Building on an earlier study of global trends in sandy beach macrofauna communities, based on published surveys of 161 beaches, we examine trends in biological factors, especially mean individual body size and community density. Mean individual body size decreases across the gradient from reflective to dissipative beaches, although this decrease cannot be explained by any single factor. Density increases across this gradient so that dissipative beaches support densities of macrofauna orders of magnitude above those recorded on reflective beaches, implying that the potential for competition and other biological interactions is much greater in dissipative systems. Some latitudinal variation occurs in mean individual body size, but there are minimal latitudinal effects on density. Progressing from reflective to dissipative beaches, species richness increases much faster than predicted by the usual species area relationship, indicating that changes in the nature of the beach over this gradient, rather than simple area effects, enable many more species to colonise dissipative beaches. We concluded that the change in macrofauna communities across this gradient of beach types is not simply a response to increasing area (or beach width), but rather that an increasingly benign environment allows more species, greater densities, and more small and delicate forms to occur on dissipative beaches.