Temporal variation in chemical composition of Dictyota dichotoma (Hudson) J.V. Lamouroux (Dictyotales, Phaeophyceae) from Red Sea Coast, Egypt

Objective: To relate the chemical composition of Dictyota dichotoma (Hudson) J.V. Lamouroux (D. dichotoma) to variation of water characteristics at Hurghada, Egypt. Methods: Sea water and D. dichotoma fronds were collected from Hurghada shores, during autumn of 2014. Water samples were analyzed and fronds of D. dichotoma were biochemically quantified. Results: Sea water was characterized with high levels of salinity, P and heavy metals but with low content of nitrogen. The confined nature and the high evaporation of the Red sea contribute to the high salinity while the mining and transportation of phosphatic ore in the nearby region contribute to the high load of P and heavy metals. With the progress of season from September to November, water temperature was markedly reduced whereas pH and ionic content of water was reduced to a lesser extent, with marked alteration in ionic composition. With the progress of season towards winter, there was marked reduction in mineral composition of the fronds, shift in frond composition in favor of carbohydrates at the expense of proteins, lipids and alginates; and shift in the pigment composition in favor of chlorophylls at the expense of carotenoids and fucoxanthin. Conclusions: These facts point to active growth and photosynthetic activity during the cold period; that is, D. dichotoma is a cold water alga. D. dichotoma had moderate nutritive value, with moderate contents of carbohydrates, proteins, lipids and minerals. The mineral accumulation capacity of the fronds was more evident for N, P and K than for Ca, Mg and heavy metals.