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Mangroves under extreme environmental conditions: Isabela Island (Galapagos Islands, NE pacific) and Abu Dhabi-Dubai (UAE, Arabian Gulf)

Abstract:

The coastline of Isabela Island is dominated by reefs and rocks of volcanic origin. Four mangrove communities are linked to sandy bays (Rhizophoretum manglis); mixed formations on sandy soils and volcanic rock fragments (Lagunculario racemosae-Rhizophoretum manglis); post-coastal formations around lagoons, bays, and estuaries (Laguncularietum racemosae); and uplands marginal mangroves in an ecotone with dry forest (Conocarpetum erectae). The presence of Laguncularia racemosa occurs in substrates where salinities range from 6.9 g/l to 12.3 g/l, whereas the less common Avicennia germinans tolerate salinities as high as 12.5 g/l. At Abu Dhabi, in the southeastern Persian Gulf, wide coastal plains and arid bioclimate are the factors that determine the monospecific mangroves stands of Avicennia marina associated with nearby halophyte or subdesert xerophilic formations. The unique association, Avicenietum marinae, shows two variants: Sesuvium portulacastrum occurs with A. marina on dune formations, and Sarcocornia fruticosa and Halocnemum strobilaceum are associated with A. marina on inland with saline soils or desert plains. Soil characteristics as organic matter, Na+, K+, Mg++, and Cl- concentrations, constitute differential factors between the communities.