Program and Abstracts(PDF)

Poster presentation 10
COMMUNITY STRUCTURE, SEASONAL CHANGES AND
TEMPERATURE TOLERANCE OF EDIBLE SEAWEED, SARGASSUM
FUSIFORME (FUCALES), AT THE BOUNDARY ZONE BETWEEN
TEMPERATE AND SUBTROPICAL REGION OF JAPAN, IN RELATION
TO CLIMATE CHANGES
Yuhei Amano 1 , Yutaro Tsuchiya 1 , Gregory N. Nishihara 2 , and Ryuta Terada 1 *
1
Department of Fisheries, Faculty of Fisheries, Kagoshima University,
Shimoarata, Kagoshima 890-0056, Japan
2 Institude for East China Sea Research, Nagasaki University, Taira, Nagasaki
851-2213, Japan
*
Email: terada at fish.kagoshima-u.ac.jp
The edible macro alga, Sargassum fusiforme (Fucales), is known as an important
local fisheries resource in Kyushu and Okinawa Is., Japan. However, there is
concern that this resource is decreasing as a result of climate and other
environmental changes. Furthermore, knowledge of its ecological and
physiological characteristics is required to establish the consistent cultivation of
this seaweed in this region. The focus of this study was to reveal the phenology
and temperature tolerance of S. fusiforme in Kagoshima and Okinawa Prefectures,
where the community is close to its southern distributional limit.
A phenological study was conducted by skin diving at four sites around
Nagashima Is. (Sasue, Karakuma, Shiomi and Shoura) and at a site at Sakurajima
Island, which are both in Kagoshima Prefecture, from April 2009 through June
2010. Population density, maturation, length and weight were recorded, as well as
appropriate environmental factors (e.g., temperature, salinity, dissolved
inorganic nitrogen and phosphate). A physiological study, which examined
photosynthetic activity at various temperatures was conducted using an
Imaging-PAM Fluorometer(Heinz Walz GmbH)and Dissolved Oxygen meter
(YSI Model 58). Materials were collected from the sites in Kagoshima as well
from Okinawa Is. (i.e., Uken Beach). After collection, materials were cultured
with aeration in an aquaculture tank within a few days, at temperatures similar to
those during the collection date, and were prepared for the photosynthesis
experiments.
Dry weight and length of S. fusiforme increased in spring at each site, and showed
a peak around June. Furthermore, released egg and germlings were observed on
the receptacles in June. It is relevant to note that local fisherman harvested S.
fusiforme in May, suggesting that harvesting occurs before maturation. After
maturation, plants including holdfasts disappeared from the substrata by
September. Young shoots were confirmed in around October. According to
reports from other areas of Japan, holdfasts of this species appear to be able to
survive over the summer season, and maintain a perennial community for up to a
few years. However, our result suggests that this species in Kagoshima generally
cannot survive over the summer, and can be regarded as an annual community.
Net photosynthetic rate was highest ˚C. at 24 The relative Electron Transport Rate
(ETR) of the Photosystem II (water/plastoquinone oxido-reductase) was highest
as 30˚C, and quickly decreased at higher temperatures, suggesting that projected
increases in summer seawater temperature might influence their community
structure and the availability of this resource.
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