Floristic composition and zonation of seaweeds on Zabargad Reef (Red Sea, Egypt)

Abstract

Composition, dominance, distribution and zonation of seaweeds were investigated, using line-transect technique,in three sites of varied water activity on Zabargad reef during November 1994. Fifty-four taxa included 16 green,13 brown and 25 red macroalgae were identified, adding four new records for the Red Sea. The flora appearsrich and diverse, composed of filamentous, turf-forming, fleshy sac, foliose, erect shoot, and coralline forms. Itshowed a geographic distribution pattern similar to that of the Indo-Pacific.The seaweed vegetation appears heterogeneous, having a dissimilar construction at each side of thereef. It showed a conspicuous zonation, revealing six zones related in general to reef topography, watermovement and in a lesser extent to grazing and nutrient enrichment. The intertidal zone had a marked reducedflora due to exposure to air during low tide, and mobility of coral sand. Reef flat was the richest in speciescomposition and dominance, as it lies in a shallow, well-illuminated, and less fluctuated subtidal region. Peculiarwas the presence of high species dominance in strong surf on the windward reef crest. The reason for this is thatthe crest is extensively eroded, rich in crevices and fissures within which the algae hideaway from wave action.Moreover, strong rhizoids, dwarfing of thalli, crustose morphologies, growing in adherent to substrata weresome modifications allowing algae to persist in strong surf.