Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

<jats:p>Heatwaves under global warming have negative impacts on ecosystem primary producers. This warming effect may be synergized or antagonized by local environments such as light and nutrient availability. However, little is known about the interactive effects of warming, irradiance, and nutrients on physiology of marine macroalgae, which are dominant in coastal ecosystems. The present study examined the combined effects of warming (23 and 26 °C), irradiance (30 and 150 µmol photon m−2 s−1), and nutrients (enriched and non-enriched) on specific growth rate (SGR) and biochemical compositions of the canopy-forming marine macroalga Sargassum fusiforme. The negative effect of warming on SGR and ratio of chlorophyll (Chl) c to Chl a was antagonized by decreased irradiance. Moreover, the negative effect of temperature elevation on carbon content was antagonized by nutrient enrichment. These results suggest that the effect of warming on the growth and carbon accumulation of this species can be mitigated by decreased irradiance and nutrient enrichment.</jats:p>

DOI： 10.3390/jmse10040479

Language：English   Publishing type：Research paper (scientific journal)   Publisher：FRONTIERS MEDIA SA  

In order to understand how global warming effects on ecosystem primary production may change depending on nutrient enrichment, a new classification is proposed to disentangle and recognize the combination of interactions among several factors, based on the effect direction (positive, negative, or neutral) and its changes induced in it by the other factor (synergizing, antagonizing, inducing no change, or changing it in some other way). Marine macroalgae were chosen (as primary producers for which there is the most experimental information available) to review the relevant studies on which this new classification can be tested. It was observed the positive effects of elevated temperature and nutrient enrichment often synergized each other within the temperature range between relatively low and optimal growth levels. However, the negative effect of further temperature elevation from optimal to higher levels was antagonized by nutrient enrichment in some studies but was synergized in others, depending on the range of temperature elevation. The positive effect of nutrient enrichment was antagonized (but still positive) by temperature increase above the optimum in many cases, although the effect sometimes switched to a negative effect depending on the magnitude of nutrient enrichment. These results predict that global warming will enhance bottom-up effects on primary production in cold seasons and areas, and there will be a negative warming effect on production in hot seasons and areas, but it may be possible to mitigate this effect by appropriate levels of nutrient enrichment.

DOI： 10.3389/fmars.2022.774801

Web of Science

Language：English   Publishing type：Research paper (scientific journal)  

Ocean warming and the associated changes in fish herbivory have caused polarward distributional shifts in the majority of canopy-forming macroalgae that are dominant in temperate Japan, but have little effect on the alga Sargassum fusiforme. The regeneration ability of new shoots from holdfasts in this species may be advantageous in highly grazed environments. However, little is known about the factors regulating this in Sargassum species. Moreover, holdfast tolerance to high-temperature and nutrient-poor conditions during summer has rarely been evaluated. In the present study, S. fusiforme holdfast responses to the combined effects of temperature and nutrient availability were compared to those of sexually reproduced propagules. The combined effects of holdfast fragmentation and irradiance on regeneration were also evaluated. Propagule growth rate values changed from positive to negative under the combination of elevated temperature (20 °C-30 °C) and reduced nutrient availability, whereas holdfasts exhibited a positive growth rate even at 32 °C in nutrient-poor conditions. The regeneration rate increased with holdfast fragmentation (1 mm segments), but was unaffected by decreased irradiance. These results suggest that S. fusiforme holdfasts have a higher tolerance to high-temperature and nutrient-poor conditions during summer than propagules, and regenerate new shoots even if 1-mm segments remain in shaded refuges for fish herbivory avoidance.

DOI： 10.3390/plants10081522

PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

We determined the effects of irradiance, temperature, and desiccation on the photosynthesis of a brown alga, Sargassum muticum (Fucales), from its native distributional range in Japan by using a pulse amplitude modulation (PAM)-chlorophyll fluorometer and optical dissolved oxygen sensors. Photosynthesis-irradiance curves at three temperatures (8, 20, and 28 degrees C) showed that the maximum net photosynthetic rates (NPmax) and saturation irradiance were highest at 28 degrees C. Gross photosynthesis determined at 8-36 degrees C (every four increments) and 300 mu mol photons m(-2) s(-1) showed that the maximum gross photosynthetic rate (GP(max)) occurred at 19.5 degrees C (T-opt(GP)), which is consistent with the seawater temperature at its peaked abundance in Japan. The maximum quantum yields (F-v/F-m) of photosystem II (PSII) during the 72-h temperature exposures were above 0.60 at 8-28 degrees C but dropped at higher temperatures. Continuous exposure (12 h) to irradiance of 200 (low) and 1000 (high) mu mol photons m(-2) s(-1) at three temperatures showed remarkable decline in the effective quantum yields (Delta F/F-m') of PSII under high irradiance at 8 degrees C only; the F-v/F-m measured after 12-h dark acclimation also did not recover to initial values, signifying its sensitivity to photoinhibition at 8 degrees C. Furthermore, the alga exhibited tolerance to 2 h of desiccation with 80% of water loss from the thallus, and Delta F/F-m' recovered after 24 h of rehydration in seawater, suggesting potential of photosynthetic recovery of this alga at such low hydration threshold. In conclusion, the adaptation of S. muticum to relatively high irradiance, to broad range of temperature (8-28 degrees C), and to desiccation explains its potentially high invasive capacity.

DOI： 10.1007/s10811-021-02425-z

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

DOI： 10.1111/pre.12395

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

Recent declines of macroalgal forests due to climate change imply that the aquaculture production of macroalgae may also be negatively affected by ocean warming. It has previously been shown that nutrient enrichment can offset the negative impact of warming on the survival and growth of the cultivated macroalga Undaria pinnatifida, although it can also increase the risk of herbivory by unrecognized mesograzers. Observations of several hundreds or thousands of the isopod Cymodocea japonica around U. pinnatifida cultivation ropes in autumn, prompted the analysis of their size-frequency distribution, relationship between body size and consumption rate, and combined effects of elevated temperature and nutrient enrichment on the consumption rate of the algae by the isopod in the current study. Although the body size of the isopods collected in autumn was smaller than those collected in winter and spring, the consumption rate of 600 small isopods was similar to the rate of a large individual. Additionally, the consumption rate doubled in response to an increase in temperature from 15 to 18 degrees C and nutrient enrichment, and tripled with their combination. These results suggest that ocean warming combined with nutrient enrichment increase the risk of herbivory during U. pinnatifida cultivation, especially during isopod outbreak periods.

DOI： 10.1093/icesjms/fsaa069

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Frontiers Media SA  

DOI： 10.3389/fmars.2020.575721

Scopus

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1111/pre.12416

Scopus

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1007/s10811-019-01967-7

Scopus

Language：English   Publishing type：Research paper (scientific journal)  

© 2019 Japanese Society of Phycology The effects of irradiance, temperature, thermal- and chilling-light sensitivities on the photosynthesis of a temperate alga, Sargassum macrocarpum (Fucales) were determined by a pulse amplitude modulation (PAM)-chlorophyll fluorometer and dissolved oxygen sensors. Oxygenic photosynthesis–irradiance curves at 8, 20, and 28°C revealed that the maximum net photosynthetic rates (NPmax) and saturation irradiance were highest at 28°C, and lowest at 8°C. Gross photosynthesis and dark respiration determined over a range of temperatures (8–36°C) at 300 μmol photons m−2 s−1 revealed that the maximum gross photosynthetic rate (GPmax) occurred at 27.8°C, which is consistent with the highest seawater temperature in the southern distributional limit of this species in Japan. Additionally, the maximum quantum yields of photosystem II (Fv/Fm) during the 72-h temperature exposures were stable at 8–28°C, but suddenly dropped to zero at higher temperatures, indicative of PSII deactivation. Continuous exposure (12 h) to irradiance of 200 (low) and 1000 (high) μmol photons m−2 s−1 at 8, 20, and 28°C revealed greater declines in their effective quantum yields (ΦPSII) under high irradiance. While ΦPSII under low irradiance were very similar with the initial Fv/Fm under 20 and 28°C, values rapidly decreased with exposure duration at 8°C. At this temperature, Fv/Fm did not recover to initial values even after 12 h of dark acclimation. Final Fv/Fm of alga at 28°C under high irradiance treatment also did not recover, suggesting its sensitivity to photoinhibition at both low and high temperatures. These photosynthetic characteristics reflect both the adaptation of the species to the general environmental conditions, and its ability to acclimate to seasonal changes in seawater temperature within their geographical range of distribution.

