Aquaculture Sci.
60(3),377−388(2012)
Effect of Temperature and Light on the Photosynthetic
Performance of Two Edible Seaweeds: Meristotheca coacta
Okamura and Meristotheca papulosa
J. Agardh (Solieriaceae, Rhodophyta)
LIDEMAN1, Gregory N. NISHIHARA2, Tadahide NORO3 and Ryuta TERADA3,*
Abstract: The photosynthetic performance of two species of Meristotheca (Solieriaceae, Rhodophyta),
M. coacta and M. papulosa, was investigated under a variety of temperature and light conditions
to derive basic information regarding their physiology. A pulse amplitude modulated-chlorophyll
fluorometer (Imaging-PAM) was used to generate rapid light curves (RLCs) to provide the relative
electron transport rates (rETR) over 21 levels of photosynthetic active radiation (PAR), ranging
from 0 to 1,078μmol photons m-2 s-1 at 14 temperatures (i.e., from 8 to 34℃). The initial slope (α),
photoinhibition (β) and coefficient (γ) was calculated by fitting the RLCs to a nonlinear model of
the form rETR =γ(1-exp(-α・PAR/γ)) (exp(-β・ PAR/γ)) using a two-level hierarchical Bayesian
model. Both species required temperatures ranging from 18 to 28℃ to maintain optimal photosynthetic activity, as revealed by the estimated model parameters. The optimal PAR (PARopt) increased
with increasing temperature. Meristotheca coacta and M. papulosa can be considered well-adapted
to the current natural light and temperature conditions of southern Kyushu, Japan. Finding in this
study should be useful to the design and manage mariculture programs to conserve the natural
resources.
Key words: Meristotheca coacta; Meristotheca papulosa; Photosynthesis; Temperature
The genus Meristotheca (Solieriaceae,
Rhodophyta) is known to be widely distributed
in the Indo-Pacific area, and can often be found
along the shores of southern Japan (Yoshida
1998; Faye et al. 2005, 2007). In Japan, three
species of Meristotheca, M. coacta Okamura
(Fig. 1a), M. imbricata Faye et Masuda and M.
papulosa (Montagne) J. Agardh (Fig. 1b), can
be observed (Yoshida and Yoshinaga 2010),
and which M. imbricata is a newly described
endemic species to this region (Faye et al. 2008).
Meristotheca papulosa is one of the popular
edible seaweeds and is used as the ingredient
for salads in Japan, especially in the prefectures
of Kochi, Kumamoto, Miyazaki and Kagoshima
(Ohno 2004; Shinmura and Tanaka 2008);
therefore, for the inhabitants of these regions,
M. papulosa is an important food resource.
Additionally, carrageenan has been isolated
from some species of Meristotheca, such as
M. senegalensis (Fostier et al. 1992) and M.
procumbens (Prasad et al. 2005), and can be
considered a viable source of this valuable bioproduct.
Nevertheless, through intense harvesting and
other anthropogenic activity, concern has been
Received 27 January 2012; Accepted 12 April 2012.
1 The United Graduate School of Agricultural Sciences, Kagoshima University, Korimoto 1‑21‑24, Kagoshima 890‑8580,
Japan.
2 Institute for East China Sea Research, Nagasaki University, Taira-machi 1557‑7, Nagasaki 851‑2213, Japan.
3 Faculty of Fisheries, Kagoshima University, Shimoarata 4‑50‑20, Kagoshima 890‑0056, Japan.
*Corresponding author: E-mail, terada@fish.kagoshima-u.ac.jp (R. Terada).
378
Lideman, G. N. Nishihara, T. Noro and R. Terada
Fig. 1. Meristotheca coacta (a) and M. papulosa (b) in
their natural habitat of Ushibuka (Amakusa-Shimojima Is.)
and Cape Sata, respectively.
expressed regarding the reduction in the abundance of M. papulosa, as well as other similar
species (e. g. Shinmura and Tanaka 2008). There
remains a strong belief that stocks will continue
to decline in the near future (Shinmura 2000;
Makurazaki and Ohsumi-misaki Fisherman’s
Union, Kagoshima Prefecture, unpublished data).
