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Demographic patterns and processes in Mazzaella splendens (Gigartinales, Rhodophyta) at Second Beach, Barkley Sound Dyck, Leonard James

Abstract

In this research I examined the demography of Mazzaella splendens (Setchell et Gardener) Fredericq at Second Beach, Barkley Sound. A set of demographic patterns consistent with all previous studies of M. splendens was hypothesized and tested in a new location to determine the generality of these patterns. To that end seasonal changes in density of genets and modules of gametophytes vs. tetrasporophytes were measured approximately monthly over three years. Survival, new blade production, blade size and reproduction were also measured to determine the demographic mechanisms underlying changes in population density. Patterns consistent with all previous studies of Mazzaella splendens are: 1) change from high summer to low winter population density in wave-sheltered areas with 2) a decreasing magnitude in this fluctuation as wave exposure increases and 3) a change from summer haploid to diploid dominance as wave exposure increases. These patterns may be common throughout the species range. Seasonal alternation in phase dominance in wave-sheltered areas, consistent with all previous studies, did not occur at Second Beach. Differential survival was not present between life history phases, but there was evidence of differential production of new blades. These results do not support a previous hypothesis that the alternate isomorphic life history phases of M. splendens are diverging ecologically along r and K lines. In a wave-sheltered area, 85 - 90% of modules were smaller than the size for which previous studies had predicted differential survival between phases, but even within the appropriate size class differential survival was absent. In a wave-exposed area, haploid modules lost more tissue than diploid modules, apparently reconfiguring surface area in response to wave force. Seasonally restricted reproduction, previously observed in other populations, was not present at Second Beach. Reproduction did not negatively affect survival. Evidence for slowing of growth after the onset of reproduction, and a time requirement before onset of reproduction, were mixed.

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