Tropical Seagrass Enhalus Acoroides Research Articles

Combined effects of temperature and burial on seed germination and seedling growth rates of the tropical seagrass Enhalus acoroides

As tropical seagrass meadows decline throughout the tropics, propagule transplantation is being used as an effective restoration method. This technique promotes genetic diversity in the restored seagrass meadows. Although many environmental factors, especially temperature and burial, can influence the success of seed/seedling transplantation success, little is known about these effects on transplanted tropical seagrass propagules. To address this knowledge gap, we conducted a 92-day laboratory incubation experiment to test the effects of representive temperatures (20 °C and 30 °C) and burial status (with and without burial) on germination and seedling growth of the tropical seagrass Enhalus acoroides. Results showed that germination rate was 3-fold higher in the treatment without burial (75%) than in the treatment with burial (25%). The germination success rate in the 30 °C treatment was about two times higher than that of the 20 °C treatment. When burial and temperature were tested in combination, germination success was highest in the 30 °C without burial treatment while the lowest rates were obtained in the 20 °C and burial treatment. Further, the temperature of 30 °C benefited leaf and root growth as well. These results illustrate that burial decreased E. acoroides germination, while high temperature enhanced both germination and seedling growth. Thus, transplantation of E. acoroides propagules for tropical seagrass restoration should be conducted when seawater temperature is warm, and the seeds should be fixed on the sediment surface rather than buried.

Enhalus acoroides efficiently alleviate ocean acidification by shifting modes of inorganic carbon uptake and increasing photosynthesis when pH drops

Ocean acidification (OA) is causing increasing ecological damage, so it is worthwhile to find efficient and environmentally friendly ways to mitigate OA. The mechanism of inorganic carbon (Ci) absorption and the ability to mitigate OA of the tropical seagrass Enhalus acoroides were investigated in this study. At 2.2 mM Ci concentration, its CO2 fixation efficiency increased to 81.89 t CO2/year/Ha under pH 6.5 from 27.59 t CO2/year/Ha at pH 8.2, and even reached 88.11 t CO2/year/Ha at pH 6.5 with unlimited Ci availability, made possible by three pathways for Ci utilization, which included absorbing CO2 directly, transforming HCO3− into CO2 through extracellular carbonic anhydrase, and absorbing HCO3− directly by anion-exchange protein then transforming it to CO2 through intracellular carbonic anhydrase, as verified by inhibitor addition experiments. The carbon fixation rate increased with decreasing pH, suggesting a greater CO2 absorbing capacity for E. acoroides under acidic conditions, which further demonstrates the possibility of mitigating OA and increasing carbon fixation through conserving and restoring E. acoroides meadows. Due to the strong carbon absorption capacity of E. acoroides, it is very important to strengthen the artificial restoration of E. acoroides seagrass meadows in the environmental management of the coastline.

Effect of high light and desiccation on photosystem II in the seedlings and mature plants of tropical seagrass Enhalus acoroides during low tide

Effect of high light and desiccation on photosystem II in the seedlings and mature plants of tropical seagrass Enhalus acoroides during low tide

Rising Temperature Is a More Important Driver Than Increasing Carbon Dioxide Concentrations in the Trait Responses of Enhalus acoroides Seedlings

Increasing temperature and CO2 concentration are among the most important factors affecting marine ecosystems under climate change. We investigated the morphological, biochemical, and physiological trait responses of seedlings of the tropical seagrass Enhalus acoroides under experimental conditions. Trait responses were greater under temperature effects than increasing CO2 concentration. Seedlings under rising temperatures showed enhanced leaf growth, lower leaf nutrient content, and stimulated down-regulating mechanisms in terms of photo-physiology. Increasing CO2 concentrations did not show any significant effects independently. There was a significant interaction for some of the trait responses considered, such as leaf number and carbon content in the roots, and trends of higher starch concentrations in the leaves and lower rETRmax under combined enriched CO2 and high temperature, even though none of these interactions were synergistic. Understanding the single and interactive trait responses of seagrass seedlings to increasing temperature and CO2 concentration is of importance to determine the relative responses of early life stages of seagrasses, which may differ from adult plants, in order to form a more holistic view of seagrass ecosystem health under climate change.