The importance of M. papulosa in Makurazaki
and Ohsumi-misaki, is reinforced by the amount
harvested from these areas, where 447,771 kg
of biomass, with a value of 331.7 million yen,
was harvested in 2000, and 302,860 kg, with
a value of 195.8 million yen, was harvested in
2006. Meristotheca coacta is also widely found
in the region, occurring simultaneously with
M. papulosa. Hence, M. coacta is often taken as
by-catch during M. papulosa harvests.
The intense harvesting steadily drives a
decline in standing stock, however, habitat loss
may also be contributing to this decline. Habitat
loss has often been linked with coastal pollution
and coastal construction; however in the 21st
century global climate change induced warming of coastal waters is also a possible factor.
Indeed, climate change is driving increases in
water temperature in many regions of the world
(Domingues et al. 2008; Herr and Galland 2009).
It is understood that changes in the geographic
distribution should be expected for many species of plant and animals, including marine
algae. Such shifts in distributions may lead to
economic losses for local communities. Changes
in water temperature of the East China Sea off
the coast of Kyushu Island, Japan, have been
recorded to have increased by 1.24±0.26℃ over
a period of 1900 to 2010 ( JMA 2011b). Changing
environmental conditions can be expected to
influence the harvest of these species.
Although there are a number of ecological and
physiological studies regarding Meristotheca, the
data presently available can only provide us with
limited insight regarding the physiology of these
macroalgae. Past research largely focuses on M.
papulosa, and has examined how photosynthetic
rates vary with depth by measuring changes
in dissolved oxygen concentration (Yokohama
1973; Murase et al. 1989), in addition to how
ultraviolet radiation influences their photobiology (Maegawa et al. 1993). The lack of physiological data regarding M. coacta, as well as M.
imbricata remains conspicuous.
In the past, studies on the photobiology of
M. papulosa have used manometric and electrochemical techniques (Yokohama 1973; Murase
et al. 1989; Maegawa et al. 1989, 1993; Lideman
et al. 2011). These studies provide results along
a coarse temperature gradient, and relatively
low intensities of irradiance. Nevertheless,
municipalities in Ehime Prefecture have initiated cultivation of these species; however,
commercial-scale operation remains elusive.
One of the reasons for this lack of progress can
be traced back to our limited understanding of
their physiology. In this paper, we apply a quick
and efficient technique, first developed to study
photosynthesis in intact plants (pulse amplitude
modulated (PAM)-chlorophyll fluorometry;
Photosynthesis of Two Meristotheca
Aldea et al. 2006; Ralph et al. 2006; Kuster et al.
2007; Tsuchiya et al. 2012). We use this technology to provide detailed insight regarding the
temperature response of Meristotheca, by using
M. coacta and M. papulosa as experimental
organisms, with the hope that this knowledge
will help to advance cultivation of these species.
Materials and Methods
Specimen collection and stock maintenance
Meristotheca coacta and M. papulosa are
widely distributed along the coast of southern
Kyushu Is., Japan. Approximately 15 cm of
fronds of the two species examined in this study
were collected from different shores of Kyushu
Island. Specimens of M. coacta were collected
by SCUBA at Ushibuka town of AmakusaShimojima Is., Kumamoto Prefecture (32˚11’N,
129˚58’E) and M. papulosa were collected at
379
Ohtomari village of Cape Sata, Kagoshima
Prefecture (31˚01’N, 130˚41’E) on 15 May 2010
(Fig. 2). Meristotheca coacta and M. papulosa
were collected at water depth ranging from
1 - 5 m. Collected algae were stored in 500 ml
plastic bottles with seawater and transported
to the laboratory in a cooler at about 20℃. The
specimens were maintained for 1 to 3 days
before examination at the Faculty of Fisheries,
Kagoshima University in an aquarium tank (2.0
×1.0×0.5 m3) containing seawater at salinity of 33 PSU, pH of 8.0, water temperature of
20℃, and under photosynthetic active radiation
(PAR) of 90μmol photons m-2 s-1 (14 : 10 hours
light : dark cycle).
