Sediment macrofaunal response to the diel oxygen cycle

Abstract

Infauna exhibit a range of behavioral responses to declining dissolved oxygen concentrations that affect their burrowing and feeding behaviors. Diel oxygen cycles, common in shallow coastal areas, may drive changes in faunal behavior that affect sediment mixing. In this laboratory study we exposed 3 species, the burrowing ophiuroid Hemipholis cordifera, the tube-dwelling polychaete Owenia fusiformis, and the burrowing clam Ameritella versicolor, to 60 h of diel cycling dissolved oxygen in the overlying water, with oxygen concentration varying between 2 and 7 mg l-1. We observed the study organisms’ behaviors and evaluated their sediment mixing activity using luminophores applied to the sediment surface. We found that sediment mixing activity of all 3 taxa, measured as percent decrease in luminophore coverage, varied proportionally with dissolved oxygen concentration during the diel cycle. Observations of animal behavior did not reveal a diel pattern, though this was likely due to the temporal and spatial scale of observations. Our results also indicated that diel cycling oxygen may change faunal effects on the sediment in ways that only emerge after more than a single cycle. Measuring sediment mixing in sustained full oxygen saturation may produce misleading estimates over time, and future research should investigate how faunal responses to short-term variability can scale to have longer-term effects.