STRUCTURE AND DYNAMICS OF MUSSEL PATCHES IN TIDEPOOLS ON A ROCKY SHORE IN NOVA-SCOTIA, CANADA

The distribution, size structure, and dynamics of mussel (Mytilus trossulus, M. edulis) patches in tidepools were studied on an exposed rocky shore near Halifax, Nova Scotia, Canada. The mussel patches were dynamic, frequently coalescing with one another or disappearing, but mean change in patch area did not vary significantly among seasons or years. Recolonization of areas from which patches were removed occurred slowly, usually by recruitment. Both established and recolonized patches were generally associated with macroalgae. Mussel patches were primarily composed of individuals < 5 mm in shell length (SL) which appeared to be very slow growing. The percentage of new recruits in a patch varied among pools and between years. Predation by the dogwhelk Nucella lapillus was a major cause of mussel mortality. The size distributions of live and dead mussels in the patches differed significantly: the frequency of dead mussels < 5 mm SL was less than that of live mussels, and the frequency of dead mussels 5 to 10 mm SL was greater than that of live mussels. Dead mussels (not killed by whelks) were more frequent in October 1992 than in June 1992, while no clear temporal patterns were found in the frequency of mussels killed by whelks.