Underwater temperature and PAR at the study sites
Underwater PAR was measured near the
study sites. Off the coast of Cape Sata (31˚30’
N, 130˚38’E), we took measurements from
12 : 30 and 13 : 00 on 2 July 2011 just below
the seawater surface (0 m), and at depths of
3 m, 5 m, 10 m, 20 m, 30 m, 40 m and 50 m
with light intensity data logger MDS-Mk-V/L
(S/N200457, JFE-Advantech, Japan). The measurement was carried out every one second for
one minute at the each depth. Underwater temperature was measured with light intensity by
CTD (T/S Nansei-maru, Faculty of Fisheries,
Kagoshima University). Additionally at Nagashima
Is. (32˚14’N, 130˚9’E, which is near AmakusaShimojima Is.), measurements were taken from
11 : 30 and 12 : 00 on 7 July 2010 just below the
seawater surface (0 m), and at 5 m, 10 m, 15 m,
20 m and 25 m depths by a PAR meter (LI-250
with spherical quantum sensor LI-193SA, Li-Cor,
USA). The measurement was carried out every
one second for thirty seconds at the each depth.
PAR measurements were used to determine
the extinction coefficient (K ) that fit the following equation (Beer-Lambert law) :
ID = I 0 ・ exp (-K ・ D)
(1)
where, ID is PAR at the some depth (D) in
meters, I0 is surface PAR coefficient, and K is
the extinction coefficient
Fig. 2. Map of Kyushu Is., Japan showing the study sites
of Meristotheca coacta and M. papulosa.
380
Lideman, G. N. Nishihara, T. Noro and R. Terada
Rapid light curves (RLCs)
Rapid light curves (RLCs) were generated
by running the standard algorithm of the pulse
amplitude modulated (PAM)-chlorophyll fluorometer (Imaging-PAM, Heinz Walz GmbH,
Germany) using an incremental sequence of
actinic illumination periods, with light intensities
increasing in 21 steps from 0 to 1,078μmol photons m-2 s-1 of PAR. Relative electron transport
rate (rETR) was calculated using the equation :
rETR = 0.5・Y・PAR・AF
(2)
where, Y is the effective quantum yield of PSII
(ФPSII = (F - Fm’ )/Fm’, F is the initial fluorescence, and Fm’ is maximum fluorescence), the
factor 0.5 assumes that half of the photons are
absorbed by PSII (Schreiber et al. 1995), and
AF is the fraction of incident light assumed to
be absorbed by the sample ( i.e., 0.84).
Temperature and light effect on photosynthesis
parameters
From each specimen, 2 cm long portions of
the thalli were placed in a multi-well chamber
(Falcon, USA) with sterilized seawater, allowing for 9 replicates for each species. Chamber
temperature was controlled by a block incubator BI-535A (Astec, Japan) by placing the wellplate on the aluminum block of the incubator.
Water temperature in the chamber wells were
measured with a thermocouple in order to confirm that the water reached the desired temperature setting. The relative electron transport
rates were determined by generating RLCs with
21 PAR levels over 20 minutes, for every 2℃
increment temperature ranging from 8 to 34℃,
hence once set RLC took 4 to 6 hours.
We modeled the rETR versus PAR to calculate the maximum rETR rate in the absence of
photoinhibition (γ), the initial slope (α) of the
photosynthesis - irradiance curve (P-I curve)
and the photo-inhibition coefficient (β) by fitting the RLCs to a nonlinear model modified
after Platt et al. (1980) :
α
β
rETR=γ・ 1- exp - γ・ PAR ・ exp -γ・ PAR
(3)
Based on these parameters, we can then
estimate the values of PARsat, which defines PAR
when rETR begins to saturate (Eq. 3) and PARopt,
which defines PAR when the rETR is at a maxima.
β
β
α
α
drETR
=αexp - γ PAR - γPAR -β 1-exp - γPAR exp - γ PAR
dPAR
(4)
Furthermore, by computing the derivative of
Eq. 3 with respect to PAR, and solving the equation
drETR
when dPAR = 0, the value of PAR at the rETR
maxima can be estimated from the first real root :
PARopt =
γ α
αln β+ 1
(5)
by substituting PARopt into Eq. 3, we arrive at
the value of rETR at the maxima (rETRmax) of
the P-I curve. Saturating PAR (PARsat) was calculated using the equation :
PARsat =
rETRmax
α
(6)
Statistical analysis
Statistical analyses were done using R (R
Development Core Team 2011) and OpenBUGS
(Thomas et al. 2006). To estimate the parameters
of the nonlinear model (Eq. 2, 3 and 4), a two-level
hierarchical Bayesian model was implemented
using OpenBUGs, because maximum-likelihood
and least-squares techniques did not converge
to a solution. Uniform priors were defined for
each hyperparameter in the model, and the
parameters were then allowed to sample from the
hyperparameter distributions. We ran 4 chains of
100,000 samples each, discarded the first half of
each chain and thinned the results to obtain 1,000
samples for each chain (i.e., 4,000 samples of the
posterior distribution). The relationship between
the estimated parameters and experimental
water temperature were also examined, using
Generalized Linear Models (GLM) assuming a
Gamma distribution for the model parameters
(θ) and a linear (e.g., PARopt and PARsat) or log
(e.g., α., β, γ, and rETRmax) link-function as
appropriate. Two models were used to examine
these relationships, a linear model, where θ〜
species + temperature + species×temperature
and a quadratic model, where θ〜 species +
temperature + species×temperature + temperature2 + species×temperature2.
