Low impact of Zostera marina meadows on sediment and water microbiota under brackish conditions

BACKGROUND

Zostera marina is an important ecosystem engineer influencing shallow water environments and possibly shaping the microbiota in surrounding sediments and water. Z. marina is typically found in marine systems, but it can also proliferate under brackish conditions. Changes in salinity generally have a strong impact on the biota, especially at the salty divide between salinity 6 and 9. To better understand the impact of the salty divide on the interaction between Z. marina and the surrounding sediment and water microbiota, we investigated the effects of Z. marina meadows on the surrounding microbiota across a salinity range of 6-15 in the Baltic Sea during the summer using 16S and 18S rRNA gene amplicon sequencing.

RESULTS

Salinity was the most important factor for structuring the microbiota within both water and sediment. The presence of Z. marina affected the composition of the bacterial and eukaryotic community and bacterial alpha diversity in the sediment. However, this effect was confined to alpha-mesohaline conditions (salinity 9-15). The impact of Z. marina below salinity 9 on water and sediment microbiota was insignificant.

CONCLUSIONS

Increasing salinity was associated with a longer leaf length of Z. marina, causing an increased canopy height, which affects the sediment microbiota through reduced water velocity. Hence, we propose that the canopy effect may be the major predictor explaining Z. marina's interactions with the surrounding microbiota at salinity 9-15. These findings emphasize the importance of the physical effects of Z. marina meadow ecosystem services and have important implications for Z. marina management under brackish conditions in a changing climate.

Seagrass population dynamics and biodiversity assemblages indicate negative effects of short-term nutrient enrichment in tropical island ecosystem

This study assessed the influence of anthropogenic short-term nutrient enrichment (hereafter enriched) effects on seagrass population dynamics (recruitment, growth rate and mortality), morphometric traits, productivity, and leaf biodiversity assemblages in the islands of Andaman and Nicobar (ANI) of India and contrasted these findings with away from these enriched areas (hereafter pristine). Seagrass (Thalassia hemprichii and Cymodocea rotundata), and sediment samples were collected in the dry season (October-May) of ANI. Reconstruction techniques, an indirect measurement of plant growth was used to derive leaf plastochrone interval (PI), i.e., number of days required to produce one leaf by the seagrass. Sediment, organic matter (OM) and carbon (C) were quantified using, loss on ignition method and CHNS elemental analyser. The total N in leaves of T. hemprichii and C. rotundata increased 3.3-fold and 2.4-fold than pristine conditions. Increased N accumulation resulted in higher shoot densities, below ground biomass, and productivity for both seagrasses. T. hemprichii and C. rotundata took 26.07 and 19.76 days respectively to produce new seagrass leaf under enriched conditions. Low apex densities resulted in lower meadow migration and increased meadow fragmentation under enriched conditions. The above ground-biomass and leaf length of T. hemprichii and C. rotundata decreased under enriched conditions leading to lower leaf meiofauna abundance. The long-term average recruitment for both T. hemprichii and C. rotundata increased under enriched conditions resulting in 3.5-fold and 11-fold higher current population growth rates resulting in increased younger plants. Contrastingly, these younger plants did not survive longer under enriched conditions, reducing the long-term seagrass population longevity to 4 years, compared to 6-7 years longevity under pristine conditions. This study highlights that nutrient enrichment in tropical islands benefits seagrass in short-term but reduces seagrass meadow migration, population longevity and biodiversity assemblages, thus reducing seagrass ecosystem service provisions, which calls for urgent monitoring and conservation of seagrass ecosystems of ANI, India.

Seagrass ecosystems reduce disease risk and economic loss in marine farming production

Seaweed farming comprises over half of global coastal and marine aquaculture production by mass; however, the future of the industry is increasingly threatened by disease outbreaks. Nature-based solutions provided by enhancing functions of coinciding species or ecosystems offer an opportunity to increase yields by reducing disease outbreaks while conserving biodiversity. Seagrass ecosystems can reduce the abundance of marine bacterial pathogens, although it remains unknown whether this service can extend to reducing disease risk in a marine resource. Using a meta-analysis of articles published over the past 40 y, we find that 17 known diseases of seaweeds are attributed to bacteria that have been previously shown to be lower when associated with seagrass ecosystems. Next, we surveyed over 8,000 individual seaweeds among farms in Indonesia and found that disease risk is reduced by 75% when seaweeds are co-cultivated directly within seagrass ecosystems, compared to when seagrass ecosystems were removed. Finally, we estimate that farming seaweed with seagrass ecosystems could increase annual revenue by $292,470 - $1,015,990 USD per km2 from yield loss due to disease reduction and that ~20.7 million km2 in 107 countries and 34 territories have suitable environmental conditions for farming seaweeds with seagrass ecosystems. These results highlight the global utility for nature-based solutions as an ecologically and economically sustainable management strategy.

The largest single-species Nanozostera japonica seagrass meadow of China: Its decline, restoration attempts, and short-term effects on macrobenthos and soil bacterial communities

Seagrass beds support vital ecological functions so that when seagrass experience severe degradation, their ecosystem service functions are diminished or lost. The largest Nanozostera japonica seagrass bed in China, situated in the Yellow River Delta, has undergone significant degradation due to Spartina alterniflora invasion and the impact of Typhoon Lekima (2019). The lack of seeds and overwintering shoots makes natural seagrass recovery challenging, prompting the urgent need for seagrass ecological restoration. In the present study, seed sowing experiments were conducted with varying burial depths, seed sources, and sowing times, as well as transplantation experiments with different transplant unit sizes and intervals in the severely degraded seagrass bed. Subsequently, changes in macrobenthos and soil bacterial diversity were tracked after seagrass recovery. According to the results, the optimal burial depth for N. japonica seeds varies across different sediment types, with 4 cm being suitable for sandy soil and 2 cm for silty soil. Seeds sown in May did not survive due to high temperatures. Seeds from Dalian exhibited superior growth after sowing, making them ideal material for seed restoration projects. Transplanting N. japonica sods with 25 × 25 cm transplant units and 50-cm intervals resulted in the most robust growth, indicating it as a suitable method for adult transplantation. Following seagrass re-establishment, macrobenthos and soil bacterial diversity increased significantly. The findings of the present study provide valuable technical guidance and theoretical support for the ecological restoration of N. japonica. Future efforts should prioritize the restoration of seagrass bed ecological functions, with longer-term effects examined.

Understanding stakeholders' perception on developing seagrass-associated tourism: Evidence from marine protected areas of Bintan Island, Indonesia

Seagrass ecosystems provide vital services but face increasing threats from human activities. Marine protected areas (MPAs) aim to mitigate these threats, but inadequate funding and management hinder effective conservation. Seagrass-associated tourism presents an opportunity to fund conservation efforts, enhance MPA implementation, and improve local livelihoods. This study explores stakeholder perceptions of seagrass benefits, tourism feasibility, and threats on Bintan Island, Indonesia, using quantitative (349 household surveys) and qualitative (focus group discussion with 15 participants) methods. Our findings show strong stakeholder support for seagrass-associated tourism, but challenges such as ongoing anthropogenic threats and governance shifts in MPA management remain to be addressed. For successful seagrass-based tourism and better conservation, ongoing engagement with local communities and stakeholders is crucial. This approach not only secures conservation funding but also fosters local ownership and stewardship. The study emphasizes understanding stakeholder perceptions to develop a sustainable tourism sector and ensure more effective, inclusive management strategies.

