Phyllospadix iwatensis is a unique seagrass species adapted to rocky substrate anchorage and dioecy and belongs to marine submerged flowering plants with a distinctive evolutionary history. The chromosomal-scale genome was constructed by integrating Illumina, PacBio HiFi, and high-throughput chromosome conformation capture (Hi-C) sequencing techniques. A total of 340.56 Mb of sequences were anchored to 10 chromosomes with an anchoring rate of 96.44%. The contig and scaffold N50 values reached 30.64 Mb and 33.59 Mb, respectively. Precisely 94.64% of the 23,198 predicted protein-coding genes received functional annotation. In the meantime, 180.19 Mb of repetitive sequences were found, representing 52.91% of the assembled genome. The chromosomal-level genome data of P. iwatensis will reveal its special process of differentiation and enrich the understanding of the multiple adaptations of seagrass populations to marine habitats.

Microbial community assembly and interactions are pivotal research areas within microbial ecology, yet relevant studies in seagrass rhizospheres and phyllosphere remain relatively scarce. In this study, we utilized high-throughput sequencing technology to investigate the microbial communities in different periods and microhabitats (rhizosphere and phyllosphere) of two seagrass species (Zostera marina and Phyllospadix iwatensis). Our findings suggest that microhabitats have a more pronounced impact on the composition of seagrass-associated microbial communities compared to periods and species. Further investigations reveal that the phyllosphere microbial community exhibits a more intricate co-occurrence network and interactions than the rhizosphere microbial community. Keystone taxa show distinct functional roles in different microhabitats of seagrasses. Additionally, we observed that differences in seagrass microhabitats influence community assembly, with the rhizosphere microbial community being more influenced by deterministic processes (heterogeneous selection) compared to the phyllosphere. These findings contribute to our understanding of the intricate interactions between seagrasses and their associated microbial communities, providing valuable insights into their distribution patterns and microhabitat preferences.IMPORTANCEStudying the community structure and assembly of different microhabitats in seagrass beds contributes to revealing the complexity and dynamic processes of seagrass ecosystems. In the rhizosphere microhabitat of seagrasses, microbial communities may assist in disease resistance or enhance nutrient uptake efficiency in seagrasses. On the other hand, in the microhabitat on the surface of seagrass blades, microorganisms may be closely associated with the physiological functions and nutrient cycling of seagrass blades. Therefore, understanding the structure and assembly mechanisms of rhizosphere and phyllosphere microbial communities is crucial for exploring the interactions between seagrass and microbial communities, as well as for enhancing our comprehension of the stability and resilience of seagrass bed ecosystems.

The islands Iturup and Urup of Kuril Archipelago have been understudied in respect of seagrasses. The research aimed to fill this gap. In 2019 during the expedition of the Russian Geographical Society a part of the coastline has been surveyed by walking, the beached remains of seagrasses and the seagrasses growing on the littoral have been registered. The length of the routes was 95 km. The possible sources of negative anthropogenic impact have been examined. Herbarium collections of several institutions (LE, LECB, MHA, MW, MWG, SAK, Kamchatka Branch of Pacific Geographical Institute of the RAS, the Herbarium of Kronotsky Nature Reserve) have been explored. Three species of seagrasses occur at Iturup and Urup: Zostera marina L., Zostera asiatica Miki, and Phyllospadix iwatensis Makino. The last two species are of particular interest as they are threatened and distributed over a relatively small area. Unlike the habitats of the main part of their range located at the coasts of Japan and Korea, the habitats of the studied islands do not suffer from anthropogenic pressure. The discovered northern refuge is significant for the seagrasses conservation. Current global warming and increasing anthropogenic pressure on the southern habitat would increase its significance. It is especially important for Phyllospadix iwatensis as it turned out to be rather numerous at the studied islands. The other two species occur in small numbers there.

