Halophila Beccarii Research Articles

New Insights into the Microplastic Enrichment in the Blue Carbon Ecosystem: Evidence from Seagrass Meadows and Mangrove Forests in Coastal South China Sea.

Microplastics were recently found to aggregate in the blue carbon ecosystems (BCEs), which are known for their ability to store carbon by slowing down the water flow. However, evidence is largely lacking on how the accumulation of microplastics is related to carbon sequestration in BCEs and if this trap effect is driven by its biological characteristics. In this study, the trap effect of microplastics by BCEs was evaluated for various seagrasses (Zostera japonica, Halophila ovalis, and Halophila beccarii) and mangroves (Aegiceras corniculatum and Avicennia marina). Significant accumulation was found in the seagrass meadow dominated by H. beccarii and the mangrove forest dominated by A. marina, with microplastics enriched by 1.3 to 17.6 times compared to their corresponding unvegetated sites. The abundance of microplastics varied greatly from 17.68 ± 8.10 to 611.75 ± 81.52 particles per kg of dry sediment, with the highest abundance in A. marina mangrove sediments. A strong positive correlation was found between the abundance of microplastics and the particulate organic carbon content at all study sites (Pearson, R = 0.86, p < 0.01). Higher diversity of microplastic colors and size was found in the H. beccarii meadow, and higher diversity of shapes was found in the A. marina forest. Our results added new insights to the understanding of the mechanism of microplastic trapping by BCEs and coupled the behavior of microplastics with the organic carbon in the sediment.

The occurrence of vulnerable seagrass species Halophila beccarii Ascherson, 1871 from restored mangrove of Koduvally Estuary, south‐west coast of India

AbstractThe ocean turf grass, Halophila beccarii Ascherson, 1871 was recorded for the first time in the intertidal region of the restored mangrove ecosystem of the Koduvally Estuary on the south‐west coast of India. It was found co‐existing in the shallow muddy area of the mangroves, dominated by mangrove trees of Rhizophora mucronata and Sonneratia alba, and macroalgae, Ulva sp., Enteromorpha sp. and Chaetomorpha sp. The meadow is sparsely scattered with shoots near the mangroves, with a mean density of 720 shoots/m2. Details regarding the morphology and hydrographic conditions are described. The occurrence of H. beccarii in the Koduvally estuary is an encouraging sign of improved ecosystem health through mangrove restoration. The development of seagrass meadow in the estuary will improve the sediment stability and water quality. A further comprehensive study on the spatiotemporal variation of this species in the estuary is also recommended for conservation and management of this vulnerable seagrass species.

Efficient Heat Dissipation and Cyclic Electron Flow Confer Daily Air Exposure Tolerance in the Intertidal Seagrass Halophila beccarii Asch.

Seagrasses inhabiting the intertidal zone experience periodically repeated cycles of air exposure and rehydration. However, little is known about the photoprotective mechanisms in photosystem (PS)II and PSI, as well as changes in carbon utilization upon air exposure. The photoprotective processes upon air exposure in Halophila beccarii Asch., an endangered seagrass species, were examined using the Dual-PAM-100 and non-invasive micro-test technology. The results showed that air exposure enhanced non-photochemical quenching (NPQ) in both PSII and PSI, with a maximum increase in NPQ and Y(ND) (which represents the fraction of overall P700 that is oxidized in a given state) of 23 and 57%, respectively, resulting in intensive thermal energy dissipation of excess optical energy. Moreover, cyclic electron transport driven by PSI (CEF) was upregulated, reflected by a 50 and 22% increase in CEF and maximum electron transport rate in PSI to compensate for the abolished linear electron transport with significant decreases in pmfLEF (the proton motive force [pmf]) attributable solely to proton translocation by linear electron flow [LEF]). Additionally, H+ fluxes in mesophyll cells decreased steadily with increased air exposure time, exhibiting a maximum decrease of six-fold, indicating air exposure modified carbon utilization by decreasing the proton pump influxes. These findings indicate that efficient heat dissipation and CEF confer daily air exposure tolerance to the intertidal seagrass H. beccarii and provide new insights into the photoprotective mechanisms of intertidal seagrasses. This study also helps explain the extensive distribution of H. beccarii in intertidal zones.

