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Population ecology of the clonal red alga Mazzaella Cornucopiae from Barkley Sound, Canada Scrosati, Ricardo Augusto


This Thesis examines aspects of the population ecology of clonal algae using as a model Mazzaella cornucopiae (Rhodophyta, Gigartinaceae), an abundant species in the high intertidal zone of Prasiola Point, Barkley Sound, British Columbia, Canada. Research focused on investigating the kind of interactions that occur among fronds during growth, discussing its significance for M. cornucopiae in light of what is known for the better studied clonal and non-clonal terrestrial plants. M. cornucopiae develops from holdfasts as a turf, which results in both costs and benefits for thalli, and they are analyzed in relation to the characteristics of its habitat. Additionally, the role of holdfasts and spores for population maintenance, recolonization after disturbance, and frond regeneration after harvesting was also studied. During the growth season for Mazzaella cornucopiae, between late winter and summer, frond density and stand biomass increases simultaneously, hence no self-thinning occurred among fronds as it occurs among individual thalli of actively growing, non-clonal algae. I introduced the use of randomization tests to solve the lack of randomness i n data collection. The decrease of frond size hierarchy observed during the growth season indicates that the growth increment of small fronds per time unit was higher than that of large fronds (symmetric competition model). A n increase of frond crowding, as it occurs during the growth season, involves a cost expressed as reduced net photosynthetic rates; however, frond crowding is beneficial overall. Laboratory and field experiments indicated that high frond densities protect fronds from high desiccation and irradiance and the associated bleaching and tissue loss that spring and summer daytime lowtides bring. Additionally, frond crowding confers protection against the negative effects of wave action on frond survival. Holdfasts are fundamental for population maintenance. They are mostly perennial and constitute the main source of the annual production of fronds; the annual contribution of spores is very low. Finally, experimental pruning of fronds showed that, if commercial harvesting of this species is ever done, a spring collection of all frond biomass, without damaging holdfasts, gives the highest possible biomass yield while allowing frond biomass to be annually renewed.

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