J Appl Phycol (2013) 25:1863–1872 DOI 10.1007/s10811-013-0030-7
The effect of light and temperature on the growth and photosynthesis of Gracilariopsis chorda (Gracilariales, Rhodophtya) from geographically separated locations of Japan Ryuta Terada & Shingo Inoue & Gregory N. Nishihara
Received: 28 September 2012 / Revised and accepted: 25 March 2013 / Published online: 17 April 2013 # Springer Science+Business Media Dordrecht 2013
Abstract The effect of light and temperature on the growth and photosynthesis of the Japanese agarophyte, Gracilariopsis chorda (Gracilariaceae, Rhodophyta), was determined to better understand its physiology so that we could identify candidates for mass cultivation. Above the photosynthetic active radiation of 66 μmol photons m−2 s−1, photosynthetic rates saturated for all strains that were collected from six different locations (Hokkaido, Chiba, Tokushima, Saga, Kagoshima, and Okinawa); furthermore, either photosynthesis or growth was observed at all temperature treatments examined in our study (4–32 °C for photosynthesis, 16–32 °C for growth experiments). We identified a temperature range for optimal photosynthesis and growth, which occurred within 20.1–29.1 °C and roughly correlated with the water temperatures of the collection locations and strongly suggests that this species tolerates a wide variety of water temperature. In particular, the Kagoshima strain had the widest range of optimal temperatures (20.8–29.1 °C), whereas the Saga strain had the narrowest range (23.1– 27.3 °C). It is important to note that all the optimal temperature ranges overlapped among the strains; therefore, no definitive distinction can be determined. The broad tolerance to temperatures commonly observed from northern to southern Japan suggests that the cultivation of this species should R. Terada (*) : S. Inoue Faculty of Fisheries, Kagoshima University, 4-50-20 Shimoarata, Kagoshima 890-0056, Japan e-mail:
[email protected] G. N. Nishihara Institute for East China Sea Research, Nagasaki University, 1551-7 Taira-machi, Nagasaki 851-2213, Japan
succeed during spring to summer in the majority of the coastal regions in Japan. Keywords Gracilariaceae . Gracilariopsis chorda . Growth . Photosynthesis . Temperature
Introduction The red algal genera Gracilaria and Gracilariopsis (Gracilariaceae, Rhodophyta) are widely distributed from subarctic to tropical regions and are considered commercially important commodities due to their production of agar (Abbott 1988; Critchley 1993; Armisen 1995). Gracilariopsis chorda occurs along the coasts of East Asia including Japan, Korea, and China (Ohmi 1956; Yoshida 1998; Tseng and Xia 1999; Yoshida and Yoshinaga 2010). In Japan, some species of Gracilariaceae including this taxon are harvested for agar, as well as for local food (Critchley and Ohno 1998). Although annual production of Gracilariaceae was reported to be around 2,000–3,000 tons in Japan, it is also known to be unstable and varies with location and year (Ito 2001). Indeed, 12,200 tons of Gracilariaceae were harvested at Akkeshi lagoon of Hokkaido Prefecture in 1952, but harvests quickly disappeared by 1953 (Ohmi 1958). More recently, more than 10,000 tons of G. chorda were harvested annually during 1990–1992 in Kumamoto Prefecture, Kyushu Island; however, annual harvests have also declined in Kumamoto. By 1998, the annual harvest was only about 28 tons (Migita et al. 1993; Ito 2001). Currently, any cultivation system of Gracilariaceae including mariculture and tank culture has yet to be established in Japan, exclusive of a small number of trial experiments (Orosco
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and Ohno 1992; Chirapart and Ohno 1993). Indeed, to ensure stable and sufficient supply, large-scale cultivation using advanced aquaculture technology will be needed for production. The importance of this taxon as a source of agar has generated much effort towards the clarification of the biology as well as the development of cultivation strategies of these species (Yokoya et al. 1999). Japan spans 3,000 km from the northernmost tip of Hokkaido Island (45° N) to the tropical islands of the Ryukyu Archipelago (24° N), spanning a diverse range of climatic conditions. In Japan, G. chorda occurs throughout the archipelago, from the tropical regions of Okinawa to the subarctic regions of Hokkaido (Yoshida 1998). The successful cultivation and the stabilization of harvest of this taxon are dependent upon careful consideration of the local climate. In this study, we focused on elucidating the temperature and light requirements on photosynthesis and growth of G. chorda collected in Japanese waters by applying a hierarchical Bayesian model to derive model parameters that can be used to characterize photosynthetic active radiationdependent rates of photosynthesis as well as temperaturedependent rates of photosynthesis and growth. We also identify a range of temperatures that allow for optimal photosynthesis and growth performance based on the parameters derived from the model.