Species biodiversity and distribution of seagrass beds in several coastal areas of central Vietnam

Seagrasses provide habitat and abundant food supplies for numerous marine species and seagrass ecosystems play a vital role in protecting the coast from erosion. There were numerous seagrass studies in Vietnam, however, while these studies provide information on specific studied places, there is a lack of comparison between studies for providing a broad picture of the overall seagrass ecosystem along the coast of Central Vietnam. Hence, this study of species diversity and distribution of seagrasses along the coast of Central Vietnam was conducted to provide comparative data, which is highly valuable for the proper exploitation, management, and sustainable development of seagrass resources in Central Vietnam. This study identified eight species of seagrass belonging to two families—Hydrocharitaceae and Cymodoceaceae—in the waters around several islands in Central Vietnam. Among them Halophila beccarii in the Cua Dai estuary was listed in the Red List of Threatened Species by the International Union for Conservation of Nature (IUCN) (2017)—at risk of global extinction. The results revealed that the seagrass beds in several coastal areas of Central Vietnam have diminished over time with respect to the number of species and their distribution with causes attributed to anthropogenic activities. The seagrass canopy coverage ranged from 5 to 100% (57 ± 36.20%) near several coastal islands of Central Vietnam. The majority of seagrass is distributed in both intertidal and subtidal zones Our findings suggest that water quality and important sedimentary processes vital to ecosystem health need to be assessed throughout the coastal region.

Current status and checklist of seagrass in Sri Lanka

This work provides the revised and updated checklist of the seagrass in Sri Lanka based on primary and secondary information. It is indeed to be an update the list of Seagrass species in Sri Lanka prepared by Abeywickrama and Arulgnanam (1991), which now been nearly three decades back. More than forty (40) published pieces of literature, herbarium sheets in the National Herbarium and author’s personal observations since 2011 were reviewed. Sri Lanka belongs to the Indo-Pacific bioregion and 15 species have been recorded so far representing seven genera. They are Enhalus acoroides, Halophila beccarii , H. decipiens , H. ovalis , H. major , H. minor , H. ovata , H. stipulacea , Thalassia hemprichii , Cymodocea rotundata , C. serrulata , Halodule uninervis , H. pinifolia , Ruppia maritima , and Syringodium isoetifolium with the estimated extend to be 37,137 ha. Halophila beccarii considered as a rare species, and has only been recorded in patchily distributed with few localities in Sri Lanka. Lack of evidences to cross check the identification of H. minor (only recorded in Negombo Lagoon) and H. ovata is a main drawback. The composition and distribution of seagrasses along the coastal zone of Sri Lanka is yet to be established. Therefore, island wide comprehensive and genetic studies could be positively contributed to fulfil the data gaps in future.

Seagrass beds store less carbon but support more macrobenthos than mangrove forests

Seagrass beds (SG) have powerful ecosystem functions, but some seagrasses, e.g., Halophila beccarii, have been neglected because of their tiny plant structure and narrow and restricted distribution in the intertidal zone. In this study, we compared ecosystem structure and function between H. beccarii SG and adjacent coastal habitats through: (i) vegetation composition, (ii) carbon storage, and (iii) macrobenthic community. The vegetation carbon storage was only 0.1% of that in mangrove forests (MG). The sediment carbon storage (0–60 cm) of SG (67.4 ± 20.2 MgCorg·ha−1) was 74.31% of MG (90.7 ± 12.9 MgCorg·ha−1) and 13.51% higher than unvegetated flats (UnV) (55.1 ± 17.7 MgCorg·ha−1). The macrobenthic abundance, biomass and secondary productivity in SG were significantly higher than those in MG, indicating that SG support more macrobenthos than MG. However, SG experienced more disturbances than MG and UnV. Therefore, it is necessary to strengthen the protection of H. beccarii SG to preserve their essential functions and services.

