8TH ASIAN PACIFIC PHYCOLOGICAL FORUM
The hormesis effects of low-dose
Co gamma irradiation
on high-temperature tolerance in cultivated Sargassum
horneri (Fucales, Phaeophyceae)
Received: 3 February 2018 /Revised and accepted: 15 May 2018
Springer Science+Business Media B.V., part of Springer Nature 2018
Radiation hormesis is a phenomenon in which low doses of ionizing radiation can have stimulatory effects on biological systems.
The temperate brown alga Sargassum horneri was the subject of this study on the hormetic effects of low-dose
radiation on macroalgae incubated in vitro at high temperatures. Sargassum horneri embryos were irradiated with 15, 20, and
Co radiation and then incubated in vitro at 18, 21, 24, 27, and 30 °C. The same radiation treatment was also applied to S.
horneri embryos grown in situ in outdoor mass cultivation. Non-irradiated in vitro control cultures had optimal growth at 21 °C,
but irradiated cultures had optimal growth at 27 °C and growth was significantly enhanced by 32% compared to the control
cultures at 21 °C. In contrast, in situ cultures of S. horneri in outdoor 10-ton seawater tanks showed that irradiated thalli had less
total biomass as compared to non-irradiated control thalli. While low doses of gamma radiation may induce high-temperature
tolerance resulting in better growth rates under the highly controlled in vitro culture conditions, these effects were not clearly
observed in the in situ outdoor mass-cultivation.
Many scientific studies have been conducted on the large,
temperate brown macroalga Sargassum horneri, which has a
widespread distribution along the coasts of China, Korea, and
Japan, and which is of interest as a biomedical source of
fucoidans and other bioactive compounds (Hoshino et al.
1998; Vo and Kim 2013), as well as for its suitability as a
fast-growing species for the construction of artificial seaweed
beds for habitat restoration (Choi et al. 2008;Pangetal.2009).
Free-floating populations of this species have also been doc-
umented in the East China Sea (Komatsu et al. 2009) and
floating masses of S. horneri invade the shores of Northern
Taiwan each spring (Komatsu et al. 2014,personal
observation). However, despite the fact that the floating S.
horneri arriving on the shores of Taiwan bear mature recepta-
cles and are reproductively viable, there are no persistent pop-
ulations of this temperate species in subtropical Taiwan
(personal observation, Lin et al. 2017). Komatsu et al.
(2014) showed that the upper temperature limit for the natural
range of S. horneri is 28 °C; therefore, high summertime sea-
water temperatures in Taiwan are likely a significant factor in
preventing S. horneri from establishing persistent local popu-
lations. However, the species is of interest for potential culti-
vation in Taiwan due to its economic utility, rapid growth rate,
and the large quantity of S. horneri biomass that enter the
waters of northern Taiwan. Therefore, development of
methods to allow S. horneri to tolerate higher temperatures
or to survive the summer months through other means is a
necessary prerequisite for its successful cultivation in Taiwan.
BHormesis^ is a term first introduced into scientific litera-
ture by Southam and Ehrllich (1943), used to describe a pos-
itive effect resulting from the application of a low dose of any
agent to a given system that would, at higher doses, be toxic to
that system. Radiation hormesis therefore is the stimulatory
effect produced in biological systems by low doses of ionizing
* Roger Huang
Department of Aquaculture, National Taiwan Ocean University,
Journal of Applied Phycology