BackgroundSeagrasses are higher marine flowering plants that evolved from terrestrial plants, but returned to the sea during the early evolution of monocotyledons through several separate lineages. Thus, they become a good model for studying the adaptation of plants to the marine environment. Sequencing of the mitochondrial (mt) genome of seagrasses is essential for understanding their evolutionary characteristics.ResultsIn this study, we sequenced the mt genome of two endangered seagrasses (Zostera japonica and Phyllospadix iwatensis). These data and data on previously sequenced mt genomes from monocotyledons provide new evolutionary evidence of genome size reduction, gene loss, and adaptive evolution in seagrasses. The mt genomes of Z. japonica and P. iwatensis are circular. The sizes of the three seagrasses (including Zostera marine) that have been sequenced to date are smaller than that of other monocotyledons. Additionally, we found a large number of repeat sequences in seagrasses. The most abundant long repeat sequences were 31–40 bp repeats. Our study also found that seagrass species lost extensive ribosomal protein genes during evolution. The rps7 gene and the rpl16 gene of P. iwatensis are exceptions to this trend. The phylogenetic analysis based on the mt genome strongly supports the previous results. Furthermore, we identified five positive selection genes (atp8, nad3, nad6, ccmFn, and matR) in seagrasses that may be associated with their adaptation to the marine environment.ConclusionsIn this study, we sequenced and annotated the mt genomes of Z. japonica and P. iwatensis and compared them with the genome of other monocotyledons. The results of this study will enhance our understanding of seagrass adaptation to the marine environment and can inform further investigations of the seagrass mt genome.

Surfgrass Phyllospadix iwatensis is a dominant seagrass species along the east coast of Shandong Peninsula, China. Like other seagrasses in the world, surfgrass has been declining in the past decades. To assess the possibility of transplanting P. iwatensis in the coastal area, a new surfgrass transplant system was designed and applied to conduct a surfgrass transplantation experiment in a tide pool and a subtidal area, and its survival, morphological and physiological parameters were examined from May 2019 to June 2020. The results showed that after a year since transplantation, more than 65% of the transplants survived and the survival rate was higher in the subtidal site than in the tide pool. The morphological measurements including shoot height, leaf width, number of leaves per shoot, rhizome diameter and elongation rate, and number of roots per shoot were all higher in the subtidal area than in the tide pool, showing that the P. iwatensis transplants grew better in the subtidal area than in the tide pool in the study area. These results indicated that surfgrass can be transplanted in the two areas, and it is probably more suitable in subtidal area than in tide pool in the study area.

In May 2019, UAV photogrammetry using drones (unmanned aircraft) was conducted to investigate the spatial distribution characteristics of the seagrass habitat in Wan Island. Wan Is. sea was divided into 3 geographical areas (Site A, B, C) by referring to the seagrass distribution identified by the National Coastal seagrass forest precision survey (Ministry of Oceans and Fisheries, 2015), and contour lines were extracted from grid depth data. In addition, a 3-D benthic topographic map using DTM (Digital Terrain Model) was created to understand the characteristics and slope of the benthic topographic map. Through the analysis of the seagrass distribution results and the water depth results, it was confirmed that the boundary between the seagrass distribution in the outer and coastal areas converges to different water depth limits (within 10 m, and within 5 m), which is estimated to be based on the characteristics of the outer sea area. As a result of the analysis of the benthic topography, it was confirmed that the slope of the well-covered distribution was relatively gentle below 0.2~0.8 degrees, and the well-covered distribution was limited to the vicinity of the boundary where the slope changed rapidly. As a result of comparing the area of the seagrass distribution survey in 2015 and 2019, it was confirmed that the area was 238.4 ha and 1,070.9 ha, respectively, which was 4.5 times more widerly when performing Drone survey than diving survey. In order to understand the surrounding environment of the seagrass distribution site, satellite image data and license fishing ground information map at the time of drone shooting (May 2019) were checked. As a result, seaweed (Kelp, Sea mustard seaweed, Seaweed, Seaweed fulvescens, etc.) and shellfish (Abalone) were densely distributed, and most of the facilities except for Seaweed fulvescens farms were separated from their habitat. Drone survey confirmed <i>Zostera marina</i>, <i>Zostera caulescens</i>, and <i>Zostera japonica</i> in Wan Is., but no <i>Phyllospadix iwatensis</i> and <i>Halophila nipponica</i> were identified in 2015. It was confirmed that there was a limit to classifying the types of vegetation due to the characteristics of <i>Phyllospadix iwatensis</i> attached to the rock substrate, and in the case of <i>Halophila nipponica</i> with short leaves of 2 to 3 cm, they were not exposed to the water even at low tide, so there was a limit to detection using drones. These research results are expected to be useful data for grasping the characteristics of a wide range of seagrass habitats in other seas in the future.

