Epilithic phytoplankton community composition and seasonal dynamics at Jeddah coast, Red Sea

Abstract EN

Intertidal epilithic microalgae play very important role as feed of higher organisms.

Taxonomical community composition of epilithic phytoplankton assemblages and their seasonal dynamics in relation to environmental factors were studied at Jeddah coast, the Red Sea.

Temperature, pH and salinity varied from 21.60 to 32.30°C, 8.04 to 8.60 and 36.40 to 39.70 psu, respectively.

Among nutrients, the concentrations of NO3-N, NO2-N, NH3-N, PO4-P and SiO3-S were 0.26-2.99, 0.22-5.14, 0.13-4.70, 0.49-3.52 and 0.22-14.63 µg.L−1, respectively from spring to winter 2013.

The abundance of epilithic phytoplankton showed strong positive correlation with temperature (r = 0.76), NO2-N (r = 0.80), PO4-P (r = 0.76) and SiO3-S (r = 0.70).

A total of 86 epilithic phytoplankton species belonging to 6 families was indentified: 73 Bacillariophyceae, 6 Cyanophyceae, 3 Dinophyceae, 2 Chlorophyceae, 1 Conjugatophyceae and 1 Raphitodphyceae.

The phytoplankton abundance varied from 0.64 ×103 to 17.66 ×103 cells cm−2 during the study with an average of 4.87 ×103 cells cm−2, and the highest cell abundance was found to be occurred in spring.

Diatom was the dominant group of in total standing crop throughout the study.

Among diatom, the centric and pennate diatoms were 61.63 and 23.26%, respectively to total epilithic phytoplankton.

The occurrence frequency analysis revealed that high frequently observed epilithic phytoplankton were Licmophora flabellate and Pinnularia gibba in autumn, and Navicula granii was in summer.