Summary
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.
The atmosphere plays a fundamental role in the transport of microbes across the planet but it is often neglected as a microbial habitat. Although the ocean represents two thirds of the Earth's ...surface, there is little information on the atmospheric microbial load over the open ocean. Here we provide a global estimate of microbial loads and air-sea exchanges over the tropical and subtropical oceans based on the data collected along the Malaspina 2010 Circumnavigation Expedition. Total loads of airborne prokaryotes and eukaryotes were estimated at 2.2 × 10
and 2.1 × 10
cells, respectively. Overall 33-68% of these microorganisms could be traced to a marine origin, being transported thousands of kilometres before re-entering the ocean. Moreover, our results show a substantial load of terrestrial microbes transported over the oceans, with abundances declining exponentially with distance from land and indicate that islands may act as stepping stones facilitating the transoceanic transport of terrestrial microbes.The extent to which the ocean acts as a sink and source of airborne particles to the atmosphere is unresolved. Here, the authors report high microbial loads over the tropical Atlantic, Pacific and Indian oceans and propose islands as stepping stones for the transoceanic transport of terrestrial microbes..
Atmospheric methane (CH4) is the second strongest greenhouse gas and it is emitted to the atmosphere naturally by different sources. It is crucial to define the dimension of these natural emissions ...in order to forecast changes in atmospheric CH4 mixing ratio in future scenarios. However, CH4 emissions by seagrass ecosystems in shallow marine coastal systems have been neglected although their global extension. Here we quantify the CH4 production rates of seagrass ecosystems in the Red Sea. We measured changes in CH4 concentration and its isotopic signature by cavity ring-down spectroscopy on chambers containing sediment and plants. We detected CH4 production in all the seagrass stations with an average rate of 85.09 ± 27.80 µmol CH4 m-2 d-1. Our results show that there is no seasonal or daily pattern in the CH4 production rates by seagrass ecosystems in the Red Sea. Taking in account the range of global estimates for seagrass coverage and the average seagrass CH4 production, the global CH4 production and emission by seagrass ecosystems could range from 0.09 to 2.7 Tg yr-1. Because CH4 emission by seagrass ecosystems had not been included in previous global CH4 budgets, our estimate would increase the contribution of marine global emissions, hitherto estimated at 9.1 Tg yr-1, by about 30%. Thus, the potential contribution of seagrass ecosystems to marine CH4 emissions provides sufficient evidence of the relevance of these fluxes as to include seagrass ecosystems in future assessments of the global CH4 budgets.
Mangrove forests are highly productive tropical and subtropical coastal systems that provide a variety of ecosystem services, including the sequestration of carbon. While mangroves are reported to be ...the most intense carbon sinks among all forests, they can also support large emissions of greenhouse gases (GHGs), such as carbon dioxide (CO2) and methane (CH4), to the atmosphere. However, data derived from arid mangrove systems like the Red Sea are lacking. Here, we report net emission rates of CO2 and CH4 from mangroves along the eastern coast of the Red Sea and assess the relative role of these two gases in supporting total GHG emissions to the atmosphere. Diel CO2 and CH4 emission rates ranged from −3452 to 7500 µmol CO2 m−2 d−1 and from 0.9 to 13.3 µmol CH4 m−2 d−1 respectively. The rates reported here fall within previously reported ranges for both CO2 and CH4, but maximum CO2 and CH4 flux rates in the Red Sea are 10- to 100-fold below those previously reported for mangroves elsewhere. Based on the isotopic composition of the CO2 and CH4 produced, we identified potential origins of the organic matter that support GHG emissions. In all but one mangrove stand, GHG emissions appear to be supported by organic matter from mixed sources, potentially reducing CO2 fluxes and instead enhancing CH4 production, a finding that highlights the importance of determining the origin of organic matter in GHG emissions. Methane was the main source of CO2 equivalents despite the comparatively low emission rates in most of the sampled mangroves and therefore deserves careful monitoring in this region. By further resolving GHG fluxes in arid mangroves, we will better ascertain the role of these forests in global carbon budgets.
