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Seagrass ecosystems are storehouses of both autochthonous and allochthonous organic matter due to their presence at the land and sea interface. This organic matter acts as a food source and plays an important role in biodiversity assemblages within seagrass ecosystems. The present study assessed the density of the bivalve (Cardita calyculata) along a gradient of sediment Organic Matter (OM %) in the mono-specific seagrass meadows of Thalassia hemprichii to those in adjacent bare sediments in the Andaman and Nicobar Islands (ANI) of India. The present study also assessed the correlation between sediment OM with Cardita's density and seagrass morphometric traits. C. calyculata density was 2-fold higher in T. hemprichii meadows (647.7±27.0 ind. m-2) than in the bare sediment (306±14.3 ind. m-2). Bivalve abundance correlated positively with OM in the seagrass meadows but showed no correlation in the unvegetated areas. The root branching of seagrass was higher, leading to increased C. calyculata density, suggesting a strong correlation of seagrass meadows with bivalves in nutrient-rich environments. The correlations between C. calyculata density and various plant traits were positive. Our study suggests that in the oligotrophic coastal ecosystems of the ANI, the positive influence of sediment OM of seagrass meadows on C. calyculata density is significant. Further studies looking at various interactions between seagrass and C. calyculata are essential to establish the precise interrelationship between seagrass and the biodiversity of associated faunal assemblages. [ABSTRACT FROM AUTHOR]

Introduction: Diabetes mellitus (DM) is an endocrine disorder characterized by high blood glucose levels. One of the approaches for treating DM is by regulating the postprandial blood glucose via inhibition of α-glucosidase enzymes. Seagrass is known as a plant containing bioactive compounds, especially for therapy antidiabetic. This research aims to evaluate the α-glucosidase inhibition activity of three species seagrasses (Enhalus acoroides, Thalassia hemprichii and Cymodocea rotundata) from the Banten Bay, Indonesia. Methods: The extracts of all parts (root, leaf, and stem) from three seagrasses were prepared with maceration method using 80% ethanol solvents. The α-glucosidase inhibitory activity was conducted by microplate reader at 400 nm using acarbose as a positive control. Furthermore, the kinetics of α-glucosidase inhibition, phytochemical screening, and total phenolics content were evaluated against extract which has the most potential α-glucosidase inhibition. Results: The result showed that the 80% ethanol extracts of Enhalus acoroides (IC50 values 168.15 ± 2.71 µg/mL) had the most potential α-glucosidase inhibitors activity compared with the positive control acarbose, Thalassia hemprichii and Cymodocea rotundata (IC50 values 197.27 ± 3.07 µg/mL, 425.86 ± 5.15 µg/mL and 429.28 ± 8.89 µg/mL). The kinetic type of inhibition against α-glucosidase was noncompetitive inhibition. The phytochemical compounds were phenols, flavonoid, terpenes, and tannin with the total phenolic content was 28.76 ± 2.46 mgGAE/g. Conclusion: Enhalus acoroides has the strongest inhibitor of α-glucosidase and can be further developed for DM therapy agents. [ABSTRACT FROM AUTHOR]

In order to increase our understanding of the microbial diversity associated with seagrass Thalassia hemprichii in Xincun Bay, South China Sea, 16S rRNA gene was identified by highthrough sequencing method. Bacteria associated with seagrass T. hemprichii belonged to 37 phyla, 99 classes. The diversity of bacteria associated with seagrass was similar among the geographically linked coastal locations of Xincun Bay. Proteobacteria was the dominant bacteria and the α-proteobacteria had adapted to the seagrass ecological niche. As well, α-proteobacteria and Pseudomonadales were associated microflora in seagrass meadows, but the interaction between the bacteria and plant is needed to further research. Burkholderiales and Verrucomicrobiae indicated the influence of the bay from anthropogenic activities. Further, Cyanobacteria could imply the difference of the nutrient conditions in the sites. γ-proteobacteria, Desulfobacterales and Pirellulales played a role in the cycle of sulfur, organic mineralization and meadow ecosystem, respectively. In addition, the less abundance bacteria species have key functions in the seagrass meadows, but there is lack knowledge of the interaction of the seagrass and less abundance bacteria species. Microbial communities can response to surroundings and play key functions in the biochemical cycle. [ABSTRACT FROM AUTHOR]

Increasing threats to natural ecosystems from local and global stressors are reinforcing the need for baseline data on the distribution and abundance of organisms. We quantified spatial and/or temporal patterns of seagrass distribution, shoot density, leaf area index, biomass, productivity, and sediment carbon content in shallow water (0-5 m) at Lizard Island, Great Barrier Reef, Australia, in field surveys conducted in December 2011 and October 2012. Seagrass meadows were mapped using satellite imagery and field validation. A total of 18.3 ha of seagrass, composed primarily of Thalassia hemprichii and Halodule uninervis, was mapped in shallow water. This was 46% less than the area of seagrass in the same region reported in 1995, although variations in mapping methods may have influenced the magnitude of change detected. There was inter-annual variability in shoot density and length, with values for both higher in 2011 than in 2012. Seagrass properties and sediment carbon content were representative of shallow-water seagrass meadows on a mid-shelf Great Barrier Reef island. The data can be used to evaluate change, to parameterize models of the impact of anthropogenic or environmental variability on seagrass distribution and abundance, and to assess the success of management actions. [ABSTRACT FROM AUTHOR]

The article discusses a study on differences in the community structures of meiofauna in seagrass beds and adjacent unvegetated sediments. Topics covered include meiofaunal taxa and nematode genera identified from a tropical seagrass bed of Thalassia hemprichii in Ludao, Taiwan, infaunas possessed by both habitats, and the need for seagrass conservation strategies to consider seagrass beds' peripheral bare area.

