Abstract
Seagrasses rank among the most productive ecosystems with important implications in climate change mitigation. Tropical and subtropical seas hold the largest seagrass species richness. A total of 12 different seagrass species have been reported from the Red Sea. However, there is little information on seagrass diversity and distribution along the Saudi Arabian coast of the Red Sea. This study aims to capture: (i) the distribution and composition of seagrasses from 18 degrees N to 28 degrees N latitudes on a broader scale, and (ii) the species composition, distribution and abundance of seagrasses by detailed investigations at three locations along the Saudi Arabian coast: Sharma, Umluj and Jazan, representing the northern, central and southern Red Sea. The most commonly observed seagrass species along the Red Sea were Halodule uninervis (17 observations), Thalassia hemprichii (13 observations) and Halophila stipulacea (11 observations). Halophila stipulacea was the most dominant species at each of the three locations studied in more detail. Syringodium isoetifolium and Thalassodendron ciliatum were found only at Umluj, while H. ovalis and T. hemprichii were found only at Jazan. H. uninervis was observed at both Umluj and Jazan. Shoot lengths of H. stipulacea and H. uninervis showed significant differences among the three locations. The average above-ground biomass of seagrasses differed significantly among locations (analysis <0.05; multiple tests), with the highest biomass for Halophila stipulacea recorded at Jazan (81 +/- 24 gDW m(-2)) and an average biomass for T. ciliatum of 74 +/- 16 gDW m(-2) at Umluj. The species T. ciliatum was the only taxa that exhibited significant differences (p < 0.05) in the abundance of seagrasses among the three locations. This work contributes further to our understanding of the distribution and diversity of seagrasses in the Red Sea, confirming a high seagrass richness with at least ten different species along the Saudi Arabian coast of the Red Sea.