381
Photosynthesis of Two Meristotheca
Results
Underwater temperature and PAR at the study sites
Meristotheca coacta and M. papulosa was
widely distributed along the coast of southern
Kyushu Is. including our study sites : Cape Sata,
Amakusa and Nagashima Is. Generally, both
species were growing on the rocky substrata at
depths between 3 to 30 m.
Underwater PAR measured offshore of Cape
Sata, at the depths of 0 m to 50 m ranged from
2,143 to 11μmol photons m-2 s-1 on 2 July 2011.
Near Nagashima Is., PAR at depths of 0 m to
25 m ranged from 248 to 10μmol photons m-2 s-1
on 7 July 2010 (Fig. 3), during the measurements,
we experienced fine clear skies at Cape Sata;
however, the skies were mostly cloudy at near
Nagashima Is.. The Beer-Lambert equation was
fitted to PAR measurements taken at the two
study sites using a linear regression on the logtransformed PAR and was determined to be :
Cape Sata :
I(D) = 1,717 e-0.11・D (R 2 = 0.986)
Nagashima : I(D) = 185e-0.12・D
(R 2 = 0.969)
where, the extinction coefficients (K) determined for waters near Cape Sata and Nagashima
Is. were 0.11 and 0.12, respectively. The coefficient of surface PAR for the Cape Sata and
Nagashima Is. models were 1,717μmol photons
m-2 s-1 and 185μmol photons m-2 s-1, respectively.
In general, maximum irradiance at the
coastal area at noon was around 2,000 to
2,200μmol photons m-2 s-1 during the study
period (April to August). Underwater PAR,
based on the parameters estimated at each location and assuming a surface irradiance of 2,000
(or 2,200)μmol photons m-2 s-1, respectively,
are provided in Table 1 for reference. At Cape
Sata, estimated maximum irradiance of the
habitat for the two species (ca. 3 - 30 m depth)
ranged from 1,451 (1,596) to 81 (89)μmol
photons m-2 s-1. For those of Nagashima Is.
PAR ranged from 1,395 (1,535) to 55 (66)μmol
photons m-2 s-1. It is relevant to note that water
temperature measured offshore of Cape Sata, at
the depths of 0 m to 50 m ranged from 24.9 to
18.2℃ on 2 July 2011 (Table 1).
Rapid light curves (RLCs)
Unlike typical photosynthesis - irradiance
curves that increase monotonically until reaching some asymptote, the rETR of these species
were hump-shaped and expressed clear photoinhibition at high PAR (Fig. 4). At any given
temperature and PAR, the rETR of M. coacta
tended to be higher than that of M. papulosa.
Table 1. Underwater temperature at Cape Sata measured
on 2 July 2011 and estimated-underwater PAR* at Cape
Sata and Nagashima Is. if the surface irradiance was 2,000
or 2,200μmol photon m-2 s-1
Temperature
(℃)
Depth
(m)
Cape Sata
3
5
10
20
25
30
40
50
24.9
24.1
23.1
21.2
20.1
19.4
18.4
18.2
*Extinction
Fig. 3. Underwater photosynthetic active radiation (PAR,
μmol photons m-2 s-1) in Cape Sata (12 : 30 to 13 : 00, 2 July
2011) and Nagashima Is. (11 : 30 to 12 : 00, 7 July 2010).
Estimated underwater PAR**
(μmol photon m-2 s-1)
Cape Sata
Nagashima
2,000
2,200
2,000
2,200
1,451
1,171
686
235
138
81
28
9
1,596
1,288
755
259
152
89
30
10
1,395
1,098
602
181
100
55
16
5
1,535
1,207
663
200
110
60
18
5
coefficient was determined by measured data
on 2 July 2011 (Sata) and 7 July 2010 (Nagashima).
