Latitudinal distribution of Tridacna spp. along Egyptian coasts of the Red Sea and Gulf of Aqaba

Giant clams that belong to Subfamily Tridacninae are influential members of coral reefs ecosystems in tropical and sub-tropical areas. They provide these ecosystems with multiple ecological roles. Tridacnids are the largest bivalve worldwide and are harvested easily, leading to continual decline in their numbers. Their abundances and geographical distribution urgently need to be assessed if their recovery and restoration efforts are to be successful. Latitudinal distribution and species composition of Tridacna were studied within 16 sites along Egyptian coasts of the Red Sea and Gulf of Aqaba, using Underwater visual census surveys. Four species were recorded: T. maxima, T. squamosa, T. Squamosina and T. rosewateri. T. rosewateri was recorded for the first time in the Red Sea. Abundances and distribution of the explored species varied greatly within the selected sites; T. maxima was the dominant species along the study area with abundance of 6.19±2.63/125m2 transect; meanwhile, only three individuals of T. rosewateri were observed in Marsa Egla and Marsa Asalaya. The surveyed species showed significant latitudinal distribution, as the four species exhibited incremental gradual distribution from North to south amongst sites, Marsa Asalaya showed the highest abundance (29.67±9.79 /125m2 transect); the variation in distribution and abundance of Tridacna spp. between and among the studied sites indicated that variable factors might be influencing the distribution and abundance of the giant clams’ population along coasts of the Egyptian Red Sea and Gulf of Aqaba.