Action: Asian clams: Reduce oxygen in the water
- A controlled laboratory study conducted in the USA found that Asian clams were resistant to extreme very low levels of oxygen, irrespective of water temperature or length of immersion in the test conditions.
Very low levels of oxygen in the water for a prolonged period may kill Asian clams Corbicula spp. However, even mild reductions in oxygen may offer advantages by increasing the vulnerability of the clams to predation. When attacked, bivalves protect their soft tissues by closing their protective valves. This reduces vulnerability to small predators, but ventilation and oxygen uptake are suspended. In a laboratory study it was found that after a simulated attack, Asian clams under low oxygen conditions reopened their valves sooner than clams under high oxygen conditions, suggesting that low oxygen levels increases vulnerability to predation (Saloom & Duncan 2005).
Saloom M.E. & Duncan R.S. (2005) Low dissolved oxygen levels reduce anti-predation behaviours of the freshwater clam Corbicula fluminea. Freshwater Biology, 50, 1233-1238.
Supporting evidence from individual studies
A controlled laboratory study in 1999 on specimens from a dam and artificial stream in Texas, USA (Matthews & McMahon 1999) found that Asian clams Corbicula fluminea survived low oxygen levels for extended time periods. They survived an average of 12, 35 and >84 days at 25°C, 15°C and 5°C, respectively. Survival rates were comparable with the control (normal oxygen levels). However, larger clams were less tolerant to low oxygen than smaller ones. Groups of clams were acclimated to 5°, 15° or 25°C for 14 days. A group of 30 adult clams were held in water that was either aerated (control) or had reduced oxygen at 5°, 15° and 25°C. In low oxygen treatments, partial pressure of oxygen was reduced to less than 5% of full air saturation by continually bubbling the water with nitrogen. The water was changed every 2-3 days. Testing ceased when all clams had died or after a maximum of 12 weeks. Oxygen concentrations and survival of clams were recorded daily.