Search

Most canopy-forming macroalgae have disappeared from temperate reefs in southern Japan, one of the ocean warming hotspots, but Sargassum nipponicum is surviving in this region. As this species' annual shoots emerge from holdfasts during summer, both plant components may be highly tolerant to warm and nutrient-poor conditions in this season. The present study examined the effects of temperature and nutrient conditions on holdfast growth, shoot emergence from holdfasts, and shoot growth in S. nipponicum samples collected in Tanegashima Island, southern Japan. The summer temperature in this region (30 °C) allowed holdfast growth and shoot emergence but inhibited shoot growth. Nutrient-poor conditions had limited effects on the first two parameters but suppressed shoot growth. These results suggested that during warm summers and under nutrient-poor conditions in southern Japan, shoots can emerge from S. nipponicum holdfasts but cannot further grow. Additionally, nutrient loading from a nearby river was higher at the only site dominated by S. nipponicum, than at the other sites where this species was absent on Tanegashima Island. This was observed especially between autumn and winter, implying that such a nutrient-rich environment may contribute to shoot growth in S. nipponicum and to the persistence of its population in the area. [ABSTRACT FROM AUTHOR]

SUMMARY: The effect of temperature, light‐spectrum, desiccation and salinity gradients on the photosynthesis of a Japanese subtidal brown alga, Sargassum macrocarpum (Fucales), was determined using a pulse amplitude modulation‐chlorophyll fluorometer and dissolved oxygen sensors. Temperature responses of the maximum (Fv/Fm in darkness) and effective (ΔF/Fm′ at 50 μmol photons m−2 s−1; = ΦPSII) quantum yields during 6‐day culture (4–36°C) remained high at 12–28°C, but decreased at higher temperatures. Nevertheless, ΔF/Fm′ also dropped at temperatures below 8°C, suggesting light sensitivity under chilling temperatures because Fv/Fm remained high. Photosynthesis–irradiance responses at 24°C under red (660 nm), green (525 nm), blue (450 nm) and white light (metal halide lamp) showed that maximum net photosynthesis under blue and white light was greater than under red and green light, indicating the sensitivity and photosynthetic availability of blue light in the subtidal light environment. In the desiccation experiment, samples under aerial exposure of up to 8 h under dim‐light at 24°C and 50% humidity showed that ΔF/Fm′ quickly declined after more than 45 min of emersion; furthermore, ΔF/Fm′ also failed to recover to initial levels even after 1 day of rehydration in seawater. Under the emersion state, the ΔF/Fm′ remained high when the relative water content (RWC) was greater than 50%; in contrast, it quickly dropped when the RWC was less than 50%. When the RWC was reduced below 50%, ΔF/Fm′ did not return to initial levels, regardless of subsequent re‐hydration, suggesting a low capacity of photosynthesis to recover from desiccation. The stenohaline response of photosynthesis under 3‐day culture is evident, given that ΔF/Fm′ declined when salinity was beyond 20–40 psu. Adaptation to subtidal environments in temperate waters of Japan can be linked to these traits. [ABSTRACT FROM AUTHOR]

The threat of declining seaweed beds has been a concern around the world. Seagrass and seaweed (brown algae) beds are essential habitats supporting fisheries. However, approximately 22% of these habitats have been lost in Japan due to increased coastal landfill sites and ports. This study aims to rehabilitate the depletion of these habitats by constructing an artificial reef in Wakasa Bay, Japan, and monitoring Sargassaceae succession in the second and fourth years after the construction was completed. In this study, we set up four sites on the artificial reef. Then we identified the seaweed species composition and coverage of the Sargassaceae using underwater visual observation by scuba divers. The seaweed coverage was already over approximately 80% in the second year after construction. The Sargassum horneri and S. confusum dominated during the first and second sampling in the second year after construction, and Myagropsis myagroides and S. patens during the third and fourth sampling in the fourth year after construction. Thus, the recovery of species composition takes longer than that of coverage. Therefore, observing species composition recovery is essential when constructing the artificial reef., (© 2024. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