Restoration of degraded seagrass meadows: Effects of plant growth-promoting rhizobacteria (PGPR) inoculation on Zostera marina growth, rhizosphere microbiome and ecosystem functionality

The utilization of plant growth-promoting rhizobacteria (PGPR) holds great promise for the restoration of damaged terrestrial plant ecosystems. However, there is a significant knowledge gap regarding the application of PGPR in rehabilitating aquatic ecosystems. In this study, we conducted a mesocosm experiment to investigate the effects of Raoultella ornithinolytica F65, Pantoea cypripedii G84, Klebsiella variicola G85, Novosphingobium profundi G86, and Klebsiella pneumoniae I109 on eelgrass (Zostera marina L.), which is a crucial marine angiosperm. The application of these strains resulted in a significant increase in the new leaf area of eelgrass, with improvements of 55.4%, 14.4%, 39.1%, 20.6%, and 55.7% observed, respectively. Moreover, PGPR inoculation enhanced shoot biomass, rhizome elongation, leaf carbon and nitrogen content, as well as photosynthetic pigments. Furthermore, it stimulated enzymatic activities within the rhizosphere soil and positively influenced its physicochemical properties. The Illumina Miseq sequencing results revealed a positive shift in the bacterial community, leading to an enrichment of functional groups associated with nitrogen fixation and degradation of aromatic compounds. These findings underscore the significant potential of PGPR as a transformative tool for enhancing seagrass growth and survival, offering innovative strategies for the restoration of degraded seagrass meadows. This research not only advances our understanding of microbial-plant interactions in aquatic ecosystems but contributes to the broader goals of ecosystem revitalization and biodiversity conservation.

Anoxic seagrass leaf environments as potential hotspots for toxin production and N2O emission

Epiphytes on seagrass leaves can render parts of the leaf phyllosphere anoxic in darkness owing to leaf/epiphyte respiration and O2 diffusion constraints. In such anoxic microenvironments, anaerobic microbes can potentially produce phytotoxins and greenhouse gases, but the actual occurrence of such processes in seagrass epiphytic biofilms remain uncertain. We used microsensors to measure O2, NO, N2O and H2S concentration gradients, as well as NO and O2 dynamics within epiphytic biofilms on seagrass (Zostera marina) leaves under changing environmental conditions. The bacterial community composition of epiphytic biofilms was analyzed with 16S rRNA gene amplicon sequencing. Flavobacteriaceae and Rhodobacteraceae were dominant bacterial community members accounting for ˃50 % of the relative abundance, and sulfate-reducing bacteria (Desulfobacterota) were omnipresent in the epiphytic biofilms. We found pronounced production of NO, N2O and H2S in anoxic parts of the seagrass phyllosphere, with NO and H2S reaching maximal concentrations of 1.0 and 4.4 μmol L-1, respectively, under slow flow and hypoxic seawater conditions, while the highest N2O concentration in the epiphytic biofilms reached 5.9 μmol L-1 in hypoxic, nitrate-rich seawater. Part of the phytotoxic NO and H2S diffused into the seagrass leaves, while no NO escaped the biofilm. In contrast, N2O emission from the biofilm in hypoxic and eutrophic seawater reached 9.6 μmol N2O m-2 day-1. Such release of the potent greenhouse gas N2O from seagrass leaves with epiphytic biofilms under eutrophic conditions could potentially offset the carbon burial capacity of seagrass meadows. Ocean eutrophication can thus stimulate denitrification and sulfate reduction within anoxic leaf microenvironments, negatively impacting seagrass fitness and ecological function.

A bibliometric analysis of seagrass sediment: Interpretation and prospects for research hotspots

Seagrass sediment is intricately linked to their ecological functions, collectively forming the foundation of the seagrass ecosystem, and providing a range of essential ecosystem services, underscoring their significant research importance. This study aims to analyze the emerging hotspots and evolving trends in research on seagrass sediment over the past two decades (2003-2023), identify current research gaps, and forecast future directions for investigation. We extracted data from 3,390 studies identified in the Web of Science that have published pivotal research on seagrass sediment. Over this period, investigations into seagrass sediment have progressively transitioned from focusing on seagrass ecology to examining global change impacts on these sediments, ultimately shifting towards blue carbon research. Notably, there remains a paucity of studies addressing the sediments of small and tropical seagrasses. Furthermore, while the sedimentation mechanisms related to seagrasses represent an active area of inquiry, comprehensive analyses regarding these mechanisms are still limited. This study underscores the critical need for further exploration into sedimentation processes involving seagrasses as well as calls for enhanced integration within blue carbon ecosystem sediment studies pertaining to seagrass habitats.

Specialists regulate microbial network and community assembly in subtropical seagrass sediments under differing land use conditions

Microorganisms in the sediment play a pivotal role in the functioning and stability of seagrass ecosystems and their dynamics are influenced by the nutrient acquisition strategies of host plants. While the distinct impacts of microbial generalists and specialists on community dynamics are recognized, their distribution patterns and ecological roles within seagrass ecosystems remain largely unexplored. To address this issue, we conducted an analysis of community assembly processes and co-occurrence relationships of both microbial generalists and specialists within sediment profiles (0-100 cm) from seagrass habitats subjected to differing land use conditions. The results revealed that seagrasses in Yifeng Estuary experienced the large proportion of cultivated land and exhibited higher organic carbon content in the 0-20 cm surface sediment layer. Nitrogen-cycling bacteria were predominantly associated with seagrasses from Yifeng Estuary, whereas Vibrio spp. was more prevalent in seagrasses from Liusha Bay. Notably, seagrass Halophia beccarii (YHB) in Yifeng Estuary harbored higher niche breadths for both microbial generalist and specialist compared to Halodule uninervis (LHU) and Halophia ovalis (LHO) from Liusha Bay. Stochastic processes were pivotal in shaping seagrass sediment microbial communities, with a higher immigration rate observed in YHB, suggesting greater microbial turnover in this area. Additionally, YHB sediment presented lower drift and higher dispersal limitation among generalists compared to LHU and LHO, whereas the pattern was reversed among specialists. Specialists were found to play a crucial role in shaping microbial interactions within YHB sediment, with genera Halioglobus identified as keystone species in the network. The specialists were further found to significantly influence microbial β-diversity in seagrass sediment directly. Overall, our findings illustrated how microbial generalists and specialists were distributed in seagrass sediments in response to land use changes and provided new insights into the potential roles of microbial regulation in degraded seagrass ecosystems.

