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Watanabe Y.,Kagoshima University | Nishihara G.N.,Nagasaki University | Tokunaga S.,Kagoshima Prefectural Fisheries Technology and Development Center | Terada R.,Kagoshima University
Journal of Applied Phycology

Phenology, irradiance, and temperature characteristics of an edible brown alga, Undaria pinnatifida (Laminariales), were examined from the southernmost natural population in Japan, both by culturing gametophytes and examining the photosynthetic activity of sporophytes using dissolved oxygen sensors and pulse amplitude-modulated chlorophyll fluorometer (IMAGING-PAM). Our surveys confirmed that sporophytes were present between winter and early summer, but absent by July. IMAGING-PAM experiments were used to measure maximum effective quantum yield (ΦII at 0 μmol photons m-2 s-1) for each of 14 temperatures (8-36 °C). Oxygen production was also determined over a coarser temperature gradient. Net photosynthesis and ΦII (at 0 μmol photons m-2 s-1) were observed to be temperature-dependent; the maximum ΦII was estimated to be 0.67, occurred at 21.2 °C, and was nearly identical to the optimal temperature of the net photosynthetic rate (21.7 °C). A net photosynthesis-irradiance (P-E) model revealed that saturation irradiance (Ek) was 119.5 μmol photons m-1 s-1, and the compensation irradiance (Ec) was 17.4 μmol photons m-1 s-1. Culture experiments on the gametophytes revealed that most individuals could not survive temperatures over 28 °C and that growth rates were severely inhibited. Based on our observations, temperatures greater than 20 °C are likely to influence photosynthetic activity and gametophyte survival, and therefore, it is possible that this species might become locally extinct if seawater temperatures in this region continue to rise. © 2014 Springer Science+Business Media Dordrecht. Source

Ashida H.,Japan National Research Institute of Fisheries And Environment of Inland Sea | Horie M.,Kagoshima Prefectural Fisheries Technology and Development Center
Fisheries Science

To illustrate the spawning characteristics of skipjack tuna Katsuwonus pelamis in the Northwestern Pacific Ocean, we examined seasonal changes in the histological condition of gonads, spawning fraction, and batch fecundity (BF) of skipjack tuna caught around Amami-Oshima in the northern Nansei Islands, Japan, from May 2011 to July 2013. Females classified as “mature” appeared from June to October, and mature males were present from April to November. Spawning began in June when the sea surface temperature (SST) exceeded 24 °C and peaked in August. Although the SST was still above 24 °C, spawning ended in September when the SST started decreasing continuously. The minimum size (fork length, FL) at first maturity was 40.5 cm for females and 37.6 cm for males. The BF (mean ± SD) and relative batch fecundity (RBF) were estimated at 93,700 ± 21,800 oocytes and 56.8 ± 14.3 oocytes/g, respectively. The total spawning fraction (spawning intervals) during the spawning season was estimated at 0.53 (1.88 days). These results indicate that the spawning activity of skipjack tuna around Amami-Oshima changes seasonally depending on SST. © 2015, Japanese Society of Fisheries Science. Source

Nagai S.,Japan National Research Institute of Fisheries Science | Miyamoto S.,Kaneka Corporation | Ino K.,Kaneka Corporation | Tajimi S.,Kumamoto Prefectural Fisheries Research Center | And 2 more authors.
Harmful Algae