DOI： 10.1111/pre.12398

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Language：English   Publishing type：Research paper (scientific journal)  

© 2019, © 2019 International Phycological Society. Effects of photosynthetically active radiation (PAR) and temperature on the photosynthesis of a subarctic edible brown alga, Saccharina angustata (Laminariaceae, Laminariales), from Hokkaido, Japan, were determined using a pulse amplitude modulation (PAM)–chlorophyll fluorometer and optical dissolved oxygen sensors. Photosynthesis–PAR experiments at 8, 16, and 20 °C revealed highest net photosynthetic rates at 16 °C; whereas, the temperature effect on maximum quantum yield (Fv/Fm) showed the highest Fv/Fm at 7.0 to 8.4 °C. These temperatures corresponded to the optimum temperatures for growth of Japanese Saccharina species. The maximum gross photosynthetic rate from gross photosynthesis–temperature curve was at 21.2 °C. Though consistent with the highest seawater temperature in the study site, it is close to the limit for thermal inhibition, because Fv/Fm above 20 °C was compromised after 48–72 h of incubation. Continuous 6-h exposures to PAR of 200 µmol (low) and 1000 µmol (high) photons m−2 s−1 at 8, 16, and 20 °C caused chronic photoinhibition in the alga, with greater declines in effective quantum yields of photosystem II (ΦPSII) and failure of recovery in post-dark acclimation Fv/Fm under high PAR. This physiological performance provides a basis for understanding the persistence of S. angustata near its southern boundary in the western Pacific.

DOI： 10.1080/00318884.2019.1571355

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

The combined effects of irradiance and temperature on photosystem II (PSII) photochemical efficiency were investigated in the microscopic sporophyte and macroscopic gametophyte stages of the cultivated red algae Pyropia yezoensis f. narawaensis and Pyropia tenera (Bangiales) from Kyushu Island, Japan. Continuous 12-h exposures to 10, 100, and 1000 molphotonsm(-2)s(-1) at 8, 20, and 28 degrees C revealed that sporophyte and gametophyte stages of both species have different tolerance characteristics to irradiance and temperature. Effective quantum yields (phi(PSII)) of sporophytes declined at 100 and 1000molphotonsm(-2)s(-1), and their maximum quantum yields (F-v/F-m) did not fully recover even after 12h of dark acclimation, indicating photodamage. Furthermore, this depression was greatest at 8 degrees C, suggesting low temperature-enhanced photoinhibition. Larger declines of phi(PSII) and subsequent failure of F-v/F-m recovery in the gametophyte were observed only at 1000 mol photons m(-2)s(-1), suggesting that the macroscopic stage is more tolerant to relatively higher irradiance than the sporophyte. Farming protocols, including the timing of conchospore seeding, as well as depth range and duration for Nori-net cultivation need to be optimized to ensure sustainable production of these high-valued seaweed cultivars.

DOI： 10.1007/s10811-018-1621-0

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Language：English   Publishing type：Research paper (scientific journal)  

© 2018, Springer Nature B.V. The effect of photosynthetically active radiation (PAR) and temperature on the photosynthesis of a temperate Japanese edible brown alga, Cladosiphon umezakii (Chordariaceae, Ectocarpales), from Honshu Island, Japan, was determined in the heteromorphic life history stages (macroscopic and microscopic) by using pulse-amplitude modulation (PAM) fluorometry and optical dissolved oxygen sensors. The microscopic stage is well-adapted to relatively low PAR environment, as revealed by its lower maximum net photosynthesis (NPmax), saturation (Ek), and compensation PAR (Ec), and higher value of the initial slope (α) compared to the macroscopic stage. Both stages share similar temperature optima (ToptGP 15.9–25.8 °C for macroscopic stage, 12.6–27.4 °C for microscopic stage), suggesting the possible occurrence of both generations in their habitats throughout the year. While these optimum temperatures are within the range of seawater temperature in the distribution of this species, they are close to the physiological limit of thermal inhibition. Continuous exposures (6 h) to 200 (low) and 1000 (high) μmol photons m−2 s−1 at 8, 16, and 28 °C revealed greater declines in effective quantum yields of photosystem II (ΦPSII) in the microscopic stage, confirming its low PAR adaptation. Low temperature-induced photoinhibition was likewise observed in both stages. Existing farming methods for Japanese Cladosiphon (especially for subtropical Cladosiphon okamuranus from Ryukyu Islands, Japan) may need to be modified to meet the optimum requirements of C. umezakii in the temperate region of Japan.

DOI： 10.1007/s10811-018-1655-3

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Language：English   Publishing type：Research paper (scientific journal)  

© 2018, Japanese Society of Fisheries Science. Artificial reefs have been introduced onto the subtidal sandy or rocky bottoms of Japanese coasts to expand the marine macroalgal beds that enhance the production of commercially important organisms. Previous studies showed that these artificial reefs were sequentially colonized by annual and perennial macroalgae. However, little is known about the competitive relationship between these annual and perennial species during succession. In the present study, we examined the successional change in macroalgal biomass on an artificial reef in Wakasa Bay, Japan, and tested the effects of removing annual and perennial species on the thallus length of successional perennial and annual species, respectively. The reef introduced between March and April 2008 was dominated by the annual brown alga Sphaerotrichia divaricata in July 2008, the annual brown alga Sargassum horneri in March 2009, and the perennial species Sargassum patens and Sargassum piluliferum in February 2010. The removal of S. horneri during autumn 2008 resulted in an increased thallus length in S. patens/S. piluliferum in March 2009, but had no effect in February 2010. Similarly, the removal of S. patens/S. piluliferum during autumn 2008 resulted in an increased thallus length in S. horneri in March 2009, but had no effect in February 2010. These results suggest that S. horneri and S. patens/S. piluliferum have a negative effect on the growth of each other in the first year of colonization, although the presence of S. horneri in the first year seems to have a minimal effect on the dominance of S. patens/S. piluliferum in the second year.

DOI： 10.1007/s12562-018-1263-9

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japanese Society of Fisheries Science  

DOI： 10.2331/suisan.WA2650

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J-GLOBAL

Language：English   Publishing type：Research paper (scientific journal)  

© 2018 Japanese Society of Phycology Although the stable nitrogen isotope ratio (δ15N value) of macroalgae is used to indicate sources of dissolved inorganic nitrogen in coastal marine environments, little is known about the effects of isotope fractionation on the δ15N value. We compared the δ15N values of Undaria pinnatifida cultivated at an inner bay and an exposed site (sites A and B, respectively) in Shizugawa Bay on the northeastern Pacific coast of Japan. Values for algal growth indicators, including thallus length, area, and weight, were higher at site B than at site A. The δ15N value of U. pinnatifida was significantly lower at site B (4.7 ± 1.0‰; mean ± standard deviation) than at site A (6.7 ± 0.4‰). This difference in the δ15N value of U. pinnatifida could not be explained by the δ15N value of seawater NO3 (source isotopic signature), which was similar at the two sites (7.5 ± 0.3‰). The pooled data from the two sites indicated that the δ15N value of U. pinnatifida decreased with increasing thallus size. The results suggest that the δ15N value of U. pinnatifida is influenced by isotope fractionation.