Temperature, sediment resuspension, and salinity drive the prevalence of Vibrio vulnificus in the coastal Baltic Sea

The number of Vibrio-related infections in humans, e.g., by Vibrio vulnificus, has increased along the coasts of the Baltic Sea. Due to climate change, vibriosis risk is expected to increase. It is, therefore, pertinent to design a strategy for mitigation of the vibriosis threat in the Baltic Sea area, but a prerequisite is to identify the environmental conditions promoting the occurrence of pathogenic Vibrio spp., like V. vulnificus. To address this, we sampled three coastal Baltic sites in Finland, Germany, and Denmark with salinities between 6 and 21 from May to October 2022. The absolute and relative abundances of Vibrio spp. and V. vulnificus in water were compared to environmental conditions, including the presence of the eelgrass Zostera marina, which has been suggested to reduce pathogenic Vibrio species abundance. In the water column, V. vulnificus only occurred at the German station between July and August at salinity 8.1-11.2. Temperature and phosphate (PO43-) were identified as the most influencing factors for Vibrio spp. and V. vulnificus. The accumulation of Vibrio spp. in the sediment and the co-occurrence with sediment bacteria in the water column indicate that sediment resuspension contributed to V. vulnificus abundance. Interestingly, V. vulnificus co-occurred with specific cyanobacteria taxa, as well as specific bacteria associated with cyanobacteria. Although we found no reduction in Vibrio spp. or V. vulnificus associated with eelgrass beds, our study underscores the importance of extended heatwaves and sediment resuspension, which may elevate the availability of PO43-, for Vibrio species levels at intermediate salinities in the Baltic Sea.

IMPORTANCE

Elevated sea surface temperatures are increasing the prevalence of pathogenic Vibrio at higher latitudes. The recent increase in Vibrio-related wound infections and deaths along the Baltic coasts is, therefore, of serious health concern. We used culture-independent data generated from three Baltic coastal sites in Denmark, Germany, and Finland from May to October (2022), with a special focus on Vibrio vulnificus, and combined it with environmental data. Our temporal model shows that temperature, combined with sediment resuspension, drives the prevalence of V. vulnificus at intermediate salinities in the coastal Baltic Sea.

Metagenomic Sequencing Elucidated the Microbial Diversity of Rearing Water Environments for Sichuan Taimen (Hucho bleekeri)

BACKGROUND

Sichuan taimen (Hucho bleekeri) is a fish species endemic to China's upper Yangtze River drainage and has significant value as an aquatic resource. It was listed as a first-class state-protected wild animal by the Chinese government due to its very limited distribution and wild population at present.

METHODS

To elucidate the diversity of microorganisms in rearing water environments for H. bleekeri, metagenomic sequencing was applied to water samples from the Maerkang and Jiguanshan fish farms, where H. bleekeri were reared.

RESULTS

The results revealed that Pseudomonadota was the dominant phylum in the microbial communities of the water samples. Among the shared bacterial groups, Cyanobacteriota, Actinomycetota, Planctomycetota, Nitrospirota, and Verrucomicrobiota were significantly enriched in the water environment of Jiguanshan (p < 0.01), while Bacteroidota was more enriched in that of Maerkang (p < 0.01). Additionally, the Shannon diversity and Simpson index of the microbial community in the water environment of Maerkang were lower than in that of Jiguanshan.

CONCLUSIONS

The present study demonstrated the similarities and differences in the microbial compositions of rearing water environments for H. bleekeri, which are expected to benefit the artificial breeding of H. bleekeri in the future.

Soundscape analysis can be an effective tool in assessing seagrass restoration early success

Restoration of vulnerable marine habitats is becoming increasingly popular to cope with widespread habitat loss and the resulting decline in biodiversity and ecosystem services. Lately, restoration strategies have been employed to enhance the recovery of degraded meadows of the Mediterranean endemic seagrass Posidonia oceanica. Typically, habitat restoration success is evaluated by the persistence of foundation species after transplantation (e.g., plant survival and growth) on the short and long-term, although successful plant responses do not necessarily reflect the recovery of ecosystem biodiversity and functions. Recently, soundscape (the spatial, temporal and frequency attribute of ambient sound and types of sound sources characterizing it) has been related to different habitat conditions and community structures. Thus, a successful restoration action should lead to acoustic restoration and soundscape ecology could represent an important component of restoration monitoring, leading to assess successful habitat and community restoration. Here, we evaluated acoustic community and metrics in a P. oceanica restored meadow and tested whether the plant transplant effectiveness after one year was accompanied by a restored soundscape. With this goal, acoustic recordings from degraded, transplanted and reference meadows were collected in Sardinia (Italy) using passive acoustic monitoring devices. Soundscape at each meadow type was examined using both spectral analysis and classification of fish calls based on a catalogue of fish sounds from the Mediterranean Sea. Seven different fish sounds were recorded: most of them were present in the reference and transplanted meadows and were associated to Sciaena umbra and Scorpaena spp. Sound Pressure Level (SPL, in dB re: 1 μPa-rms) and Acoustic Complexity Index (ACI) were influenced by the meadow type. Particularly higher values were associated to the transplanted meadow. SPL and ACI calculated in the 200-2000 Hz frequency band were also related to high abundance of fish sounds (chorus). These results showed that meadow restoration may lead to the recovery of soundscape and the associated community, suggesting that short term acoustic monitoring can provide complementary information to evaluate seagrass restoration success.

Horizontal gene transfer from chloroplast to mitochondria of seagrasses in the yellow-Bohai seas

Seagrasses are ideal for studying plant adaptation to marine environments. In this study, the mitochondrial (mt) and chloroplast (cp) genomes of Ruppia sinensis were sequenced. The results showed an extensive gene loss in seagrasses, including a complete loss of cp-rpl19 genes in Zosteraceae, most cp-ndh genes in Hydrocharitaceae, and mt-rpl and mt-rps genes in all seagrasses, except for the mt-rpl16 gene in Phyllospadix iwatensis. Notably, most ribosomal protein genes were lost in the mt and cp genomes. The deleted cp genes were not transferred to the mt genomes through horizontal gene transfer. Additionally, a significant DNA transfer between seagrass organelles was found, with the mt genomes of Zostera containing numerous sequences from the cp genome. Rearrangement analyses revealed an unreported inversion of the cp genome in R. sinensis. Moreover, four positively selected genes (atp8, nad5, atp4, and ccmFn) and five variable regions (matR, atp4, atp8, rps7, and ccmFn) were identified.

Halophila stipulacea: A Comprehensive Review of Its Phytochemical Composition and Pharmacological Activities

Halophila stipulacea (Forsskål and Niebuhr) Ascherson is a small marine seagrass that belongs to the Hydrocharitaceae family. It is native to the Red Sea, Persian Gulf, and Indian Ocean and has successfully invaded the Mediterranean and Caribbean Seas. This article summarizes the pharmacological activities and phytochemical content of H. stipulacea, along with its botanical and ecological characteristics. Studies have shown that H. stipulacea is rich in polyphenols and terpenoids. Additionally, it is rich in proteins, lipids, and carbohydrates, contributing to its nutritional value. Several biological activities are reported by this plant, including antimicrobial, antioxidant, anticancer, anti-inflammatory, anti-metabolic disorders, and anti-osteoclastogenic activities. Further research is needed to validate the efficacy and safety of this plant and to investigate the mechanisms of action underlying the observed effects.