Materials and methods Specimen collection and maintenance Gracilaria chorda (Fig. 1) was collected from various locations in Japan during 2005 (Fig. 2)—St. 1: Hakodate City (41.812° N, 140.704° E), Hokkaido Prefecture (July 21); St. 2: Katsuura City (35.133° N, 140.284° E), Chiba Prefecture (June 23); St. 3: Komatsushima City (34.000° N, 134.599° E), Tokushima Prefecture (July 23); St. 4: Saga City (33.139° N,
J Appl Phycol (2013) 25:1863–1872 50°N
45°N
Hokkaido 40°N
35°N
Chiba Tokushima Saga Kagoshima
30°N
25°N 120°E
Okinawa 130°E
140°E
150°E
Fig. 2 Map of Japan showing the collecting sites of Gracilariopsis chorda in this study
130.318° E), Saga Prefecture (May 23); St. 5: Kagoshima City (31.343° N, 130.559° E), Kagoshima Prefecture (April 28); and St. 6: Kin Town (26.449° N, 127.944° E), Okinawa Prefecture (March 8). The collected samples were stored in plastic bottles containing seawater and directly transported to the laboratory in a cooler (15 to 22 °C). Samples were maintained at the Faculty of Fisheries, Kagoshima University, Japan in an aquarium tank (2.0×1.0×0.5 m) containing seawater of 33 PSU salinity, pH 8.0, and at temperatures of 15 to 22 °C under a 14:10 light/dark cycle at 90 μmol photons m−2 s−1. Temperature in the aquarium tank was selected on the basis of natural seawater temperature at the collecting date. Samples collected were identified morphologically as well as through phylogenetic analysis using the mitochondria encoded cox2-3 and plastid encoded rbcL-S (rubisco) spacer regions (unpublished). Voucher herbarium specimens are deposited in the Kagoshima University Museum (KAG). Unialgal cultures of immature tetrasporophytes were established to provide material suitable for experiments using the protocols of Terada and Yamamoto (2000) and Nishihara et al. (2004). Each material was incubated in a 300- or 500-mL flask with Provasoli’s enriched seawater (PES; McLachlan 1973) at 20 °C, 52 μmol photons m−2 s−1 of photosynthetically active radiation (PAR; measured with a LI-192SA, LI-COR, with underwater spherical quantum sensor LI-250), and a diurnal cycle of 12:12. The material processed in this manner was typically free of epiphytes and other visible contamination and were suitable for growth experiments. Photosynthesis measurements
Fig. 1 Gracilariopsis chorda in the natural habitat in Kagoshima City, Japan (plant length: approx. 50 cm)
A 7.5-L glass aquarium filled with sterile water was connected to a water temperature controller (CL-80F, Taitec) and used as a water bath. Explants (approx. 2 cm in length) were cut from the main axis of the samples in the aquarium tank and were acclimatized overnight in sterilized seawater in the incubator (Muraoka et al. 1998; Serisawa et al. 2001).
