Quantitative aspects of seagrass communities, particularly of those dominated by Halophila stipulacea, in Sinai (Northern Red Sea)

Seagrass communities of the Sinai coast may be divided into three groups according to their dry weight biomass. Thalassodendron ciliatum communities compose the first group reaching over 100 kg dry wt. m^-2. Communities dominated by Thalassia hemprichii, Cymodocea rotundata, Syringodium isoetifolium, Halophila stipulacea and all submerged and some intertidal communities dominated by Halodule uninervis compose the second group, in which biomass ranges from a few hundred grams to several kg dry wt. m^-2. The third group includes all communities dominated by Halophila ovalis, some intertidal communities of Halodule univervis and seeding communities of Halophila stipulacea. The most productive communities of H. stipulacea are those of shallow waters, but not the intertidal ones. The share of leaves in these communities increases with depth down to about 10 m, as compared with the subterranean parts, whereas leaf size continues to increase down to about 20 m. As vegetation density decreases below 10 m, the photosynthesizing area of the community also decreases below this depth, despite an increase in individual leaf area. Halodule uninervis communities show an even more pronounced increase of biomass from the intertidal belt downwards, within the limited depth range they occupy.