Occurrence and distribution of antibiotic pollution and antibiotic resistance genes in seagrass meadow sediments based on metagenomics

Seagrass meadows are one of the most important coastal ecosystems that provide essential ecological and economic services. The contamination levels of antibiotic and antibiotic resistance genes (ARGs) in coastal ecosystems are severely elevated owing to anthropogenic disturbances, such as terrestrial input, aquaculture effluent, and sewage discharge. However, few studies have focused on the occurrence and distribution of antibiotics and their corresponding ARGs in this habitat. Thus, we investigated the antibiotic and ARGs profiles, microbial communities, and ARG-carrying host bacteria in typical seagrass meadow sediments collected from Swan Lake, Caofeidian shoal harbor, Qingdao Bay, and Sishili Bay in the Bohai Sea and northern Yellow Sea. The total concentrations of 30 detected antibiotics ranged from 99.35 to 478.02 μg/kg, tetracyclines were more prevalent than other antibiotics. Metagenomic analyses showed that 342 ARG subtypes associated with 22 ARG types were identified in the seagrass meadow sediments. Multidrug resistance genes and RanA were the most dominant ARG types and subtypes, respectively. Co-occurrence network analysis revealed that Halioglobus, Zeaxanthinibacter, and Aureitalea may be potential hosts at the genus level, and the relative abundances of these bacteria were higher in Sishili Bay than those in other areas. This study provided important insights into the pollution status of antibiotics and ARGs in typical seagrass meadow sediments. Effective management should be performed to control the potential ecological health risks in seagrass meadow ecosystems.

Rapid seagrass meadow expansion in an Indian Ocean bright spot

The areal extent of seagrass meadows is in rapid global decline, yet they provide highly valuable societal benefits. However, their conservation is hindered by data gaps on current and historic spatial extents. Here, we outline an approach for national-scale seagrass mapping and monitoring using an open-source platform (Google Earth Engine) and freely available satellite data (Landsat, Sentinel-2) that can be readily applied in other countries globally. Specifically, we map contemporary (2021) and historical (2000-2021; n = 10 maps) shallow water seagrass extent across the Maldives. We found contemporary Maldivian seagrass extent was ~ 105 km2 (overall accuracy = 82.04%) and, notably, that seagrass area increased threefold between 2000 and 2021 (linear model, + 4.6 km2 year-1, r2 = 0.93, p < 0.001). There was a strongly significant association between seagrass and anthropogenic activity (p < 0.001) that we hypothesize to be driven by nutrient loading and/or altered sediment dynamics (from large scale land reclamation), which would represent a beneficial anthropogenic influence on Maldivian seagrass meadows. National-scale tropical seagrass expansion is unique against the backdrop of global seagrass decline and we therefore highlight the Maldives as a rare global seagrass 'bright spot' highly worthy of increased attention across scientific, commercial, and conservation policy contexts.

Impact of human disturbance on biogeochemical fluxes in tropical seascapes

Tropical seascapes rely on the feedback relationships among mangrove forests, seagrass meadows, and coral reefs, as they mutually facilitate and enhance each other's functionality. Biogeochemical fluxes link tropical coastal habitats by exchanging material flows and energy through various natural processes that determine the conditions for life and ecosystem functioning. However, little is known about the seascape-scale implications of anthropogenic disruptions to these linkages. Despite the limited number of integrated empirical studies available (with only 11 out of 81 selected studies focusing on the integrated dynamics of mangroves, seagrass, and corals), this review emphasizes the importance of biogeochemical fluxes for ecosystem connectivity in tropical seascapes. It identifies four primary anthropogenic influences that can disturb these fluxes-nutrient enrichment, chemical pollution, microbial pollution, and solid waste accumulation-resulting in eutrophication, increased disease incidence, toxicity, and disruptions to water carbonate chemistry. This review also highlights significant knowledge gaps in our understanding of biogeochemical fluxes and ecosystem responses to perturbations in tropical seascapes. Addressing these knowledge gaps is crucial for developing practical strategies to conserve and manage connected seascapes effectively. Integrated research is needed to shed light on the complex interactions and feedback mechanisms within these ecosystems, providing valuable insights for conservation and management practices.

Seagrass-mediated rhizosphere redox gradients are linked with ammonium accumulation driven by diazotrophs

Seagrasses can enhance nutrient mobilization in their rhizosphere via complex interactions with sediment redox conditions and microbial populations. Yet, limited knowledge exists on how seagrass-derived rhizosphere dynamics affect nitrogen cycling. Using optode and gel-sampler-based chemical imaging, we show that radial O2 loss (ROL) from rhizomes and roots leads to the formation of redox gradients around below-ground tissues of seagrass (Zostera marina), which are co-localized with regions of high ammonium concentrations in the rhizosphere. Combining such chemical imaging with fine-scale sampling for microbial community and gene expression analyses indicated that multiple biogeochemical pathways and microbial players can lead to high ammonium concentration within the oxidized regions of the seagrass rhizosphere. Symbiotic N2-fixing bacteria (Bradyrhizobium) were particularly abundant and expressed the diazotroph functional marker gene nifH in Z. marina rhizosphere areas with high ammonium concentrations. Such an association between Z. marina and Bradyrhizobium can facilitate ammonium mobilization, the preferred nitrogen source for seagrasses, enhancing seagrass productivity within nitrogen-limited environments. ROL also caused strong gradients of sulfide at anoxic/oxic interfaces in rhizosphere areas, where we found enhanced nifH transcription by sulfate-reducing bacteria. Furthermore, we found a high abundance of methylotrophic and sulfide-oxidizing bacteria in rhizosphere areas, where O2 was released from seagrass rhizomes and roots. These bacteria could play a beneficial role for the plants in terms of their methane and sulfide oxidation, as well as their formation of growth factors and phytohormones. ROL from below-ground tissues of seagrass, thus, seems crucial for ammonium production in the rhizosphere via stimulation of multiple diazotrophic associations.

IMPORTANCE

Seagrasses are important marine habitats providing several ecosystem services in coastal waters worldwide, such as enhancing marine biodiversity and mitigating climate change through efficient carbon sequestration. Notably, the fitness of seagrasses is affected by plant-microbe interactions. However, these microscale interactions are challenging to study and large knowledge gaps prevail. Our study shows that redox microgradients in the rhizosphere of seagrass select for a unique microbial community that can enhance the ammonium availability for seagrass. We provide first experimental evidence that Rhizobia, including the symbiotic N2-fixing bacteria Bradyrhizobium, can contribute to the bacterial ammonium production in the seagrass rhizosphere. The release of O2 from rhizomes and roots also caused gradients of sulfide in rhizosphere areas with enhanced nifH transcription by sulfate-reducing bacteria. O2 release from seagrass root systems thus seems crucial for ammonium production in the rhizosphere via stimulation of multiple diazotrophic associations.