-0.11*D ; Nagashima Island,
**Cape Sata, I
(D) = I (0) e
I(D) = I(0) e-0.12*D, I(D), PAR at the objective depth (m); I(0),
PAR at the surface; D, objective depth (m).
382
Lideman, G. N. Nishihara, T. Noro and R. Terada
By fitting Eq. 3 to the results using hierarchical
Bayesian methods, we were able to elucidate
the parameters of the model across all water
temperatures, as well as derive estimates of
PARsat, PARopt, and rETRmax. The parameters of
the model as well as the derived estimates were
then examined in detail using GLM (Fig. 5) to
elucidate their dependence on temperature.
Fig. 4. The rapid light curves as determined by the hierarchical Bayesian analysis of Meristotheca coacta and M.
papulosa determined over a temperature gradient of 8℃ (a),
10℃ (b), 12℃ (c), 14℃ (d), 16℃ (e), 18℃ ( f ), 20℃ (g),
22℃ (h), 24℃ ( i ), 26℃ ( j ), 28℃ (k), 30℃ ( l ), 32℃ (m),
34℃ (n). The solid and dash lines indicate the fitted model
for M. coacta and M. papulosa, respectively. rETR, relative
electron transport rate; PAR, photosynthetic active radiation.
Temperature dependence of the photosynthetic
model coefficients
The mean values of the maximum rETR in
the absence of photoinhibition (γ), ranged
from 14.0 to 47.0μmol e- m-2 s-1 for M. coacta
and 12.0 to 19.8μmol e- m-2 s-1 for M. papulosa
over the range of temperatures examined
and did not appear to be related to temperature (Fig. 5a). The log-link gamma GLM fit to
this data, revealed the insignificance of temperature×species interactions (F(1,24) = 0.0732,
P = 0.7891) and of temperature dependence
(F(1,26) = 1.6425, P = 0.2117). However, a species
effect was detected (F(1,26) = 55.1018, P < 0.0001),
indicating that that values for M. coacta were
significantly higher than that of M. papulosa.
There was an estimated 15.1μmol e- m-2 s-1 difference in the parameter estimates of the maximum rETR rates among these species.
The mean values of the initial slope (α) of
M. papulosa and M. coacta ranged from 0.023
to 0.093μmol e- (μmol photons)-1 and 0.065
to 0.156μmol e- (μmol photons)-1, respectively and were dome-shaped (Fig. 5b). Unlike
the GLM for the parameter γ, a quadratic
equation was fitted to α. Species effects were
significant in the model (F(1,26) = 209.3376,
P < 0.0001)), where α was greater for M. coacta.
The value of α also significantly varied with the
square of the temperature (F(1,24) = 144.8558,
P < 0.0001), which justifies the use of the quadratic model. For the quadratic case, the model
can then be used to provide estimates of the
maximum value of α and the temperature of
its occurrence. In this case, maximal values
occurred at 19.7℃ and 20.8℃ and were 0.148
μmol e- (μmol photons)-1 and 0.078μmol
e- (μmol photons)-1 for M. coacta and M.
papulosa, respectively.
Photosynthesis of Two Meristotheca
383
Fig. 5. The model parameters determined by the hierarchical Bayesian model express a variety of temperature dependence for both Meristotheca coacta (●) and M. papulosa (▲). (a) The maximum relative electron transport rates (rETR)
in absence of photoinhibition, γ, are independent of temperature. (b) The initial slope of rapid light curves, α, can be
described by a quadratic function of temperature. (c) The photoinhibition coefficient, β, can also be described by a quadratic function of temperature. (d) The maximum rETR that was observed when photosynthetic active radiation (PAR)
reaches its optimal value, rETRmax, can be described by a quadratic equation. (e) The PAR at which rETR rates begin to
saturate, PARsat, is a linear function of temperature. ( f ) The PAR at which maximum rETR was observed, PARopt , is a
linear function of temperature. The data are jittered about the experimental temperature to improve clarity and the bars
indicate the 95% credible interval.
