrophytes, where Bacillariophyceae and Chlorophyceae were more associated with Ceratophyllum demersum and Myriophyllum spicatum (r=0.7 and 0.6, respectively) in hot season. However, Cyanophyceae was more abundant on Myriophyllum spicatum (r=0.7) in cold season. In addition, the interaction between epiphytes, macrophytes and environmental factors were observed.