The role of zooxanthellae in the growth of the giant clam Tridacna maxima in outdoor aquaculture system, Red Sea, Egypt

The Tridacninae subfamily of giant clams is essential for the biological functioning of coral reefs in the Indo-Pacific region. Although there has been seen rise in the commercial mariculture of giant clams in developing countries in the Indo-Pacific region, there is still a deficiency in understanding the factors that influence the growth rate of Tridacna species. In this study, we intend to tackle the scarcity of understanding by investigating the factors that influence the growth rate of T. maxima under culture condition. These factors include seasonal fluctuations, temperature, mantle colours, density of zooxanthellae, and light energy absorption. I t was revealed that the growth patterns of this species are influenced by monthly and seasonal fluctuations, as well as parameters like as temperature, mantle colours, density of zooxanthellae, and light energy absorption. The monthly and seasonal fluctuations in growth rates are directly linked to temperature variations. Specifically, extreme temperatures in winter and summer are associated with reduced growth rates, whereas mild temperatures in spring and fall are associated with higher growth rates. The colour of the mantle also indicated a potential three-way interaction between the growth rate, the colour of the symbionts, and the density of zooxanthellae. i.e. Individuals with brown-colored symbionts displayed higher growth rates and a greater density of zooxanthellae. The number of zooxanthellae varied significantly among different colour variants. Brown individuals had much higher concentrations of symbionts in comparison to blue-brown and blue individuals. Understanding the multifaceted links among environmental conditions, symbiotic interactions, and growth dynamics is crucial for developing successful conservation and management methods for protecting T. maxima populations.