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An incubation chamber was devised to accommodate the specimen and the oxygen electrode (Model 5905, YSI), while minimizing the water volume. There was some variation in water volume among experiments and care was taken to prevent the formation of bubbles. The volume for each experiment was recorded. Each incubation chamber contained a magnetic stir bar and plastic mesh to prevent the specimen from being damaged by the rotating stir bar. Dissolved oxygen concentrations were recorded every 5 min for a total of 30 min, and the measurements were repeated for five individuals for each species location. PAR was provided by a metal halide lamp (ML-70, Rei-Sea) and adjusted with neutral density screens. After each experiment, samples were extracted in the dark at 4 °C using 10 mL N,N-dimethylformamide solvent for 24 h. Chlorophyll-a (chl-a) was calculated according to Porra et al. (1989) using the following equation: chl a μg mL1 ¼ 12:0 ðAbs663:8 Abs700 Þ 3:11 ðAbs646:8 Abs700 Þ
ð1Þ
where Abs663.8 is the absorbance at 663.8 nm, Abs646.8 the absorbance at 646.8 nm, and Abs700 the absorbance at 700 nm. The effects of seven temperatures (8, 12, 16, 20, 24, 28, and 32 °C) on the net photosynthetic rates were examined (the sample from Hokkaido was also measured at 4 °C) at 200 μmol photons m−2 s−1. The influence of PAR on net photosynthetic rates was examined at 24 °C, based on the estimated optimum temperature range for all localities as determined by the temperature experiment. Neutral density screens were used to establish seven levels of PAR (i.e., 0, 20, 50, 100, 140, 200, and 400 μmol photons m−2 s−1) for Chiba, Tokushima, Saga, and Kagoshima and eight levels (i.e., as above including 500 μmol photons m−2 s−1) of PAR for Okinawa. Note that for 0 μmol photons m−2 s−1, the incubation chamber was made opaque with at least two layers of thick aluminum foil. Photosynthesis and respiration rates were determined by calculating the slope of the dissolved oxygen with respect to time and then normalized by the amount of chlorophyll-a determined from the samples. Growth measurements We could not examine how temperature affects the growth rates for all of the locations as was done for the photosynthesis experiments and only examined G. chorda from Hokkaido, Kagoshima, Saga, and Okinawa. Five to six individuals for temperatures of 16, 20, 24, 28, and 32 °C were incubated in PES (as described above) at 52 μmol photons m−2 s−1 for 15 days. The wet weight at days 0, 5, 10, and 15 was measured after gently dabbing away excess moisture with a sterile tissue. Daily growth rates were estimated by dividing the
difference in the wet mass after 15 days, given that the wet weight changed linearly with time. Data analyses The PAR-dependent photosynthetic rates were modeled after Webb et al. (1974) using a rectangular hyperbola, a PAR r ð2Þ NP ¼ Pmax 1 exp Pmax where NP is the net photosynthetic rate, Pmax is the maximum gross photosynthetic rate, α is the initial slope of the model and is an indicator of sensitivity to light under low PAR conditions, and r is the respiration rate. Estimates for saturating PAR (Ek) were derived from the parameters, where Ek ¼ Pmax a , and indicates PAR where gross photosynthesis saturates. To provide estimates of the parameters, Eq. 1 was parameterized as a hierarchical Bayesian model, where the posterior distribution of each parameter was sampled from a weakly informative Cauchy distribution, whose scale and shape parameters were sampled from a uniform hyperprior distribution (Gelman et al. 2004, 2008). No hyperprior was used for model error (i.e., an error term was determined for each location), which was sampled from a noninformative normal distribution, with a uniform shape parameter. The temperature-dependent photosynthesis and growth rates were modeled using a modified Arrhenius function (Alexandrov and Yamagata 2007) for the results of each location and was modeled as, y ¼ ymax g