Long-term variations in the structure of the Phyllospadix iwatensis community in the intertidal zone of Krabovaya Bay (Shikotan Island, Kuril Islands) under the influence of natural and anthropogenic factors were described based on the materials of the research expeditions of 1987, 1997, and 2013 with additions of literature data for 1949, 1955, and 1963. Throughout the entire period of study, the following associated macrobenthos species were recorded always in the Ph. iwatensis community: the sponge Halichondria panicea, the sipunculid Phascolosoma agassizii, the isopod Idotea ochotensis, the hermit crab Pagurus middendorffii, and the gastropods Buccinum percrassum, Nucella heyseana, and Littorina sitkana. It was shown that the organic pollution of the bay induced an increase in the species richness and population density of associated species with a simultaneous reduction in the share of dominant species biomass. After an earthquake and the tectonic subsidence of the island, the species richness of the community was found to be reduced, while the biomass of the dominant species increased. The total biomass of the community increased throughout the study period. The degree of change in the ecological state of the Phyllospadix community in the intertidal zone of Krabovaya Bay was estimated by comparison of cumulative abundance/biomass curves.

Phyllospadix iwatensis, a foundation species of the angiosperm-dominated marine blue carbon ecosystems, has been recognized to be a vulnerable seagrass. Its degradation has previously been reported to be associated with environmental changes and human activities, while there has been a limited number of studies on its inherent characteristics. In this study, both the physiological and molecular biological data indicated that the oxygen-evolving complex (OEC) of P. iwatensis is prone to photoinactivation, which exhibits the light-dependent trait. When exposed to laboratory light intensities similar to typical midday conditions, <10% of the OEC was photoinactivated, and the remaining active OEC was sufficient to maintain normal photosynthetic activity. Moreover, the photoinactivated OEC could fully recover within the same day. However, under harsh light conditions, e.g., light intensities that simulate cloudless sunny neap tide days and continual sunny days, the OEC suffered irreversible photoinactivation, which subsequently resulted in damage to the photosystem II reaction centers and a reduction in the rate of O2 evolution. Furthermore, in situ measurements on a cloudless sunny neap tide day revealed both poor resilience and irreversible photoinactivation of the OEC. Based on these findings, we postulated that the OEC dysfunction induced by ambient harsh light conditions could be an important inherent reason for the degradation of P. iwatensis.

This survey was conducted to investigate the species, area, water depth and density of seagrass to the south east coast using field survey (SCUBA diving) and drone aerial photography. The occurrence seagrass in this survey were 6 station of Geoje (Yegu, Gujora, Dadae, Dapo, Geunpo, and Daepo) and 5 station of Tongyeong (Chuwon, Bongam, Changgwa, Yeomho, and Chukpo), and Zostera marina, Zostera caespitosa, and Halophila nipponica were investigated. Habitat area was the largest at 20,788 m2 in the Dadae and the smallest area was 51 m2 in the Chukop. Density was highest at 182.4 shoots/m2 in Geunpo and lowest at 89.6 shoots/m2 in Yeomho. Most of the water depths were around 3 m, but in Bongam, it was found that even at 7 m depth, the form of the Zostera marina was grassland and the Zostera caespitosa was distributed in the form of a patch. Compared with the previous studies, the area was increased or decreased depending on the survey region, but the occurrence species did not find Zostera caulescens, Zostera japonica, Phyllospadix iwatensis.

Seagrasses are marine flowering plants found in tropical and sub-tropical areas that live in coastal regions between the sea and land. All seagrass species evolved from terrestrial monocotyledons, providing the opportunity to study plant adaptation to sea environments. Here, we sequenced the chloroplast genomes (cpGenomes) of three Zostera species, then analyzed and compared their cpGenome structures and sequence variations. We also performed a phylogenetic analysis using published seagrass chloroplasts and calculated the selection pressure of 17 species within seagrasses and nine terrestrial monocotyledons, as well as estimated the number of shared genes of eight seagrasses. The cpGenomes of Zosteraceae species ranged in size from 143,877 bp (Zostera marina) to 152,726 bp (Phyllospadix iwatensis), which were conserved and displayed similar structures and gene orders. Additionally, we found 17 variable hotspot regions as candidate DNA barcodes for Zosteraceae species, which will be helpful for studying the phylogenetic relationships and interspecies differences between seagrass species. Interestingly, nine genes had positive selection sites, including two ATP subunit genes (atpA and atpF), two ribosome subunit genes (rps4 and rpl20), two DNA-dependent RNA polymerase genes (rpoC1 and rpoC2), as well as accD, clpP, and ycf2. These gene regions may have played key roles in the seagrass adaptation to diverse environments. The Branch model analysis showed that seagrasses had a higher rate of evolution than terrestrial monocotyledons, suggesting that seagrasses experienced greater environmental pressure. Moreover, a branch-site model identified positively selected sites (PSSs) in ccsA, suggesting their involvement in the adaptation to sea environments. These findings are valuable for further investigations on Zosteraceae cpGenomes and will serve as an excellent resource for future studies on seagrass adaptation to sea environments.