The brown seaweed Sargassum carpophyllum J. Agardh is an unused warm-temperate species in the family Sargassaceae that has been expanding its distribution along the coastal areas of Japan in recent years. In this study, 3 types of phlorotannins were identified from the EtOAc fraction of the 80% MeOH extract of S. carpophyllum. From the spectroscopic (1H NMR, 13C NMR, and HMBC) and ESI/MS data and comparison with those of prior literature, it was demonstrated that the compounds are oligomers of phlorethol, which is one of the subclasses of phlorotannins, that is triphlorethol B (phloroglucinol trimer), tetraphlorethol C (phloroglucinol tetramer), and pentaphlorethol A (phloroglucinol pentamer). Among the phlorethols, tetraphlorethol C and pentaphlorethol A were isolated and identified for the first time from a brown seaweed collected from the East China Sea, including the coastal areas of Japan. The identified phlorethols were tested for their antioxidant properties. In the antioxidant assay using liposomes, the phlorethols showed comparable inhibitory effects to epigallocatechin gallate (tea polyphenol) and α-tocopherol (liposoluble vitamin) on lipid peroxidation by 4 mM 2,2′-azobis(2-methylpropionamidine) dihydrochloride. In addition, it was revealed that pentaphlorethol A has a superoxide anion scavenging activity (50% effective concentration: 21 μM) higher than that (50% effective concentration: 46 μM) of ascorbic acid (hydrosoluble vitamin). [ABSTRACT FROM AUTHOR]

SUMMARY: "Monitoring Sites 1000" – Japan's long‐term monitoring survey was established in 2003, based on the Japanese Government policy for the conservation of biodiversity. Ecological surveys have been conducted on various types of ecosystems at approximately 1000 sites in Japan for 15 years now and are planned to be carried out for 100 years. Since 2008, seaweed communities had been monitored at six sites, featuring the kelp (e.g. Saccharina and Ecklonia; Laminariales) and Sargassum (Fucales) communities in the subarctic and temperate regions of Japan. Annual surveys were carried out during the season when these canopy‐forming seaweeds are most abundant. A non‐destructive quadrat sampling method, with permanent quadrats placed along transects perpendicular to the shoreline, was used to determine species composition, coverage, and vertical distribution of seaweeds at these sites; while destructive sampling was done every 5 years to determine biomass. The occurrence of canopy‐forming species Saccharina japonica (var. japonica) and Ecklonia cava have appeared to be stable at the Muroran (southwestern part of Hokkaido Island) and Shimoda (Pacific coast of middle Honshu Island) sites, respectively; whereas the coverage of Ecklonia radicosa (= Eckloniopsis radicosa) at the Satsuma‐Nagashima site in southern part of Kyushu Island was highly variable until its sudden disappearance from the habitat in 2016. Thalli of E. radicosa lost most of their blades through browsing by herbivorous fish, and thus, this may be one of the causes of the decline. A shift in the community structure related to environmental changes had also been observed at some other sites. Pre‐ and post‐disaster data revealed the impact of the 2011 earthquake and tsunami disasters, including a shift in the vertical distribution of Ecklonia bicyclis (= Eisenia bicyclis) to shallower depths at the Shizugawa site in the Pacific coast of northern Honshu Island, due to seafloor subsidence. [ABSTRACT FROM AUTHOR]

SUMMARY: Sargassum ringgoldianm is a canopy‐forming perennial macroalga dominant in a shallow waters along the central Pacific coast of Honshu, Japan, where macroalgal forests have been drastically declining by browsing of herbivorous fish since the 1990s. Accordingly, we tried to reveal seasonal fluctuation of browsing damage on S. ringgoldianum. In the course of the investigation, we found signs of receptacle regeneration in S. rinngoldianum, which has been reported in a few species of the order Fucales. Regenerations occurred most frequently from 3.0 mm to 3.9 mm of the basal part of original receptacles and were also observed at the tips of remaining stalks as well as branchlets that seemed to lose original receptacles. The regenerated receptacles formed antheridia and oogonia, and released eggs from them, suggesting that regenerated receptacles are functional. In addition, no regeneration was observed in only three individuals among 51 plants observed. We show herein a high regenerative ability of wounded receptacles in S. ringgoldianum. This frequent regeneration of functional receptacles is important for the persistence of the population. [ABSTRACT FROM AUTHOR]

SUMMARY: 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. [ABSTRACT FROM AUTHOR]

The annual macroalga Sargassum horneri often forms a dense canopy at the sea surface. To evaluate the effects of the vertical structure and presence of the sea-surface canopy of S. horneri on the distribution of its epifauna, we collected epifauna from four different vertical portions of S. horneri at Kitsunezaki, west coast of Oshika Peninsula, Miyagi, Japan. The vertical portions of the thalli were defined as follows: sea surface (S), the portion that was always lying on the sea surface; intermediate (I), which was periodically lying on the sea surface with tidal changes; underwater (U), which was always submerged; and bottom (B), the portion around the holdfast. The mean total density of epifauna in the sea-surface portions (S and I) was significantly higher than that in the underwater portions (U and B). Harpacticoid copepods and bivalve spat accounted for more than 90% of the epifauna in all portions. It seems that the canopy of S. horneri collects bivalve larvae and other epifauna from the water column by sweeping the sea surface with the changing of the tide. We proposed the 'Seasonal Coincidence Hypothesis' to explain the dense occurrence of bivalve spat on S. horneri in this study. [ABSTRACT FROM AUTHOR]