g¼
ηf ð η 1Þ þ f η
! Ha T Topt f ¼ exp R ðT þ 273:15Þ Topt þ 273:15
ð3Þ
ð4Þ
ð5Þ
where T is the water temperature, y is either the photosynthetic rate or growth rate, ymax is either the maximum net photosynthetic rate (NPmax) or the maximum growth rate, η is the ratio of the activation energy below (Ha) and above (Hd) the optimal temperature (Topt), and R is the universal gas constant (i.e., 8.3145 J mol−1 K). The parameters of these functions were also estimated from the sampled posterior distributions as determined by a hierarchical Bayesian model, where the prior distributions for the parameters were from a weakly informative Cauchy distribution with uniform hyperpriors on the scale and shape parameters (Gelman et al. 2004, 2008). As in the case of the PAR-dependent photosynthesis model, the errors were
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Seawater temperature Seasonal changes of seawater temperature in 2005 near the study site were analyzed from the data derived from the website of JODC Data On-line Service System by the Japan Oceanographic Data Center [http://www.jodc.go.jp/data/ coastal/obs_data_index.html]. Original data were measured by the following institutions at various depth and intervals— Shiriuchi (41.533° N, 140.423° E, Hokkaido Prefecture, 35 km southwest from St. 1): Kamiiso County Fishermen’s Union, surface water, every 10:00 a.m.; Futtsu (35.278° N, 139.85° E, Chiba Prefecture, 50 km northeast of St. 2): Chiba Prefectural Fisheries Research Center, 3 m deep, every 10:00 a.m.; Tokushima (34.103° N, 134.605° E, 10 km north of St. 3): Fisheries Research Center of Tokushima Prefecture, surface water, every 10:00 a.m.; Ohmuta (33.000° N, 130.397° E, Fukuoka Prefecture, 17 km southeast of St. 4): Fukuoka Fisheries and Marine Technology Research Center, surface water, every highest tide of the day; Kagoshima (31.597° N, 130.573° E, Kagoshima Prefecture, 20 km north of St. 5): Kagoshima Aquarium, pumped from 5 m deep, every 11:30 a.m.; and Okinawa (26.694° N, 127.872° E, Motobu Town, Okinawa Prefecture, 27 km north of St. 6): Okinawa Churaumi Aquarium, pumped from 20 m deep, every 10:00 a.m. The detailed method for measurement is described on the JODC website.
Results Net photosynthetic rates Net photosynthetic rates initially increased from 0 μmol m−2 s−1 and approached an asymptote at PAR much less than the maximum experimental value of 600 μmol photons m−2 s−1 for all locations (Fig. 3, Table 1). The rectangular hyperbola fit to the data revealed that values of Pmax, α, r, and Ek tended to vary among locations, regardless of being
40
a
20 0 −20
40
b
20
Net photosynthesis rate (mmol O2 μg chl−a−1s−1)
individually sampled from a noninformative uniform prior distribution. All statistical analyses were conducted in R (R Core Team 2012), and the posterior distributions of the parameters were determined using Hamiltonian Monte Carlo sampling (Stan Development Core Team 2012). For each model, four chains were initialized randomly and 50,000 iterations were completed, all chains converged with a scale reduction statistic of 1.0 (Gelman and Rubin 1992). To identify an optimal range of temperatures for production, we examined the model of the temperature-dependent photosynthesis and growth data and identified the temperature range where the mean net photosynthetic rates or growth rates were equal to or greater than lower 95 % high density interval.
