RATES AND STYLES OF BIOTURBATION BY SHALLOW-WATER ANTARCTIC EPIFAUNA (SCALLOPS AND BRITTLE STARS): IMPLICATIONS FOR THE STRATIGRAPHIC RECORD
Animal activity reworked the top 2-3 cm in the aquaria in less than two days. O. victoriae disturbed the sediment by burying itself 2-3 cm deep and gashing the surface using breaststroke locomotion; the average ophiuroid bioturbation rate was 0.086 m2 day-1. Scallops moved by expelling jets of water from their mantle cavities. Movements include swimming (propulsion through water column), lateral turning (>90° rotation on sediment surface), clapping (<90° rotation on sediment surface), and flipping (claps turning the scallop over onto its preferred valve). Scallops averaged 14 movements day-1 ind-1. Clapping was the most common movement (50%) followed by lateral turning (37%). Water jets ejected during movement eroded sediment to form divots to a depth of 4 cm and reworked sediment at an average rate of 0.12 m2 month-1 ind-1.
The high bioturbation rate exceeds the sedimentation rate in EC (< few mm/yr). This bioturbation is diffusive and concentrated at the sediment-water interface, leaving no discrete traces or fingerprints of its biologic origin while simultaneously disrupting laminae as they form. Biological activity obliterates sedimentary structures in EC sediments and may similarly affect the sedimentary record in other areas under multi-year sea ice.