Ryuta Terada

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.

Invasion of novel habitats uncouples haplo-diplontic life cycles

Bakers Law predicts uniparental reproduction will facilitate colonization success in novel habitats. While evidence supports this prediction among colonizing plants and animals, few studies have investigated shifts in reproductive mode in haplo‐diplontic species in which both prolonged haploid and diploid stages separate meiosis and fertilization in time and space. Due to this separation, asexual reproduction can yield the dominance of one of the ploidy stages in colonizing populations. We tested for shifts in ploidy and reproductive mode across native and introduced populations of the red seaweed Gracilaria vermiculophylla. Native populations in the northwest Pacific Ocean were nearly always attached by holdfasts to hard substrata and, as is characteristic of the genus, haploid–diploid ratios were slightly diploid‐biased. In contrast, along North American and European coastlines, introduced populations nearly always floated atop soft‐sediment mudflats and were overwhelmingly dominated by diploid thalli without holdfasts. Introduced populations exhibited population genetic signals consistent with extensive vegetative fragmentation, while native populations did not. Thus, the ecological shift from attached to unattached thalli, ostensibly necessitated by the invasion of soft‐sediment habitats, correlated with shifts from sexual to asexual reproduction and slight to strong diploid bias. We extend Bakers Law by predicting other colonizing haplo‐diplontic species will show similar increases in asexuality that correlate with the dominance of one ploidy stage. Labile mating systems likely facilitate colonization success and subsequent range expansion, but for haplo‐diplontic species, the long‐term eco‐evolutionary impacts will depend on which ploidy stage is lost and the degree to which asexual reproduction is canalized.

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.

The effect of irradiance and temperature on the photosynthesis of a native alga Sargassum fusiforme (Fucales) from Kagoshima, Japan

Abstract: The effect of irradiance and temperature on the photosynthesis of a Japanese native brown alga, Sargassum fusiforme, was determined by using dissolved oxygen sensors and pulse amplitude–modulated fluorometry. In situ measurements of the effective quantum yield (ΦPSII) decreased as irradiance increased at 12:00 PM and recovered in the late afternoon, indicating that a proportionately greater number of reaction centres were closed. Likewise, laboratory measurement after 6 hours of exposure to low and high (300 and 1000 μmol photons m−2 s−1, respectively) irradiances showed a relatively greater decrease in ΦPSII at high irradiance, and both treatments recovered overnight. A model of the net photosynthesis–irradiance relationship determined at 20°C revealed that the net photosynthetic rate quickly increased at irradiances below the estimated saturation irradiance of 391 μmol photons m−2 s−1 [95% Bayesian credible interval (BCI) of 299–515 μmol photons m−2 s−1]. Gross photosynthesis and dark respiration rates determined over a range of temperatures (8–36°C) revealed that the maximal gross photosynthetic rate was 24.1 (BCI: 21.5–26.8) μg O2 gww−1 min−1 at 22.9°C (BCI: 19.8–25.8), and the dark respiration rate increased nonlinearly from a low of 0.5 μg O2 gww−1 min−1 at 8°C to a high of 8.9 μg O2 gww−1 min−1 at 36°C. The highest value of the quantum yield (Fv/Fm = ΦPSII at 0 μmol photons m−2 s−1) was estimated to occur at 22.9°C (BCI: 21.8–23.9) and was 0.72 (BCI: 0.70–0.73). The specimens examined appeared to be well adapted to the natural temperature range of the study site. Although the irradiances on the fronds were strong enough to induce a drop in quantum yield, our evidence clearly suggests that full recovery occurs overnight.

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.

Taxonomic Notes on Marine Algae from Malaysia. III. Seven Species of Rhodophyceae

Abstract Six species of marine red algae are reported from Malaysia for the first time and their characteristic features are described: one species of the Halymeniaceae (Cryptonemiales), Cryptonemia crenulata (J. Agardh) J. Agardh; two species of the Solieriaceae (Gigartinales), Solieria anastomosa P. Gabrielson et Kraft and Kappaphycus cottonii (Weber-van Bosse) Doty ex P. Silva; three species of the Gracilariaceae (Gracilariales), Gracilaria multifurcata Børgesen, Gracilaria tenuistipitata Chang et Xia and Gracilariopsis bailiniae Zhang et Xia. Furthermore, spermatangial plants of Gracilaria firma Chang et Xia that confirm its presence in Malaysian waters are reported.

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.

Bispinodinium angelaceum gen. et sp. nov. (Dinophyceae), a new sand-dwelling dinoflagellate from the seafloor off Mageshima Island, Japan(1).

A new athecate dinoflagellate, Bispinodinium angelaceum N. Yamada et Horiguchi gen. et sp. nov., is described from a sand sample collected on the seafloor at a depth of 36 m off Mageshima Island, subtropical Japan. The dinoflagellate is dorsiventrally compressed and axi‐symmetric along the sulcus. The morphology resembles that of the genus Amphidinium sensu lato by having a small epicone that is less than one third of the total cell length. However, it has a new type of apical groove, the path of which traces the outline of a magnifying glass. The circular component of this path forms a complete circle in the center of the epicone and the straight “handle” runs from the sulcus to the circular component. Inside the cell, a pair of elongated fibrous structure termed here the “spinoid apparatus” extends from just beneath the circular apical groove to a point near the nucleus. Each of two paired structures consists of at least 10 hyaline fibers and this is a novel structure found in dinoflagellates. Phylogenetic analyses based on the SSU and LSU RNA genes did not show any high bootstrap affinities with currently known athecate dinoflagellates. On the basis of its novel morphological features and molecular signal, we conclude that this dinoflagellate should be described as a new species belonging to a new genus.

Effect of temperature and irradiance on the uptake of ammonium and nitrate by Laurencia brongniartii (Rhodophyta, Ceramiales)

The effects of temperature (20, 24 and 28 °C) and irradiance (15 and 40 μmol photon m−2 s−1) on the nitrate and ammonium uptake rates of the subtropical red alga, Laurencia brongniartii, were investigated to prepare for tank cultivation. Nitrate uptake followed saturation kinetics and was faster at higher irradiances and temperatures. In contrast, ammonium uptake was linear over the experimental range and was not affected by an increase in temperature. A parameter, β, was calculated to compare substrate uptake rates of nitrate along the linear portion of the uptake curve with that of ammonium. For nitrate, β was lower at low irradiance and higher at high irradiance (β = 0.007 ± 0.003 and 0.030 ± 0.002 [μmol N L−1 (μmol N gww−1 d−)−1], respectively). However, β was 0.023 ± 0.002 and 0.034 ± 0.002 [μmol N L−1 (μmol N gww−1 d−1)−1] for ammonium, suggesting a preference for ammonium over nitrate.