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0 −20
40
c
20 0 −20
40
d
20 0 −20
40
e
20 0 −20
40
f
20 0 −20 0
100
200
300
400
500
Photosynthetic active radiation (μmol photons m−2 s−1) Fig. 3 Photosynthetic active radiation (PAR)-dependent net photosynthetic rates (NP) for six strains of Gracilariopsis chorda from a Hokkaido, b Chiba, c Tokushima, d Saga, e Kagoshima, and f Okinawa. The black discs and bars indicate the mean and standard deviation of the measured NP rates, the solid line indicates the mean value of the hierarchical Bayesian model fitted to the data, and the dashed lines indicate the 95 % high density interval of the model estimates
cultivated under identical conditions (Fig. 4a–e, Table 2). The mean maximum rates of net photosynthesis ranged from a low of 29.2 mg O2 g chl-a−1 s−1 for the Tokushima strain to a high of 47.2 mg O2 g chl-a−1 s−1 for the Saga strain (Fig. 4a). Excluding the Tokushima strain, the other strains all had statistically similar values of Pmax and ranged from a low of 26.8 mg O2 g chl-a−1 s−1 to a high of 33.0 mg O2 g chl-a−1 s−1. The mean values for the slope coefficient
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Table 1 Photosynthetically active radiation (PAR)-dependent net photosynthesis (NP) model parameters for Gracilariopsis chorda from Hokkaido, Chiba, Tokushima, Saga, Kagoshima, and Okinawa. Parameters are determined for a hierarchical Bayesian model of a Location
Hokkaido Chiba Tokushima Saga Kagoshima Okinawa
rectangular hyperbola, where the mean and the 95 % highest density interval of the posterior distributions of the model parameters are provided
Pmax (mg O2 s−1 μgchl-a−1 (μmol photons m−2 s−1)−1)
α (mg O2 s−1 μgchl-a−1)
r (mg O2 s−1 μgchl-a−1 (μmol photons m−2 s−1)−1)
Ek (μmol photons m−2 s−1)
Lower
Mean
Upper
Lower
Mean
Upper
Lower
Mean
Upper
Lower
Mean
Upper
27.4 27.4 26.9 43.8 26.8 28.3
29.7 29.4 29.2 47.2 29.4 30.6
31.9 31.5 31.4 50.6 31.6 33.0
0.45 0.59 0.27 0.38 0.42 1.07
0.62 0.77 0.35 0.46 0.63 1.45
0.83 0.95 0.43 0.53 0.85 1.86
8.5 6.8 3.0 6.9 8.6 11.5
10.7 8.8 5.0 9.3 10.8 13.8
12.9 10.6 6.9 11.9 13.3 16.1
122 104 272 384 110 46
191 142 372 482 188 66
264 185 477 577 271 90
Pmax is the maximum NP, α is the light sensitivity at low PAR, r is the respiration rate, and Ek is the saturating PAR
range of α determined for all of the strains from the analysis was 0.27 to 1.86 mg O2 g chl-a−1 s−1 (μmol photons m−2 s−1)−1. The respiration rates also varied with strain and ranged from 3.0 to 16.1 mg O2 g chl-a−1 s−1. High mean respiration rates were
(α) showed more variations with strain than Pmax (Fig. 4b). Tokushima had the lowest values (0.35 mg O2 g chl-a−1 s−1 (μmol photons m−2 s−1)−1); in contrast, Okinawa had the highest values (1.45 mg O2 g chl-a−1 s−1 (μmol photons m−2 s−1)−1). The Fig. 4 Range of model parameter values determined for the net photosynthesis (NP) experiment of six strains of Gracilariopsis chorda. The left column of the figures provide range estimates of a maximum photosynthetic rates (Pmax), b low light sensitivity (α), c respiration (r), and d the saturating photosynthetic active radiation (PAR, Ek) for PARdependent NP, and the remaining figures provide range estimates of e maximum net photosynthetic rates (NPmax), f optimal temperature (Topt), g activation energy ratio (η), and h the activation energy below Topt (Ha) of temperaturedependent NP
Okinawa Kagoshima Saga Tokushima Chiba Hokkaido
a
20
Okinawa Kagoshima Saga Tokushima Chiba Hokkaido 30
40
e
50
20
Pmax (mgO2 μg chl−a s−1) Okinawa Kagoshima Saga Tokushima Chiba Hokkaido
b
0.0
Okinawa Kagoshima Saga Tokushima Chiba Hokkaido
Okinawa Kagoshima Saga Tokushima Chiba Hokkaido 0.5
1.0
1.5