A matter of choice: Understanding the interactions between epiphytic foraminifera and their seagrass host Halophila stipulacea

In sub/tropical waters, benthic foraminifera are among the most abundant epiphytic organisms inhabiting seagrass meadows. This study explored the nature of the association between foraminifera and the tropical seagrass species H. stipulacea, aiming to determine whether these interactions are facilitative or random. For this, we performed a "choice" experiment, where foraminifera could colonize H. stipulacea plants or plastic "seagrasses" plants. At the end of the experiment, a microbiome analysis was performed to identify possible variances in the microbial community and diversity of the substrates. Results show that foraminifera prefer to colonize H. stipulacea, which had a higher abundance and diversity of foraminifera than plastic seagrass plants, which increased over time and with shoot age. Moreover, H. stipulacea leaves have higher epiphytic microbial community abundance and diversity. These results demonstrate that seagrass meadows are important hosts of the foraminifera community and suggest the potential facilitative effect of H. stipulacea on epiphytic foraminifera, which might be attributed to a greater diversity of the microbial community inhabiting H. stipulacea.

Removal of detritivore sea cucumbers from reefs increases coral disease

Coral reefs are in global decline with coral diseases playing a significant role. This is especially true for Acroporid corals that represent ~25% of all Pacific coral species and generate much of the topographic complexity supporting reef biodiversity. Coral diseases are commonly sediment-associated and could be exacerbated by overharvest of sea cucumber detritivores that clean reef sediments and may suppress microbial pathogens as they feed. Here we show, via field manipulations in both French Polynesia and Palmyra Atoll, that historically overharvested sea cucumbers strongly suppress disease among corals in contact with benthic sediments. Sea cucumber removal increased tissue mortality of Acropora pulchra by ~370% and colony mortality by ~1500%. Additionally, farmerfish that kill Acropora pulchra bases to culture their algal gardens further suppress disease by separating corals from contact with the disease-causing sediment-functioning as mutualists rather than parasites despite killing coral bases. Historic overharvesting of sea cucumbers increases coral disease and threatens the persistence of tropical reefs. Enhancing sea cucumbers may enhance reef resilience by suppressing disease.

Impacts of hurricanes and disease on Diadema antillarum in shallow water reef and mangrove locations in St John, USVI

The 1983-1984 mortality event of the long-spined sea urchin Diadema antillarum reduced their population by up to 99% and was accompanied by a phase shift from coral dominated to algal dominated reefs in the Caribbean. Modest rebounds of D. antillarum populations in the Caribbean have been noted, and here we document the impacts of two major hurricanes (2017, Irma and Maria) and the 2022 disease outbreak on populations of D. antillarum found by targeted surveys in the urchin zone at nine fringing reef and three mangrove sites on St. John, USVI. D. antillarum populations at the reef sites had declined by 66% five months after the hurricanes but showed significant recovery just one year later. The impact of recent disease on these populations was much more profound, with all reef populations exhibiting a significant decline (96.4% overall). Fifteen months after the disease was first noted, D. antillarum at reef sites exhibited a modest yet significant recovery (15% pre-disease density). D. antillarum populations in mangrove sites were impacted by the hurricanes but exhibited much higher density than reef sites after the disease outbreak, suggesting that at D. antillarum in some locations may be less vulnerable to disease.

Non-linear effects of non-host diversity on the removal of free-living infective stages of parasites

Among the ecological functions and services of biodiversity is the potential buffering of diseases through dilution effects where increased biodiversity results in a reduction in disease risk for humans and wildlife hosts. Whether such effects are a universal phenomenon is still under intense debate and diversity effects are little studied in cases when non-host organisms remove free-living parasite stages during their transmission from one host to the next by consumption or physical obstruction. Here, we investigated non-host diversity effects on the removal of cercarial stages of trematodes, ubiquitous parasites in aquatic ecosystems. In laboratory experiments using response surface designs, varying both diversity and density at same time, we compared three combinations of two non-hosts at four density levels: predatory crabs that actively remove cercariae from the water column via their mouth parts and gills, filter feeding oysters that passively filter cercariae from the water column while not becoming infected themselves, and seaweed which physically obstructs cercariae. The addition of a second non-host did not generally result in increased parasite removal but neutralised, amplified or reduced the parasite removal exerted by the first non-host, depending on the density and non-host combination. These non-linear non-host diversity effects were probably driven by intra- and interspecific interactions and suggest the need to integrate non-host diversity effects in understanding the links between community diversity and infection risk.

Seagrass genomes reveal ancient polyploidy and adaptations to the marine environment

We present chromosome-level genome assemblies from representative species of three independently evolved seagrass lineages: Posidonia oceanica, Cymodocea nodosa, Thalassia testudinum and Zostera marina. We also include a draft genome of Potamogeton acutifolius, belonging to a freshwater sister lineage to Zosteraceae. All seagrass species share an ancient whole-genome triplication, while additional whole-genome duplications were uncovered for C. nodosa, Z. marina and P. acutifolius. Comparative analysis of selected gene families suggests that the transition from submerged-freshwater to submerged-marine environments mainly involved fine-tuning of multiple processes (such as osmoregulation, salinity, light capture, carbon acquisition and temperature) that all had to happen in parallel, probably explaining why adaptation to a marine lifestyle has been exceedingly rare. Major gene losses related to stomata, volatiles, defence and lignification are probably a consequence of the return to the sea rather than the cause of it. These new genomes will accelerate functional studies and solutions, as continuing losses of the 'savannahs of the sea' are of major concern in times of climate change and loss of biodiversity.

Epiphytic and endophytic microbiome of the seagrass Zostera marina: Do they contribute to pathogen reduction in seawater?

Seagrass meadows provide crucial ecosystem services for coastal environments and were shown to reduce the abundance of waterborne pathogens linked to infections in humans and marine organisms in their vicinity. Among potential drivers, seagrass phenolics released into seawater have been linked to pathogen suppression, but the potential involvement of the seagrass microbiome has not been investigated. We hypothesized that the microbiome of the eelgrass Zostera marina, especially the leaf epiphytes that are at direct interface between the seagrass host and the surrounding seawater, inhibit waterborne pathogens thereby contributing to their removal. Using a culture-dependent approach, we isolated 88 bacteria and fungi associated with the surfaces and inner tissues of the eelgrass leaves (healthy and decaying) and the roots. We assessed the antibiotic activity of microbial extracts against a large panel of common aquatic, human (fecal) and plant pathogens, and mined the metabolome of the most active extracts. The healthy leaf epibiotic bacteria, particularly Streptomyces sp. strain 131, displayed broad-spectrum antibiotic activity superior to some control drugs. Gram-negative bacteria abundant on healthy leaf surfaces, and few endosphere-associated bacteria and fungi also displayed remarkable activities. UPLC-MS/MS-based untargeted metabolomics analyses showed rich specialized metabolite repertoires with low annotation rates, indicating the presence of many undescribed antimicrobials in the extracts. This study contributes to our understanding on microbial and chemical ecology of seagrasses, implying potential involvement of the seagrass microbiome in suppression of pathogens in seawater. Such effect is beneficial for the health of ocean and human, especially in the context of climate change that is expected to exacerbate all infectious diseases. It may also assist future seagrass conservation and management strategies.

