Gregory N. Nishihara

Effect of irradiance and temperature on the photosynthesis of a cultivated red alga, Pyropia tenera (= Porphyra tenera), at the southern limit of distribution in Japan

The effect of irradiance and temperature on the photosynthesis of the red alga, Pyropia tenera, was determined for maricultured gametophytes and sporophytes collected from a region that is known as one of the southern limits of its distribution in Japan. Macroscopic gametophytes were examined using both pulse‐amplitude modulated fluorometry and/or dissolved oxygen sensors. A model of the net photosynthesis–irradiance (P‐E) relationship of the gametophytes at 12°C revealed that the net photosynthetic rate quickly increased at irradiances below the estimated saturation irradiance of 46 μmol photons m−2 s−1, and the compensation irradiance was 9 μmol photons m−2 s−1. Gross photosynthesis and dark respiration for the gametophytes were also determined over a range of temperatures (8–34°C), revealing that the gross photosynthetic rates of 46.3 μmol O2 mgchl‐a−1 min−1 was highest at 9.3 (95% Bayesian credible interval (BCI): 2.3–14.5)°C, and the dark respiration rate increased at a rate of 0.93 μmol O2 mgchl‐a−1 min−1°C−1. The measured dark respiration rates ranged from −0.06 μmol O2 mgchl‐a−1 min−1 at 6°C to −25.2 μmol O2 mgchl‐a−1 min−1 at 34°C. The highest value of the maximum quantum yield (Fv/Fm) for the gametophytes occurred at 22.4 (BCI: 21.5–23.3) °C and was 0.48 (BCI: 0.475–0.486), although those of the sporophyte occurred at 12.9 (BCI: 7.4–15.1) °C and was 0.52 (BCI: 0.506–0.544). This species may be considered well‐adapted to the current range of seawater temperatures in this region. However, since the gametophytes have such a low temperature requirement, they are most likely close to their tolerable temperatures in the natural environment.

Photosynthesis and growth rates of Laurencia brongniartii J. Agardh (Rhodophyta, Ceramiales) in preparation for cultivation

Laurencia brongniartii is usually found at depths below 4 m, but can be found in shallow subtidal areas in crevices and on the walls of a coral reef in Amami Oshima Island, Kagoshima Prefecture, Japan, where irradiances were significantly lower than those at similar depths in open water. In preparation for the possible cultivation of this species for its antibiotic compounds, the effects of temperature and irradiance on photosynthesis and growth were measured. Photosynthesis and growth rates of L. brongniartii explants were highest at 26 and 28 °C, which closely corresponded to temperatures found during August to late December when it was most abundant. The estimated maximum photosynthesis rate (Pmax) was 4.41 μmol photon m−2 s−1 at 26 °C and 4.07 μmol photon m−2 s−1 at 28 °C. Saturating irradiance occurred at 95 μmol photon m−2 s−1 at 26 °C and 65 μmol photon m−2 s−1 at 28 °C. In contrast, growth experiments at 41.7 μmol photon m−2 s−1 caused bleaching of explants and the maximum growth rate observed during the study was 3.02 ± 0.75% day−1 at 28 °C and 25 μmol photon m−2 s−1. The difference in the saturating irradiance for photosynthesis and the irradiance that caused bleaching in growth experiments suggests that long-term exposure to high irradiance was detrimental and should be addressed before the initiation of large scale cultivation.

Species richness of marine macrophytes is correlated to a wave exposure gradient

Wave exposure is one of the fundamental variables of the coastal environment and many coastal processes are affected by waves and wave‐induced water motion. Directly or indirectly, waves affect the lives of many coastal macroalgae and seagrasses. Although the idea that waves can affect macrophyte distribution and biodiversity is not new, it remains poorly examined. We looked at how a gradient of wave exposure, determined using the surf similarity number, influences the species richness of macrophytes among phyla and functional form groups. We suggest that wave exposure is a biologically and statistically significant variable and that the species richness of most phyla and groups decrease with increasing exposure. More interestingly, the analysis suggests that the Phaeophyta and the thick‐leathery functional form group, which are associated with important coastal habitats (i.e. submarine forests), increases in species richness as exposure increases. It appears that the effect of wave exposure varies with phyla and functional form group. Consequently, we reinforce the belief that studies that address the biodiversity and distribution of macrophytes must include wave exposure as a measured variable, to provide any meaningful synthesis of the ecology of these organisms.