Ecklonia cava (EC) has been widely utilized as an ingredient in commercial products such as functional foods and cosmeceuticals. Recently it has been found that Sargassum horneri (SH) has been invading on Jeju Island coast area by its huge blooming. Moreover, both seaweeds are considering as important ingredients in traditional medicine specifically in East-Asian countries (China, Japan, and Korea). In the present study, we attempted to compare anti-inflammatory properties of 70% ethanolic extracts of EC (ECE), SH (SHE), and their different combinations on lipopolysaccharide (LPS)-activated RAW 264.7 cells. Results indicated that 8 : 2 combinations of ECE : SHE significantly inhibited LPS-activated inflammatory responses (cytokines, protein, and gene expression) in RAW 264.7 macrophage cells compared to the respective extracts and other combinations. The synergistic effect of ECE and SHE was found to be prominent than the effects of ECE or SHE alone. These observations provide useful information for the industrial formulation of functional materials (functional foods and cosmeceuticals) using these two particular seaweeds in Jeju Island of South Korea. [ABSTRACT FROM AUTHOR]

Brown seaweed, Sargassum thunbergii is thought to be effective for As, Cu and Zn sensor. Green seaweed, Ulvales, red seaweed, Caulacanthus ustulatus and Ahnfeltiopsis flabelliformis are thought to be effective for just Cu sensor. High Zn concentration and large volume of Zn drainage water from the closed Kanayama mine flowed into sea and drainage water and groundwater containing Cu, Zn and As contacted with muck along the coast also flowed into sea in the closed Shizuki mine. Cu, Zn and As concentrations for many kinds of seaweed sampled at the two mines and no contamination places, the Kii and Izu Peninsula, were measured. Cu Zn and As concentrations for Sargassum thunbergii are 1000, several 100 and several 100 ppm at the Shizuki mine and 10, several 1000 and 100 ppm at the Kanayama mine, and 10, several 10 and 100 ppm at the no contamination places. [ABSTRACT FROM AUTHOR]

The brown macroalgal genus Sargassum forms beds around the Japanese coast; these beds are important for marine ecosystem functioning and fisheries. In recent years, a northward shift in the distribution patterns of southern Sargassum spp. has been postulated as a result of warming in the western Pacific. To examine this theory, we surveyed species richness and diversity of genus Sargassum algae around the Ryukyu Islands, Japan, which is the northern limit of selected Sargassum species native to tropical and subtropical regions. We collected from Iriomote Island (Ryukyu Archipelago) specimens of a species resembling Sargassum denticarpum, which is endemic to Vietnam. The specimens had the following morphological characteristics in common with S. denticarpum: (1) terete or slightly compressed primary branches, (2) simple lanceolate primary and lateral leaves with dentate margins in all stages, (3) spherical-to-elliptical vesicles with or without spines and wings, (4) monoecious, and (5) compressed receptacles with spines on the margins. In addition, internal transcribed spacer 2 ( ITS2) sequences of the Ryukyu specimens and of S. denticarpum collected in Vietnam clearly showed that the two are closely related. On the basis of these morphological and molecular characteristics, we present the first report of S. denticarpum in Japan. [ABSTRACT FROM AUTHOR]

Although sediment deposition has detrimental effects on macroalgal settlement and recruitment, fucoid algae (mainly Sargassum duplicatum) thrive on rocky reefs always overlaid with fine sediments in sheltered sites of Kagoshima, Japan. The aim of the present study was to assess their ability to settle and recruit onto sediment-covered substrata. A transplant experiment using boulders with Sargassum juveniles attached showed that the 30-day survival rate was as high as 50% even for the juvenile stage (<10 mm) on boulders completely buried with sediment. In addition, an outdoor tank experiment testing the effects of different sediment thicknesses (0-4 mm) on already settled 4-day old S. duplicatum germlings indicated significant reductions in growth by the presence of sediment cover even at 0.5 mm but no significant increase in mortality up to 2 mm. Furthermore, an in situ experiment in which sterilized cobbles were placed at a sediment-covered site to allow sediment to settle over them before the embryo release showed a uniformly high recruitment of Sargassum over the cobbles. This suggests the presence of unknown mechanisms to allow the settlement of propagules on substrata thinly but completely covered by fine sediments. [ABSTRACT FROM AUTHOR]

