Responses to temperature, heavy metal and sediment stress by the giant clam Tridacna squamosa

Increasing seawater temperature, heavy metal concentration and sediment load, all represent environmental stress factors found in the Gulf of Thailand. In the present study we investigate and compare the physiological responses of exposure to increased water temperature (+ 3°C) and copper (50 μg Cu/l) by the giant clam Tridacna squamosa, and the behavioural response to sedimentation. Both temperature and copper caused significant decrease in Pg: R ratios, although by different physiological responses. In clams exposed to copper, the decrease in Pg: R is caused by reduced photosynthesis, whereas the clams exposed to increased temperature maintained a high photosynthetic rate, but significantly increased their respiration. Clams responded to additional sediment with increased activity. This augmented activity was further increased for clams previously stressed by copper.