Characteristics of the complete chloroplast genome of Halophila beccarii

Halophila beccarii has been listed as a vulnerable species in ICNU. In this study, the complete plastid genome sequence of H. beccarii was successfully sequenced by the technology of Illumina. The whole plastid genome length was 168,585 bp and contained a typical quadripartite structure including one large single-copy (LSC) region (80,881 bp), one small single-copy (SSC) region (4,730bp) and a pair of inverted repeats (IR) regions (41,487bp). The GC content of this genome was 38.5%. The whole genome contained 132 genes including 88 protein-coding genes, 36 tRNA genes, and 8 rRNA genes. The phylogenetic analysis indicated that H. beccarii and Thalassia hemprichii formed a distinct clade.

ANTIOXIDANT ACTIVITY OF HALOPHILA OVALIS AND HALOPHILA BECCARII (HYDROCHARITACEAE): TWO IMPORTANT SEAGRASS SPECIES OF CHILIKA LAGOON, INDIA

Objective: The present study was undertaken to evaluate the total phenolic and flavonoid content and the antioxidant property of two important seagrass species namely, Halophila ovalis and Halophila beccarii occurring in Chilika lagoon, Odisha, India.&#x0D; Methods: Total Phenolic Content (TPC) of the extracts of Halophila species was determined by Folin-Ciocalteu method with little modifications and the total flavonoid content (TFC) was measured by aluminum chloride colorimetric assay. The antioxidant activity of different extracts was investigated by DPPH and ABTS radical scavenging activity. IC50 values were calculated for the DPPH and ABTS methods.&#x0D; Result: The study revealed that the methanol extract of H. ovalis has greater antioxidant activity than H. beccarii. Methanol extract of both the species (H. ovalis and H. beccarii) was found to possess high phenolic content at value of 70.25 mg GAE/g of extract and 48.53 mg GAE/g of extract respectively. Similarly flavonoid contents was found highest in methanol extract for both H. ovalis (76.82 mg quercetin equivalent/ g of extract) and H. beccarii (64.28 mg quercetin equivalent/ g of extract). The antioxidant activity of different extracts of these two species were evaluated using DPPH and ABTS radical assay. The methanol extract of both H. ovalis and H. beccarii showed high radical scavenging activity with IC50 values of 37.77 μg/ml and 52.25 μg/ml for DPPH and 25.62 μg/ml and 45.45 μg/ml for ABTS respectively.&#x0D; Conclusion: The study revealed the potential of the Halophila species as natural sources of antioxidants having considerable commercial importance.

Seagrass diversity in Brunei Darussalam: first records of three species

Borneo is one of the regions expected to have the highest diversity of seagrasses in the world. However, the diversity of seagrasses has scarcely been studied in Brunei Darussalam. The diversity of seagrasses at the intertidal and subtidal zones in Brunei was extensively surveyed in 2016. Six species of seagrasses were found at Pulau Muara Besar and Pulau Bedukang, and this was the first time that three of them (Halophila beccarii, Halodule pinifolia, and Cymodocea rotundata) had been recorded in Brunei. The total area of seagrass distribution around the two islands was approximately 1.5 km2. The present study extends the distribution of seagrasses on Borneo and suggests that Brunei has a rich seagrass diversity and an aquatic ecosystem supported by the seagrasses.

EVALUATION OF IN VITRO ANTIDIABETIC ACTIVITY OF METHANOLIC EXTRACT OF SEAGRASS HALOPHILA BECCARII

Objectives: The objectives of this study were to analyze the in vitro antidiabetic activity of methanolic extract of seagrass.Methods: The methanolic extract of Halophila beccarii was tested for its in vitro antidiabetic potential through inhibition of carbohydrate digestive enzymes such as α- amylase and α-glucosidase, glucose diffusion assay, glucose adsorption capacity, and enhancement of glucose uptake activity in yeast cells.Results: The crude extract of H. beccarii showed strong inhibition of ɑ-amylase and ɑ-glucosidase as on comparison with the standard enzyme inhibitor acarbose. The antidiabetic activity was found to be concentration dependent, and the antihyperglycemic activity was demonstrated through the inhibition of the glucose movement and facilitated diffusion of glucose. The rate of glucose diffusion across the membrane was found to be increased from 30 to 180 min.Conclusion: The seagrass collected from Pulicat Lake was identified as H. beccarii based on the morphology of the plant, shape of the leaves, and brown pigmentation on the leaves. According to the results, H. beccarii showed antidiabetic activity by the inhibition of carbohydrate digestive enzymes and glucose movement; hence, it is significantly reduced the post-postprandial hyperglycemia.