Abstract: This study aimed to elucidate the relationship between the chemical composition and the growth of a marine alga, Sargassum horneri (Turner) C. Agardh (abbreviated as S. horneri) harvested from the Chikuzen Sea, Fukuoka, Japan, as well as the changes in the chemical composition during pre-heating of harvested S. horneri. Both its length and weight reached maximum levels late in March. The mean chemical composition of S. horneri from December 2004 to May 2005 was 87.7% moisture, 1.0% protein, 0.1% lipid, 3.4% ash and 5.7% total dietary fiber. The ash contents of the male plants were higher in February but lower in March and April than those of the female plants. The lipid contents of the males were higher in March than those of the female plants. The protein content reached its maximum in February. The total dietary fiber content began to increase in February and reached its maximum at the end of March. The total dietary fiber content increased after full growth and maturity. S. horneri is a potential source of dietary fiber and minerals as a food ingredient. [Copyright &y& Elsevier]

Abstract: Otolith microstructure analysis was used to reveal the temporal patterns of settlement, planktonic duration and size-at-settlement (SAS) of young-of-the-year (YOY) of the rockfish Sebastes inermis in a Sargassum bed in Sendai Bay, northern Japan, during 2000 and 2001. Individual growth rates (IGR) during the planktonic period and after settlement for each settled group were also studied and compared to those of YOY collected in a Zostera marina bed. In both years, YOY settled in distinctive groups at new and full moon phases. SAS was surprisingly invariant (21.4–22.7mm total length) while planktonic duration varied widely (range: 73–123 days), even within settlement groups and between years (mean=88 days in 2000; mean=105 days in 2001). In both years, IGR were remarkably lower during the planktonic period (range: 0.09–0.29mm/d) than after settlement (range: 0.54–0.73mm/d), demonstrating that Sargassum and Zostera marina beds are important nursery grounds for S. inermis. In conclusion, the analysis of variation in SAS vs planktonic duration along with the selection pressures on settlement size, were the most important driving factors in the settlement dynamics of this rockfish. [Copyright &y& Elsevier]

The genetic structure and phylogeography of the brown seaweed Sargassum horneri/filicinum complex in Japan were studied based on the mitochondrial cox3 haplotype. The cox3 haplotypes found were divided into three clades in a statistical parsimony network, among which there were large numbers of steps. Contrary to the reported large amount of drifting S. horneri along the Japanese coast, the three clades were dividedly distributed on the Japanese coast: the northern Pacific, the central Pacific, and western Japan. The western Japan S. horneri had haplotypes that were phylogenetically closer to those of S. filicinum than to the northern and central Pacific S. horneri populations. The S. filicinum populations were included within the western Japan clade and grouped together with the S. horneri samples from western Japan. Taken together with the unstable morphological diagnosis, this result suggests that S. filicinum should be reduced into a synonymy of S. horneri. The TMRCA analysis suggested that the divergence time of each clade may go back to the last interglacial period and a skyline plot suggested that the last glacial maximum had only a small effect on the population size of S. horneri. The geographic subdivision of the three groups, in spite of a large amount of drifting mats, suggests a limited contribution of drifting mats to gene flow on a large geographic scale. On a small geographic scale, a small number of haplotypes were shared between S. horneri-type and S. filicinum-type populations. This result suggests that populations of these two types are partially, though not completely, isolated from each other, possibly by selfing in S. filicinum-type populations or by a difference in peak reproduction. [ABSTRACT FROM AUTHOR]

Species of the genus Sargassum (Fucales, Phaeophyceae) belonging to the Schizophycus group (in subgenus Sargassum sensu lato) from the Ryukyu Islands, southern Japan, were morphologically reinvestigated, and two entities were recognized: Sargassum ryukyuense sp. nov. and Sargassum pinnatifidum. The new species is characterized by: 1) compressed primary branches; 2) simple lanceolate primary and lateral leaves with an undulate and dentate margin in all stages; 3) lateral branches issuing alternate-distichously on the main branches in one plane; 4) long and flattened receptacles arranged alternate-distichously on terminal branches; 5) main and lateral branches on the stem issuing as foliar expansions in the early stage of development; and 6) vesicles with a simple coronal leaf. This new species resembles S. pinnatifidum in features 1), 3) and 5). However, it differs from S. pinnatifidum in features 2), 4) and 6). Furthermore, this new species can be distinguished from all previously described species based on the complete set of diagnostic features above and by the presence of long lingulate receptacles with short stalks. The new species is known to be endemic in the Ryukyu Islands and adjacent waters of southern Japan. [ABSTRACT FROM AUTHOR]