Short Communication: Restoration of seagrass Enhalus acoroides using a combination of generative and vegetative techniques

Abstract. Ambo-Rappe R, La Nafie YA, Syafiuddin, Limbong SR, Asriani N, Handayani NT, Lisdayanti E. 2019. Short Communication: Restoration of seagrass Enhalus acoroides using a combination of generative and vegetative techniques. Biodiversitas 20: 3358-3363. Seagrass areas have been declining in extent worldwide, with associated loss in seagrass ecosystem functions and services. Seagrass restoration is important to mitigate, halt and reverse such declines and their consequences. Generative propagation has benefits in terms of genetic biodiversity, however, survival of seagrass seedlings has often been poor especially in high energy environments. Terrestrial restoration often uses shade trees to protect vulnerable seedlings. This study aimed to evaluate the feasibility of a similar approach in the marine environment, using adult plants to protect seedlings of the tropical seagrass Enhalus acoroides (L.f.) Royle. Enhalus seeds taken from a donor bed were germinated and grown into seedlings, then planted in a location with high hydrodynamic exposure at three different densities (high, medium, and low). Adult Enhalus transplants were co-planted to provide three levels of protection: fifty (high), ten (medium), and none (no protection). Results showed that high-density seedling co-planting with high protection from adult transplants had significantly (p< 0.05) higher six-month survival rate compared to the other treatments. Our results indicate that, even in high energy environments, co-planting seedlings with adult transplants may combine the advantages of generative and vegetative propagation methods, promoting greater short-term effectiveness in terms of seedlings survival and growth in the restored seagrass meadows.

Two novel diterpenes from the stems and leaves of tropical seagrass Enhalus acoroides in the South China sea

Two novel diterpenes Enhoidin A (1) and Enhoidin B (2) featuring an unusual gibberellane skeleton were isolated from the stems and leaves of Enhalus acoroides. Their structures were elucidated on the basis of spectroscopic analysis including 1D and 2D NMR techniques and HR-ESI-MS. This is the first time that this type of lactone ring between C-18 and C-20 has been found among gibberellanes from the tropical seagrasses. Evaluation of the all compounds for cytotoxicity against four human cancer cell lines (MCF-7, HCT-116, HepG-2 and HeLa), and showed moderate cytotoxic activities.

Population genetic structure of the threatened tropical seagrass Enhalus acoroides in Hainan Island, China

Knowledge of the genetic structure of ecologically important species provides insight into population dynamics and persistence, which is important for decisions concerning ecosystem conservation and management. Seagrass ecosystems are being degraded in China due to coastal anthropogenic disturbances like eutrophication and pollution, but their genetic ecology is still poorly understood. In this study, we collected Enhalus acoroides samples from three lagoons and five offshore open-water sites along the east coast of Hainan Island to investigate its genetic diversity and structure using ten microsatellite loci. A total of 66 alleles were found, and the genetic diversity indices (i.e. mean number of alleles per locus, allelic richness and heterozygosity) varied among the eight populations. Assignment tests showed that the E. acoroides populations consists of three genetic clusters. Impeded gene flow among lagoonal populations was found, while connectivity existed among the open-water populations. This pattern seemed to be shaped by geographic isolation and ocean currents. Based on the genetic contribution analysis, we recommended that the E. acoroides populations at Tielugang and Gangdong need protection priority given they contribute higher genetic diversity, but are currently high risk populations under threats of pollution and physical disturbance.