The mean values of the photoinhibition coefficient (β) of these species ranged from 0.014
to 0.381μmol e- (μmol photons)-1 for M.
coacta and from 0.004 to 0.157μmol e- (μmol
photons)-1 for M. papulosa and were U-shaped
in nature (Fig. 5c). This parameter was also
analyzed using the quadratic GLM, where the
quadratic term was significant (F(1,24) = 19.7729,
P = 0.0002). No interactions were evident
(F(1,23) = 0.9393, P = 0.3430), but species was an
important factor in the model (F(1,26) = 37.8215,
P < 0.0001). A minima could be estimated
near 27.6℃ and 29.1℃ for M. coacta and M.
papulosa, respectively and were 0.041μmol e(μmol photons)-1 for M. coacta and 0.009μmol
e- (μmol photons)-1 for M. papulosa.
384
Lideman, G. N. Nishihara, T. Noro and R. Terada
The mean values of rETRmax could also be
examined using a quadratic model (Fig. 5d),
and these values increased from low temperatures and peaked near 25.5℃. Indeed,
the quadratic terms were significant (F(1,24) =
188.3459, P < 0.0001) as was the species effect
(F(1,26) = 25.2488, P < 0.0001). Interactions among
species and temperature was also significant
(F(1,23) = 8.9195, P = 0.0068). A more detailed
examination of the model indicated that rETRmax
peaked with a value of 13.3μmol e- m-2 s-1 at
26.0℃ for M. coacta and was 11.7μmol e- m-2 s-1
at 25.1℃ for M. papulosa.
Regarding the mean values for PARsat, which
indicates the value of PAR when rETR began
to saturate, they monotonically increased with
increasing temperature (Fig. 5e). Indeed,
temperature and species were significant factors in the differences determined for PARsat
(F(1,25) = 339.128, P < 0.0001 and F(1,26) = 80.949,
P < 0.0001) and there were significant interactions among temperature and species
(F(1,24) = 37.383, P < 0.0001). It is apparent that
the PAR needed to saturate rETR was more sensitive to temperature and greater in magnitude
for M. papulosa.
Similarly, the PAR where rETRmax was
observed (at PARopt) monotonically increased
with temperature (Fig. 5f ), with a significant
temperature effect (F(1,25) = 435.62, P < 0.0001)
and a significant species effect (F(1,26) = 112.09,
P < 0.0001). There were also significant interactions describing the relationship between species and temperature (F(1,24) = 56.66, P < 0.0001),
where PARopt for M. papuloa was generally
higher and more sensitive to temperature, compared to M. coacta.
Discussion
In our study, the initial slope (α) of M. papulosa
and M. coacta showed higher values at temperatures from 18 to 28℃ (Fig. 5b). Meanwhile, the
photoinhibition coefficient (β) of the two species decreased from low temperatures (Fig. 5c),
and rETRmax increased from low temperatures
to a peak between 25 to 26℃ (Fig. 5d). This
result suggests that the optimal temperature
of two species is most likely within the range
of 18 to 28℃, and corresponds well to an earlier study of M. papulosa that examined dissolved oxygen production and respiration rates
(Lideman et al. 2011), and are well within the
range of water temperatures observed in their
natural habitat.
More specifically, we can define a range of
temperatures that are optimal for the photosynthetic activity of these species based on
the model results. Let the optimal temperature
range for some parameters be defined as the
parameter (e.g., values of α, β, and rETRmax)
estimates that are at least 95% of the estimated
maximum or minimum parameter values. Hence,
for rETRmax, 95% of the maximum would be 12.6
μmol e- m-2 s-1 for M. coacta and 11.1μmol
e- m-2 s-1 for M. papulosa, which leads to temperature range of 22.9 - 29.1℃ and 22.7 - 27.4℃,
respectively. Similarly, for α the temperature
ranges can then be determined, which were
16.1 - 23.3℃ for M. coacta and 18.2 - 23.4℃ for
M. papulosa. In the case of β, we examine the
values that are at least 95% of the parameter
minima, therefore temperatures ranged from
24.8 - 30.3℃ for M. coacta and 26.3 - 31.8℃ for
M. papulosa. However, these estimates are for
individual parameters, therefore we must combine this information to produce a general estimate of optimal temperature range. Hence, let
the optimal temperature range be the range of
temperatures that are the union of the temperature ranges determined for each of the parameters. This reveals that the optimal temperature
range for M. coacta is 16.1 to 30.3℃ and for M.
papulosa, it is 18.2 to 31.8℃.
