Red Sea Seagrass Research Articles

Cytotoxicity and apoptotic effect of Methanolic extract of Red Sea seagrass, Enhalus acoroides (Linn.f.) Royle, against hepatocellular carcinoma cell line (HepG-2) and phytochemical characterization

Cytotoxicity and apoptotic effect of Methanolic extract of Red Sea seagrass, Enhalus acoroides (Linn.f.) Royle, against hepatocellular carcinoma cell line (HepG-2) and phytochemical characterization

Cymodocea rotundata Methanolic Extract, Red Sea Seagrass, Induces Anti-proliferative and Cell Cycle Arrest in Human Breast Cancer and Liver Cancer in vitro

Cymodocea rotundata Methanolic Extract, Red Sea Seagrass, Induces Anti-proliferative and Cell Cycle Arrest in Human Breast Cancer and Liver Cancer in vitro

A comparative study of the bioavailability of Red Sea seagrass, Enhalus acoroides (L.f.) Royle (leaves, roots, and rhizomes) as anticancer and antioxidant with preliminary phytochemical characterization using HPLC, FT-IR, and UPLC-ESI-TOF-MS spectroscopic analysis

BackgroundSeagrasses are unique marine flowering plants. Enhalus acoroides (L.f.) Royle (family Hydrocharitaceae), a new record for the Egyptian coast of the Red Sea, was the grass of choice. A comparative study on Enhalus acoroides (L.f.) Royle (leaves, roots and rhizomes) was done to determine the plant organ that shows the highest antiproliferative and antioxidant activities. The total phenolic content was determined using the Folin–Ciocalteu method. The total flavonoid content was estimated by the aluminum chloride assay. Fourier transform infrared (FT-IR) analysis was performed to detect the chemical functional groups in the extract. High-performance liquid chromatography (HPLC) was done for the qualitative and quantitative evaluation of phenolic compounds. UPLC-ESI-TOF–MS was performed for metabolomics profiling of the extract. Antioxidant activity was determined using the DPPH scavenger percentage method. Antiproliferation assay against hepatocellular carcinoma HepG2, human breast cancer cell lines MCF-7, MDA-MB-231 was performed for the three seagrass organs. Mitochondrial membrane potential (ΔΨm) was measured after treatment with three extracts against MCF-7 cell line.ResultsThe highest phenolic content is found in the leaves, while roots exhibited the highest DPPH scavenger percentage. The total concentration of phenolic compounds detected by HPLC was leaves > rhizomes > roots. Also leaves exhibit the highest antiproliferative activity and mitochondrial membrane potential depletion effect against MCF-7 cell line tested. UPLC-ESI-TOF–MS metabolite profiling of leaves detected different secondary and primary metabolites to which the activity was retained. Leaves are a new candidate to be used in the treatment of cancer.ConclusionEnhalus acoroides (L.f.) Royle leaves extract is a new nutraceutical candidate. Further in-depth studies are required on Enhalus acoroides (L.f.) Royle leaves.Graphical abstract

Seasonality of methane and carbon dioxide emissions in tropical seagrass and unvegetated ecosystems

Seagrass ecosystems are important carbon dioxide sinks that can sequester carbon for centuries as organic matter in sediment. They are also a major source of methane, a potent greenhouse gas, which limits their carbon sink capacity. However, data are lacking on their methane emission dynamics. Here, we conduct a one-year survey of carbon dioxide and methane concentrations and air-sea fluxes in Red Sea seagrass, mudflat, and coral backreef ecosystems. All ecosystems were sources of methane and carbon dioxide. Methane concentrations were lowest in the reef lagoon. We suggest that lagoons may be a globally important source of greenhouse gases. Methane concentrations were lower in seagrass than mudflat ecosystems at temperatures below 29.2 °C. Seagrass had the highest annual methane air-sea fluxes but the lowest global warming potential in carbon dioxide equivalent due to a decrease in its flux. Hence, seagrasses can help climate change mitigation compared to bare sediments.

Host-association as major driver of microbiome structure and composition in Red Sea seagrass ecosystems.