Spatial and temporal distribution of submerged aquatic vegetation in a tropical coastal lagoon habitat in Viet Nam

AbstractSubmerged aquatic vegetation (SAV) is considered as a keystone habitat, contributing significantly to structure and function of coastal lagoons. However, limited understanding of the factors driving SAV distribution and abundance across a wide range of salinity in tropical coastal lagoons has restricted the effectiveness of managing and preserving the ecosystem services in coastal lagoon habitats. This study examined the distribution and abundance of SAV species in the growing season in relation to water physico-chemical variables and grain sizes of sediment types in a tropical lagoon in Viet Nam. The results revealed thatNajas indicaandHalophila beccariiwere the dominant species in the community of 7 SAV species, accounting for 70% of the total cover and 55% of the total biomass sampled. Variation partitioning showed that both water and sediment variables were important in explaining spatial distribution and abundance of SAV species across the coastal lagoon. Salinity was the most significant predictor variable that accounted for the variation of SAV species data. The study implied that changes of salinity and silt (versus sand) particles can lead to different SAV assemblages in the lagoon.

A first record of Halodule pinifolia Miki den Hartog, and new locality of nationally endangered Halophila beccarii Asch, from the eastern coast of Sri Lanka

This study presents the first record of Halodule pinifolia on the eastern coast of Sri Lanka, approximately 310 km along the coastline from the previously recorded location (Kapparathota, Weligama). Further, this study describes the new locality of the nationally endangered seagrass species Halophila beccarii to Valaichchenai Lagoon, 26.5 km north of Batticaloa Lagoon, where it was previously recorded, along with the presence of two other species, Halophila ovalis and Halodule uninervis . While the species composition the seagrass habitat of Valaichchenai Lagoon might change in the near future due to the impact of climate change, multiple threats already exist at these newly discovered seagrass habitats, including multiday fishing vessel movements, the collection of shells on the seagrass beds, and solid waste dumping into the lagoon. Decline of seagrass abundance in Valaichchenai Lagoon would negatively impact the food security and income generation of fishers. Therefore, a well-established legislative framework and systematic long-term monitoring of seagrass in Valaichchenai Lagoon are essential in order to develop seagrass conservation plans before populations decline significantly or become locally extinct.

Clonal and genetic diversity of the threatened seagrass Halophila beccarii in a tropical lagoon: Resilience through short distance dispersal

Halophila beccarii is a threatened tropical seagrass which has a narrow, restricted distribution in the shallow coastal areas of the Indo-Pacific. The monoecious H. beccarii reproduces both sexually or asexually and such mixed reproduction mode is important to stay resilient in a dynamic coastal environment. This study examined genetic diversity and structure of H. beccarii to determine its survival strategy within a tropical coastal lagoon of Southeast Asia (Central Viet Nam). Seven microsatellite loci gave an overall low level of allelic richness (Ar=1.9), gene diversity (HE=0.233) and clonal diversity (R=0.27). A small neighborhood size and short dispersal distance together with a significant fine-scale genetic structure within each site indicated that its survival strategy is through local seed recruitment over very short distances and a limited local clonal extension (<5m). These estimations together with a low selfing rate, no inbreeding and significant recent bottlenecks, all indicated that the main resilience strategy of H. beccarii meadows is through sexual reproduction and within site dispersal. Implications for conservation are that environmental conditions of the lagoon should allow to maintain a local recruitment, establishment and development of H. beccarii beds at site level.