Regarding their response to PAR, we observed
inhibitory effects at high irradiances, based on
the RLC determined at each temperature and
for each species, adding much needed information to earlier studies, such as Lideman et al.
(2011), which only examined PAR < 600μmol
photons m-2 s-1. The initial slope (α) of M.
coacta was always higher than that of M. papulosa at each temperature condition examined
(Fig. 5b). However, the PARsat and PARopt for
the former were always lower than those of the
latter (Fig. 5f), suggesting that M. coacta can
Photosynthesis of Two Meristotheca
photosynthesize and survive under lower levels
of PAR. Perhaps this difference is related to
their habitats, because the prostrated appearance of M. coacta, found growing on the rocks,
is sometimes shaded by M. papulosa and other
organisms (Fig. 1).
The experiments on M. coacta and M. papulosa demonstrated that optimal temperatures
were typically of values observed in the field,
where temperatures were 20 to 25℃. This was
expected given that photosynthetic performance is one of the most important processes
that drives the life-cycle of photosynthetic
organisms. The close correlations between
laboratory-derived estimates of optimal temperature and the field-temperature of the habitats of marine algae are well demonstrated in a
variety of species and among phyla. Nishihara
et al. (2004) has shown that the red alga
Laurencia brongniartii J. Agardh performs
optimally at temperature ranging from 22 to
28℃, which is also within typical values of water
temperature observed in its preferred coral
reef habitat. Ohno et al. (1994) demonstrated
that Kappaphycus alvarezii (Doty) Doty ex Silva
from subtropical waters of Japan also grew well
at temperatures between 25 and 28℃. More
relevantly, the photosynthetic parameters of
Gracilaria cornea J. Agardh ( = Hydropuntia
cornea ( J. Agardh) Wynne) was optimal at temperature of 25℃ (Dawes et al. 1999), which is
with the range of our results for subtropical red
algae species.
Species was a significant factor influencing
the relationship between the parameters of the
GLM models with respect to temperature, suggesting that the responses to temperatures are
species specific. However, it is important to
note that maximal rates of rETR (i.e., rETRmax)
for each species occurred at roughly similar temperatures with wide standard errors.
This may partially explain why they are often
found together in the intertidal zone. It is also
important to note that the β of M. coacta was
higher than M. papulosa especially at higher
temperatures, suggesting that M. papulosa is
less susceptible to high PAR in warmer waters.
Perhaps, this can partly explain the presence
385
of M. papulosa in regions of Africa, Southwest
Asia, China, Southeast Asia, Australia and New
Zealand, and the prevalence of M. coacta in
Japan (Yoshida 1998), Korea (Lee and Kang
2001), Taiwan (Huang 2000) and the Philippines
(Kraft et al. 1999).
By modeling the P- I curve and the relationship between the estimated parameters and
temperature, the response of these organisms
over the range of experimental temperatures
can be predicted. This is important, since the
development of protocols and cultivation systems require the appropriate models as input.
The results of this study can be used as the
base to develop highly optimized design equations that will maximize production while minimizing costs at the commercial scale.
The analysis of the experiments provided
us with a range of temperatures that were
optimal for maximum photosynthetic activity.
These temperatures correspond well to those
determined in the natural habitat, which is reassuring given that discrepancies between experimental results and field data are not uncommon
(Lobban and Harrison 1997). However, it
should be noted that there was a mismatch
between PAR measured in situ and PAR that
maximized rETR, which will require further
investigation (Tsuchiya et al. 2012). Models
describing the rETR performance of M. coacta
and M. papulosa and the temperature dependence of the model parameters should help to
accelerate the cultivation of these species by
fine-tuning the cultivation strategies used for
these economically important red algae.
PARsat and PARopt value of M. coacta and M.
papulosa (Figs. 5e, 5f) measured in this study
increased with increasing of water temperature (Collins and Boylen 1982; Palmisano et al.
1987; Henley 1992, 1993). We suggest that if
the water temperature increases, these species may be able to grow more effectively in
the shallow waters of their environment, rather
than in deeper water. As a sublittoral algal species, M. coacta and M. papulosa required PAR
with a wider range compared, to Lüning (1981),
which suggested that in the upper and midsublittoral, algae species only require light
386
Lideman, G. N. Nishihara, T. Noro and R. Terada
ranging from 150 to 250μmol photons m-2 s-1.