The role of the microbiome in sustaining seagrasses has recently been highlighted. However, our understanding of the seagrass microbiome lacks behind that of other organisms. Here, we analyse the endophytic and total bacterial communities of leaves, rhizomes, and roots of six Red Sea seagrass species and their sediments. The structure of seagrass bacterial communities revealed that the 1% most abundant OTUs accounted for 87.9% and 74.8% of the total numbers of reads in sediment and plant tissue samples, respectively. We found taxonomically distinct bacterial communities in vegetated and bare sediments. Yet, our results suggest that lifestyle (i.e. free-living or host-association) is the main driver of bacterial community composition. Seagrass bacterial communities were tissue- and species-specific and differed from those of surrounding sediments. We identified OTUs belonging to genera related to N and S cycles in roots, and members of Actinobacteria, Bacteroidetes, and Firmicutes phyla as particularly enriched in root endosphere. The finding of highly similar OTUs in well-defined sub-clusters by network analysis suggests the co-occurrence of highly connected key members within Red Sea seagrass bacterial communities. These results provide key information towards the understanding of the role of microorganisms in seagrass ecosystem functioning framed under the seagrass holobiont concept.

Warming enhances carbon dioxide and methane fluxes from Red Sea seagrass (<i>Halophila stipulacea</i>) sediments

Abstract. Seagrass meadows are autotrophic ecosystems acting as carbon sinks, but they have also been shown to be sources of carbon dioxide (CO2) and methane (CH4). Seagrasses can be negatively affected by increasing seawater temperatures, but the effects of warming on CO2 and CH4 fluxes in seagrass meadows have not yet been reported. Here, we examine the effect of two disturbances on air–seawater fluxes of CO2 and CH4 in Red Sea Halophila stipulacea communities compared to adjacent unvegetated sediments using cavity ring-down spectroscopy. We first characterized CO2 and CH4 fluxes in vegetated and adjacent unvegetated sediments, and then experimentally examined their response, along with that of the carbon (C) isotopic signature of CO2 and CH4, to gradual warming from 25 ∘C (winter seawater temperature) to 37 ∘C, 2 ∘C above current maximum temperature. In addition, we assessed the response to prolonged darkness, thereby providing insights into the possible role of suppressing plant photosynthesis in supporting CO2 and CH4 fluxes. We detected 6-fold-higher CO2 fluxes in vegetated compared to bare sediments, as well as 10- to 100-fold-higher CH4 fluxes. Warming led to an increase in net CO2 and CH4 fluxes, reaching average fluxes of 10 422.18 ± 2570.12 µmol CO2 m−2 d−1 and 88.11±15.19 µmol CH4 m−2 d−1, while CO2 and CH4 fluxes decreased over time in sediments maintained at 25 ∘C. Prolonged darkness led to an increase in CO2 fluxes but a decrease in CH4 fluxes in vegetated sediments. These results add to previous research identifying Red Sea seagrass meadows as a significant source of CH4, while also indicating that sublethal warming may lead to increased emissions of greenhouse gases from seagrass meadows, providing a feedback mechanism that may contribute to further enhancing global warming.

Role of vegetated coastal ecosystems as nitrogen and phosphorous filters and sinks in the coasts of Saudi Arabia

Vegetated coastal ecosystems along the Red Sea and Arabian Gulf coasts of Saudi Arabia thrive in an extremely arid and oligotrophic environment, with high seawater temperatures and salinity. Mangrove, seagrass and saltmarsh ecosystems have been shown to act as efficient sinks of sediment organic carbon, earning these vegetated ecosystems the moniker ‘blue carbon’ ecosystems. However, their role as nitrogen and phosphorus (N and P) sinks remains poorly understood. In this study, we examine the capacity of blue carbon ecosystems to trap and store nitrogen and phosphorous in their sediments in the central Red Sea and Arabian Gulf. We estimated the N and P stocks (in 0.2 m thick-sediments) and accumulation rates (for the last century based on 210Pb and for the last millennia based on 14C) in mangrove, seagrass and saltmarsh sediments from eight locations along the coast of Saudi Arabia (81 cores in total). The N and P stocks contained in the top 20 cm sediments ranged from 61 g N m−2 in Red Sea seagrass to 265 g N m−2 in the Gulf saltmarshes and from 70 g P m−2 in Red Sea seagrass meadows and mangroves to 58 g P m−2 in the Gulf saltmarshes. The short-term N and P accumulation rates ranged from 0.09 mg N cm−2 yr−1 in Red Sea seagrass to 0.38 mg N cm−2 yr−1 in Gulf mangrove, and from 0.027 mg P cm−2 yr−1 in the Gulf seagrass to 0.092 mg P cm−2 yr−1 in Red Sea mangroves. Short-term N and P accumulation rates were up to 10-fold higher than long-term accumulation rates, highlighting increasing sequestration of N and P over the past century, likely due to anthropogenic activities such as coastal development and wastewater inputs.