Abstract Surfgrass Phyllospadix iwatensis has been declining in the past decades. Transplantation is considered to be the best option to restore the degraded surfgrass beds due to its low seed production. To develop a surfgrass transplanting strategy to increase transplant survival rate and also to minimize damage to donor beds when harvesting transplants, an experiment was conducted to assess the effects of rhizome and root trimming on transplant survival and growth. P. iwatensis shoots with different rhizome and root trimming treatments were planted in a subtidal area in Mashanli at the east end of Shandong Peninsula, China in September 2018, and after the transplantation, a bi-monthly sampling had been conducted for one year. The results showed that, at the early stage of transplantation, the transplant survival rates of all four treatment groups decreased to the lowest at four months after transplantation, and then gradually increased until reaching at least 103.2% in all the treatment groups at the end of the experiment, and the transplants with roots on both short and long rhizomes had a significantly higher survival rate than those without roots. The results also showed that, although the morphological measurements, as well as the above- and below-ground productivity varied greatly with time and among different treatments during the study period, most of them showed no significant differences between treatments at the end of the experiment. These results suggest that surfgrass shoots with roots and a short rhizome are the most strongly recommended transplant candidates, and those with a short rhizome without roots are also good candidates, which might help make full use of harvested plants, optimize transplant harvesting strategies, and hence minimize damage to donor meadows.

ABSTRACT The investigation of fruit morphology and pericarp anatomy of the genera Phyllospadix and Zostera from the Zosteraceae family enabled us to identify their fruit types based on fruit wall anatomical structure. Drupes of the Prunus type with lignified inner zone of the mesocarp and the endocarp are specific for Phyllospadix iwatensis, whereas in Zostera asiatica dorsally dehiscent follicles of the Myristica type lacking sclerenchyma in the pericarp are found. In addition, Zosteraceae pericarp structure was analyzed and compared with four other families of higher Alismatales: Potamogetonaceae s.l., Posidoniaceae, Ruppiaceae, and Cymodoceaceae. Their exocarp and mesocarp consisted of thin-walled cells and the endocarp comprised a single layer of sclerenchymatous cells. This type of pericarp differentiation is supposed to be the sуnapomorphy of terminal families of Alismatales. The fruits of Zostera and Phyllospadix have a more complex pericarp structure in comparison to the synapomorphic type of pericarp differentiation of higher Alismatales – in Phyllospadix iwatensis both the mesocarp and the endocarp are lignified, whereas in Zostera asiatica the sclerenchyma is lacking. The fruits of Zostera and Phyllospadix are treated as specialised types, and recognised as autapomorphic characters of Zosteraceae among higher Alismatales.

Diversity, distribution and conservation of seagrass in coastal waters of the Liaodong Peninsula, North Yellow Sea, northern China: Implications for seagrass conservation

Poorly esterified pectin was isolated from the seagrass Phyllospadix iwatensis Makino, 1931 and modified using acidic hydrolysis in 0.5 M HCl. The concentration of anhydrogalacturonic acid, the degree of methoxylation, and the molecular weight distribution were determined in the native and hydrolyzed pectins. The sorption capacity of these pectins with regard to strontium and yttrium ions was evaluated at pH 6.0. It was found that the molecular weight of the native pectin decreased by 2.9 times during hydrolysis; the relative content of anhydrogalacturonic acid in the native pectin increased by 14%, while the degree of esterification decreased from 5.22 to 0%. The sorption capacity of the hydrolyzed pectin increased for strontium and yttrium ions by 40 and 48%, respectively. In our study, hydrolyzed pectin fully retained the ability to bind metal ions from their solutions at a low concentration.