α
22
10
0.0
15
d
0
Okinawa Kagoshima Saga Tokushima Chiba Hokkaido 200
24
26
g
2.5
r (mg O2 μg chl−a−1 s−1) Okinawa Kagoshima Saga Tokushima Chiba Hokkaido
32
Topt (°C) Okinawa Kagoshima Saga Tokushima Chiba Hokkaido
5
28
f
20
c
0
24
NPmax (mg O2 μg chl−a−1 s−1)
400
E k (μmol photons m
−2
600
s−1)
η
5.0
7.5
h
0
25
50
Ha (kJ mol−1)
75
100
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Table 2 Temperature (T)-dependent net photosynthesis (NP) model parameters for Gracilariopsis chorda from Hokkaido, Chiba, Tokushima, Saga, Kagoshima, and Okinawa. Parameters are Location
Topt (°C)
determined for a hierarchical Bayesian model of a modified Arrhenius model, where the mean and the 95 % highest density interval of the posterior distributions of the model parameters are provided
NPmax (mg O2 s−1 μgchl-a−1)
η
Ha (kJ mol−1 K−1)
Lower
Mean
Upper
Lower
Mean
Upper
Lower
Mean
Upper
Lower
Mean
Upper
Hokkaido Chiba Tokushima Saga
22.1 24.2 23.1 25.5
23.1 25.2 23.9 26.0
24.1 26.1 24.7 26.6
17.7 21.2 20.2 29.0
19.3 22.0 21.3 30.3
21.4 22.7 22.4 31.6
2.8 3.2 1.8 2.2
4.3 5.9 2.3 2.8
6.2 8.6 2.8 3.5
61 27 68 73
79 33 82 85
94 39 95 97
Kagoshima Okinawa
22.7 21.4
23.4 22.3
24.1 23.1
20.8 20.7
21.8 21.5
22.7 22.4
1.6 1.5
2.0 1.9
2.5 2.4
68 61
82 79
95 94
Topt is the temperature at which the net photosynthesis is at a maximum (NPmax), and η is the ratio of the activation energy below (Ha) and above the Topt
observed for the Okinawa strain (13.8 mg O2 g chl-a−1 s−1), whereas the lowest values were observed from the Tokushima strain (5.0 mg O2 g chl-a−1 s−1). Photosynthetic rates saturated within the bounds of the experimental setup and the saturating PAR values for all of the strains ranged from 46 to 577 μmol photons m−2 s−1 (Fig. 4d). The Okinawa strain saturated at the lowest mean value of PAR (66 μmol photons m−2 s−1) and the Saga strain did not saturate in photosynthetic rates until a mean value of 482 μmol photons m−2 s−1. Temperature dependence of the net photosynthetic rates at 200 μmol photons m−2 s−1 was well described by the modified Arrhenius model, and a distinct peak in net photosynthetic rates could be identified in all of the strains at intermediate water temperatures (Fig. 5). In all of the strains examined, the net photosynthetic rates increased gradually from relatively low water temperatures (4 °C), reached a peak between 22 and 26 °C, and then decreased in value with increasing temperatures. The fitted models provide the best estimates of the mean values, given the data and model. Differences in mean values of maximum net photosynthetic rates (Fig. 4e) were apparent between the Saga strain (30.3 mg O2 g chl-a−1 s−1) and the remaining strains (mean values range from 19.3 to 22.0 mg O2 g chl-a−1 s−1); however, among the remaining strains, there were no distinct differences. Indeed, maximum net photosynthetic rates ranged from 19.3 to 31.6 mg O2 g chl-a−1 s−1 for all strains. The water temperatures, where these maximum rates were associated with, follow a relatively similar pattern, where the mean optimal water temperature for the Saga strain was the highest at 26.0 °C (Fig. 4f). The optimal water temperatures for all strains ranged from 21.4 to 26.6 °C. The general shape of the modified Arrhenius model can be described by the parameter Ha and Hd, where Ha determines the gradient of the curve below the optimum temperature and Hd determines the gradient of the curve above the optimum temperature. Given that η ¼ HHda , an increase in η is equivalent to an proportional increase in Hd. The values of η for all of the
