Tidal movement of sandy beach macrofauna

Abstract

This paper investigates possible changes in the organisation of the intertidal macrofauna community of Arrawarra Beach, NSW, over a range of tidal heights. The beach was divided into seven levels at low tide and 10 core samples for fauna were taken at each level during both high and low tide and at two evenly spaced tidal stages in between. For each tidal stage the distribution of the macrofauna across the shore was investigated for the existence of sub- communities across the tidal gradient using cluster analysis. This analysis failed to demonstrate a consistent “zonation” across the tidal cycle, although three sub-communities or assemblages were apparent high tide and the sample time before it. Movement of separate species populations was investigated over the tidal cycle using chi-squared analysis and an associated pseudo-probability test. Only one species (the polychaete Arabella iricolor iricolor) showed a significant change in distribution across the shore with time; however, small population numbers for many of the species may have confounded the concept of the potential movement with water level of sandy beach macrofauna as: i) a series of subcommunities; and ii) individual species. It is concluded that beach macrofaunal communities are organised as a seriation of species across the shore rather than in distinct “zones”.