Impact of a Pulse Human Disturbance Experiment on Macrofaunal Assemblages on an Australian Sandy Beach

Environmental control is widely accepted as the principal structuring force of the macrobenthos on sandy beaches: abundance, biomass, and species diversity of benthic assemblages are closely linked to variations in environmental conditions. Thus, disturbance events that modify habitat properties in these ecosystems are hypothesized to translate into strong and consistent community-wide responses; this is the central hypothesis of this study, which was tested by examining trajectories of macrobenthic assemblages in relation to the experimental introduction of a pulse disturbance event that consisted of concentrated vehicle traffic (600 passes over 3 days) applied to the intertidal zone in a multiple before–after control-impact design. Small-scale spatial heterogeneity and short-term temporal variability were pronounced for all composite descriptors of assemblages (i.e., total abundance, species richness, and diversity) as well as community structure. The experimental pulse disturbance in the form of increased off-road vehicle traffic lowered macrobenthic densities by 27–52% and resulted in significant temporal shifts of assemblage structure. These biological responses were, however, not always unequivocally linked to the disturbance event in all cases, because background variation in the absence of experimental manipulation of traffic could be of comparable magnitude. Thus, human pulse disturbance effects can operate against a matrix of considerable natural spatiotemporal variability over small scales on sandy beaches. This heterogeneity has traditionally not been sufficiently incorporated into our understanding of the dynamics of the macrobenthos on sandy beaches and emphasizes the need for more experimental approaches on sandy shores