Macrophytes stranded on a beach provide food and habitat for many kinds of animals and play important roles in coastal ecosystems. Macrophytes stranded on a sampling beach (56 m long) along a sargassacean forest (400 m long and 88 m wide) were collected every 10 days from late April 2003 to late May 2004. The weight of macrophytes stranded per meter of beach amounted to 1733 g dry wt/m per year. Sargassacean plants were dominant and constituted 72.9% (1263 g dry wt/m per year) of whole stranded macrophytes. Large numbers of macrophytes were stranded just after heavy winter storms and the maximum weight of stranded macrophytes in winter was 407 g dry wt/m. Stranded macrophytes also increased in May to July; the deterioration period of sargassacean species in this region, and the maximum weight in this period was 233 g dry wt/m. The number of sargassacean plants stranded with holdfast increased only in winter. These results suggest that winter storms have an important role in stranding sargassacean plants at Yoro Beach. [ABSTRACT FROM AUTHOR]

Annual net production of the five Sargassaceae species was investigated in Yoro, western Wakasa Bay, Sea of Japan. The Sargassaceae species were collected at a depth of 2.0–2.5 m and subjected to stratified clipping for 13 months. Annual net production was estimated at 2407 g dry wt/m2 for Sargassum patens, 2132 g dry wt/m2 for Sargassum macrocarpum, 1458 g dry wt/m2 for Sargassum siliquastrum, 1197 g dry wt/m2 for Myagropsis myagroides, and 1471 g dry wt/m2 for Sargassum piluliferum. The ratio of annual net production to maximum biomass (P/Bmax) for these species ranged between 1.3 and 1.7, being higher than in previous studies which used the same method. Winter storms with strong wave exposure and relatively calm condition in Yoro were considered to augment P/Bmax. The total losses estimated from the different units of stratified clipping were compared. If larger and less segregated units were applied, the total loss would decrease. It was suggested that a 50 cm stratum would be applicable to the larger species (3 m or longer) and a stratum of 20 cm or less would be applicable to mid-sized or smaller species (less than 3 m). [ABSTRACT FROM AUTHOR]

The histology of the gill structure of Caprella (Amphipoda: Caprellidea) (i.e. C. danilevskii, C. subinermis, C. penantis R-type and C. verrucosa) collected from the Sargassum community of north-eastern Japan, was observed under transmission electron microscopy. The epithelial gill cells of C. danilevskii, C. subinermis, and C. verrucosa were composed of a well-developed apical infolding system (AIS) and basolateral infolding system (BIS) associated with a large number of mitochondria, whereas those of C. penantis R-type, which possessed large, leaf-like gills with distinct pillar structures, had weakly developed AIS and BIS. Experiments on the salinity tolerance of the four species of Caprella indicated that the median lethal concentration (LC50) of the four species at 20°C ranged from 12.97 to 18.84 practical salinity unit (p.s.u.) with survival rates greater than 80% in salinity conditions over 25.37 p.s.u. even on day 5. The characteristics of the gills and the wide salinity tolerance of Caprella spp. indicate that Caprella spp. inhabiting the Sargassum community are euryhaline marine organisms. [ABSTRACT FROM AUTHOR]

Summary The authors examined seasonal patterns in 20 sargassaceous species (maximum stipe length of ≥45 cm) from 902 patches of drifting seaweeds in the south-eastern coastal waters of the Izu Peninsula, central Japan, between spring and autumn, 1991-1993. The first analysis, dealing with plants occurring for three consecutive years, examined the top three ranked species determined from monthly pooled means of frequency of appearance in these 3 years. The second analysis examined not only the top-ranked species in monthly means in each year, but also the continuity of appearance of species among years. The third analysis was made from dendrogram analysis based on monthly samples from each year. The first and second analyses revealed three seasonally discernible changes. From April to June, dominance shifted from Sargassum horneri (Turner) C. Agardh to Sargassum yamamotoi Yoshida with a stable transition; in July, S . yamamotoi , Sargassum macrocarpum C. Agardh, Sargassum crispifolium Yamada and Sargassum piluliferum (Turner) C. Agardh appeared consistently in an unstable domination with low frequency of appearance by Sargassum nipponicum Yendo, Sargassum fulvellum (Turner) C. Agardh, S . macrocarpum or S. crispifolium ; in August to October, there was a stable shift from S . macrocarpum to Sargassum micracanthum (Kützing) Endlicher and Sargassum ringgoldianum Harvey. In the third analysis, monthly samples from each year were divided into four groups, characterized using the top five ranks. This characterization indicated that the top-ranked species shifted from S. horneri to S. yamamotoi , to S . macrocarpum and to S . micracanthum with the change of seasons. Because of an overlap in the characteristic species in these three analyses, seven species (S. horneri , S . micracanthum , S. yamamotoi , S . macrocarpum , S . ringgoldianum , S . nipponicum and S . crispifolium ) were regarded as dominant species. Results are compared to our previous study and it is suggested that the similarity in the pattern of plant community during seasonal changes over the period from April to June and in July resulted from both stable and unstable changes, respectively, but discrepancies in the pattern of plant community during seasonal change from August to October were the result of differences in the frequency of appearance of S . ringgoldianum and S . macrocarpum in August 1991. These results indicated that the seasonal changes of dominant species in the plant community from April to October in this study area were periodic except in July. [ABSTRACT FROM AUTHOR]