strains ranged from 1.5 to 8.6, where the Chiba and Hokkaido strains expressed the widest ranges of 3.2–8.6 and 2.8–6.2, respectively (Fig. 4g). Mean values of η were lowest for the Okinawa strain (1.9). Values of Ha were relatively similar, with the Chiba strain having the lowest mean Ha value (33 kJ mol−1). Ha ranged from 27 to 97 kJ mol−1. Growth rates The temperature-dependent rates of growth were examined from strains for Hokkaido, Saga, Kagoshima, and Okinawa using the modified Arrhenius model (Fig. 6, Table 3). There was a distinct peak in growth rates for all strains, which occurred between 23.1 and 26.3 °C. By fitting Eqs. 2–4 to the data using hierarchical Bayesian modeling, we were able to estimate the model parameters (Fig. 7, Table 3). Unlike the photosynthesis experiments, there was little variation in model parameters among strains in the growth rate experiment, with the majority of the parameters having overlapping 95 % high density intervals among strains. The mean maximum growth rates (Fig. 7a) were lowest for the Saga strain (0.72 mg day−1), whereas the remaining strains had relatively similar values. Indeed, for the remaining strains, the maximum growth rates ranged from 0.94 to 2.03 mg day−1. However, the 95 % high density intervals of the optimal water temperature for all strains overlapped (Fig. 7b), and these values ranged from 23.1 to 26.3 °C. The mean values of η ranged from 1.6 (Saga) to 2.0 (Hokkaido), with an aggregate range of 1.3 to 2.6 (Fig. 7c). Values for Ha ranged from 146 to 219 kJ mol−1, and the mean values were 182 kJ mol−1 for the Kagoshima and Okinawa strains and 183 kJ mol−1 for the Hokkaido and Saga strains (Fig. 7d). The discrepancy between the model and the data is a feature of hierarchical Bayesian models, where the information contained in the estimates of the model parameters are “shared” through the hyperpriors. Hence, there is a narrow 95 % highest density interval around the model in Fig. 6b,
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where the results from the Chiba strain were relatively precise. This is in contrast to the Fig. 6c, given the imprecision in the growth rate estimates of the Tokushima strain. In this case, the model estimates lower values for growth rate and the 95 % highest density intervals are wide.
a
3 2 1
40 30
a
0
20
4
10 0
30
3 2
b
Growth rate (mg d−1)
40
Net photosynthesis rate (mmol O2 μg chl−a−1s−1)
20 10 0 40 30
c
20 10 0 40 30
1 0 4 3 2
0
d
4
10 0
30
c
1
20
40
b
d
3 2
e 1
20 10
0
0
16
20
24
28
32
Water temperature (°C) 40 30
f
20 10 0 4
8
12
16
20
24
28
32
Water temperature (°C) Fig. 5 Temperature-dependent net photosynthetic rates (NP) for six strains of Gracilariopsis chorda from a Hokkaido, b Chiba, c Tokushima, d Saga, e Kagoshima, and f Okinawa. The black discs and vertical bars indicate the mean and standard deviation of the measured NP rates, the solid line indicates the mean value of the hierarchical Bayesian model fitted to the data, the dashed lines indicate the 95 % high density interval of the model estimates, and the horizontal solid line indicates the optimal temperature range for photosynthesis
Fig. 6 Temperature-dependent growth rates for four strains of Gracilariopsis chorda from a Hokkaido, b Chiba, c Kagoshima, and d Okinawa. The black discs and vertical bars indicate the mean and standard deviation of the measured growth rates, the solid line indicates the mean value of the hierarchical Bayesian model fitted to the data, the dashed lines indicate the 95 % high density interval of the model estimates, and the horizontal solid line indicates the optimal temperature range for growth
Optimal temperature ranges for photosynthesis and growth Based on the definition of the temperature range where the mean net photosynthetic rates or growth rates were equal to or greater than 95 % high density interval, the optimal temperature range from net photosynthesis occurred between 20.1 and