Drivers of the Low Metabolic Rates of Seagrass Meadows in the Red Sea

Tropical seagrass meadows are highly productive ecosystems that thrive in oligotrophic environments. The Red Sea is characterized by strong N-S latitudinal nutrient and temperature gradients, which constrain pelagic productivity. To date, the influence of these natural gradients have not been assessed in metabolic rates for local seagrass communities. Here we report metabolic rates (gross primary production, respiration, and net community production) in four common species of seagrass (Halodule uninervis, Halophila ovalis, Halophila stipulacea, and Thalassia hemprichii) along latitudinal and thermal gradients in the Red Sea. In addition, we quantified leaf nutrient concentration (nitrogen, phosphorous, and iron), and correlate this with latitude. Our results show that average metabolic rates and aboveground biomass of seagrass meadows in the Red Sea were generally in the lower range when compared to global values reported for the same species forming meadows. The optimum temperature of Red Sea seagrass meadows varied among species with declines along the sequence: H. stipulacea > T. hemprichii > H. uninervis ~ H. ovalis. Gross primary production for H. uninervis – a seagrass thermophile – was lowest in higher latitudes and increased toward lower latitudes during the summer months. While temperature was identified as a strong driver of metabolic rates across seagrass meadows, leaf concentration of phosphorous and iron (but not nitrogen), were below nutrient sufficiency thresholds, indicating these two elements might be limiting for seagrass meadows in the Red Sea.

Egyptian red sea seagrass as a source of biologically active secondary metabolites

Background and objective The Red Sea seagrass Halophila stipulacea (Forsskal) Ascherson and Thalassodendron ciliatum (Forsskal) den Hartog were poorly investigated either for their biological activities or for chemical constituents. This study aims to investigate the phytochemical constituent of both grass, along with studying the different biological activities (osteoclastogenesis, antioxidant activity, and anticancer activity) of the crude extract as well as purified compounds. Materials and methods The present study used three different in-vitro bioassay methods to screen the fractions and/or isolated compounds of both seagrass, to assess their possible biological activity. Osteoclastogenesis assay, antioxidant activity, and anticancer activity were carried out using different assays of the different anticancer mechanism of action. Results and conclusion Ten secondary metabolites were isolated and identified for the first time from Red Sea seagrass H. stipulacea (Forsskal) Ascherson: (1) p-hydroxybenzoic acid, (2) bis(2-ethyl hexyl) phthalate, (3) benzoic acid, (4) p-hydroxybenzaldehyde, (5) thymidine, (6) stigmasterol, (7) oleic acid, (8) linoleic acid, (9) linoleic methyl ester, and (10) apigenin. Furthermore, a new dihydrochalcone and a known flavonoid were isolated and identified from Red Sea seagrass T. ciliatum (Forsskal) den Hartog: (11) 2,4′ dihydroxy-4-methoxy-6-glucosyl dihydrochalcone (Thalassodendron B) and (12) rutin. Fractions of both seagrass showed promising biological activities.