Indeed, saturating irradiances show some correlation with habitat, but generally they are
low compared to full sun (Reiskind et al. 1989).
Moreover, above the saturation point (PARsat),
the light-dependent reactions are producing
more ATP and NADPH that can be used by
the light-independent reaction for CO2 fixation,
and therefore, increasing irradiance no longer
causes any increase in photosynthetic rate ( i.e.,
full saturated) (Barsanti and Gualtieri 2006).
Meristotheca coacta and M. papulosa generally can be found at the depth from 3 to 30 m
deep. In this study, estimated maximum PAR at
a depth of 30 m (Fig. 3, Table 1) corresponded
to the mean values for the PARsat estimated
at the temperatures from 18 to 22℃ (Fig. 5e).
These temperatures also corresponded to the
temperatures measured at the depth of the
study site (Table 1). We believe that the low
value of the extinction coefficients is one mechanism that enables the success of these species
in sublittoral waters.
Additionally, Tsuchiya et al. (2011) reported
that the seasonal changes of seawater temperature near the study site (Kagoshima Bay) in
2009 and 2010 ranged from 15.6℃ in February
to 29.4℃ in August. Especially, the temperature
in April to August were recorded 18 to 28℃.
Indeed, from 2006 to 2010 offshore of the study
site, average monthly surface temperatures in
April to August were also recorded to be from
18 to 28℃ by JMA (2011b). Increasing temperatures as a result of global warming ( JMA
2011a) may lead these macroalgae to change
in spatial distribution in the future, because of
the interactive links between PAR and water
temperature on photosynthetic activity, given
that these physical variables are one of the most
important abiotic factors influencing the distribution of marine species (Lalli and Parsons
1997). It is important to note that in this region,
the average winter and seawater temperatures
have increased by about 1.1 and 0.7℃, respectively over the last 38 years (Tsuchiya et al.
2011). How this will affect the distribution of
these economically important species remains
to be determined.
Hence, we must diligently monitor the changing environment, because although these two
edible seaweeds, M. coacta and M. papulosa, are
currently adapted to the natural light and temperature circumstances of southern Kyushu Is.,
Japan, changing water temperatures may have a
drastic effect on their distribution. Furthermore,
the models determined from this study should
greatly contribute to the design and management of mariculture programs and cultivation
systems. Based on our results we suggest that
either of the species can be successfully cultivated from April to August in this region.
Acknowledgements
We would like to expresses our thank to C.
Kawashima, M. Uchiyama and the crew of T/S
Nansei-maru, Faculty of Fisheries, Kagoshima
University, for their kind contributions to the
measurement of underwater irradiance. This
research was sponsored in part by Grant-inAid for Scientific Research (#22510033) from
the Japanese Ministry of Education, Culture,
Sport and Technology (RT), and the Nagasaki
University Strategy for Fostering Young
Scientist with funding provided by the Special
Coordination Funds for Promoting Science and
Technology of Ministry of Education, Culture,
Sport, Science and Technology (GNN). This
research was also the part of dissertation submitted by the first author in partial fulfillment of
the Ph.D. degree.
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食用海藻 2 種,キクトサカとトサカノリ(紅色植物門ミリン科)の
光合成活性における光と温度の影響
LIDEMAN・Gregory N. NISHIHARA・野呂忠秀・寺田竜太
食用海藻であるキクトサカとトサカノリ(紅色植物門ミリン科)の生理特性を把握するために,様々
な温度と光の条件での光合成活性を測定し,2 種の動態を考察した。測定にはパルス変調クロロフィ
ル蛍光測定法(Imaging-PAM)を用い,8-34℃の間の14温度条件と,光量 0-1,078μmol photon m-2 s-1
の間の21条件の組合せで電子伝達速度(rETR)を測定した。初期勾配(α),光阻害(β),係数(γ)
は 2 段階階層ベイズモデルを用いて非線形の光曲線モデルを得た。モデルで見積もられた至適な光合
成活性は両種とも18-28℃の温度範囲で得られ,光合成に至適な光量(PARopt)は温度の増加と共に上
昇した。また,両種は九州南部での生育地・水深における光や温度によく適応していた。これらの結
果は海面養殖等における環境条件の検討に有効と考えられた。