In this study, the Kaneka DNA chromatography chip (KDCC) for the Alexandrium species was successfully developed for simultaneous detection of five Alexandrium species. This method utilizes a DNA-DNA hybridization technology. In the PCR process, specifically designed tagged-primers are used, i.e. a forward primer consisting of a tag domain, which can conjugate with gold nanocolloids on the chip, and a primer domain, which can anneal/amplify the target sequence. However, the reverse primer consists of a tag domain, which can hybridize to the solid-phased capture probe on the chip, and a primer domain, which can anneal/amplify the target sequence. As a result, a red line that originates from gold nanocolloids appears as a positive signal on the chip, and the amplicon is detected visually by the naked eye. This technique is simple, because it is possible to visually detect the target species soon after (<5 min) the application of 2 μL of PCR amplicon and 65 μL of development buffer to the sample pad of the chip. Further, this technique is relatively inexpensive and does not require expensive laboratory equipment, such as real-time Q-PCR machines or DNA microarray detectors, but a thermal cycler. Regarding the detection limit of KDCC for the five Alexandrium species, it varied among species and it was <0.1-10 pg and equivalent to 5-500 copies of rRNA genes, indicating that the technique is sensitive enough for practical use to detect several cells of the target species from 1 L of seawater. The detection sensitivity of KDCC was also evaluated with two different techniques, i.e. a multiplex-PCR and a digital DNA hybridization by digital DNA chip analyzer (DDCA), using natural plankton assemblages. There was no significant difference in the detection sensitivity among the three techniques, suggesting KDCC can be readily used to monitor the HAB species. © 2015 Elsevier B.V. Source

Watanabe Y.,Kagoshima University | Nishihara G.N.,Nagasaki University | Tokunaga S.,Kagoshima Prefectural Fisheries Technology and Development Center | Terada R.,Kagoshima University
Phycological Research

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 46μmol photons m-2s-1, and the compensation irradiance was 9μmol photons m-2s-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 46.3μmol O2 mgchl-a-1min-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 0.93μmol O2 mgchl-a-1min-1°C-1. The measured dark respiration rates ranged from -0.06μmol O2 mgchl-a-1min-1 at 6°C to -25.2μmol O2 mgchl-a-1min-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. © 2014 Japanese Society of Phycology. Source

Kawamata S.,Japan National Research Institute of Fisheries Engineering | Yoshimitsu S.,Kagoshima Prefectural Fisheries Technology and Development Center | Tanaka T.,Kagoshima Prefectural Fisheries Technology and Development Center | Igari T.,Kagoshima Prefectural Fisheries Technology and Development Center | Tokunaga S.,Kagoshima Prefectural Fisheries Technology and Development Center
Journal of Sea Research

Sedimentation can provide indirect benefits to the survival of macroalgae in areas with potentially high grazing pressure. Field studies were performed in an embayment with extensive urchin barrens but also with locally persistent fucoid beds, on the coast of Kagoshima, south-western Japan, to elucidate the physical and biological processes responsible for the maintenance of the beds. Rocky subtidal reefs devoid of fine sediment were almost completely barren and dominated by sea urchins (primarily Echinometra sp. A), while fucoid algae (predominantly Sargassum duplicatum) densely populated cobble sites overlaid with a thin layer of fine sediment (medium grain size: 0.15-0.25. mm). Quadrat samplings in areas intermixed with urchin barrens and sand flats as well as experimental addition of sediment suggested that Echinometra sp. was readily excluded from hard substratum overlaid with even only a thin layer of fine sediment. Quadrat surveys and a transplant experiment conducted at the border area between a cobble bed with a thin cover of fine sediment and a sediment-free boulder one indicated that sea urchins (mainly composed of Echinometra sp. and Diadema spp.) rarely invaded the sediment-covered bed to graze. Wave measurements at the entrance (8. m deep) of the embayment over a 3.5-year period showed that the study area had long-term extremely calm conditions (84% of significant wave heights < 0.1. m) and seasonal or transient moderate disturbances due to relatively high waves (significant wave height: 0.8-1.3. m). However, the 2-year time series of root-mean-square wave orbital velocity estimates at different sites consistently suggested that the wave-action intensities at urchin barrens were still too high for deposition of fine sediments which occurred in more wave-sheltered persistent fucoid area. Nearly 2-year investigations on sediment level change and on cobble substrates together with overlying sediment in the fucoid area suggested that the absence of fatal sediment inundation and maintenance of the thin overlying sediment layer (mean thickness < ca 2. mm) throughout the year allowed settlement and growth of sand-tolerant fucoids by preventing urchin grazing. © 2011 Elsevier B.V. Source

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