Effects of hypoxia on animal burrow construction and consequent effects on sediment redox profiles

We conducted a laboratory experiment to investigate the effects of mild hypoxia on the burrowing behavior of three marine species (the hard clam Mercenaria mercenaria, the polychaete worm Neanthes virens, and the amphipod Leptocheirus plumulosus) and consequent effects on sediment redox profiles. Animals were introduced into defaunated sediment and allowed to burrow for four months at mildly hypoxic (2 mg l− 1) and normoxic (7 mg l− 1) dissolved oxygen (DO) levels. Sediment redox profiles were measured 10 times during the course of the experiment. At the end of the experiment, the sediment was imaged using computer-aided tomography to quantify burrow volume and location. For the three species, burrow volume remained constant over DO treatments, but amphipod and clam burrows were shallower in hypoxic treatments compared with normoxic treatments. Redox profile discontinuity (RPD) depth was shallower in hypoxic treatments compared with normoxic treatments for experiments without animals, indicating that water column oxygen concentration alone influences diffusion of oxygen into the sediment. Worms, but neither clams nor amphipods, increased the RPD depth relative to no-animal controls in both hypoxic and normoxic treatments, but the effect was greater in normoxic conditions. These results suggest that although hypoxia can reduce burrowing depth, infauna can still increase the depth to which oxygen penetrates the sediment, but not to the same degree as they would under normoxic conditions.