Tridacna gigas are mollusks that gain nutrients via filter feeding and harbor symbiotic zooxanthellae. This relationship creates clam mantles of different colors. Our study examines whether the orientation of giant clams,or their mantle color, is related to its location on the reef. For both the South Beach reef flat (22 clams) and Heron Bommie fore reef (20 clams) near Heron Island, Queensland, Australia we recorded each clam’s orientation and mantle color. Average giant clam orientations at South Beach reef flat of 160.7° ± 88.7° SD and Heron Bommie back reef of 212.4° ± 100.8° SD showed no statistically significant difference (p>0.05). Average giant clam orientation distribution per compass rose quadrant at each site showed no statistically significant differences (p>0.05). These results indicate that giant clams orient randomly at both locations. This could be due to similar currents, or their inability to choose placement. Observational data displayed high amounts of one color at each site, purple (68%)at the reef flat and brown (45%)at the fore reef.This could be due to a difference in zooxanthellae inhabiting each reef zone. Adding information on depth and temperature could provide evidence of whether different zooxanthellae species inhabit giant clams based location.

Orientation Preference and Mantle Color of Tridacna gigas at Two Sites (reef flat and fore reef) of Heron Island, Great Barrier Reef, Australia