| dc.description | This thesis examines the biological and physical processes influencing the structure and dynamics of mussel (Mytilus trossulus, M. edulis ) assemblages in tidepools and on the surrounding emergent rock on a wave-exposed rocky shore near Halifax, Nova Scotia, Canada. Over 17 mo, more than 96% of mussels colonizing the natural substratum were too large to be settling larvae, indicating the importance of post-settlement dispersal of mussels. Patterns of colonization after 5--16 mo reflected patterns measured at sampling intervals of 2--7 d, suggesting that spatial variation in initial colonization is important in determining the abundance and distribution of mussels on this shore. I examined the relative roles of supply of colonists and substratum type in determining colonization patterns of mussels by comparing colonization rates on artificial collectors and natural substrata. Patterns of abundance and size distribution of mussel colonists differed markedly between artificial collectors and natural substrata. Colonization rate on natural substrata was related to a suite of biological (macroalgal and barnacle cover) and physical factors (water flux, tidal height, flushing time). I examined the effects of predation by the whelk Nucella lapillus on established mussel assemblages by manipulating the densities of whelk recruits and post-recruits. Reduction of the density of whelk post-recruits influenced the percentage cover and size distribution of mussels and had a greater effect on emergent rock than in tidepools, reflecting differences in density of whelk post-recruits between habitats. I could not detect an effect of whelk recruits on mussel cover or size distribution. I experimentally investigated the influence of rates of recruitment, immigration, predatory and non-predatory mortality, and growth of individuals by transplanting artificially constructed mussel patches to tidepools and emergent rock. In addition, I monitored the movement of tagged mussels and estimated the probabilities of wave dislodgment of mussels from measurements of water velocity and attachment strength of mussels. The structure and dynamics of mussel patches both in tidepools and on emergent rock were influenced by all of these processes. However, these experiments indicated that physical processes (wave dislodgment) were more important than biological processes (predation) in determining the structure and dynamics of mussel assemblages on this shore. The results of this thesis indicate that patterns of distribution and abundance of mussels on this shore develop slowly due to the slow growth rate of individuals. I conclude that dispersal and redistribution of juvenile and adult mussels by wave disturbance are very important in colonization by mussels and in the dynamics of established mussel assemblages. | en_US |