DOI： 10.1111/pre.12332

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.2216/18-26.1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Netherlands  

In Japan, fresh cultivated green alga, Caulerpa lentillifera (Caulerpaceae, Bryopsidales), are packed into polystyrene containers without seawater. They can stay fresh for 1 week inside the container under room temperature, suggesting a high tolerance to desiccation. This tolerance was evaluated in the present study by employing methods based on pulse amplitude modulation (PAM) fluorometry. The chronological change of the photochemical efficiency of photosystem II (PSII) of C. lentillifera in response to desiccation under conditions experienced during the commercial shipping was examined. Desiccation experiments were carried out for 2, 4, 8, and 12 days at 20 °C. Maximum quantum yields (Fv/Fm) were measured at the initial state, after each desiccation period, and after 10-min and 3, 6, and 24-h re-immersion in seawater. Fv/Fm of samples after a 2-day desiccation remained relatively high (0.78 ± 0.04 standard deviation (SD)), while those after 4- and 8-day desiccation periods decreased and yet were considered active with values greater than 0.40 following rehydration. Samples under the 12-day desiccation had the greatest decline in Fv/Fm, (0.10 ± 0.10), along with 72% critical water loss. Failure of the seaweed to recover from desiccation stress further indicates deactivation of the photosystem, which is perhaps associated with multiple cellular alterations that result at the end in a dysfunctional alga. The packaging system that makes use of polystyrene containers for thermal insulation and an absorbent sheet for moisture control may have provided an optimal environment for the seaweed to extend its “freshness” up to 1 week by maintaining photochemical efficiency.

DOI： 10.1007/s10811-018-1442-1

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1111/pre.12220

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Netherlands  

Mass cultivation of the chlorophyte Chaetomorpha crassa has the potential to serve as a biological filter for the reduction of eutrophication in summertime Japanese waters. In order to clarify the suitability of C. crassa for this purpose, seasonal changes in its photosynthesis, growth, NO3–N uptake, nitrogen content, and salinity tolerance were investigated trimonthly from May 2011 to February 2012, with samples collected in Nagatsuraura Lagoon, northern Japan. Significant effects of seawater temperature on photosynthesis, growth, and nitrogen accumulation were also detected in all four seasons, and all parameters at summer temperatures (24–28 °C) were significantly greater than those at the temperatures of other seasons (8–20 °C). Moreover, compared to the other three seasons, C. crassa showed significantly higher growth rates at 16–4 psu and higher survival percentages at 8–2 psu during the summer. In conclusion, due to its high capacity for growth and nitrogen accumulation, and greater physiological tolerance of low salinity during the elevated temperature period, large-scale cultivation of C. crassa could play a significant role in the bioremediation of both saline and brackish waters during summer.

DOI： 10.1007/s10811-017-1381-2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

The combined effects of photosynthetically active radiation (PAR) and temperature on the photosynthesis of a temperate Japanese brown alga, Sargassum patens (Fucales), were determined by field and laboratory measurements. Underwater measurements of the natural population of this alga in Kagoshima, Japan, revealed that the effective quantum yield (I broken vertical bar (PSII) ) declined with increasing incident PAR, with minimum I broken vertical bar (PSII) occurring during noon to early afternoon. I broken vertical bar (PSII) recovered in the evening, indicating dynamic photoinhibition. In laboratory experiments, I broken vertical bar (PSII) was also negatively correlated with PAR, which decreased after 12 h of continuous exposure to 200 (low) and 1000 (high) mu mol photons m(-2) s(-1) at 8, 20, and 28 A degrees C. Maximum quantum yield (F (v) /F (m) ) at 8 A degrees C with low PAR failed to recover after 12 h of dark acclimation, suggesting the influence of low temperature in chronic photoinhibition. Photosynthesis-irradiance (P-E) curves likewise revealed lower net photosynthetic rates and photoinhibition at 8 A degrees C. Gross photosynthesis and dark respiration experiments determined over a range of temperatures (8-40 A degrees C) revealed that the maximum gross photosynthetic rate (GP (max)) occurred at 26.9 A degrees C. F (v) /F (m) after 72 h of temperature exposures was stable at 8-32 A degrees C; but it was deactivated at 36 and 40 A degrees C. This species is well-adapted to the current range of temperature in the temperate region of Japan (7-28 A degrees C). However, the combined effects of low temperature and PAR may influence algal photosynthetic efficiency and so may be limiting at the marginal region of northern distribution of this temperate species.

DOI： 10.1007/s10811-017-1344-7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley-Blackwell  

The rapid evolution of non-native species can facilitate invasion success, but recent reviews indicate that such microevolution rarely yields expansion of the climatic niche in the introduced habitats. However, because some invasions originate from a geographically restricted portion of the native species range and its climatic niche, it is possible that the frequency, direction, and magnitude of phenotypic evolution during invasion have been underestimated. We explored the utility of niche shift analyses in the red seaweed Gracilaria vermiculophylla, which expanded its range from the northeastern coastline of Japan to North America, Europe, and northwestern Africa within the last 100 years. A genetically informed climatic niche shift analysis indicates that native source populations occur in colder and highly seasonal habitats, while most non-native populations typically occur in warmer, less seasonal habitats. This climatic niche expansion predicts that non-native populations evolved greater tolerance for elevated heat conditions relative to native source populations. We assayed 935 field-collected and 325 common-garden thalli from 40 locations, and as predicted, non-native populations had greater tolerance for ecologically relevant extreme heat (40°C) than did Japanese source populations. Non-native populations also had greater tolerance for cold and low-salinity stresses relative to source populations. The importance of local adaptation to warm temperatures during invasion was reinforced by evolution of parallel clines: Populations from warmer, lower-latitude estuaries had greater heat tolerance than did populations from colder, higher-latitude estuaries in both Japan and eastern North America. We conclude that rapid evolution plays an important role in facilitating the invasion success of this and perhaps other non-native marine species. Genetically informed ecological niche analyses readily generate clear predictions of phenotypic shifts during invasions and may help to resolve debate over the frequency of niche conservatism versus rapid adaptation during invasion.

DOI： 10.1111/eva.12592

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PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Netherlands  

High cellulose contents have been found in the thalli of species belonging to the green seaweed genus Chaetomorpha, indicating that they have high potential of cultivating for bioethanol production. The aim of this study was to produce critical information as a guide for the selection of suitable Chaetomorpha species from coastal areas of Japan for commercial cultivation. Three common Japanese Chaetomorpha species, Chaetomorpha crassa, Chaetomorpha moniligera, and Chaetomorpha spiralis, were collected from Matsushima Bay, northern Japan. A series of laboratory experiments were set up to compare photosynthesis, nutrient uptake, and growth, and tolerance of high temperature and low salinity. Compared with C. spiralis and C. moniligera, C. crassa exhibited significantly greater photosynthesis and growth, which was likely related to its greater nutrient uptake ability. In addition, C. crassa showed higher survival at high temperatures of 30 and 35 °C, and at low salinities of 8–4 psu. Therefore, due to its greater growth ability and higher physiological tolerance to high temperature and low salinity, C. crassa should be considered a suitable candidate with great potential for mass cultivation.

