Bioturbation by the common Antarctic scallop (Adamussium colbecki) and ophiuroid (Ophionotus victoriae) under multi-year sea ice; ecologic and stratigraphic implications

The abundant epifaunal scallop Adamussium colbecki and ophiuroid Ophionotus victoriae bioturbate the seafloor under the multi-year sea ice in Explorers Cove, western McMurdo Sound, Antarctica by churning the upper few centimeters of the sandy substrate. Laboratory investigation of these animals' activities demonstrates that the scallops on average resuspend 45 cm (super 3) d (super -1) ind (super -1) via water jets ejected during swimming and clapping movement and that the ophiuroids on average disrupt 861 cm (super 3) d (super -1) ind (super -1) via rowing motion and self-burial in the upper centimeters of the substrate. At observed densities in Explorers Cove, bioturbation rates greatly exceed sediment accumulation rates and physical reworking processes, resulting in homogenized sediment lacking both lamination and discrete traces that would signal its biogenic modification. Adamussium colbecki employs water jets to resuspend the limited phytodetritus needed by the suspension-feeding scallop in the quiet sub-sea ice conditions and produces depressions approximately 3 cm deep that increase substrate surface area and microtopography in Explorers Cove. The scallop thus acts as an ecosystem engineer, modifying the sediment and controlling the flux of materials between the substrate and water as it claps for food gathering rather than for predator evasion like other scallops. The resulting rapid, shallow diffuse bioturbation differs from the more commonly reported vertical bioturbation by infaunal animals recorded in cores, yet it exerts strong control on the sedimentary record and may be characteristic of low-energy, oligotrophic environments beneath multi-year sea ice around Antarctica where a lack of fast predators and low sedimentation rate allow proliferation of epifaunal animals.