Species composition and diversity of epiphytic microalgae on Myriophyllum spicatum in the El-Ibrahimia Canal, Egypt

The El-Ibrahimia Canal is one of the main irrigation sources in Egypt, that it supplies perennial irrigation to approximately 600 000 ha (one-fourth of the Egyptian cultivated land). An annual study on species composition of microalgae attached to the submerged hydrophyte Myriophyllum spicatum L. was carried out from midautumn 2016 to midsummer 2017. Epiphytic microalgae were represented by 109 species related to 66 genera. Diatoms were the most abundant group (66–95%) followed by green algae (3.3–25%). Aulacoseira granulata, Cyclotella ocellata, Cymbella affinis, Gomphonema parvulum, Navicula cuspidata, Navicula muralis, Nitzschia dissipata, Nitzschia hungerica, Staurosirella leptostauron, and Ulnaria ulna were the most dominant species. Regarding morphology-based functional groups (MBFGs) taxonomic approach, the epiphytic microalgae species were represented by six MBFGs (I, III, IV, V, VI and VII). The MBFG VI (mainly diatoms) was the leading group with a minimum average percentage of 59.9% during the summer season and a maximum of 95.06% during the winter season. The mean annual values of cell density fluctuated greatly between 8.6 × 106 (during the spring season) and 4.7 × 107 cells g−1 plant wet weight (during winter season). The changes in microalgae biovolumes have the same trend as cell density, with mean seasonal values of 3.89 × 109, 2.56 × 1010, 1.16 × 109, and 3.21 × 109 µm3 g−1 plant wet weight during autumn, winter, spring and summer seasons, respectively. Diversity index values ranged between 2.0 and 3.0, revealing a light pollution status of the canal. In general, the species composition and diversity of epiphytic algae along the El-Ibrahimia Canal are highly dependent on site and the physico-chemical properties of canal water affected by agricultural practice around it.