Change in the transfer profile of orally administered tetrodotoxin to non-toxic cultured pufferfish Takifugu rubripes depending of its development stage.

To investigate the effects of growth (organ development) on tetrodotoxin (TTX) dynamics in the pufferfish body, TTX-containing feed homogenate was administered to 6- and 15-month old non-toxic cultured specimens of the pufferfish Takifugu rubripes at a dose of 40 mouse units (MU) (8.8 μg)/20 g body weight by oral gavage. After 24 h, the specimens were killed and the skin tissues (dorsal and ventral), muscle, liver, digestive tract, and gonads were separated. TTX content (μg/g) in each tissue, determined by liquid chromatography/mass spectrometry, revealed that the TTX distribution profile, particularly the TTX content of the liver, greatly differed between the two ages; the TTX score of 15-month old fish (3.3 μg/g) was nearly 5-fold that of 6-month old fish (0.68 μg/g). The total remaining TTX amount per individual (relative amount to the given dose) was 31% in 6-month old fish, of which 71% was in the skin, and 84% in 15-month old fish, of which 83% was in the liver. The gonadosomatic index (GSI) and hepatosomatic index (HSI) scores, and histologic observations of the gonads and liver suggest that although there is little difference in maturation stage between these two ages, there are clear distinctions in the developmental stage of the liver. The results suggest that the TTX dynamics in T. rubripes are linked to the development of the liver, i.e., the TTX taken up into the pufferfish body via food organisms is eliminated or transferred mainly to the skin in young fish with an undeveloped liver, but as the fish grow and the liver continues to develop, most of the TTX is transferred to and accumulated in the liver.

Phenology, irradiance and temperature characteristics of a freshwater red alga, Nemalionopsis tortuosa (Thoreales), from Kagoshima, southern Japan

Phenology, irradiance and temperature characteristics of a freshwater benthic red alga, Nemalionopsis tortuosa Yoneda et Yagi (Thoreales), were examined from Kagoshima Prefecture, southern Japan for the conservation of this endemic and endangered species. Field surveys confirmed that algae occurred in shaded habitats from winter to early summer, and disappeared during August through November. A net photosynthesis–irradiance (P–E) model revealed that net photosynthetic rate quickly increased and saturated at low irradiances, where the saturating irradiance (Ek) and compensation irradiance (Ec) were 10 (8–12, 95% credible interval (CRI)) and 8 (6–10, 95% CRI) μmol photon m−2 s−1, respectively. Gross photosynthesis and dark respiration was determined over a range of temperatures (8–36°C) by dissolved oxygen measurements, and revealed that the maximum gross photosynthetic rate was highest at 29.5 (27.4–32.0, 95%CRI) °C. Dark respiration also increased linearly when temperature increased from 8°C to 36°C, indicating that the increase in dark respiration at higher temperature most likely caused decreases in net photosynthesis. The maximum quantum yield (Fv/Fm) that was determined using a pulse amplitude modulated‐chlorophyll fluorometer (Imaging‐PAM) was estimated to be 0.51 (0.50–0.52, 95%CRI) and occurred at an optimal temperature of 21.7 (20.1–23.4, 95%CRI) °C. This species can be considered well‐adapted to the relatively low natural irradiance and temperature conditions of the shaded habitat examined in this study. Our findings can be applied to aid in the creation of a nature‐reserve to protect this species.

