Variations in invertebrate densities within the Severn Estuary have been examined on four shores over a period of two years. Variability due to seasonal changes was combined with a patchy distribution of some species, while others showed consistent densities at the same tidal level and at different sampling times. Some species showed more consistent densities in winter than in summer. Biological interactions, varying periods of spawning and recruitment and beach instability are thought to be three of the major factors influencing distribution. No marked community changes such as seen in some sublittoral areas have been found.