DOI： 10.1007/s10811-017-1306-0

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Flow fields in Shizugawa Bay on the Sanriku ria coast, which faces the Pacific Ocean, were investigated using hydrographic observations for the purpose of understanding oceanographic conditions and the process of water exchanges in the bay after the 2011 earthquake off the Pacific coast of Tohoku. In spring to summer, density-driven surface outflow is part of estuarine circulation and is induced by a pressure gradient force under larger longitudinal gradients in density along with lower salinity water in the innermost part of the bay, regardless of wind forcing. In winter to summer, another density-driven current with a thermal structure is induced by a pressure gradient force under the smaller longitudinal density gradients in calm wind conditions. Particularly in winter, Tsugaru Warm Current water can be transported in the surface layer inside the bay. Wind-driven bay-scale circulation with downwind and upwind currents in the surface and deeper layers, respectively, is induced by strong longitudinal wind forcing under the smaller longitudinal density gradients, irrespective of season. Particularly in fall to spring, this circulation can cause the intrusions of oceanic water associated with Oyashio water and Tsugaru Warm Current water in the deeper layer. These results suggest that wind- and density-driven currents can produce the active exchange of water from inside and outside the bay throughout the year.

DOI： 10.1007/s10872-017-0442-0

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Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

© 2018 National Shellfisheries Association. All rights reserved. The sea urchin Mesocentrotus nudus is commercially harvested between June and August in northeastern Japan. A previous study showed that feeding on Saccharina japonica between April and June resulted in gonad quantity and quality improvement in this species from a barren. No information is available on the optimal culture period for harvest before the fishing season. The purpose of this study was to determine whether gonad size and quality (color, texture, and taste) can be improved before the fishing season and to verify the possibility of an early harvest. The sea urchins M. nudus were collected from a barren and placed under two types of culture conditions: suspended cages in a bay and a laboratory circulation system. They were fed S. japonica between December and May or March. Gonad indices, hardness, and color [L∗, a∗, and b∗, and ΔEab∗ (a unit of acceptable commercial color difference from a fishing ground for each treatment)], and free amino acid (FAA) contents of the urchin gonads at the start of rearing experiments and at the end of cage (C) and laboratory feeding (LF) cultures were measured. These variables were also compared between LF and laboratory-starved urchins to confirm the dietary effect of this kelp. Gonad indices in treatments C and LF were significantly higher than those at the start of the experiment and those in laboratory starvation (P < 0.01), although there was no significant difference between C and LF. Gonads in treatment C were significantly softer than that at the start of the experiment (P < 0.0001). ΔEab∗ of gonads in treatment C was the lowest, indicating that the gonad color was close to the preferred color. There was no significant difference in the total FAA content between C and LF treatments, whereas, of the umami FAA, glutamic acid content was significantly higher in gonads from C than LF. Of the bittertasting FAA, tyrosine and valine contents were significantly higher in LF gonads than in C gonads. These results suggested that gonad size, hardness, and color of M. nudus were improved before the fishing season by initiating culture in December with S. japonica feeding.

DOI： 10.2983/035.037.0318

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

To elucidate the effects of seawater temperature on long-term recruitment of juvenile Strongylocentrotus intermedius, annual changes in the juvenile density were monitored for 25 years from 1987 to 2011 off the coast of Rebun Island in the Sea of Japan off northern Hokkaido, Japan. The densities of 8-9 month and 1 year old juveniles fluctuated greatly from 0 to 47.2 ind/m(2) and from 1.2 to 79.2 ind/m(2), respectively. However, the recruitment occurred frequently and the densities of 1 year old juveniles exceeded 20 ind/m(2) in 1987, 1989, 1992, 1997, 2004, and 2007, indicating a high level of recruitment. Significant negative correlations between the densities of 8-9 month old juveniles and the monthly average water temperature from June to September of the previous year were detected (p &lt; 0.05). In particular, the correlation was the most significant in June (p &lt; 0.01). The densities were high (&gt; 20 ind/m(2)) at 10-11 degrees C and low (&lt; 10 ind/m(2)) at 12-13 degrees C. As a previous study indicates that the gonads develop from growth to spent stage during these months in Rebun Island, no significant increased water temperature in the northeastern Sea of Japan may be concerned with gonad maturation and spawning of adult population, leading to success in juvenile recruitment. (C) 2017 Published by Elsevier B.V.

DOI： 10.1016/j.rsma.2017.07.006

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER JAPAN KK  

The color of Undaria pinnatifida after boiling is an important factor determining its marketable value. Our previous study showed that decreased nutrients and elevated irradiance resulted in increases of lightness and yellowness (i.e., discoloration) of this alga. However, little is known about the optimal levels of nutrients and irradiance required to decrease these color values and the combined effects of these factors and boiling. We conducted two culture experiments to test the effects of nutrients (non-enriched and 1.25, 5, and 25% PESI enriched treatments), irradiance (0, 10, 30, and 180 A mu mol m(-2) s(-1)), and boiling on lightness L*, redness a*, and yellowness b* of this alga. L* and b* did not differ between non-enriched and 1.25-5% PESI treatments, but were lower in the 25% PESI treatment. L* and b* were lowest at 0-10 A mu mol m(-2) s(-1), although negative growth occurred at 0 A mu mol m(-2) s(-1). Decreased irradiance had a positive or little effect on a* before boiling, but had a negative effect after boiling. These results suggest that around 25% PESI and 10 A mu mol m(-2) s(-1) were the optimal levels to decrease the three color values of this species after boiling.

DOI： 10.1007/s12562-017-1113-1

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

In northern Japan, Saccharine kelps are natural diets for sea urchins and are known to enhance sea urchin gonad size. However, little is known about the effects of the kelp diet on gonad quality and consistency among individuals. In the present study, Mesocentrotus nudus adults collected from a barren were cultured in a suspended cage from late February to early June 2014 in Shizugawa Bay, Miyagi Prefecture. They were fed stipes of Undaria pinnatifida for 56 d followed by fresh Saccharine japonica kelp for 42 d. At the end of the culture period, gonad indices, gonad hardness, gonad color (L* (lightness), a* (redness), b* (yellowness)), free amino acid (FAA) contents in the gonads, and sensory qualities of the cultured sea urchins (EC) were measured and compared to those of the natural population from the barren (EB) and those from the Eisenia bicyclis kelp bed (EK) in the bay. Gonad index and L* values of EC urchins were higher than those of urchins from the barren at the start of culture (SCB). Total color (L*, a*, b*) of the gonads of EC and EK urchins were similar. Gonad hardness of EC and EK urchins was similar and lower than that of EB urchins, and the coefficients of variation of gonad index, color, and hardness were lower than those from the barren (SCB and EB). Sweet tasting alanine contents of the gonads of EC urchins were markedly higher than those of the gonads from the other urchin specimens. Bitter tasting FAA contents of the EC urchin gonads were higher than those of EK and EB urchins, although arginine and lysine contents were lower than those of EB urchins. Sensory scores of overall taste of EC urchins were higher than those of EB urchins and similar to EK urchins, possibly due to the increased alanine content. These results suggest that gonad size, color, hardness, taste, and consistency among individuals of M. nudus collected from barrens can be improved to reach levels similar to those of urchins from the E. bicyclis kelp bed by cage culture with short-term feeding of Saccharine kelps. Changes in gonad qualities seemed to be mainly due to S. japonica as the food source because hard U. pinnatifida stipes were rarely eaten and had markedly low protein content. Extension of cage culture duration with S. japonica feeding from spring to summer would increase gonad size and further improve gonad quality.