ABSTRACT: Seasonal growth and maturation patterns of two Sargassum horneri populations were surveyed in Hiroshima Bay on the western Seto Inland Sea. Both S. horneri populations began to exhibit rapid growth in autumn, exceeding a daily increase in plant length of 10 mm/day. However, there are several differences in seasonal timing for maturation and reaching maximum plant size. Plants of the Ohno-seto population, inhabiting the innermost area of Hiroshima Bay, reached their maximum plant size in December and became senescent after January. Plants of the Matsugahana population, inhabiting the mouth of the bay, continued to grow during winter and reached their maximum plant size in April. Senescence occurred after May. The largest difference in the seasonal patterns of the two S. horneri populations is most likely to be in the timing of maturation. In the Ohno-seto population, receptacle formation of the plants begins in November, and the eggs are released from late November to January. The plants settled as embryos spend the winter in an early stage of development. In the Matsugahana population, on the contrary, the plants spend the winter as adults and gradually produce receptacles. Abundant egg release of the Matsugahana population occurred in April and May. [ABSTRACT FROM AUTHOR]

SUMMARY Seasonal patterns of drifting seaweeds in the south-eastern coastal waters of Izu Peninsula of central Japan were examined by sampling 966 patches from spring to autumn 1991–1993. In total, 57 plant species appeared, including 10 epiphytic algal species. Monthly totals of the number of species, excluding epiphytic algae, were highest in May (33) and August (27), though 19–21 species of sargassaceous algae were found from May to August. The number of species, excluding epiphytic algae, in one patch of drifting seaweeds was 1 to 11 (x = 2.93 ± 2.06) with high richness in May a result of almost entirely sargassaceous species. The wet weight of each patch and maximum stipe length of plants varied from 5 to 6970 g and from 20 to 840 cm (x = 536.1 ± 782.3 g and 110.6 ± 76.8 cm), respectively, with highs in April and May. Out of 18 species common to all years, 10 species dominated the top or second rank in monthly pooled frequency of appearance. Seasonal changes of these 10 major species were examined. Sargassum horneri (Turner) C. Agardh and Hizikia fusiformis (Harvey) Okamura were abundant in April, but were replaced partly by Sargassum muticum (Yendo) Fensholt in May and largely by Sargassum yamamotoi Yoshida in June. In July, Sargassum nipponicum Yendo and Sargassum piluliferum (Turner) C. Agardh dominated. Subsequently, the major species shifted to Sargassum ringgoldianum Harvey and S . yamamotoi in August, Sargassum micracanthum (Kützing) Endlicher, Sargassum macrocarpum C. Agardh and Zostera marina Linnaeus in September, and S . ringgoldianum and S . micracanthum in October. However, the occurrence of S . yamamotoi , S . nipponicum and S . piluliferum in June or July were particularly heterogeneous compared with other areas of Japan. Dendrogram analysis was done based on frequency of appearance. Pooled monthly samples were divided into three groups characterized from the dominant species, degree of domination, weight,... [ABSTRACT FROM AUTHOR]

This study was designed to determine the critical photon irradiance for growth and daily compensation point of juvenile Sargassum macrocarpum. Sampling and measurement of natural light conditions were carried out in the S. macrocarpum population at a depth of 8 m off Kiwado in Fukawa Bay, Yamaguchi Prefecture, Japan, from April to June 1998. Photosynthesis and respiration of the juvenile thalli, and diurnal changes in solar irradiance were measured for the same period. The critical photon irradiance for growth of the juvenile thalli observed on the population floor was 1.0--1.5% on the sea surface. The photosynthetic rate of leaf of juvenile thalli increased linearly with increasing photon irradiance when light levels were lower than 50 m M/m 2 per s. The respiratory rate and light compensation point of the juvenile thalli were 2.49 m L O2/cm 2 per h and 4.98 m M/m 2 per s, respectively. The daily compensation point was estimated with a mathematical model based on pho-tosynthesis light equations and diurnal changes in solar irradiance. For a day of average solar irra-diance over the period of the present study, the estimated daily compensation point of the juvenile thalli was 1.3% on the sea surface. This value agreed well with the observed critical photon irradi-ance for growth of juvenile S. macrocarpum on the population floor. The results of the study confirm that the mathematical model is effective for estimating the daily compensation point. [ABSTRACT FROM AUTHOR]