Effect of PAR and temperature on the photosynthesis of the Japanese alga, Ecklonia radicosa (Laminariales), based on field and laboratory measurements

Abstract: The effect of photosynthetically active radiation (PAR) and temperature on the photosynthesis of a Japanese brown alga, Ecklonia radicosa, was determined by using dissolved oxygen sensors and pulse-amplitude modulated (PAM) fluorometry. The effective quantum yield (ΦPSII) of the sporophytes, in a natural population in shallow water, showed a characteristic noontime decline that indicated the influence of high PAR. However, ΦPSII of sporophytes in deeper water (−10 to −20 m) did not appear to be affected and maintained relatively high values of ΦPSII. In laboratory measurements of ΦPSII, after 12 h of continuous low and high PAR (100 and 1000 μmol photon m−2 s−1), a relatively greater decrease in ΦPSII in the high PAR treatment was observed. Furthermore, despite an overnight dark acclimation, the maximum quantum yield (Fv/Fm) under the high PAR treatment did not fully recover. A net photosynthesis–irradiance (P-E) curve was generated at 20°C, which revealed low compensation and saturation irradiances (Ec and Ek) of 14 and 45 μmol photon m−2 s−1, suggesting adaptation to a low PAR environment. Results from experiments to determine the net/gross photosynthesis and dark respiration rates revealed that the maximal gross photosynthetic rates occurred at 27.5°C and were 5.18 μg O2 gww−1 min−1; whereas, the dark respiration rate increased exponentially with a mean value of 1.35 μg O2 gww−1 min−1 at 22°C. Fv/Fm was relatively stable at low temperature, and the highest value (0.73) occurred at 16.5°C. The field survey and laboratory experiments revealed that E. radicosa is well adapted to relatively low PAR and water temperatures typical of warm temperate coastal regions in Japan. The poor response to high PAR and the inability of sporophytes to fully recover overnight from high PAR exposure indicates that the vertical distribution of this species is driven by the PAR environment.

Photosynthetic responses of Pyropia yezoensis f. narawaensis (Bangiales, Rhodophyta) to a thermal and PAR gradient vary with the life-history stage

Abstract: The effect of photosynthetically active radiation (PAR) and temperature on photosynthesis of the cultivated red alga, Pyropia yezoensis f. narawaensis (Saga-#5 Strain, Bangiales), was determined for microscopic sporophytes and macroscopic gametophytes with pulse-amplitude fluorometry and dissolved oxygen sensors. A clear difference in the temperature response of the maximum quantum yield (Fv/Fm) and oxygenic gross photosynthesis (GP) was revealed between the two life-history stages. The sporophyte Fv/Fm was not sensitive to temperature, although the model revealed an Fv/Fm maximum (0.60) at 16.7°C. In contrast, the gametophyte Fv/Fm was clearly sensitive to temperature and attained a maximum mean value of 0.55 at 14.7°C. The relationship between GP and temperature was also different. The maximum rates of GP of the sporophyte occurred at 30.7°C and was 17.1 μg O2 mgchl-a−1 min−1 (15.4–19.4, 95% Bayesian credible interval); however, maximum rates of GP for the gametophyte were much higher (110 μmol O2 mgchl-a−1 min−1) and occurred at a lower temperature (14.4°C). The response of oxygenic net photosynthesis to PAR also varied, and the initial slope (α), the saturation PAR (Ek) and the maximum photosynthetic rate (Pmax) of the gametophyte were much higher than the sporophyte. Therefore, we hypothesised that in species with a heteromorphic life history, such as those in the genus Pyropia, physiological responses to environmental gradients would be dissimilar.