DOI： 10.1016/j.aquaculture.2017.04.033

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The subsidence caused by an earthquake can be regarded as a large-scale depth manipulation experiment that can provide valuable information about the formation of marine subtidal communities. To assess the causes of subtidal zonation patterns in macroalgae, we established a permanent survey area (4 m wide x 30 m long offshore) and conducted a long-term monitoring survey of the kelp Eisenia bicyclis and its associated assemblages on a rocky shore of the Oshika Peninsula in northeastern Japan where a 0.9 m subsidence occurred due to the 2011 Tohoku Earthquake. After the subsidence, the distribution of E. bicyclis expanded toward the shallower area, but the density of adults remained unchanged while recruitment declined at the offshore margin. In contrast, the perennial species Sargassum confusum and Sargassum siliquastrum tended to occupy the intermediate depth area and their vertical ranges of distribution did not change over time. No clear change was observed in the distribution of grazers. The most dominant herbivorous snail Omphalius rusticus was evenly distributed over the survey area while the distribution of the sea urchin Hemicentrotus pulcherrimus was limited to the shallower area. We hypothesized that the distributional expansion of the perennial Sargassum species toward the shallower area was prevented by active snail grazing during the microscopic stages of the plants as well as spatial competition with the kelp E. bicyclis. Survival of the subsided E. bicyclis at the lower limit was longer than predicted, indicating that a subsidence event could produce time-lagged effects. (C) 2017 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.rsma.2017.05.009

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Color is one of the important factors that determine the commercial value of cultivated marine macroalgae such as the brown alga Undaria pinnatifida (Laminariales; Phaeophyta) in Japan. Macroalgal color is fundamentally derived from the algal photosynthetic pigment content, which is affected by abiotic factors. However, little is known about the quantitative relationship between pigment content and color and the direct effects of abiotic factors on the color of marine macroalgae. We conducted a 24-day indoor culture experiment to assess the combined effects of nutrient availability (enriched and nonenriched seawater), seawater temperature (15 and 5 A degrees C), and irradiance (180 and 30 mu mol photons m(-2) s(-1)) on the concentrations of six pigments (chlorophyll (Chl) a, Chl c (1), Chl c (2), fucoxanthin, violaxanthin, and zeaxanthin) and three color values (lightness L*, redness a*, and yellowness b*) of U. pinnatifida sporophytes. Negative correlations between pigment content and color values of the cultured algae were detected. Reduced nutrient availability, decrease in temperature, and elevated irradiance resulted in decreased pigment contents and increased color values. Moreover, a significant interaction between nutrient availability and temperature indicated that the positive effect of nutrient enrichment was antagonized by a decrease in temperature. These results suggest that U. pinnatifida can discolor under nutrient-poor, winter temperature, and saturated irradiance conditions. To increase the commercial value of this species, artificial nutrient enrichment during spring or cultivation from a deeper depth may be effective.

DOI： 10.1007/s10811-016-1036-8

Web of Science

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY  

Understanding the evolutionary processes that have created diversity and the genetic potential of species to adapt to environmental change is an important premise for biodiversity conservation. Herein, we used mitochondrial trnW-L and cox3 and plastid rbcL-S data sets to analyze population genetic variation and phylogeographic history of the brown alga Sargassum fusiforme, whose natural resource has been largely exterminated in the Asia-Northwest Pacific in the past decades. Phylogenetic trees and network analysis consistently revealed three major haplotype groups (A, B, and C) in S. fusiforme, with A and B distributed in the Japan-Pacific coast. Group C consisted of three subgroups (C1, C2, and C3) which were distributed in the Sea of Japan, the Yellow-Bohai Sea, and East China Sea, respectively. Isolation-with-migration (IMA) analysis revealed that the three groups diverged approximately during the mid-Pleistocene (c.756-1,224 ka). Extended Bayesian skyline plots (EBSP) showed that groups A and B underwent relatively long-term stable population size despite a subsequent rapid demographic expansion, while subgroups C2 and C3 underwent a sudden expansion at c. 260 ka. F-ST and AMOVA detected low population-level genetic variation and high degrees of divergence between groups. The cryptic diversity and phylogeographic patterns found in S. fusiforme not only are essential to understand how environmental shifts and evolutionary processes shaped diversity and distribution of coastal seaweeds but also provide additional insights for conserving and managing seaweed resources and facilitate predictions of their responses to future climate change and habitat loss.

DOI： 10.1111/eva.12455

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Scopus

PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY  

Previous experiments with a factorial design have revealed the effects of several environmental factors on species performance and their interactions, which indicate synergistic or antagonistic effects. Temperature, nutrient availability, and irradiance are well-known environmental factors that affect the growth and chemical composition of brown algae. However, relatively few studies have tested their combined effect on brown algal growth and chemical composition using a three-way factorial design. We conducted a culture experiment to test the combined effects of elevated summer temperatures (23 and 26 degrees C), irradiance (180 and 30 mol photon m(-2) s(-1)), and nutrient availability (enriched and non-enriched seawater) on four relative growth rates (RGRs; based on wet weight, blade width, length, and area) and three chemical compositions (including carbon, nitrogen, and phlorotannin content) in juvenile sporophytes of the kelp Eisenia bicyclis. RGR based on blade width was the most sensitive to abiotic factors among all RGRs. A significant interaction between temperature and nutrient availability on this RGR suggested that the negative effect of elevated temperature was antagonized by a reduction in nutrient availability. Similarly, the positive effect of elevated irradiance on carbon content was synergized by reduced nutrient availability. Moreover, the negative effect of increased irradiance on nitrogen content was antagonized by elevated temperature in nutrient-enriched treatments, but not in non-enriched treatments. The content of carbon-based phlorotannins increased with reduced nutrient availability but not with elevated irradiance. These results suggest that these abiotic factors have complex interactions on the growth and chemical composition of this species.

DOI： 10.1111/pre.12170

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Short-term flow fluctuations in the southern central part of Onagawa Bay were examined using long-term mooring and hydrographic data observed during the period from May 2013 to April 2014. The short-term flow fluctuations were dominant in the periodic bands of 15-27 days and shorter than 10 days. The principal and minor components of these flow fluctuations were respectively along and across the local isobaths, which are almost parallel in the north direction. The northward flow fluctuations along the local isobaths were correlated with the northeastward wind fluctuations in both periodic bands, and these correlations were more evident from fall to winter. On the basis of these results, the northward flows are regarded as wind-induced barotropic coastal jets. On other hand, the eastward flow fluctuations across the local isobaths were related to inflow and outflow via the bay mouth or the Izushima Channel. Inflow and outflow with reverse flow at lower depths formed in summer, but those with vertically uniform flow tended to form in winter. The main summertime inflow and outflow were driven by horizontal gradients in density. These permit us to regard the main summertime inflow and outflow as gravitational circulation. Also, the summertime inflow can be intermittently caused by internal waves.