Surfgrass Phyllospadix iwatensis is the dominant seagrass species in the coastal area of Mashanli, which lies at the east end of Shandong Peninsula, China. To our surprise, some Zostera marina and Zostera caespitosa patches have been recently found adjoining the surfgrass meadows. How the two Zostera species adapt to the high-energy habitats where Phyllospadix spp. thrive, and what kind of differences there are in the morphology and anatomy among the three species are unknown. To understand their adaptation strategies to the environment, we observed their morphological feature and anatomical structure of the three seagrass species by optical microscope. The results showed that much narrower leaves were observed in P. iwatensis, much higher plant density was observed in Z. caespitosa and Z. marina and much lower plant height was observed in Z. marina, which might have contributed to their adaptation in the environment. While for the supporting tissues (the epidermis, mesophyll cells, and vascular bundles for leaves, as well as the epidermis, exodermis and stele for rhizomes), the number of mesophyll cells in the leaves and the proportion of the other tissues in the cross sections in the leaves and rhizomes were significantly different among species. The results suggested that the three species adapt to the high-energy environment through different strategies.

As a result of the Great East Japan Earthquake and associated tsunami in March 2011, the Fukushima Daiichi Nuclear Power Plant (FDNPP) released a large amount of radioactive material into the environment, resulting in contamination of many marine organisms. In this study, 15 marine algal species and a seagrass species were collected from the sublittoral zone of the Iwaki Coast of Fukushima Prefecture from May 2012 to June 2015 and analyzed for variations in 110mAg, 134Cs, and 137Cs over time. The results indicated that (1) 110mAg, 134Cs, and 137Cs were present in all marine plants collected in May 2012, (2) the concentration of 110mAg in the seagrass Phyllospadix iwatensis decreased significantly over time while the ecological half-life of 110mAg in P. iwatensis was longer at locations closer to the FDNPP, and (3) the 110mAg/137Cs radioactivity ratio of P. iwatensis was remarkably high until 2015, indicating that detectable 110mAg was present in the coastal environment 4 years after the accident. The concentration of 110mAg in P. iwatensis was higher than those in other marine algae, demonstrating a species-specific mechanism of accumulation.

Antioxidants with antimelanogenic activity are potentially useful for the attenuation of skin hyperpigmentation disorders. In a previous study, luteolin 7-sulfate isolated from Phyllospadix iwatensis Makino, a marine plant, was shown to inhibit cellular melanin synthesis. The aim of the present study was to examine its action mechanism, focusing on the regulation of tyrosinase (TYR) expression in cells. Cell-based assay was undertaken using murine melanoma B16-F10 cells and primary human epidermal melanocytes (HEMs). Luteolin 7-sulfate showed lower toxicity compared to luteolin in B16-F10 cells. At the non-toxic concentration ranges, luteolin 7-sulfate attenuated melanin synthesis, stimulated by α-melanocyte-stimulating hormone or forskolin. Luteolin 7-sulfate attenuated forskolin-induced microphthalmia-associated transcription factor (MITF) and TYR expressions at the mRNA and protein levels in B16-F10 cells. It also attenuated the phosphorylation of cAMP-responsive element binding protein (CREB) stimulated by forskolin. Luteolin 7-sulfate also attenuated melanin synthesis in primary HEMs. This study demonstrates that luteolin 7-sulfate attenuates TYR gene expression through the intervention of a CREB- and MITF-mediated signaling pathway, leading to the decreased melanin synthesis.

Разработана технология и рецептура сухого концентрата напитка функционального назначения на основе пектина из морской травы Phyllospadix iwatensis с добавлением экс-

The community of Phyllospadix iwatensis is studied using materials from expeditions of A.V. Zhirmunsky Institute of Marine Biology (National Scientific Center of Marine Biology, Far Eastern Branch, Russian Academy of Sciences) and archive data (1949-2013) of the Laboratory of Chorology covering the species habitat area from Peter the Great Bay in the south to middle Kuril Islands in the north. The core of the community is identified. It has changing species composition; the changes correspond to geographical boundaries of the cenotic systems of Peter the Great Bay, the Lesser Kuril Islands, and Iturup Island. However, these boundaries do not coincide with the boundaries of the species-edificator habitat that embraces several cenotic systems. Spatial alterations of the cenotic systems are caused by landscape changes conditioned by general geomorphological situation and ecological conditions in the intertidal zone.

The marine seagrass-boring isopod, Limnoria rhombipunctata sp. nov. (Limnoriidae) is described from the rhizome of Phyllospadix iwatensis seagrass, in shallow coastal waters off Chiba Prefecture, Japan. L. rhombipunctata sp. nov. is distinguished from other Limnoria species by the unique carinae of pleonite 5 and pleotelson, two branched lacinia mobilis of the right mandible, 3 flagellar articles of antenna 1, and triangular epipod of the maxilliped. Specimens of L. magadanensis, a species similar to L. rhombipunctata sp. nov., are re-examined and compared with L. rhombipunctata sp. nov.