Different organs of Enhalus acoroides (Hydrocharitaceae) can serve as specific bioindicators for sediment contaminated with different heavy metals

The tropical seagrass Enhalus acoroides is considered as a potential bioindicator for heavy metals. To date, studies on the accumulation of heavy metals in each specific seagrass organ have been limited. In this study, surface sediment and E. acoroides samples collected at six distinct beds from the coast of Khanh Hoa province, Vietnam, were evaluated for their heavy metal concentrations (Cd, Cu, Pb and Zn) to determine which organs of E. acoroides could be used as bioindicators for heavy metals. The metal concentrations in both the sediment and the seagrass organs were measured using inductively coupled plasma mass spectrometry (ICP-MS). Bio-concentration factor (BCF) and Metal pollution index (MPI) were determined on the seagrass organs, and Pearson's correlation and ANOVA were used for statistical analysis. The results showed that the highest BCF values of Cd and Zn were found in leaves, the highest BCF value of Cu was found in the rhizomes and the highest BCF value of Pb was found in the roots. Generally, MPI was lower in the sediment than in seagrass organs at the same locations. For Cd, Pearson's correlation showed that a significant positive correlation was only observed between sediment and leaves with respect to BCF. A significant positive correlation of BCF for Cu was observed between sediment and rhizome while significant positive correlations of BCF for Cu, Pb and Zn were observed between sediment and roots. Based on the results, it can be concluded that E. acoroides leaves should be used as a bioindicator for Cd and Zn, rhizomes for Cu, and roots for the three metals Cu, Pb and Zn.

Development of novel microsatellite markers in a tropical seagrass, Enhalus acoroides

Using the dual-suppression polymerase chain reaction technique, 12 novel polymorphic nuclear microsatellite DNA markers were isolated from the tropical seagrass Enhalus acoroides. The isolated markers provided the polymorphisms of 2–13 alleles per locus in 3 populations located in Japan, China, and the Philippines. The values of the expected heterozygosity fell in the following ranges: 0.000–0.693 (Japan), 0.000–0.623 (China), and 0.000–0.765 (Philippines). Compared to the Philippines population (1 monomorphic locus), a relatively higher proportion of the SSR loci did not show polymorphism in the marginal habitats of E. acoroides (5 loci in Japan; 5 loci in China). These markers may be useful for population and conservation genetics of E. acoroides.

Phylogenetic diversity of endophyte assemblages associated with the tropical seagrass Enhalus acoroides in Thailand

Seagrasses are flowering plants inhabiting coastal and marine environments, with a worldwide distribution. They serve as feeding, breeding and nursery grounds for economically important marine organisms including endangered species. The tropical seagrass Enhalus acoroides was collected from Had Khanom-Mu Ko Thale Tai National Park, southern Thailand. The objectives of this study were to investigate for the presence of endophyte assemblages in E. acoroides, as well as to describe the diversity of endophytes based on LSU, ITS1, 2, 5.8S rDNA sequence analyses. Forty-two fungal assemblages were isolated and identified through molecular data. This resulted in a diversity of fungal groups of Ascomycota (98%) and Basidiomycota (2%). Three major Ascomycota classes including the Sordariomycetes (36%), Eurotiomycetes (33%) and Dothideomycetes (24%) were determined. The predominant ascomycete orders were the Hypocreales, followed by the Eurotiales and the Capnodiales, respectively. Additionally one taxon belonged to the Russulales, Basidiomycota and was possibly mycorrhiza. This study confirms that E. acoroides harbors a wide diversity of fungal endophytes, and provides a baseline for further studies on fungal-host plant interactions.

Proximate analysis of the flour and starch from Enhalus acoroides (L.f.) Royle seeds

The seeds of the tropical seagrass Enhalus acoroides were analyzed for their nutritive components to assess their dietary value for humans. Proximate analysis of flour prepared by grinding the dried seeds gave the following results: 9.8% moisture; 8.8% protein; 0.2% fat; 72.4% carbohydrates; 2.4% crude fiber; 6.4% ash; 933 mg/kg calcium; 2392 mg/kg phosphorous; and 2813 mg/kg iron. Correspondingly, proximate analysis of the starch prepared from the flour with a 50% yield, resulted in the following: 11% moisture; 0.8% protein; 0.1% fat; 87.6% carbohydrates; 0.4% crude fiber; 0.5% ash; 320 mg/kg calcium; 210 mg/kg phosphorous and; 220 mg/kg iron. Comparison of the proximate analysis results and the calculated caloric values of the seagrass seed flour and starch showed similarity with those of terrestrial origin.