Population structure and ecological performance of the mangrove Avicennia marina (Forssk.) Vierh. on the Arabian Gulf coast of Qatar

Abstract

Abundance and size distribution of mangal vegetation was studied in four transects in relation to edaphic and microtopographic variability. Distribution of juveniles is related to prevailing biotic and abiotic factors. Abundance is lower at higher elevations (lower salinity) with a higher ratio in the large size class compared with trees at lower elevations. Juvenile numbers are not related to the size of the canopy. Instead numbers increase at lower elevations, accumulating in the basin at low tide mark. Tidal cycles interact with microtopography and exert a major effect on the population structure and the fate of juveniles. A stable population structure is deduced at intermediate elevations with equal numbers of large and small size classes amounting to 37% of the population. High nutritional conditions and ecophysiological adaptations permit the establishment of seedlings carried by tidal water. The mangrove population is expanding on mud deposition in the basin behind the tidal delta that is building up in the area. Although the physical environment has a marked effect on the dispersal and establishment of seedlings, masking growth and reproductive rates of parent trees, it is the biotic attributes of the juveniles that are much more effective in determining the ecosystem's boundary for the expanding population.