Understanding the ecology of assemblages requires investigation into patterns of distribution and abundances of organisms and the physical and biological processes that structure these patterns. This thesis uses intertidal and subtidal turfing algal assemblages as habitats in which to test hypotheses about the types of ecological processes that can structure patterns of distribution and abundances of algae and the spatial and temporal generality of these processes.

First, patterns of composition, distributions and abundances of species comprising turf were examined at a number of spatial and temporal scales. Identification of the scales at which assemblages of organisms vary is extremely important since the processes that structure assemblages operate at these scales. The most striking pattern was the great small scale spatial variability in the composition, distributions and abundances of species in intertidal and subtidal turfing algal assemblages. Moreover, this small scale spatial variability was temporally consistent. That is, at each of eight times of sampling the greatest proportion of variability in assemblages was explained at the scale of tens of centimetres. Small scale variability, therefore, appears to be an important feature of turfing algal assemblages. It suggests that processes operating on small spatial and temporal scales have more effect on patterns of variability of turfs than do processes occurring at larger scales.

Patterns of recruitment were examined to evaluate the model that processes occurring pre-recruitment are responsible for the great small scale spatial variability in turfs. The hypothesis that the composition, distributions and abundances of species of recruits would vary on similarly small spatial scales as found in established turfs was rejected. Assemblages of recruits differed only between intertidal and subtidal habitats. Similarly, abundances of individual taxa of recruits either varied between habitats, or not at any spatial scale. Thus, while recruitment may contribute to variability in turfing algal assemblages, it cannot fully explain it.

It is likely that post-recruitment processes such as disturbances, competition and grazing act on patterns produced by recruitment, increasing variability to levels similar to that found in established turfs. Three such precesses were studied and their potential for influencing patterns of variability in turf was evaluated. These precesses were disturbance due to the effect of a canopy of Sargassum on the underlying turf, effects of ephemeral algae on abundances and sizes of coralline algal recruits and effects of grazing my microinvertebrates living within the turf.

Foremost, this thesis found that small scale spatial and temporal variability can be an important component of assemblages and should not be considered as "noise". Although patterns occurring at any scale warrant investigation, perhaps those that explain the greatest proportion of variability should be the focus of attention. Second is the issue of scale and its consequences for the way assemblages are interpreted. The perceived effects of various processes and their contribution to the overall variability of assemblages can depend on the spatial scales at which they are examined. These two issues emphasise the need for experiments to include replication on spatial scales smaller than the one at which initial observations were made. Finally, this thesis shows that care must be taken in making generalizations about the types of processes that structure patterns of distribution and abundances of assemblages. Small scale variability can be a conspicuous and important component of assemblages that warrants investigation.