DOI： 10.1007/s10872-016-0360-6

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

AimOceanic currents are among the most pervasive hydrodynamic features in shaping community dynamics, population connectivity and phylogeographical structure of intertidal species. Here, we test whether population structure and biogeographical gradients of genetic diversity in the brown alga Sargassum thunbergii are correlated with oceanic currents in the north-west Pacific (NWP).
LocationNorth-west Pacific (25.07 degrees N-43.36 degrees N).
MethodsNuclear internal transcribed spacer-2 and mitochondrial cox3 sequences were obtained from 835 and 810 individuals of S. thunbergii respectively. Parsimony networks and phylogenetic trees (maximum parsimony and Bayesian inference) were constructed to evaluate phylogeographical structure. Pairwise F-ST estimates and analyses of molecular variance (AMOVA) at various hierarchical levels (latitude, longitude, marine provinces, biogeographical basins and zoogeographical zones) were conducted to elucidate population genetic differentiation. migrate software was used to estimate the number of migrants between adjacent populations.
ResultsSeveral lines of evidence indicate that S. thunbergii is characterized by shallow population structure. Geographical distances do not correlate with population pairwise genetic differentiations. The corridor/stepping-stone model-based coalescent analyses reveal high levels of asymmetric gene flow among S. thunbergii populations, with the numbers of migrants largely corresponding to the directions of oceanic current systems in the NWP. Genetic signatures also indicate that Jeju Island, Korea might act as a transition zone for dispersal of S. thunbergii in the NWP driven by the Kuroshio Current, thus facilitating subsequent transportation northward into the Sea of Japan and the Yellow-Bohai Sea.
Main conclusionsPopulation genetic homogeneity in S. thunbergii was mainly structured by oceanic currents rather than palaeoclimatic events. Our study illustrates an important phylogeographical case of how coastal hydrodynamic factors contributed to population connectivity and geographical shifts of genetic diversity for marine organisms without a pelagic stage.

DOI： 10.1111/jbi.12856

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：INT PHYCOLOGICAL SOC  

In northern Japan, the production of Saccharina japonica exhibits marked annual fluctuation due to changes in seawater temperature and nutrient availability during winter and spring. To better understand this phenomenon, we examined the combined effects of temperature (5 degrees C, 10 degrees C, 15 degrees C and 20 degrees C) and nutrient availability (seawater enriched with 25% Provasoli's enriched seawater vs nonenriched seawater) on photosynthesis, growth and survival and nitrogen and chlorophyll a contents of juvenile sporophytes (2-3 cm) and larger size class sporophytes (100-150 cm) from southern Hokkaido. Both juvenile sporophytes and discs from 100-150-cm-class sporophytes cultured in enriched seawater showed significantly higher growth rates and photosynthetic activities than those cultured in nonenriched seawater. This difference likely was due to the significantly higher nitrogen and chlorophyll a contents of thalli grown in enriched seawater. Significant effects of temperature on growth and photosynthesis were also detected. A significant interaction between temperature and nutrient availability for relative growth rate (RGR) was detected. The positive effect of elevated nutrient availability on RGRs was magnified by an increase in temperature from 5 degrees C to 15 degrees C for juvenile sporophytes and from 5 degrees C to 10 degrees C for 100-150-cm-class sporophytes; whereas, the negative effect of elevated temperature from 10 degrees C to 15 degrees C on RGRs of 100-150-cm-class sporophytes was antagonised by a reduction in nutrient availability. In contrast to the 100% survival rate in enriched seawater, dead juvenile sporophytes and discs from 100-150-cm-class sporophytes were found at 15 degrees C and 20 degrees C in nonenriched seawater, and the survival rates decreased with increasing temperature. Therefore, the growth and survival of sporophytes of S. japonica are significantly affected by nutrient availability and temperature, which may lead to marked fluctuations in annual production.

DOI： 10.2216/16-91.1

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER JAPAN KK  

Deforestation of the kelp Ecklonia cava has been widely reported in Japan, and may be due to physiological stress caused by warm seawater temperatures and low nitrogen availability. To test this hypothesis, we examined the effects of temperature (20, 26, 28, and 30 A degrees C) and nitrogen conditions (seawater enriched with 25 % PESI vs. non-enriched seawater) on photosynthesis, growth and survival, and nitrogen and chlorophyll a content of juvenile sporophytes (3-4 cm) along the coast of the Izu Peninsula, Japan. The juvenile sporophytes cultured in enriched medium showed significantly greater photosynthetic activity and relative growth rates than those cultured in non-enriched seawater at 20-28 A degrees C, likely because of the much higher nitrogen and chlorophyll a content in the enriched medium. A significant effect of temperature on photosynthesis and relative growth rates was also detected under both nitrogen conditions. However, in contrast to the excellent survival exhibited in the enriched medium, dead juveniles were observed in non-enriched seawater at all temperatures, and survival rates decreased with increasing temperature. These results reveal that growth and survival of E. cava juvenile sporophytes are negatively affected by low nitrogen availability and high seawater temperature, which may result in deforestation of this kelp.

DOI： 10.1007/s12562-016-0998-4

Web of Science

Language：English   Publisher：SPRINGER  

DOI： 10.1007/s10811-015-0654-x

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Recent studies on global warming report that increases in seawater temperature cause coastal ecosystem changes, including a shift in marine algal distribution in temperate regions. To assess the influence of increased seawater temperature on ecophysiological responsiveness and potential shifts in abundance and distribution of kelp, we investigated the seasonal changes in standing biomass, growth, and maturation of natural populations of Saccharina japonica by taking monthly measurements in 2005, 2006, and 2007 in Matsushima Bay, northern Honshu, Japan, which is the southernmost range of this species. Compared to kelps collected in 2005, a sharp decline in standing biomass, later sporophyte occurrence, early growth, greater erosion, and failed sporophyte reproduction were found in kelps collected in 2006, which was a year characterized by relatively high seawater temperature. The population of S. japonica was absent in 2007, when the seawater temperature was higher than that in 2005 and 2006. These results suggest that the seawater temperature in Matsushima Bay is unfavorable for the development and reproduction of this cold-water kelp. If seawater temperatures in this bay remain high over long time periods because of continuous global warming, the southern limit of distribution of S. japonica likely will shift further north.

DOI： 10.1007/s10811-014-0417-0

Web of Science

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Apart from certain studies on Macrocystis pyrifera (Linnaeus) C. Agardh, very few in situ experimental studies on production have been carried out to verify that "bottom-up effects" (relating to nutrient supply) are more important than "top-down" effects (relating to herbivory) in temperate kelp forests. The effects of nutrient supply on recruitment and production of hatchery-raised gametophytes of Saccharina japonica, cultivated on a rope, and wild Saccharina religiosa, cultivated on a rope and on new concrete reefs placed at the sea bottom, were examined at an experimental site with artificial nutrient addition continuously from October 2008 to May 2009 and compared to kelp that was cultivated from October 2008 to May 2009 without nutrient supply, at a natural site in Tomari (Sea of Japan, southwestern Hokkaido, Japan). At both sites, sea urchins were removed for exclusion of top-down effect. At the natural site, no hatchery-raised S. japonica and wild S. religiosa grew on the rope. No wild S. religiosa grew on the porous-concrete reefs and rocks. At the nutrient-enhanced site, S. japonica and S. religiosa grew rapidly on the rope, at rates of 47.7 and 33.3 plants/10 cm length rope, respectively. S. religiosa grew on the concrete reefs at a concentration of 9.7 plants/0.3 m(2). At the nutrient-enhanced site, the concentrations of NH4-N, NO3-N, NO2-N, and PO4-P ranged from 35.2-173.2, 2.1-10.9, 0.3-1.5, and 0.8-2.6 mu mol L-1, respectively, being markedly higher than those at the natural site, where these nutrient concentrations were almost equal to the averages off Tomari. These results indicate that the production of Saccharina kelp is restricted by bottom-up effects (at a low nutrient concentration) in the Sea of Japan, southwestern Hokkaido. Nutrient supply would be essential for growth enhancement of Saccharina kelp production in a marine environment around Japan where, in recent times, water temperatures have increased by ca. 0.5 A degrees C and nutrient concentrations have decreased.

