| Summary: | 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.
|
|---|