SUMMARY:The productive structure and productivity of a Sargassum macrocarpum C. Agardh population were studied from June 1993 to July 1994 in Fukawa Bay facing the Sea of Japan, Yamaguchi Prefecture. S. macrocarpum formed a dense population at a depth of 8 m in the study area. Using the stratified clip technique, monthly changes in the productive structure from 1993 to 1994 were clarified. The dry weight of leaves and main branches increased with the elongation of branches. Thalli in the middle to high stratum began to bear receptacles from March 1994 and the dry weight of receptacles was approximately one-third of the standing crop in June. The loss of leaves increased from April to June 1994, and the loss of main branches and receptacles from June to July 1994. Productivity of branches and receptacles reached maxima of 4.67 g dry wt/m2 per day from February to March and 5.33 g dry wt/m2 per day from April to May, respectively. Productivity of the leaves, however, was almost constant at approximately 2 g dry wt/m2 per day from July 1993 to March 1994. Therefore, maximum productivity of the S. macrocarpum population of 7.17 g dry wt/m2 per day occurred from February to March. Annual net production of newly sprouting branches in June 1993 was 1600.1 g dry wt/m2 per year based on the summation method, which was calculated from the monthly changes in the productive structure. [ABSTRACT FROM AUTHOR]

• Vesicles of Sargassum horneri tended to increase with increasing algal body weight. • Contribution rate of vesicles of S. horneri to acoustic reflection was high. • Target strength (TS) of algal bodies increased with increasing algal body weight. • Weight-dependent TS of S. horneri followed this equation: TS w = 11.1 log 10 W -71.1. • Biomass of S. horneri can be estimated by acoustic measurements. A species of macroalgae, Sargassum horneri , which has gas-filled vesicles, plays important roles as nursery grounds, feeding grounds, and hiding grounds for coastal fauna. In addition, it recently emerged as a new coastal fishery resource in Japan. However, its acoustic reflection intensity is unknown, resulting in the impossibility of quantitatively estimating its biomass via an acoustic survey with a quantitative echosounder. We measured the target strength (dB re 1 m2) of S. horneri and clarified its characteristics. The measurements were taken using a 120 kHz quantitative echosounder in the fishing port of Iwate Prefecture in June and July 2014. Seven samples were collected by scuba diving in the coastal waters surrounding the port. Each individual sample was divided every 30 cm, and each divided layer was suspended at a depth of about 4–5 m, and its target strength was measured. Then, we divided S. horneri into vesicles and other parts. Each part was exsiccated at 80 °C for over 10 h. The dry weights of the vesicle and algal body were then measured. The weight of the vesicles of S. horneri tended to increase with an increase in algal body weight. The target strength increased with increasing algal body weight (Target strength = 11.1 log 10 Weight -71.1, R2 = 0.81) and vesicle weight. We considered that the contribution of the gas in the vesicles to the target strength was high, which is similar to the swim bladder of fish, as the acoustic reflection intensity of the vesicle was as strong as what has been reported for the gas in the swim bladder, and the intensity increased owing to the increase in vesicle weight accompanying the increase in algal body weight. Thus, S. horneri biomass could be estimated by acoustic survey using the target strength revealed in our study. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Presents three new species of Sargassum wakayamaense in Japan. Sargassum wakayamaense Yoshida; Sargassum araii; Sargassum bulbiferum.

This article presents comparative photosynthetic capacities of different parts of Sargassum (S) horneri. Studies of photosynthetic characteristics of Sargassum plants are fundamental to understanding their ecological properties. The photosynthetic rate increased with increasing water current speed in adult Sargassum plants. The present study gives different photosynthetic characteristics among various parts in S. horneri, which has been used as a food or a vegetable at some local places in Japan. A Sargassum horneri plant consists of a holdfast, a primary lateral from which leaves and lateral branches are formed. Leaf formation rate per day was determined by measuring the number of leaves at the beginning and at the end of a period, during which the plants were maintained in the sea at their natural depth.

The article focuses on the relationship between distribution of sargassum species and water movement. In the coastal region of Oshima Peninsula in Wakasa Bay, central Japan, the distribution of nine species of Sargassum was investigated in relation to water movement in March 1983. Sargassum macrocarpum appeared at stations with weak water movement, growing dominantly beyond the depth of 6 meter, whereas it occurred up to the depth of 3 meter where water motion was relatively weak.