Novel aerobic, Gram-negative bacteria with DNA G+C contents below 50 mol% were isolated from the culturable microbiota associated with the Mediterranean seagrass Posidonia oceanica. 16S rRNA gene ...sequence analyses revealed that they belong to the genus Marinomonas. Strain IVIA-Po-186 is a strain of the species Marinomonas mediterranea, showing 99.77 % 16S rRNA gene sequence similarity with the type strain, MMB-1(T), and sharing all phenotypic characteristics studied. This is the first description of this species forming part of the microbiota of a marine plant. A second strain, designated IVIA-Po-101(T), was closely related to M. mediterranea based on phylogenetic studies. However, it differed in characteristics such as melanin synthesis and tyrosinase, laccase and antimicrobial activities. In addition, strain IVIA-Po-101(T) was auxotrophic and unable to use acetate. IVIA-Po-101(T) shared 97.86 % 16S rRNA gene sequence similarity with M. mediterranea MMB-1(T), but the level of DNA-DNA relatedness between the two strains was only 10.3 %. On the basis of these data, strain IVIA-Po-101(T) is considered to represent a novel species of the genus Marinomonas, for which the name Marinomonas balearica sp. nov. is proposed. The type strain is IVIA-Po-101(T) (=CECT 7378(T) =NCIMB 14432(T)). A third novel strain, IVIA-Po-185(T), was phylogenetically distant from all recognized Marinomonas species. It shared the highest 16S rRNA gene sequence similarity (97.4 %) with the type strain of Marinomonas pontica, but the level of DNA-DNA relatedness between the two strains was only 14.5 %. A differential chemotaxonomic marker of this strain in the genus Marinomonas is the presence of the fatty acid C(17 : 0) cyclo. Strain IVIA-Po-185(T) is thus considered to represent a second novel species of the genus, for which the name Marinomonas pollencensis sp. nov. is proposed. The type strain is IVIA-Po-185(T) (=CECT 7375(T) =NCIMB 14435(T)). An emended description of the genus Marinomonas is given based on the description of these two novel species, as well as other Marinomonas species described after the original description of the genus.
In intertidal systems, the type and role of interactions among sediment microorganisms, animals, plants and abiotic factors are complex and not well understood. Such interactions are known to promote ...nutrient provision and cycling, and their dynamics and relationships may be of particular importance in arid microtidal systems characterized by minimal nutrient input. Focusing on an arid mangrove ecosystem on the central Red Sea coast, we investigated the effect of crab bioturbation intensity (comparing natural and manipulated high levels of bioturbation intensity) on biogeochemistry and bacterial communities of mangrove sediments, and on growth performance of
, over a period of 16 months. Along with pronounced seasonal patterns with harsh summer conditions, in which high sediment salinity, sulfate and temperature, and absence of tidal flooding occur, sediment bacterial diversity and composition, sediment physicochemical conditions, and plant performance were significantly affected by crab bioturbation intensity. For instance, bioturbation intensity influenced components of nitrogen, carbon, and phosphate cycling, bacterial relative abundance (i.e.,
and
) and their predicted functionality (i.e., chemoheterotrophy), likely resulting from enhanced metabolic activity of aerobic bacteria. The complex interactions among bacteria, animals, and sediment chemistry in this arid mangrove positively impact plant growth. We show that a comprehensive approach targeting multiple biological levels provides useful information on the ecological status of mangrove forests.
Bioturbation is one of the most important processes that governs sediment biocenosis in intertidal systems. By facilitating oxygen penetration into anoxic layers, bioturbation alters the overall sediment biogeochemistry. Here, we investigate how high crab bioturbation intensity modifies the mangrove sediment bacterial community, which is the second largest component of mangrove sediment biomass and plays a significant role in major biogeochemical processes. We show that the increase in crab bioturbation intensity, by ameliorating the anoxic condition of mangrove sediment and promoting sediment bacterial diversity in favor of a beneficial bacterial microbiome, improves mangrove tree growth in arid environments. These findings have significant implications because they show how crabs, by farming the mangrove sediment, can enhance the overall capacity of the system to sustain mangrove growth, fighting climate change.