Saltmarsh and seagrass beds on the south-eastern coast of Bangladesh: vegetation characteristics and adjacent fisheries diversity

AbstractSaltmarsh and seagrass communities are coastal macrophytes. These communities perform a number of important ecological functions, one of which is to support substantial fishery resources either as a nursery ground or a refuge from predators. The Bangladesh coast houses saltmarsh and seagrass resources but there has been sparse information on the diversity of fisheries adjacent to these plant communities. Consequently, this study was carried out to obtain information on the shoot density and biomass of the dominant saltmarsh (Porteresia coarctata) and seagrass (Halophila beccarii) species together with the diversity of fisheries adjacent to saltmarsh and seagrass beds on the south eastern coast of Bangladesh. The below-ground biomass of P. coarctata was found to be significantly higher than the above-ground biomass, presumably so as to survive under harsh environmental conditions, for example strong wave exposure. The standing crops and shoot density of the seagrass H. beccarii showed a similar pat...

Karyomorphometric analysis of somatic chromosomes of selected seagrasses of families Hydrocharitaceae and Cymodoceaceae

Chromosome numbers of eleven seagrass species were determined. The highest chromosome number was recorded in Halodule spp. (2n=44) and the lowest chromosome number was observed in Cymodocea rotundata (2n=14). Chromosome numbers were identical or closely related among different species in the same genus. Karyomorphology was mapped for nine species (Halodule pinifolia, Halodule uninervis, Halodule wrightii, Syringodium isoetifolium, Enhalus acoroides, Halophila beccarii, Halophila ovalis (subsp. ovalis and ramamurthiana) Halophila ovata and Thalassia hemprichii). Length of the chromosomes of these species varied from 7.81 to 336.63μm while the fundamental arm number ranged between 36 and 85. The results confirm the karyotypic variation among the studied species, indicating that this characteristic can be used to confirm taxonomic identity of species which are morphologically very similar (eg. Halodule spp.). All tested species were diploid, except for Cymodocea rotundata.

A new record of the seagrass Halophila beccarii Ascherson from the Port Blair coast, Andaman and Nicobar Islands, India

Abstract During a study of the species diversity and distribution of seagrasses from the Andaman and Nicobar Islands, Halophila beccarii was recorded for the first time. This report updates the list of seagrasses for these islands from nine to ten species. Halophila beccarii was observed in an intertidal area of muddy substratum in Haddo Bay. The occurrence of this species is significant because of its new distributional record and because it is reported as a “vulnerable species” in the IUCN Red List. The morphometric characters, biomass of the species and its habitat are described in Haddo Bay.

Genetic variation in populations of the threatened seagrass Halophila beccarii (Hydrocharitaceae)

Halophila beccarii (Hydrocharitaceae), a small monoecious seagrass, has been listed as a threatened species. In this study, a total of 106 samples were collected from four Chinese populations located at the northern limit of its distribution range. Using six polymorphic microsatellites, we found low genetic variation in this species, in which the mean number of alleles per locus was 2.8, and 16 multi-locus genotypes were revealed. In the four populations, the mean number of alleles per locus ranged from 1.2 to 2, one to eight genotypes were found, and clonal diversity ranged from 0 to 0.23; observed and expected heterozygosity ranged from 0.17 to 0.40 and from 0.09 to 0.24, respectively. Strong genetic differentiation was found among the populations, and the standardized fixation index (F′ST) was 0.787. Species traits (i.e., clonal growth) and bottleneck effects due to drastic population fluctuation may contribute to the observed low genetic variation.

Variability of leaf morphology and marker genes of members of the halophila complex collected in Viet Nam

Seagrasses are marine angiosperms and adapted to aquatic life several times independently. In tropical as well as in temperate regions they play an important role in the coastal ecosystem. Classification according to morphology remains difficult due to very similar adaptations to the aquatic lifestyle and small simple flowers which are often not even formed. Especially the Halophila genus (Hydrocharitaceae) forms a complex group with an unresolved taxonomy due to overlapping morphological characters and high plasticity leading to many misidentifications. Hence, this led to the hypothesis that phylogenetic analysis on the molecular level may resolve taxonomic classification. The aim of this study is to identify and unambiguously characterize Halophila species collected in Viet Nam using tree- and character-based analysis of rbcL and matK sequences. Results obtained from molecular data and leaf morphology indicate that there are at least three species found in Viet Nam. Topologies based on single locus or combined datasets were similar but not equal. Analysis of rbcL sequences showed lowest species resolution when only Halophila beccarii Aschers was resolved at the Halophila complex. matK shows better resolution with respect to H. beccarii and H. decipiens Ostenfeld. Combined rbcL and matK consensus trees showed the highest species resolution when all species form three distinct clades representative for three difference species including H. beccarii, H. decipiens, and H. ovalis (R. Br.) Hook. f.