Evaluates the conceptacular development in Sargassum filicinum and autumnal Sargassum horneri in Japan. Unequal division of the initial cell to produce the tongue and lower cell; Pattern of conceptacle development between the Sargassum filicinum and Sargassum horneri; Secretion of a mass of mucilage by the tongue cell of both algae.

The article presents comparative studies of photosynthesis in different parts of Sargassum thunbergii. Typical Sargassum plants consist of a holdfast, a stem from which main branches or main axes are formed, and lateral branches arising from the main axes which produce leaves, vesicles and, during the mature season, receptacles. Sargassum beds in Japan are important subtidal forests as typical as the communities of Ecklonia and Eisenia, being noticed as nursery grounds for fishes and shellfishes, and as biomass resources and sources of raw material for algin industries plant elongates by apical growth, and grows rapidly in the early summer season in Wakasa Bay facing the Sea of Japan.

Cites a study on the monoecism and autumn-fruiting of Sargassum horneri collected from the coast of northern Kyushu, Japan. Description of the receptacle of S. horneri; Proportion of male and female part in a receptacle; Occurrence of hermaphrodite conceptacles.

Describes the rhizoid development of embryos of Sargassum horneri at various culture conditions of temperature and salinity in Japan. Description of marine algae; Optimal ranges of temperature and salinity for the germination rate, the elongation and the number of rhizoids; Standard deviations of vertical bars for marine algae.

The article presents information on the growth and maturation of six species of Sargassum and Cystoseira in Oshoro Bay, Hokkaido, Japan, for the period of 1980-1981. The algae attained their maximum development in July and August of the period 1980-1981. After maturation, old thalli decayed away from the upper part, while new branches grew from the remaining basal portion in the perennial species.

Examines the growth and maturation of the autumn-fruit type of Sargassum horneri in Hiroshima, Japan. Phases of the annual lifetime of the autumn fruiting population; Increase in thallus length; Observation of gamete release.

A new marine Sargassum-boring species of Limnoria (Limnoriidae) is described on the basis of specimens obtained at Kamogawa-shi, Chiba Prefecture, Japan. Limnoria aspera sp. nov. shares a reduced mandibular palp to a seta, algal-feeding, and the clavate shaped epipod of the maxilliped with the other species of non-mandibular-palp group. L. aspera sp. nov. differs morphologically from the congeneric species by secondary unguis of pereopods and unique carinae of pleonite 5 and pleotelson. We describe the sequences of the mitochondrial COI gene and the nuclear 28S rDNA gene. L. aspera sp. nov. differs by 14.218.0% in p-distance based on COI sequences from other Japanese species, L. furca and L. nagatai.

Using genome-wide SNP data obtained from high-throughput techniques based on double digest restriction site-associated DNA sequencing (ddRAD-seq), we elucidated the migration history and genetic diversity of the Japanese population of the ecologically important brown seaweed Sargassum thunbergii (Mertens ex Roth) Kuntze. STRUCTURE and NeighborNet analyses showed a clear genetic differentiation among populations of four geographic regions: Kyushu (POP1); Sea of Japan (POP2); Hokkaido and Tohoku (POP3); and Pacific coast from Kyushu to Kanto (POP4). Approximate Bayesian Computation (ABC) analysis indicated that POP4 diverged first, followed by the separation between POP2 (the largest effective population size) and POP3; POP1 was the last to form, shaped by the mixture of POP2 (73%) and POP4 (27%). High genetic diversity was detected in POP1 and POP2, whereas low genetic diversity was detected in POP3 and POP4. These results indicated that S. thunbergii populations of Kyushu and the Sea of Japan might have been maintained as large and stable populations gathered different lineages from China, Korea and/or Japan., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

This paper describes the flora of habitat-forming seaweeds (fucoids and temperate kelps) at 7673 sites of the Japanese coast encompassing its warm to cold temperate zone, recorded from 1887 to 2014. The data set includes 86 species (21,168 presence and 20,845 absence records), compiled from 355 literature sources, most of which were written in Japanese and published as grey literature in local journals or individual reports. Scientific names were consolidated under currently-accepted nomenclature based on Algaebase (). The data set compiled the seaweed flora at each study site each year, the geographical location and the scientific names. Additionally, three supporting data sets were created respectively including name of each site, synonyms of the seaweeds, and the corresponding literature list. This rich collection of data can be used to study the biogeography and long-term changes of particular species and the diversity of habitat-forming seaweeds of the Japanese coast. [ABSTRACT FROM AUTHOR]