The influence of different oxygen regimes on metabolism and behavior of a soft shell clam Mya arenaria

Hypoxia is widely distributed in coastal benthic habitats and is driven by warming, nutrient pollution and the diurnal cycles of photosynthesis and respiration. Benthic sessile species, such as the soft shell clam Mya arenaria, are commonly exposed to oxygen fluctuations in their habitats which might negatively impact the performance and metabolism of clams. To determine the effects of different oxygen regime on metabolism and behavior of M. arenaria, we exposed the clams for 21 days to chronic (constant) hypoxia at 20% of air saturation, fluctuating (cyclic) hypoxia (~10-50% of air saturation) and normoxia (100% of air saturation). To mimic conditions occurring in coastal hypoxic zones, CO2 and pH levels varied with the oxygen. We assessed the digging performance, bioirrigation capacity and bioenergetics of the clams. Acclimation to constant or cyclic hypoxia did not affect the oxygen consumption of the clams, but the oxygen consumption rates declined at low ambient oxygen concentrations regardless of the acclimation to different oxygen regimes. Clams acclimated to constant hypoxia mainly used lipids, whereas clams acclimated to cyclic hypoxia used carbohydrates as energy fuel. Clams acclimated to constant or cyclic hypoxia dug slower compared to the clams acclimated to normoxia. Furthermore, bioirrigation capacity decreased in clams acclimated to constant hypoxia. Our results indicate that constant and cyclic hypoxia impair bioturbation and bioirrigation capacity of clams which has implications for their ecological function as ecosystem engineers in benthic soft bottom habitats.