Halophila beccarii Aschers (Hydrocharitaceae) Responses to Different Salinity Gradient

Halophila beccarii Aschers., a small monoecious seagrass with rosette leafy shoot and well-developed rhizome or underground stem that acts as anchors occurs in environment with salinity fluctuation e.g., brackish coastal water of mangrove system, lagoon and marine coastal areas. Shoots represent most of the above-ground component of the plant and in direct contact to the ever changing salinity but it is not known how they respond to such fluctuations. Therefore, this study examined the effects of salinity variations on above-ground response variables; number of leaves per shoot, leaf length, leaf width and petiole length of the seagrass Halophila beccarii. Survival and above-ground response variables to salinity were characterized in culture-experiments in which plants were exposed to increased salinity (from 25-30, 45 psu) and decreased salinities (from 25-25, 20, 15, 10, 6, 4, 2, 0.9, 0.52 and 0 psu) treatments at two-week intervals. No plants mortality and significant changes in number of leaves per shoot were observed with increased or decreased salinity treatments. Plants continued to survive even in hypotonic environment to 0 psu. Halophila beccarii was significantly affected by increased or decreased salinity altering the dimensions of leaves. Leaf length and leaf width became shorter and narrower at lower (4-0.52 psu) and higher (45 psu) salinity. These results suggest that the seagrass H. beccarii could be negatively affected by hypo- or hypersalinity conditions, although salinity changes did not alter the tolerance of this species. Halophila beccarii tolerated hyposaline conditions better than hypersaline conditions.