Preserving coastal ecosystem through micro-zonation analysis of Karimunjawa, Indonesia

Small island ecosystems and their inhabitants face a significant threat from global warming, jeopardizing their sustainability. These communities are particularly vulnerable to the impact of climate change, as they heavily rely on natural resources for their livelihoods and are more vulnerable than mainland regions. Therefore, it is essential to take urgent action to address the challenges small island states face and promote their resilience in the face of climate change. To preserve the coastal ecosystems in Karimunjawa Islands, Indonesia, this study proposes an alternative spatial plan through micro-zonation analysis. The study conducted literature reviews and field surveys to collect data and develop recommendations for the current spatial plans through spatial, descriptive statistics, and comparative analysis. The findings show that the sea surface temperatures of Karimunjawa and Kemujan Island have increased by 1-2 ℃. Stress levels were found for coral reefs at the bleaching warning position for all Karimunjawa Island marine areas, including Kemujan Island. Legon Lele and Tanjung Gelam were found to have suspended sediment traces and indications of heavy metal contamination, making them the research focus. The Karimunjawa micro-zonation boundaries were obtained, especially in the Legon Lele and Tanjung Gelam areas, with an area of 640.63 and 817.45 ha, respectively. The proposed micro-zonation for Karimunjawa National Park refers to watershed-sedimentary cells, making it an example of implementing integrated coastal management (ICM) spatial boundaries in Karimunjawa and other nations. By applying this micro-zonation, coastal ecosystem rehabilitation efforts can be carried out precisely.

Tools to Enumerate and Predict Distribution Patterns of Environmental Vibrio vulnificus and Vibrio parahaemolyticus

Vibrio vulnificus (Vv) and Vibrio parahaemolyticus (Vp) are water- and foodborne bacteria that can cause several distinct human diseases, collectively called vibriosis. The success of oyster aquaculture is negatively impacted by high Vibrio abundances. Myriad environmental factors affect the distribution of pathogenic Vibrio, including temperature, salinity, eutrophication, extreme weather events, and plankton loads, including harmful algal blooms. In this paper, we synthesize the current understanding of ecological drivers of Vv and Vp and provide a summary of various tools used to enumerate Vv and Vp in a variety of environments and environmental samples. We also highlight the limitations and benefits of each of the measurement tools and propose example alternative tools for more specific enumeration of pathogenic Vv and Vp. Improvement of molecular methods can tighten better predictive models that are potentially important for mitigation in more controlled environments such as aquaculture.

Vegetative fragment production as a means of propagule dispersal for tropical seagrass meadows

BACKGROUND AND AIMS

Long distance dispersal (LDD) contributes to the replenishment and recovery of tropical seagrass habitats exposed to disturbance, such as cyclones and infrastructure development. However, our current knowledge regarding the physical attributes of seagrass fragments that influence LDD predominantly stems from temperate species and regions. The goal of this paper is to measure seagrass fragment density and viability in two tropical species, assessing various factors influencing their distribution.

METHODS

We measured the density and viability of floating seagrass fragments for two tropical seagrass species (Zostera muelleri and Halodule uninervis) in two coastal seagrass meadows in the central Great Barrier Reef World Heritage Area, Australia. We assessed the effect of wind speed, wind direction, seagrass growing/senescent season, seagrass meadow density, meadow location and dugong foraging intensity on fragment density. We also measured seagrass fragment structure and fragment viability; i.e., potential to establish into a new plant.

KEY RESULTS

We found that seagrass meadow density, season, wind direction and wind speed influenced total fragment density, while season and wind speed influenced the density of viable fragments. Dugong foraging intensity did not influence fragment density. Our results indicate that wave action from winds combined with high seagrass meadow density increases seagrass fragment creation, and that more fragments are produced during the growing than the senescent season. Seagrass fragments classified as viable for Z. muelleri and H. uninervis had significantly more shoots and leaves than non-viable fragments. We collected 0.63 (±0.08 SE) floating viable fragments 100 m-2 in the growing season, and 0.13 (±0.03 SE) viable fragments 100 m-2 in the senescent season. Over a third (38%) of all fragments collected were viable.

CONCLUSION

There is likely to be a large number of viable seagrass fragments available for long distance dispersal. This study's outputs can inform dispersal and connectivity models that are used to direct seagrass ecosystem management and conservation strategies.

Macrophytes and their wrack as a habitat for faecal indicator bacteria and Vibrio in coastal marine environments

Waterborne pathogenic bacteria, including faecal indicator bacteria and potentially pathogenic Vibrio, are a global concern for diseases transmitted through water. A systematic review was conducted to analyse publications that investigated these bacteria in relation to macrophytes (seagrasses and macroalgae) in coastal marine environments. The highest quantities of FIB were found on brown algae and seagrasses, and the highest quantities of Vibrio bacteria were on red algae. The most extensively studied macrophyte group was brown algae, green algae were the least researched. Macrophyte wrack was found to favor the presence of FIB, but there is a lack of information about Vibrio quantities in this environment. To understand the role of Vibrio bacteria that are pathogenic to humans, molecular methods complementary to cultivation methods should be used. Further research is needed to understand the underlying mechanisms of FIB and potentially pathogenic Vibrio with macrophytes and their microbiome in the coastal marine environment.

Signs of local adaptation by genetic selection and isolation promoted by extreme temperature and salinity in the Mediterranean seagrass Posidonia oceanica

Adaptation to local conditions is known to occur in seagrasses; however, knowledge of the genetic basis underlying this phenomenon remains scarce. Here, we analysed Posidonia oceanica from six sites within and around the Stagnone di Marsala, a semi-enclosed coastal lagoon where salinity and temperature exceed the generally described tolerance thresholds of the species. Sea surface temperatures (SSTs) were measured and plant samples were collected for the assessment of morphology, flowering rate and for screening genome-wide polymorphisms using double digest restriction-site-associated DNA sequencing. Results demonstrated more extreme SSTs and salinity levels inside the lagoon than the outer lagoon regions. Morphological results showed significantly fewer and shorter leaves and reduced rhizome growth of P. oceanica from the inner lagoon and past flowering events were recorded only for a meadow farthest away from the lagoon. Using an array of 51,329 single nucleotide polymorphisms, we revealed a clear genetic structure among the study sites and confirmed the genetic isolation and high clonality of the innermost site. In all, 14 outlier loci were identified and annotated with several proteins including those relate to plant stress response, protein transport and regulators of plant-specific developmental events. Especially, five outlier loci showed maximum allele frequency at the innermost site, likely reflecting adaptation to the extreme temperature and salinity regimes, possibly due to the selection of more resistant genotypes and the progressive restriction of gene flow. Overall, this study helps us to disentangle the genetic basis of seagrass adaptation to local environmental conditions and may support future works on assisted evolution in seagrasses.