DOI： 10.1007/s10811-013-0196-z

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

In northern Japan, massive production of high-quality specimens of the kelp Undaria pinnatifida prior to the traditional harvest season is strongly needed to meet commercial demand. To address this need, we tested the effects of controlled thinning by cutting small plants on the growth and maturation of sporophytes cultivated in Matsushima Bay, northern Japan. In early December 2009, the stocking densities of cultivated kelps were thinned to 10 and 5 plants per 4 cm thread section in two experimental groups. In contrast, no thinning was conducted during cultivation until March 2010 in the control group (about 16-20 plants per 4 cm thread section). Morphological features, photosynthesis, and carbon and nitrogen contents were compared among the three groups. Compared to kelps of control group, total length, stipe width, the length and width of sporophyll, and dry weights of blade and sporophyll showed significantly higher values in kelps of the two experimental groups. However, stipe length of kelps of control group was significantly greater than those of the two experimental groups. The photosynthetic rates and nitrogen contents of kelps of the two experimental groups were significantly greater than those of the control from January to March. No significant differences occurred in all these parameters between kelps of the two experimental groups. Based on these results, the growth and maturation of U. pinnatifida sporophytes can be promoted greatly by experimental thinning, and this will improve production of high-quality specimens of kelps and increase economic returns before the traditional harvest season.

DOI： 10.1007/s10811-013-0071-y

Web of Science

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Although large perennial brown algae are known to show great morphological plasticity responding to specific environmental factors such as depth and wave exposure, there are few reports showing this morphological variability taking into account age or size composition. Here, we conducted age- and size-based morphological comparison between the perennial brown alga Sargassum macrocarpum C. Agardh from their upper depth limit, middle depth, and lower depth limit at an exposed coast in northern Kyoto, Japan. Model II regression was fitted for the relationships between age or stipe diameter (SD) and morphological variables including SD, holdfast weight (HW), number of main branches (MBN), total weight of main branches (MBW), thallus weight (TW), and thallus length (TL) of 30 specimens collected seasonally from each depth zone. The differences between depths in these regression equations were analyzed using SMATR. Although SD, HW, and MBN of the specimens did not differ between depths under both age- and SD-basis, there were significant differences between depths in MBW, TW, and TL, suggesting that the differences in TW between depths are resulted from differences in MBW. Whereas TW at the lower depth limit was lower than that at the upper depth limit or middle depth in many months, TL at the upper depth limit was shorter than that at the middle depth or lower depth limit in some months. These results suggest that S. macrocarpum at shallower depths tend to have short and bushy morphology, whereas those at deeper depths have long and less bushy morphology.

DOI： 10.1007/s10811-013-0002-y

Web of Science

Language：English  

To elucidate sexual differences in gonad size and color in sympatric two sea urchins (Strongylocentrotus nudus and Hemicentrotus puicherrimus), we examined S. nudus and H. puicherrimus with gametes in the gonads, in the Sargassum yezoense bed in the Oshika Peninsula, northern Honshu, Japan during July-November and September-June, respectively, from 2008 to 2010. The changes in the gonad indices of H. pulcherrimus in the Sargassum bed were compared with those in the Undaria pinnatIda and Saccharinajaponica kelp bed, using a data set obtained from Ogasawara et al. (2011). The gonad indices, by sex, of S. nudus rapidly decreased from September to a minimum in November, while those of H. pulcherrimus decreased from October to a minimum in December, February or April. For both species of sea urchin, the proportion of brown-colored gonads increased with a decrease in the gonad indices during spawning. A significant positive correlation between brown-colorization and gonad size was also detected. In H. pulcherrimus, the female gonad size was smaller than that of males during the spawning stage in both the Sargassum bed and the kelp bed. Gonadal regrowth of females during post-spawning was much slower in the Sargassum bed.

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Improved cultivation technology for the kelp Undaria pinnatifida is greatly needed to increase production to meet increasing commercial demand. A previous cultivation trial indicated that the crop yield of U. pinnatifida sporophytes could be increased greatly by thallus excision in late February due to compensatory growth of the remaining tissues. To develop this potential new cultivation technology, it is essential to identify the time period during which this kelp can compensate and its physiological responses to thallus excision. In this study, U. pinnatifida sporophytes were excised at about 30 cm above the meristem at the beginning of January, February, March, and April, respectively. Morphological features, photosynthesis, nutrient uptake, and carbon and nitrogen contents of excised kelps were measured and compared with these parameters in control kelps grown without excision. Both experimental and control kelps were farmed together in Matsushima Bay, northern Japan. The kelps excised in January and February showed significant increases in the lengths and dry weights of the blade, photosynthetic rates, nutrient uptake rates, and carbon and nitrogen contents compared with the control kelps, and the growth phase was prolonged for at least 1 month. No significant increases were found in dry weights and carbon and nitrogen contents of sporophylls until early April, which indicated that the maturation period was delayed. At the end of this experiment, the nitrogen contents of sporophyll tissues formed after excisions were significantly lower than those of tissues formed before excisions. In contrast, the kelps excised in March and April showed no significant increases in morphological and physiological parameters compared with control kelps. These results suggest that U. pinnatifida sporophytes exhibited great compensation when excisions were conducted during the growing phase in January and February but not in March and April when the maturation phase had started. The regulation of resource allocation to growth and maturation after thallus excisions in January and February likely results in prolongation of the growth phase and maturation phase in excised kelps.

DOI： 10.1007/s10811-013-9989-3

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

In recent years, the crop yield of cultivated Undaria pinnatifida (Harvey) Suringar has not been able to meet commercial demand and so advances in cultivation technology are strongly needed to increase production. Interestingly, cultivation work has shown the yield of U. pinnatifida sporophytes may be increased significantly by thallus excision, which may cause compensatory growth of the remaining tissues. To test this hypothesis and clarify correlative mechanisms, we examined seasonal morphological characteristics, photosynthetic rates, nutrient uptake rates, and carbon and nitrogen contents of U. pinnatifida sporophytes after thallus excision at a point 30 cm from the meristem in late February and compared these parameters with control kelps grown without excision, which were cultivated together in Matsushima Bay, northern Japan. Compared to control kelps, the length and dry weight of blades increased significantly after excision, and the growth phase was prolonged for about 1 month. The photosynthetic rates, nutrient uptake rates, and carbon and nitrogen contents of excised kelps were significantly higher than those of the controls. After vegetative growth stopped, resources accumulating in thalli were translocated significantly to sporophylls for maturation, indicating maturation was not negatively affected by thallus excision. These results indicate U. pinnatifida exhibits a very strong compensatory ability in response to thallus excision and consequently, the yield could be increased due to an increase in harvest frequency.

DOI： 10.1007/s10811-012-9925-y

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

The kelp Undaria pinnatifida has a widespread latitudinal range in Japan, with populations exposed to very different temperature regimes. To test the hypothesis that U. pinnatifida exhibits genetic differentiation in its temperature response, juvenile sporophytes from a warmer location (Naruto, southern Japan) and two colder locations (Okirai Bay and Matsushima Bay, northern Japan) were collected and transplanted to long lines, cultivated under the environmental conditions in Matsushima Bay. These plants were bred using successive self-crossing methods for three generations and the characteristics of photosynthesis, growth, survival, and nitrogen contents of the third-generation juvenile sporophytes (2-3 cm) then were measured and compared. The plants from Naruto showed significantly higher photosynthetic activities and respiration than those from the northern populations at warmer temperatures of 20-35A degrees C. The juvenile sporophytes from all three locations had similar growth rates below 18A degrees C, but significant differences were observed at 18-24A degrees C. The optimum temperatures for growth were 14-16A degrees C in plants that originated from Okirai Bay and Matsushima Bay and 18A degrees C in plants that originated from Naruto. These results reflected the differences in latitude. Dead plants were observed at high temperatures of 22 and 24A degrees C in the northern population plants, whereas no plants from Naruto died. Juvenile sporophytes from Naruto exhibited the greatest capacity to accumulate high nitrogen reserves. These results suggest that the differences in high-temperature tolerance in juvenile U. pinnatifida sporophytes from geographically separated populations are due to genetic differentiation rather than phenotypic plasticity.