The effect of irradiance and temperature on the photosynthesis of Hydropuntia edulis and Hydropuntia eucheumatoides (Gracilariaceae, Rhodophyta) from Vietnam

Abstract: The effect of irradiance and temperature on the photosynthesis of two Vietnamese edible algae, Hydropuntia edulis and H. eucheumatoides (Gracilariaceae, Rhodophyta), were determined using dissolved oxygen sensors and pulse amplitude–modulated fluorometry. Modeling the net photosynthesis–irradiance (P-E) responses of these species at 26°C revealed that the net photosynthetic rates quickly increased at irradiances below the estimated saturation irradiance (Ek) of 137 and 74 μmol photons m−2 s−1, with a compensation irradiance (Ec) of 40 and 29 μmol photons m−2 s−1, respectively. Gross photosynthesis and dark respiration rates determined over a range of temperatures (14°C −42°C) revealed that the highest gross photosynthetic rates were 7.1 and 4.7 mg O2 gww−1 min−1 and occurred at 31.2°C and 30.5°C, respectively [95% Bayesian credible interval (BCI): 30.4–31.8 and 29.0–31.8]. The dark respiration rates for both species initially increased linearly and began to decline above 34°C. The measured dark respiration rates ranged from 0 to 2.3 mg O2 gww−1 min−1. The values of maximum effective quantum yield (ΦPSII at 0 μmol photons m−2 s−1) occurred at 22.4°C (BCI: 21.2–23.3) and was 0.48 for H. edulis and at 22.8°C (BCI: 22.1–23.3) and was 0.49 for H. eucheumatoides. The temperature response of these species indicated that they were well adapted to the annual range of seawater temperatures in the study site but were likely close to the marginal temperatures for the optimum photosynthesis.

Spatial variations in nutrient supply to the red algae Eucheuma serra (J. Agardh) J. Agardh

The nutrient supply rates within the canopy of the economically important red algal species, Eucheuma serra J. Agardh were determined experimentally in a recirculating flow‐chamber. A single individual was placed in the working section of the 2000 × 200 × 250 mm3 acrylic flow‐chamber and subjected to unidirectional water velocities from 1.0 to 9.3 cm s−1. Rates of nutrient supply were determined using 9.7 mm diameter CaSO4 (gypsum) spheres that were attached to the thallus inside and outside of the canopy. The supply rates within the canopy were 56% less than outside of the canopy. Increases in internal and external water velocity asymptotically increased the nutrient supply rates regardless of location. A model was developed to examine how changes in ammonium and nitrate supply compared with the physiologically maximum uptake rates of these nutrients. The results suggest that when the ammonium concentration in the water was 20 µmol L−1 uptake rates were limited by the supply rate especially at velocities below 5 cm s−1, whereas in the case of 20 µmol L−1 of nitrate, the supply of nitrate was more than adequate to maximize nutrient uptake.

Effects of wave energy on the residence times of a fluorescent tracer in the canopy of the intertidal marine macroalgae, Sargassum fusiforme (Phaeophyceae)

We determined the relationship between the residence times of water within the canopy of the intertidal macroalgae, Sargassum fusiforme (Harvey) Setchell to the energy caused by hydrodynamic mixing. We measured the residence times (t) of fluorescein dye injected into the canopy (31 ± 9 ind/quadrat; canopy plan form area 6 × 1 m2) to estimate the length of time gametes persist within the canopy. The total kinetic energy (TKE) and wave energy (WE) was measured during dye dispersal, which ranged from 0.002 to 0.009 m2/s2 and 0.001 to 0.016 m2/s2, respectively. The experiments revealed that the canopy significantly (P < 0.0001) increased t, which was 56 ± 35 s inside of the canopy compared with 14 ± 4 s outside. Moreover, the relationship between t and energy could be statistically modeled with a power function, and for the results inside of the canopy, t = 3.67 TKE−0.50 for turbulent kinetic energy and t = 1.83 WE−0.38 for wave energy. Outside of the canopy, t = 0.98 TKE−0.50 and t = 1.83 WE−0.38 Based on the values of t determined for within the canopy, we developed a dispersion model to explore how gametes dispersed within the canopy. The estimated dispersion coefficient (D) with respect to WE, could be modeled as D = 403 WE0.55 and ranged from 10 to 42 cm2/s for the WE examined in the study. Areal gamete densities modeled in the canopy increased in density for increasing WE at short (0.5 h) durations of gamete discharge; however, the relationship reversed above 2 h of discharge.