Evidence-based target setting informs blue carbon strategies for nationally determined contributions

The magnitude and pace of global climate change demand ambitious and effective implementation of nationally determined contributions (NDCs). Nature-based solutions present an efficient approach to achieving mitigation, adaptation and resilience goals. Yet few nations have quantified the diverse benefits of nature-based solutions to evaluate and select ecosystem targets for their NDCs. Here we report on Belize's pursuit of innovative, evidence-based target setting by accounting for multiple benefits of blue carbon strategies. Through quantification of carbon storage and sequestration and optimization of co-benefits, we explore time-bound targets and prioritize locations for mangrove protection and restoration. We find increases in carbon benefits with larger mangrove investments, while fisheries, tourism and coastal risk-reduction co-benefits grow initially and then plateau. We identify locations, currently lacking protected status, where prioritizing blue carbon strategies would provide the greatest delivery of co-benefits to communities. These findings informed Belize's updated NDCs to include an additional 12,000 ha of mangrove protection and 4,000 ha of mangrove restoration, respectively, by 2030. Our study serves as an example for the more than 150 other countries that have the opportunity to enhance greenhouse gas sequestration and climate adaptation by incorporating blue carbon strategies that provide multiple societal benefits into their NDCs.

The spatial distribution of infectious agents in wild Pacific salmon along the British Columbia coast

Although infectious agents can act as strong population regulators, knowledge of their spatial distributions in wild Pacific salmon is limited, especially in the marine environment. Characterizing pathogen distributions during early marine residence, a period considered a survival bottleneck for Pacific salmon, may reveal where salmon populations are exposed to potentially detrimental pathogens. Using high-throughput qPCR, we determined the prevalence of 56 infectious agents in 5719 Chinook, 2032 Coho and 4062 Sockeye salmon, sampled between 2008 and 2018, in their first year of marine residence along coastal Western Canada. We identified high prevalence clusters, which often shifted geographically with season, for most of the 41 detected agents. A high density of infection clusters was found in the Salish Sea along the east coast of Vancouver Island, an important migration route and residence area for many salmon populations, some experiencing chronically poor marine survival. Maps for each infectious agent taxa showing clusters across all host species are provided. Our novel documentation of salmon pathogen distributions in the marine environment contributes to the ecological knowledge regarding some lesser known pathogens, identifies salmon populations potentially impacted by specific pathogens, and pinpoints priority locations for future research and remediation.

Computational estimation of sediment symbiotic bacterial structures of seagrasses overgrowing downstream of onshore aquaculture

Coastal seagrass meadows are essential in blue carbon and aquatic ecosystem services. However, this ecosystem has suffered severe eutrophication and destruction due to the expansion of aquaculture. Therefore, methods for the flourishing of seagrass are still being explored. Here, data from 49 public coastal surveys on the distribution of seagrass and seaweed around the onshore aquaculture facilities are revalidated, and an exceptional area where the seagrass Zostera marina thrives was found near the shore downstream of the onshore aquaculture facility. To evaluate the characteristics of the sediment for growing seagrass, physicochemical properties and bacterial ecological evaluations of the sediment were conducted. Evaluation of chemical properties in seagrass sediments confirmed a significant increase in total carbon and a decrease in zinc content. Association analysis and linear discriminant analysis refined bacterial candidates specified in seagrass overgrown- and nonovergrown-sediment. Energy landscape analysis indicated that the symbiotic bacterial groups of seagrass sediment were strongly affected by the distance close to the seagrass-growing aquaculture facility despite their bacterial population appearing to fluctuate seasonally. The bacterial population there showed an apparent decrease in the pathogen candidates belonging to the order Flavobacteriales. Moreover, structure equation modeling and a linear non-Gaussian acyclic model based on the machine learning data estimated an optimal sediment symbiotic bacterial group candidate for seagrass growth as follows: the Lachnospiraceae and Ruminococcaceae families as gut-inhabitant bacteria, Rhodobacteraceae as photosynthetic bacteria, and Desulfobulbaceae as cable bacteria modulating oxygen or nitrate reduction and oxidation of sulfide. These observations confer a novel perspective on the sediment symbiotic bacterial structures critical for blue carbon and low-pathogenic marine ecosystems in aquaculture.

Economic losses related to the reduction of Posidonia ecosystem services in the Gulf of Gabes (Southern Mediterranean Sea)

In the early XXth century, the Gulf of Gabes in SE Tunisia used to host the most extended Posidonia oceanica seagrass beds in the Mediterranean basin and was a highly productive hotspot of benthic species. Since the 70's, >500 million t of wet toxic phosphogypsum discharges from a fertilizer industrial complex have led to the gradual loss of ∼90 % of its initial surface. This drastic shrinkage is accompanied by significant value losses originated from the direct and indirect-use services of which the most important ones are small scale fisheries and carbon storage function. Using market valuations of a number of services we estimate economic losses at 105 million € in 2014 (∼915€/ha), i.e., around 115 % of the added value of the gabesian fertilizer factories for the same year. Value losses should increase in the near future in relation with the COP26 agreements which boosted the open carbon credit market. Without actions to reduce negative production externalities caused by the fertilizer industry in the Gulf of Gabes it would not be possible to recover Posidonia ecosystems in this region leading to further economic, ecologic, and cultural losses.

Current advances in seagrass research: A review from Viet Nam

Seagrass meadows provide valuable ecosystem services but are fragile and threatened ecosystems all over the world. This review highlights the current advances in seagrass research from Viet Nam. One goal is to support decision makers in developing science-based conservation strategies. In recent years, several techniques were applied to estimate the size of seagrass meadows. Independent from the method used, there is an alarming decline in the seagrass area in almost all parts of Viet Nam. Since 1990, a decline of 46.5% or 13,549 ha was found. Only in a few protected and difficult-to-reach areas was an increase observed. Conditions at those sites could be investigated in more detail to make suggestions for conservation and recovery of seagrass meadows. Due to their lifestyle and morphology, seagrasses take up compounds from their environment easily. Phytoremediation processes of Thalassia hemprichii and Enhalus acoroides are described exemplarily. High accumulation of heavy metals dependent on their concentration in the environment in different organs can be observed. On the one hand, seagrasses play a role in phytoremediation processes in polluted areas; on the other hand, they might suffer at high concentrations, and pollution will contribute to their overall decline. Compared with the neighboring countries, the total C _org stock from seagrass beds in Viet Nam was much lower than in the Philippines and Indonesia but higher than that of Malaysia and Myanmar. Due to an exceptionally long latitudinal coastline of 3,260 km covering cool to warm water environments, the seagrass species composition in Viet Nam shows a high diversity and a high plasticity within species boundaries. This leads to challenges in taxonomic issues, especially with the Halophila genus, which can be better deduced from genetic diversity/population structures of members of Hydrocharitaceae. Finally, the current seagrass conservation and management efforts in Viet Nam are presented and discussed. Only decisions based on the interdisciplinary cooperation of scientists from all disciplines mentioned will finally lead to conserve this valuable ecosystem for mankind and biodiversity.