Abstract: A sub-acute experiment that tested carbon and nitrogen metabolisms and the plant's antioxidant defence system was used to investigate the effects of nitrate enrichment and salinity reduction on the tropical seagrass Thalassia hemprichii that had previously been grown in low light conditions. Shading significantly reduced leaf growth rate, nitrate reductase activity and non-structural carbohydrate (NSC) content in both aboveground and belowground tissues, but enhanced superoxide dismutase and guaiacol peroxidase (POD) activities and free amino acids in aboveground tissue. After shade removal, salinity reduction with pre-shading decreased minimum fluorescence and maximum fluorescence under all nitrate conditions. Pre-shading aggravated the negative effect of nitrate enrichment and salinity reduction on leaf growth rate. Nitrate enrichment led to a greater reduction in NSC in aboveground tissues of pre-shading plants compared to the control. Furthermore, salinity reduction with pre-shading even induced effective NSC translocation from belowground to aboveground tissues. Nitrate enrichment and salinity reduction both increased POD activity in T. hemprichii grown previously in low light. Therefore, pre-shading increases the vulnerability of T. hemprichii to eutrophication and hyposalinity, which must be considered when predicting future responses and effective management of seagrass resources. [Copyright &y& Elsevier]

Generally, the foliar sheaths of seagrass contribute a large biomass to the dry weight of plants, and are found to be above-sediment biomass or, sometimes, below-sediment biomass. However, the role of foliar sheaths of seagrass in nutrient uptake has not yet been established. Thus, this study was performed to test whether the growth form of foliar sheaths affects the nutrient uptake properties of the seagrass. Two separate sets of morphotypes of the seagrass Thalassia hemprichii were collected from two different tropical meadows in coastal Hainan Island, China in the South China Sea. Ammonium (NH) and phosphate (P) uptake by solely blades and roots (experiment I), and above and below-sediment tissues (experiment II) of the two sets of specimens were examined in partitioned chambers using laboratory incubations. Curve profiles of the blade and root saturation uptake kinetics were shown to be similar for the two morphotypes of T. hemprichii. However, the above and below-sediment tissues uptake kinetics had different characteristics between the two morphotypes. For plants with above-sediment foliar sheaths, uptake by the above-sediment tissues contributed an important part of the whole plants' nutrient acquisition. In contrast, for plants with below-sediment foliar sheaths, the contribution of nutrient uptake by above-sediment foliar blade tissues seemed almost negligible. Therefore, the results demonstrated that foliar sheaths of the tropical seagrass T. hemprichii were able to absorb NH and P. Especially interesting is that the capacity for uptake by robust foliar sheaths growing beneath the sediment was remarkable (we termed this the Zhang-Huang-Thorhaug effect). The role of sheaths in nutrient acquisition found in this study is critical in elucidating seagrass nutrient uptake strategies. [ABSTRACT FROM AUTHOR]

Abstract: Seagrass grazing is an intrinsic disturbance in primarily tropical and subtropical areas. While there is a general parabolic response in seagrass growth to grazing intensity, there is less knowledge on the role of grazing frequency, as well as potential interactions between grazing intensity and frequency. This study experimentally investigated physiological responses in Thalassia hemprichii to simulated (leaf cutting) grazing regimes with different intensities (25% vs. 75%) and frequencies (1 times vs. 3 times) over 35 days in Chwaka Bay (Zanzibar, Tanzania). The results showed that the two high-intensity treatments (75% removal) had 37–41% lower growth rate than the low-intensity/low-frequency treatment, and rhizome sugar and starch content were both affected in a similar way. A 36% lower starch content in the simulated low-intensity/high-frequency regime (25%×3) compared to the one of low-intensity/low-frequency (25%×1) also shows an interaction between grazing intensity and frequency. This suggests that high-intensity (and to some extent frequency) grazing regimes, in comparison to low-intensity regimes, could negatively affect T. hemprichii growth, energy reserves, and thereby the ability to deal with additional stress like light limitation or grazing. [Copyright &y& Elsevier]

We report the absence of a persistent seed bank in Thalassia hemprichii in NW Philippine seagrass beds. The survival of buried seeds was assessed experimentally since such a capacity is a prerequisite for the formation of seed bank. We found a rapid germination of non-dormant seeds and development into seedlings. Such seedlings could not survive under buried conditions (5 and 10 cm) for longer than a week. [Copyright &y& Elsevier]

Abstract: In a survey of the Myeik Archipelago, we documented seven seagrass species in the southern region. Three seagrass species (Cymodocea rotundata, Enhalus acoroides, and Halophila ovalis) have previously been reported in the Myeik Archipelago; three species (Halodule pinifolia, Halodule uninervis, Syringodium isoetifolium) are new reports for the archipelago; and one species (Thalassia hemprichii) is a new report for Myanmar. [Copyright &y& Elsevier]