DOI： 10.1007/s10811-012-9891-4

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Some seaweeds protect themselves physically or chemically against epiphytes, but this antifouling effect may differ among species. Abundance, size and fertility of epiphytic Neosiphonia harveyi growing on four sargassacean basiphytes (Myagropsis myagroides, Sargassum hemiphyllum, Sargassum patens and Sargassum siliquastrum) were examined for 1 year in Wakasa Bay, Japan. The mean density of N. harveyi was lowest on S. siliquastrum, whereas the mean length of N. harveyi was similar among the four basiphyte species. To elucidate the cause of different densities among the basiphytes, settlement rates of N. harveyi carpospores were compared among the different basiphytes under a culture condition. Although the initial number of attached carpospores was similar, the number of carposporelings attached S. siliquastrum fell significantly after six days of incubation. This suggests that the antifouling effect against N. harveyi functions after attachment of the epiphyte spores. SEM observation of the basiphyte blades showed more frequent and wider areas of cuticle peeling in S. siliquastrum, which may have caused the lower survival of N. harveyi. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.aquabot.2012.10.008

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Recently, withering of farmed juvenile sporophytes of the kelp Undaria pinnatifida (Harvey) Suringar has led to reduced production of this species in northern Japan, possibly because of the high water temperature and low nutrient concentration in cultivation areas. This problem may be solved by introducing parental plants with greater tolerance to high temperature and low nutrient conditions. We examined the combined effects of various temperatures (15, 20, 24, and 27 A degrees C) and nutrient availabilities (seawater enriched with 25 % PESI medium and non-enriched seawater) on the growth and survival of cultivated juvenile sporophytes (1-2 cm) collected from Matsushima Bay, Miyagi Prefecture in northern Japan and Naruto, Tokushima Prefecture in southern Japan. The relative growth rates of juvenile sporophytes from both locations were significantly greater at 15 and 20 A degrees C than at 24 and 27 A degrees C. The juvenile sporophytes cultured in enriched medium had significantly higher relative growth rates than those cultivated in non-enriched seawater. Dead juveniles were observed in non-enriched seawater at all temperatures and the survival percentage decreased with increasing seawater temperatures. Compared to the juvenile sporophytes from Matsushima Bay, those from Naruto showed greater tolerance to high temperature even under the low nutrient condition. These results suggest that the withering of juvenile sporophytes is caused by the combined effects of low nutrient availability and high temperature. A potential solution to this problem is to introduce ecotypes with greater tolerance to high temperature and low nutrient conditions from a warmer region of Japan.

DOI： 10.1007/s10811-012-9861-x

Web of Science

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English  

Language：Japanese   Publisher：京都府農林水産技術センター海洋センター  

J-GLOBAL

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER TOKYO  

As a possible factor leading to the low recruitment level of sea urchins in kelp forests, the inhibitory effect of 2,4-dibromophenol (DBP) and 2,4,6-tribromophenol (TBP) released from the large perennial brown algae Ecklonia kurome and Eisenia bicyclis on survival and metamorphosis of eight-armed larvae of the sea urchin Strongylocentrotus nudus was examined. The percentage of larvae that underwent metamorphosis in filtered sea water after 1 h exposure to one-half dilution of saturated dibromomethane solution (similar to 60 ppm) as a chemical inducer reached approximately 100% after 1 h, while that in filtered sea water containing 1 ppm TBP was reduced to 73%. This was further reduced to less than 40% in the presence of 10 and 20 ppm TBP after 2 h. In filtered sea water containing 1 and 10 ppm DBP, the proportion of metamorphosed larvae was reduced markedly to 43 and 5% after 2 h, respectively. All larvae exposed to 50 ppm TBP and to 20 and 50 ppm DBP died after 1 h. These findings suggest that DBP is more toxic than TBP for sea urchin larvae, strongly inhibiting their metamorphosis.

DOI： 10.1111/j.1444-2906.2008.01596.x

Web of Science

Language：English   Publisher：Faculty of Agriculture, Tohoku University  

Monthly collection of marine algae from the intertidal to subtidal zones in Hirota Bay (38°56&#039; N, 141°42&#039; E) on the Pacific coast of northeastern Honshu, Japan, was carried out from August 2005 to July 2006. A total of 95 species were listed, 12 of which belong to Chlorophyta, 24 to Phaeophyta, 58 to Rhodophyta, and one to sea grass. In these algae, the 10 species, Urospora penicilliformis, Pachydictyon coriaceum, Chordaria flagelliformis, Myagropsis myagroides, Bangia gloiopeltidicola, Lithophyllum okamurae, Titanoderma tumidulum, Chondracanthus tenellus, Polysiphonia abscissa and P. sphaerocarpa, were newly recorded to the marine algae from the coasts adjacent to Hirota Bay. The floral index of I/H value in Hirota Bay was 1.1, suggesting that the marine algal flora in Hirota Bay belongs to the typical subarctic zone.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：INTER-RESEARCH  

The vertical distribution and food of Strongylocentrotus nudus and Hemicentrotus pulcherrimus in fucoid beds at depths of 0.3 to 2.4 m and coralline flats at depths of 2.4 to 4.7 m were studied monthly from May 2001 to May 2002 off the Oga Peninsula, Akita prefecture, northern Japan. No seasonal migration of S. nudus from coralline flats to the fucoid beds occurred, as sufficient food was available in the form of sessile animals. Crustose corallines were generally predominant in the gut contents of sea urchins in fucoid beds, where their density was extremely low. Hemicentrotus pulcherrimus inhabit both fucoid beds and coralline flats. The main foods required for this sea urchin's gonad production are the dominant algae and sessile animals found in each algal community. The low amounts of fucoids in the gut contents of each species suggest low consumption, possibly because of difficulty in grazing fully grown and erect thalli and feeding deterrents.

DOI： 10.3354/meps07121

Web of Science

Language：English   Publisher：Faculty of Agriculture, Tohoku University  

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publisher：Association of Wildlife and Human Society  

Marine algae from Sasunohama, on the southern coast of Oshika Peninsula (38°24′N, 140°22′E), northeast Honshu, were collected monthly from April 2002 to March 2003, and the floral characteristics were analyzed. The species identified were two sea grasses and 106 species of marine algae, 17 of which belonged to Chlorophyta, 24 to Phaeophyta and 65 to Rhodophyta. The I/H value, the ratio of the number of species with isomorphic alternation of generations to heteromorphic alternation of generations (Nakahara and Masuda 1971), in Sasunohama was 1.4, whereas that in Tomarihama, adjacent to the north, was 1.2 (Agatsuma et al. 2000), and that in Matsushima Bay, adjacent to the south, was 1.8 (Takamatsu 1936). Of the fucoid species principally distributed in the warm-current floral region, five were from Sasunohama, nine from Tomarihama and 13 from Matsushima Bay. The results suggest that the algal florae in Sasunohama belong to the subarctic region.

DOI： 10.20798/biospherecons.7.1_29

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