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Table 3 Temperature (T)-dependent growth rate (GR) model parameters for Gracilariopsis chorda from Hokkaido, Chiba, Kagoshima, and Okinawa. Parameters are determined for a hierarchical Bayesian model Topt (°C)
Location
Hokkaido Saga Kagoshima Okinawa
of a modified Arrhenius model, where the mean and the 95 % highest density interval of the posterior distributions of the model parameters are provided
GRmax (mg O2 s−1 μgchl-a−1)
η
Ha (kJ mol−1 K−1)
Lower
Mean
Upper
Lower
Mean
Upper
Lower
Mean
Upper
Lower
Mean
Upper
24.4 24.3 23.2 23.1
25.1 25.1 24.8 24.0
25.7 25.7 26.3 24.9
1.13 0.66 0.94 1.27
1.30 0.72 1.45 1.61
1.45 0.78 2.03 1.88
1.6 1.3 1.3 1.5
2.0 1.6 1.9 1.9
2.4 1.9 2.6 2.4
147 147 147 146
182 183 182 182
218 219 218 219
Topt is the temperature at which growth is at a maximum (GRmax), and η is the ratio of the activation energy below (Ha) and above the Topt
29.1 °C, where the Kagoshima strain had the widest range (20.8–29.1 °C) and the Saga strain had the narrowest range (23.1–27.3 °C). Similarly, the optimal temperature range as determined from the growth experiments ranged from a low of
20.1 °C to a high of 28.0 °C. In this case, the Chiba strain had the widest range (22.3–27.8 °C) and the Saga strain had the narrowest (24.1–28 °C). Seawater temperature
Okinawa
a
Kagoshima Saga Hokkaido 0.5
1.0
1.5
2.0
Growth rate ( mg d−1) Okinawa
b
Kagoshima Saga Hokkaido 23
24
25
26
Topt (°C) Okinawa
Seawater temperatures from the six different regions were highest in August and lowest in February (or January, March), respectively (Fig. 8). However, the local value of temperature was different from the locations. In Shiriuchi near St. 1, the highest temperature from the monthly mean temperature was 21.9 °C in August, whereas the lowest was 7.3 °C in February and March. In Futtsu (near St. 2), Tokushima (near St. 3), and Ohmuta (near St. 4), the highest temperature was 27.6 °C, 26.8 °C, and 27.4 °C (Aug), and the lowest was 9.8 °C (Jan), 11.2 °C (Jan), and 9.1 °C (Feb), respectively. Meanwhile, winter temperatures of Kagoshima and Okinawa, both in southern Japan, was relatively higher than the other four sites. The lowest and highest temperatures were 15.6 °C (Feb) and
35
c
Kagoshima
30
Saga
25
Hokkaido
Shiriuchi (Hokkaido) Futtsu (Chiba) Tokushima Ohmuta (Fukuoka) Kagoshima
20 1.0
1.5
η
2.0
2.5
15
Okinawa
10 Okinawa
d
5
Kagoshima
0
Saga
J F M A M J J A S O N D Month
Hokkaido 140
160
180
200
220
Ha (kJ mol−1) Fig. 7 Range of model parameter values determined for the growth experiment of four strains of Gracilariopsis chorda, where a shows the maximum growth rates, b optimal temperature (Topt), c activation energy ratio (η), and d the activation energy below Topt (Ha)
Fig. 8 Seasonal changes of seawater temperature in 2005 at the six different locations in Japan: Shiriuchi, Hokkaido Prefecture; Futtsu, Chiba Prefecture; Tokushima, Tokuchima Prefecture; Ohmuta (Ariake Bay), Fukuoka Prefecture; Kagoshima, Kagoshima Prefecture; and Motobu, Okinawa Prefecture. Data were derived from the website of the JODC Data On-line Service System by the Japan Oceanographic Data Center [http://www.jodc.go.jp/data/coastal/obs_data_index.html]
J Appl Phycol (2013) 25:1863–1872
20.5 °C (Mar) and 28.8 °C (Aug) and 28.9 °C (Aug), respectively.
Discussion The strains of G. chorda examined were able to photosynthesize at all of the temperature treatments (4–32 °C) and grow within a subset of this range (16–32 °C). Furthermore, net photosynthetic rates were strongly dependent on irradiance when PAR