Carbon and Nitrogen Concentrations, Stocks, and Isotopic Compositions in Red Sea Seagrass and Mangrove Sediments

Coastal vegetated ecosystems are intense global carbon (C) sinks; however, seagrasses and mangroves in the Central Red Sea are depleted in organic C (Corg). Here, we tested whether Corg depletion prevails across the whole Red Sea, or if sediment Corg and nitrogen (N) stocks reflect the latitudinal productivity gradient of the Red Sea. We assessed Corg and N concentrations, stocks, isotopic compositions (δ13C and δ15N), and the potential contribution of primary producers to the organic matter accumulation in seagrass and mangrove sediments along the Eastern coast of the Red Sea. Sediment Corg concentration was higher in mangroves than seagrasses, while N concentrations were similar, resulting in higher C/N ratios in mangrove than seagrass sediments. Mangrove Corg stocks (integrated over the top 10 cm) were two-fold higher than those of seagrasses, respectively. N concentrations and stocks decreased from south to north in seagrass sediments matching the productivity gradient while Corg concentrations and stocks were uniform. The δ15N decreased from south to north in seagrass and mangrove sediments, reflecting a shift from nitrate and nitrite as N sources in the south, to N2 fixation towards the north. Stable isotope mixing models showed that seagrass leaves and macroalgae blades were the major contributors to the organic matter accumulation in seagrass sediments; while mangrove leaves were the major contributors in mangrove sediments. Overall, vegetated sediments in the Red Sea tend to be carbonate-rich and depleted in Corg and N, compared to coastal habitats elsewhere. Specifically, mean Corg stocks in Red Sea seagrass and mangrove sediments (7.2 ± 0.4 and 14.5 ± 1.4 Mg C ha-1, respectively) are lower than previously reported mean global values. This new information of Blue Carbon resources in the Red Sea provides a background for Blue Carbon programs in the region while also helping to balance global estimates.

Carbon stocks and accumulation rates in Red Sea seagrass meadows

Seagrasses play an important role in climate change mitigation and adaptation, acting as natural CO2 sinks and buffering the impacts of rising sea level. However, global estimates of organic carbon (Corg) stocks, accumulation rates and seafloor elevation rates in seagrasses are limited to a few regions, thus potentially biasing global estimates. Here we assessed the extent of soil Corg stocks and accumulation rates in seagrass meadows (Thalassia hemprichii, Enhalus acoroides, Halophila stipulacea, Thalassodendrum ciliatum and Halodule uninervis) from Saudi Arabia. We estimated that seagrasses store 3.4 ± 0.3 kg Corg m−2 in 1 m-thick soil deposits, accumulated at 6.8 ± 1.7 g Corg m−2 yr−1 over the last 500 to 2,000 years. The extreme conditions in the Red Sea, such as nutrient limitation reducing seagrass growth rates and high temperature increasing soil respiration rates, may explain their relative low Corg storage compared to temperate meadows. Differences in soil Corg storage among habitats (i.e. location and species composition) are mainly related to the contribution of seagrass detritus to the soil Corg pool, fluxes of Corg from adjacent mangrove and tidal marsh ecosystems into seagrass meadows, and the amount of fine sediment particles. Seagrasses sequester annually around 0.8% of CO2 emissions from fossil-fuels by Saudi Arabia, while buffering the impacts of sea level rise. This study contributes data from understudied regions to a growing dataset on seagrass carbon stocks and sequestration rates and further evidences that even small seagrass species store Corg in coastal areas.

Foraging association of lionfish and moray eels in a Red Sea seagrass meadow

Foraging association of lionfish and moray eels in a Red Sea seagrass meadow

Bioactive Phenolic Compounds from the Egyptian Red Sea Seagrass Thalassodendron ciliatum

Five flavonoids (rutin, asebotin, 3-hydroxyasebotin, quercetin-3-O-beta-D-xylopyranoside, and a racemic mixture of catechin) and caffeic acid were isolated and identified for the first time from seagrass, Thalassodendron ciliatum, collected from the Hurghada region in Egypt. The crude extract and the isolated pure compounds were evaluated for their cytotoxic activities against HCT-116, HEPG, MCF-7, and HeLa human cancer cell lines, for their antiviral activity against Herpes Simplex and hepatitis A viruses, and for their antioxidant activity.

Bioactive Phenolic Compounds from the Egyptian Red Sea Seagrass Thalassodendron ciliatum

Bioactive Phenolic Compounds from the Egyptian Red Sea Seagrass Thalassodendron ciliatum