| dc.description.abstract |
Phaeocystis globosa is a marine phytoplankton species that forms deleterious
blooms in temperate and tropical waters. In some locations, “giant” colonies
form, although the controls on its size are unknown. During a “giant” colony
bloom, measurements were completed to characterize photosynthesis–irradiance relationships, nitrogen uptake kinetics, and nitrogen–irradiance relationships of P. globosa colonies to understand its growth characteristics and
their relationship to colony size. The photosynthetic capacity (Fv/Fm) varied
from 0.65 to 0.68 among colony sizes ranging from 3.0 to 11.0mm, indicating that all colonial cells were physiologically robust. The maximum chl aspecific photosynthetic rates (Pmax B ) ranged from 0.89 to 1.92μg C · μg−1 chl
· h−1, were maximal in the mid-sized colonies (5.5–6.5mm) and decreased
with size. The relatively low Pmax B values may be related to the high cellular
chl a of colonial cells and their acclimation to in situ irradiance. Nitrate V
max
and KS values were greater than those of ammonium, although N affinity was
greater for ammonium. No differences in light-limited rates in either nitrate or
ammonium uptake among colony sizes were observed, and no dark uptake
occurred. Both ammonium and nitrate uptake showed a saturation response
as a function of irradiance. While the driving forces for the formation of giant
colonies remain unknown, their impacts on coastal systems are substantial
and a further assessment of their growth is warranted |
vi,en |