Ecology and culture of giant clams (Tridacnidae) in the Jordanian sector of the Gulf of Aqaba, Red Sea

Abstract

This thesis is on the ecology and culture of giant clams in the northern Gulf of Aqaba. Giant clams are scarce (0.3 - 0.5 ind. per 100 m-2) in Jordan, decreasing12-fold over three decades. Two-third higher abundances in restricted (1.04 0.4 ind. 100 m-2), suggest a decline caused by overfishing and habitat loss related to urban development over four decades. In the wider Red Sea, the impact of human activities are also evident. There is a distinct reproductive seasonality of giant clams in Jordan with species-specific spawnings: T. squamosa has an extended bi-modal spawning (June-Nov.) and T. maxima a shorter unimodal spawning (Jun-Sep). Regression of the ovarian follicles is protracted over winter and maturation commenced in late winter, culminating in spring. Likewise, the landbased culture showed reproductive success in summer (Jun-Sep), with protracted larval development and mortality in winter. Modifications done on existing culture techniques for the Red Sea conditions have been successful. Molecular mitochondrial rDNA analysis, morphological taxonomic classification, and, reproductive periodicity provided for the existence of a new species of giant clam in the northern Red Sea. The molecular analysis and amended taxonomic classification are consistent in placing Tridacna nov. sp. in the subgenus Chametrachea. This is strongly supported by the similar morphological and behavioural characteristics of Tridacna nov. sp with the two members of the subgenus, T. maxima and T. squamosa, the only two extant species in the Red Sea. Furthermore, Tridacna nov. sp showed species-specific reproductive seasonality with a shorter summer spawning (May-July), smaller ova diameter (75 2 µm) and earlier ovarian maturation (Aug.) compared to the other two species.