A. Kremp et Dm. Anderson, Factors regulating germination of resting cysts of the spring bloom dinoflagellate Scrippsiella hangoei from the northern Baltic Sea, J PLANK RES, 22(7), 2000, pp. 1311-1327
The role of cyst germination as a factor in bloom initiation was investigat
ed for the dinoflagellate Scrippsiella hangoei (Schiller) Larsen from the n
orthern Baltic Sea. This species blooms in very cold, often ice-covered wat
ers, and is responsible for a significant fraction of the production in tha
t region. Dormancy, temperature, oxygen and light were studied as factors p
otentially controlling the germination of S. hangoei resting cysts. Laborat
ory-stored and field-collected cysts began to germinate in December followi
ng a mandatory dormancy period lasting 6 months. Germination after this mat
uration interval was maximal when temperatures were within a 0-9 degrees C
'window'. Mandatory dormancy is therefore the primary factor regulating the
timing of germination in this species, as temperatures in the natural envi
ronment normally fall within this range at the time when S. hangoei cysts d
eposited the preceding year have matured. Non-optimal temperatures, darknes
s and low oxygen conditions all maintain a state of quiescence in the cysts
. Cysts could germinate in darkness, but the rate of excystment was signifi
cantly higher in the light. Likewise, excystment was completely inhibited i
n anoxic conditions and was reduced under severe hypoxia, with normal germi
nation under moderate hypoxic concentrations. Temporary exposure to high su
lfide concentrations permanently reduced germination potential, indicating
that S. hangoei cysts have low resistance to oxygen deficiency. Prolonged p
eriods of anoxia at the sediment surface, as frequently occurs in the study
area, might reduce the size of the viable cyst pool and thus, alter the ma
gnitude of the inoculum for S. hangoei bloom initiation. Together, these in
ternal and external regulatory factors play important roles in the bloom dy
namics of this important dinoflagellate.