EFFECTS OF “EUTROPHICATION” ON THE SIZE AND NUCLEUS OF SYMBIOTIC ZOOXANTHELLAE

Abstract

Zooxanthellae (Symbiodinium sp) from the giant clams, Tridacna maxima, were monitored for their responses to ammonium and phosphate addition in the field. Nutrients were added into ponded microatolls at every low tide using Nutrient Dispersal Units (NDUs) moored outside the atolls to reach final concentrations of 10µm for ammonium and 2µm of phosphate. Transmission electron micrographs show that zooxanthellae size (as the maximum diameter) from nitrogen-treated clams was significantly lower than those from other treatments (P<0.05). However, the cross-sectional area of the nucleus was not significantly affected by the treatments (P>0.05). These results suggest that the condition of zooxanthellae, such as the size of zooxanthellae from giant clams is influenced by relatively small changes in the concentrations of nitrogen in the water column