Sediment Transport and Disturbance on an Intertidal Sandflat: infaunal Distribution and Recolonization

Abstract

Aspects of sediment movement in relation to the distribution and transport of infaunal crustaceans were studied on a high-energy sandflat in North Inlet, South Carolina, USA. Lower intertidal areas (+ 0.2 m) were characterized by ebb-dominated ripples of 15-20 cm wavelength and 4-5 cm amplitude. Although e b b current velocity and ripple size decreased in higher intertidal areas (+ 0.6 m), tracer experiments indicated that the depth of tidal disturbance in the sediment (0-3 cm) was not significantly different between low and high intertidal zones. Calculation of critical Froude numbers from laboratory flume experiments revealed that ripple migration occurred for some portion of ebb flow at all intertidal levels. The number of burrowing crustaceans was significantly greater in ripple crests than troughs along a transect in the lower intertidal, but not within a small sampling area at the same tidal level. Fauna1 d~stribution in bedforms was apparently related to active preference rather than passive hydrodynam~c sorting. Azoic sand placed in the intertidal zone was colonized rapidly by adult crustaceans (mostly haustoriid amphipods) settling from the water column. Acanthohaustorius millsi, a shallow sediment dweller, appeared after a single tidal day. In contrast, Pseudohaustorius caroliniensis, a deeper-living haustoriid usually not subjected to tidal disturbance, did not colonize until after 23 tidal days. These experiments indicated that azoic sediment would have attained the crustacean density of surrounding sand in approximately one month. It is suggested that the suspension of macrofauna above high-energy bottoms and subsequent removal by predators may be an important link in benthic-pelag~c coupling.