Burrowing crabs in arid mangrove forests on the southwestern Arabian Gulf: Ecological and biogeographical considerations

Abstract

Many species of mangrove crabs are essential in the formation of mangrove ecosystems, and the bioturbation resulting from the excavation of their underground chambers is directly correlated with substrate oxygenation and carbon and nitrogen cycling within the ecosystem. This study examines the ecological and biogeographical characteristics of bioengineering crab assemblages that inhabit the environmentally challenging arid mangroves in the southwestern Persian-Arabian Gulf. Results demonstrated that a hyper-arid environment could directly impact crab diversity, reducing it to only one species per niche or coastal zone. A biogeographic comparison revealed an exclusive divergence of species composition in each Gulf region. Variations in seasonal temperatures were found to have a direct influence on the abundance of species and how the zonation is driven by sediment composition and trophic relations. Two crabs – Nasima dotilliformis in the salt march (supratidal zone) and Macrophthalmus (Mareotis) depressus in the intertidal – were considered to be the most influential functional species for this hyper-arid ecosystem due to their abundance, size, bioturbation potential and niche specificity for the intertidal zone. The limited number of species within the arid mangrove system emphasised the biogeographic pressure and inherent importance of the few active bioengineering species present and adapted to the harsh conditions, indicating that the dominant crabs within the biotope are directly related to the successful evolutionary establishment of these hyperarid mangroves. The study highlights important implications for future forest management strategies of the only forest ecosystem that tolerates the extremes of the southwestern Persian-Arabian Gulf area.