Seasonal changes in the impact of infauna on sediment physical properties

Animals living in marine sediments (infauna) modify the physical characteristics of their habitats in a variety of ways. Infaunal communities also exhibit seasonal changes in abundance, community structure, and levels of activity, driven by changes in recruitment, predation, temperature, and environmental stressors such as hypoxia or physical bed disturbance. This study characterized impacts of infauna on sediments by examining seasonal changes in infaunal community and in sediment structure using a Portable Freefall Penetrometer (PFFP) and X-ray imaging. Infaunal abundance at most of the investigated sites in the York River Estuary (Virginia, USA) was lower in fall than spring, but X-ray images suggest a greater level of bioturbation in fall. At one site with finer-grained sediments, higher water content and lower sediment strength in the fall than spring were consistent with the creation of void spaces by animal activity. In muddy sands, deceleration profiles measured with the PFFP showed increased variability with depth as well as among replicate drops in the fall compared to spring. These results are consistent with increased heterogeneity in sediment structure associated with burrows and feeding voids observed in X-ray images. Interestingly, these data suggest a temporal lag between spring recruitment and high infaunal abundance and resulting impacts on physical sediment structure.