Role of cyst germination in the bloom initiation of harmful algal species in
Korean waters
Myung-Soo Han
Dept of Life Science, Hanyang University, Seoul 133-791, Korea; [email protected]
Abstract
To clarify the role of cyst germination in the bloom initiation of harmful algal species, isolation and biweekly
or monthly germination experiments on single cysts were carried out with four harmful algal species.
Germination maxima of Alexandrium tamarense were observed in winter, but little or no germination
occurred in summer. In Scrippsiella trochoidea, mass encystments were detected in the water column in July
and August when the vegetative population flourished. The vegetative population of Nostocales flourished
from August to November; however, the most active akinete germination occurred from the end of March to
early April. In Peridinium bipes, cysts collected at higher temperatures germinated more quickly than those
seeded at lower temperatures, while cysts collected in fall and early winter had a higher excystment rate than
those from spring or summer. The types of germination patterns observed indicate a temporal discrepancy
between the peak of germination success and the bloom of the vegetative population. Active germination
therefore is not likely to be a direct trigger for HAB blooms.
Introduction
favorable conditions return, akinetes germinate to
A number of phytoplankton species produce a
produce trichomes (Hori et al. 2002; van Dok &
dormant resting stage in their life histories that
Hart 1996), which act as inocula for new blooms
allows survival under adverse environmental
(Hori et al. 2002; Kravchuk et al. 2002; van Dok &
conditions. Dinoflagellate resting cysts sink to the
Hart 1996). Cysts including akinetes undoubtedly
bottom
are
play an important role as the seed of the vegetative
unsuitable for growth (Prakash 1967; Wall 1971).
population of phytoplankton (Anderson & Wall
The cyst population can provide an inoculum for a
1978; Hansson 1996). Sometimes, however, bloom
new bloom after a dormancy period (Kremp &
initiation does not result as a direct consequence of
Heiskanen
of
in situ germination of cysts. (Ishkawa & Taniguchi
Nostocales, including the noxious bloom-forming
1996, 1997). Therefore, the relationship between
species Anabaena and Aphanizomenon, form a
algal bloom formation and cyst germination rates
thick-walled reproductive structure termed akinete
remains unclear. However, it is important to
which may serve as a dormant cell under adverse
identify the effect of encystment and excystment on
conditions (Baker & Bellifemine 2000). When
algal blooming initiation. In this study, we focused
when
environmental
1999).
Certain
conditions
cyanobacteria
ICHA14 Conference Proceedings Crete 2010
on
the
seasonal
relationship
between
the
vegetative population of Nostocales was observed
development of vegetative populations and cyst
germination modes.
Material and Methods
Sampling sites were in a coastal area (Masan and
Youngil Bay) and inland lake (Juam Reservoir and
Seokchon Pond) in South Korea. Vegetative cell
and cyst abundance were analyzed by optical
microscope (Axioplan, Zeiss, Germany). The
excystment rates of Alexandrium, Scrippsiella,
Peridinium and Nostocales such as Anabaena and
Aphanizomenon were measured by cyst germination
experiments. Isolated cysts were inoculated one by
one (using a microcapillary) into individual wells of
a 96-well tissue culture plate (Falcon, USA)
containing filtered water. Cysts were incubated at
water temperatures similar to those of the sampling
–2
bottom layer, under 12–30 µmol photons m
–1
s
light with a 12 h light: 12 h dark cycle.
Fig. 1. Seasonal changes of excystment (%) and
vegetative cell numbers of (a) Alexandrium
tamarense (Kim et al. 2002), (b) Scrippsiella
trochoidea (Kim & Han 2000)
Results and Discussion
Alexandrium
in November after 7 months of active germination.
tamarense peaked in spring, but germination
Most active germination was observed from the end
success was not higher. Germination maxima
of March to early April; however,the vegetative
(80–90%) were observed during winter when A.
cells were extremely difficult to detect in the water
The
vegetative
population
almost
column (Fig. 2a). In the excystment of Peridinium
undetectable in the water column (Fig. 1a). Similar
bipes, cysts obtained from samples collected at
germination results for A. tamarense were observed
higher temperatures (>15°C) germinated more
in Hiroshima Bay (Itakura & Yamaguchi 2001). In
quickly than those seeded at lower temperatures,
Scrippsiella trochoidea, the vegetative population
while cysts collected in fall and early winter had
peaked in summer; however the germination ratio
higher excystment than those collected in spring
was much lower in the bloom season. Active
and summer, suggesting that cysts deposited at
germination was observed in autumn after 3–4
higher temperatures may act as a seed population
months of blooming and the vegetative population
for winter blooms (Fig. 2b).
tamarense
vegetative
cells
of
were
decreased dramatically (Fig. 1b). The highest
ICHA14 Conference Proceedings Crete 2010
References
Anderson, D.M. & Wall, D. (1978). Journal of
Phycology 14(2): 224-234.
Baker,
P.D.
&
Bellifemine,
D.
(2000).
Hydrobiologia 427: 65-73.
Hallegraeff, G.M., Anderson, D.M. & Cembella,
A.D. (1995). In: Manual on Harmful Marine
Microalgae, vol. 33,IOC-UNESCO,Paris,p. 228.
Hansson,
L.A.
(1996).
Limnology
and
Oceanography 41: 1312-1323.
Hori, K., et al. (2002). Biochemical Engineering
Jounal 10: 217-225.
Ishikawa, A. & Taniguchi, A. (1996). Marine
Ecology Progress Series 140: 169-178.
Ishikawa, A. & Taniguchi , A. (1997). Journal of
Plankton Research 19: 1783-1791.
Itakura, S., Yamaguchi, M. (2001). Phycologia 40:
Fig. 2. Seasonal changes of excystment (%) and
vegetative cell numbers of (a) Nostocales (Kim et
al. 2005), (b) Peridinium bipes (Kim et al. 2007)
263–267.
Kim Y.-O. & Han, M.-S. (2000). Marine Ecology
Progress Series 204: 111-118.
Kim, B.H., Lee, W.S., Kim, Y.-O., Lee H.-O. & Han,
In Korean waters, some HAB species have shown a
M.-S. (2005). Archiv für Hydrobiologie 163(1):
temporal
49-63.
discrepancy
between
the
peak
of
germination and the bloom of the vegetative
Kim, B.-H., Park, M.-H., Hwang, S.-J. & Han, M.-S.
population, meaning germination occurs very early
(2007). Aquatic Microbial Ecology 47: 213-221.
and not immediately prior to the vegetative bloom.
Kim, Y.-O., Park, M.-H. & Han, M.-S. (2002).
These results suggest that active germination does
Aquatic Microbial Ecology 29: 279-286.
not trigger a direct increase in to vegetative HAB
Kravchuk, E.S et al. (2002). Doklady Biological
population.
Sciences 384: 233-234.
In
conclusion,
cyst-forming
phytoplankton species possess their own seasonality
Kremp, A. & Heiskanen, A.S. (1999). Marine
in diverse germination modes as a survival strategy.
Biology 134: 771-777.
Li, R., Watanabe, M. & Watanabe, M.M. (1997).
Acknowledgement
Journal of Phycology 33: 576-584.
We thank Drs. Y.-O. Kim, B.-H. Kim, and M.-H.
Prakash, A. (1967). Journal of the Fisheries
Park for experimental assistance and comments
Research Board of Canada. 24: 1589-1606.
This work was supported by the research fund of
Van Dok, W. & Hart, B.T. (1996). Journal of
IBENT, HYU(HYU-2010) of Hanyang University.
ICHA14 Conference Proceedings Crete 2010
Phycology 32: 557-565.