Five novel Gram-reaction-negative aerobic marine bacterial strains with DNA G+C contents <50 mol% were isolated from the seagrass Posidonia oceanica. 16S rRNA sequence analysis indicated that they ...belonged to the genus MARINOMONAS: Major fatty acid compositions, comprising C10 : 0 3-OH, C16 : 0, C16 : 1ω7c and C18 : 1ω7c, supported the affiliation of these strains to the genus MARINOMONAS: Strains IVIA-Po-14bT, IVIA-Po-145T and IVIA-Po-155T were closely related to Marinomonas pontica 46-16T, according to phylogenetic analysis. However, DNA–DNA hybridization values <35 % among these strains revealed that they represented different species. Further differences in the phenotypes and minor fatty acid compositions were also found among the strains. Another two strains, designated IVIA-Po-181T and IVIA-Po-159T, were found to be closely related to M. dokdonensis DSW10-10T but DNA–DNA relatedness levels <40 % in pairwise comparisons, as well as some additional differences in phenotypes and fatty acid compositions supported the creation of two novel species. Accordingly, strains IVIA-Po-14bT ( = CECT 7730T = NCIMB 14671T), IVIA-Po-145T ( = CECT 7377T = NCIMB 14431T), IVIA-Po-155T ( = CECT 7731T = NCIMB 14672T), IVIA-Po-181T ( = CECT 7376T = NCIMB 14433T) and IVIA-Po-159T ( = CECT 7732T = NCIMB 14673T) represent novel species, for which the names Marinomonas alcarazii sp. nov., Marinomonas rhizomae sp. nov., Marinomonas foliarum sp. nov., Marinomonas posidonica sp. nov. and Marinomonas aquiplantarum sp. nov. are proposed, respectively.
Mangroves are important coastal ecosystems of warm climatic regions that often grow in shallow saline or brackish waters of estuaries and river mouths affected by wide tidal intervals and receive ...abundant nutrient supply. However, mangroves also occur in areas of little tidal influence and devoid of riverine inputs, where they can develop a stunted plant form. Here we report that Avicennia marina trees in the fringe of the Red Sea have maximum heights toward the lower range of that reported elsewhere (average maximum canopy height of 4.95 m), especially in the central region, where mangroves are stunted with an average tree height of 2.7 m. Maximum tree height and chlorophyll a concentration correlated positively with nitrogen concentration in the leaves of A. marina. We conclude that the stunted nature of mangrove trees in the central Red Sea is likely driven by nitrogen limitation.
Measurements of isotopic composition of marine primary producers are a valuable tool to follow and trace the source and cycling of organic matter in the marine systems, as well to describe the ...physiological status of aquatic photosynthetic organisms. Although stable isotope data abounds in the literature, relatively limited information regarding the isotopic signatures of marine primary producers is available for the Red Sea. Here we present data on carbon concentration (and nitrogen when possible) of phytoplankton, macroalgae, seagrasses, mangroves and salt-marsh plants, and examine how their isotopic signatures differed among plant types across a north-south gradient in the Red Sea. We also tested the potential use of deuterium, δD, to distinguish among primary producers whose carbon isotopic values may overlap. Our findings showed a clear differentiation of carbon and nitrogen content between the different groups of primary producers, as well as between species. Seagrasses and mangroves had on average larger carbon (30 and 49 % of C, respectively) and nitrogen content (1.8 % N) than other groups. In terms of stable carbon isotopes, seagrasses and macroalgae tended to be heavier (-7.3 ‰ and -13.3 ‰, respectively) than halophytes, mangroves, and phytoplankton, which showed statistically similar and lighter δ13C values (between -24 ‰ and -26 ‰). There was a tendency for the nitrogen isotopic composition of seagrass and macroalgae to become lighter from the southern to the northern Red Sea, in parallel to a decline in nitrogen concentration in the tissues, indicative of a higher dependence of nitrogen fixation as a source of nitrogen toward the more oligotrophic northern Red Sea. Our results showed an overlap in the δ13C and δ15N values between macroalgae and seagrasses; however, their δD values were significantly different (seagrasses -56.6 ± 2.8 ‰ and macroalgae -95.7 ± 3.4 ‰). This remarkable difference offers a promising alternative for ecological studies where a similar range of isotopic values could mask different potential sources.
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.
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