濒危海草贝克喜盐草的种群动态及土壤种子库——以广西珍珠湾为例

PDF HTML阅读 XML下载 导出引用 引用提醒 濒危海草贝克喜盐草的种群动态及土壤种子库——以广西珍珠湾为例 DOI: 10.5846/stxb201306091489 作者: 作者单位: 中国科学院生态环境研究中心,广西科学院 广西红树林研究中心,中国科学院生态环境研究中心 城市与区域生态国家重点实验室,中国科学院生态环境研究中心,中国科学院烟台海岸带研究所,广西科学院 广西红树林研究中心 作者简介: 通讯作者: 中图分类号: 基金项目: 广西"红树林和海草系统保育与生态监测"特聘专家岗位基金资助项目;广西自然科学基金资助项目(0832030);广西科学院基本科研业务费资助项目(13YJ22HS12);广西青年科学基金资助项目(2012GXNSFBA053141);国家青年科学基金项目(31000210) Population dynamics and seed banks of the threatened seagrass Halophila beccarii in Pearl Bay, Guangxi Author: Affiliation: State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-environmental Sciences, Chinese Academy of Sciences,,,State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-environmental Sciences, Chinese Academy of Sciences,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:于2012年4月-2013年4月调查了广西珍珠湾地区贝克喜盐草(Halophila beccarii Ascherson)种群的基本属性及土壤种子库储量。结果表明,不同月份间该种群的面积、覆盖率、直立茎密度、生物量、繁殖器官密度等属性差异明显,均呈现先增大后减小再增大的趋势;各个属性出现峰值的日期有所不同,面积、覆盖度、地下生物量和总生物量的最高峰值出现在10月底,而直立茎密度和地上生物量峰值最高峰值出现在8月初。贝克喜盐草珍珠湾种群有明显雌蕊先熟现象,雌花发育高峰期(8月初,5404 朵/m2)早于雄花发育高峰期(8月底,2189 朵/m2)。而果实高峰期(4125 个/m2)为10月份。地上与地下生物量之比值(1.95-0.53)随种群的发育而逐渐减小,基于此比值可判断贝克喜盐草种群所处的发育阶段。在生长高峰期,贝克喜盐草种群有较大的分布面积(21.4 hm2)、较高的覆盖度(55%)、直立茎密度(21602 茎/m2)及生物量(70.583 g/m2干重)。贝克喜盐草果实含种子为1-4粒(平均为2.22粒);1月、3月和4月土壤种子库密度分别为5749、5652、2728 粒/m2,3-4月期间土壤种子库种子损失率高达104 粒 m-2 d-1。尽管贝克喜盐草有较高的种子产量(10月份,9158 粒/m2)和较快的生长速度,但由于土壤种子库中种子损失严重且种子萌发率较低以及人为干扰对其生境的强烈干扰等因素,因此可能会对次年的种群更新产生较大的负面影响。 Abstract:Halophila beccarii Ascherson is one of two species in the oldest lineage of seagrasses, and belongs to the family Hydrocharitaceae. It is a small submerged creeper, found in the upper intertidal zone, and grows on mud or muddy sand substrates in estuarine and coastal areas. This species has been recorded to be at the coastlines of East Asia, Southeast Asia, Central Asia, Kenya and Tanzania. Global population trends indicate this species is declining, although it is fast growing and may recover quickly from disturbance. However, it also has a narrow, restricted depth range that coincides with the intertidal zone, an area subject to much anthropogenic disturbance. This species was listed as ‘Vulnerable’ by the International Union for Conservation of Nature under criterion B2. H. beccarii occupies a very limited area in China and it is threatened by many forms of disturbance. Very little ecological information has been reported from China or subtropical regions globally for this species, and existing ecological studies are restricted to tropical regions in Southeast Asia or South Asia. The lack of basic ecological information on H. beccarii in China affects our understanding of the mechanisms underlying its decline, and thus hinders efforts to conserve and manage this threatened seagrass species. To examine temporal variation in the area, percent cover, above-ground/below-ground biomass, shoot density, reproductive organ density and the sediment seed banks of H. beccarii in Pearl Bay, Guangxi, samples were taken and surveys were carried out from April 2012 to April 2013 at roughly one-month intervals. Our results indicate that the area, percent cover, shoot density, biomass and reproductive organs density of H. beccarii in Pearl Bay vary greatly at different stages of population development over an annual cycle. Generally, all population parameters initially increased from April 2012, until they reached a peak value and then decreased. It seems the growth dynamics of the population followed "n" patterns with the peak values for shoot density (21602/m2), female flower density (5404/m2) and above-ground biomass (42.712 g/m2 (DW)) occurring in early August; male flower density (2189/m2) in late August; and area (21.4 hm2), percent cover (55%), below-ground biomass (39.701 g/m2 (DW)) and total biomass (70.583 g/m2 (DW)) in late October. We conclude that the flowers of H. beccarii in Pearl Bay are strongly protogynous. The ratio for above-ground to below-ground biomass decreases continuously from 1.95 to 0.53 during population development. Mean fruit density (as calculated from October 2012) was 4125/m2. Analysis of 186 H. beccarii fruits from Pearl Bay (1.7% of fruits had one seed, 79.7% had two seeds, 13.6% had three seeds and 5.1% had four seeds), revealed that seed counts varied from 1-4 with a mean of 2.22 mature seeds per fruit. Seed reserves in the soil varied with sampling location within the meadow, with an average of 5749/m2 in January, 5652/m2 in March and 2728/m2 in April. Based on our results for the area of seagrass and soil seed bank information, we estimate that the soil seed reserve of H. beccarii in Pearl Bay in January is about 1.23 × 109. We conclude that the H. beccarii population in Pearl Bay, Guangxi has the highest area, coverage, shoot density and biomass of all the sites where this species has been recorded in China. We suggest that the continuous decrease of the ratio of above-ground to below-ground biomass with population development means that the value of this ratio can be used as indicator for distinguishing between different developmental stages of H. beccarii populations. Despite being characterized by high seed production and fast growth, this species is threatened by high levels of human induced habitat disturbance, high rates of seed loss in sediments and low seed germination rates, which are all negatively affecting the regeneration of H. beccarii populations. 参考文献 相似文献 引证文献