Abstract
The small-scale distributional pattern of a subtidal macroalga, Xiphophora gladiata (Labillardiere) Montagne ex Kjellman, at two sites on the coast of Tasmania, Australia, was examined using underwater survey to millimetre accuracy. Analysis by Morisita's index of dispersion, Iδ, showed clumping at scales of 100, 200 and (at one site) 400 mm, only the last of which could readily be explained by variations in the physical environment. It is suggested that formation of the smaller clumps is caused by biotic interactions.