Strategies for managing marine disease

The incidence of emerging infectious diseases (EIDs) has increased in wildlife populations in recent years and is expected to continue to increase with global environmental change. Marine diseases are relatively understudied compared with terrestrial diseases but warrant parallel attention as they can disrupt ecosystems, cause economic loss, and threaten human livelihoods. Although there are many existing tools to combat the direct and indirect consequences of EIDs, these management strategies are often insufficient or ineffective in marine habitats compared with their terrestrial counterparts, often due to fundamental differences between marine and terrestrial systems. Here, we first illustrate how the marine environment and marine organism life histories present challenges and opportunities for wildlife disease management. We then assess the application of common disease management strategies to marine versus terrestrial systems to identify those that may be most effective for marine disease outbreak prevention, response, and recovery. Finally, we recommend multiple actions that will enable more successful management of marine wildlife disease emergencies in the future. These include prioritizing marine disease research and understanding its links to climate change, improving marine ecosystem health, forming better monitoring and response networks, developing marine veterinary medicine programs, and enacting policy that addresses marine and other wildlife diseases. Overall, we encourage a more proactive rather than reactive approach to marine wildlife disease management and emphasize that multidisciplinary collaborations are crucial to managing marine wildlife health.

Instability and Stasis Among the Microbiome of Seagrass Leaves, Roots and Rhizomes, and Nearby Sediments Within a Natural pH Gradient

Seagrass meadows are hotspots of biodiversity with considerable economic and ecological value. The health of seagrass ecosystems is influenced in part by the makeup and stability of their microbiome, but microbiome composition can be sensitive to environmental change such as nutrient availability, elevated temperatures, and reduced pH. The objective of the present study was to characterize the bacterial community of the leaves, bulk samples of roots and rhizomes, and proximal sediment of the seagrass species Cymodocea nodosa along the natural pH gradient of Levante Bay, Vulcano Island, Italy. The bacterial community was determined by characterizing the 16S rRNA amplicon sequencing and analyzing the operational taxonomic unit classification of bacterial DNA within samples. Statistical analyses were used to explore how life-long exposure to different pH/pCO₂ conditions may be associated with significant differences in microbial communities, dominant bacterial classes, and microbial diversity within each plant section and sediment. The microbiome of C. nodosa significantly differed among all sample types and site-specific differences were detected within sediment and root/rhizome microbial communities, but not the leaves. These results show that C. nodosa leaves have a consistent microbial community even across a pH range of 8.15 to 6.05. The ability for C. nodosa to regulate and maintain microbial structure may indicate a semblance of resilience within these vital ecosystems under projected changes in environmental conditions such as ocean acidification.

The differential ability of two species of seagrass to use carbon dioxide and bicarbonate and their modelled response to rising concentrations of inorganic carbon

Seagrass meadows are one of the most productive ecosystems on the planet, but their photosynthesis rate may be limited by carbon dioxide but mitigated by exploiting the high concentration of bicarbonate in the ocean using different active processes. Seagrasses are declining worldwide at an accelerating rate because of numerous anthropogenic pressures. However, rising ocean concentrations of dissolved inorganic carbon, caused by increases in atmospheric carbon dioxide, may benefit seagrass photosynthesis. Here we compare the ability of two seagrass from the Mediterranean Sea, Posidonia oceanica (L.) Delile and Zostera marina L., to use carbon dioxide and bicarbonate at light saturation, and model how increasing concentrations of inorganic carbon affect their photosynthesis rate. pH-drift measurements confirmed that both species were able to use bicarbonate in addition to carbon dioxide, but that Z. marina was more effective than P. oceanica. Kinetic experiments showed that, compared to Z. marina, P. oceanica had a seven-fold higher affinity for carbon dioxide and a 1.6-fold higher affinity for bicarbonate. However, the maximal rate of bicarbonate uptake in Z. marina was 2.1-fold higher than in P. oceanica. In equilibrium with 410 ppm carbon dioxide in the atmosphere, the modelled rates of photosynthesis by Z. marina were slightly higher than P. oceanica, less carbon limited and depended on bicarbonate to a greater extent. This greater reliance by Z. marina is consistent with its less depleted ¹³C content compared to P. oceanica. Modelled photosynthesis suggests that both species would depend on bicarbonate alone at an atmospheric carbon dioxide partial pressure of 280 ppm. P. oceanica was projected to benefit more than Z. marina with increasing atmospheric carbon dioxide partial pressures, and at the highest carbon dioxide scenario of 1135 ppm, would have higher rates of photosynthesis and be more saturated by inorganic carbon than Z. marina. In both species, the proportional reliance on bicarbonate declined markedly as carbon dioxide concentrations increased and in P. oceanica carbon dioxide would become the major source of inorganic carbon.

Freshwater macrophytes harbor viruses representing all five major phyla of the RNA viral kingdom Orthornavirae

Research on aquatic plant viruses is lagging behind that of their terrestrial counterparts. To address this knowledge gap, here we identified viruses associated with freshwater macrophytes, a taxonomically diverse group of aquatic phototrophs that are visible with the naked eye. We surveyed pooled macrophyte samples collected at four spring sites in Florida, USA through next generation sequencing of RNA extracted from purified viral particles. Sequencing efforts resulted in the detection of 156 freshwater macrophyte associated (FMA) viral contigs, 37 of which approximate complete genomes or segments. FMA viral contigs represent putative members from all five major phyla of the RNA viral kingdom Orthornavirae. Similar to viral types found in land plants, viral sequences identified in macrophytes were dominated by positive-sense RNA viruses. Over half of the FMA viral contigs were most similar to viruses reported from diverse hosts in aquatic environments, including phototrophs, invertebrates, and fungi. The detection of FMA viruses from orders dominated by plant viruses, namely Patatavirales and Tymovirales, indicate that members of these orders may thrive in aquatic hosts. PCR assays confirmed the presence of putative FMA plant viruses in asymptomatic vascular plants, indicating that viruses with persistent lifestyles are widespread in macrophytes. The detection of potato virus Y and oat blue dwarf virus in submerged macrophytes suggests that terrestrial plant viruses infect underwater plants and highlights a potential terrestrial-freshwater plant virus continuum. Defining the virome of unexplored macrophytes will improve our understanding of virus evolution in terrestrial and aquatic primary producers and reveal the potential ecological impacts of viral infection in macrophytes.

The planetary role of seagrass conservation

Seagrasses are remarkable plants that have adapted to live in a marine environment. They form extensive meadows found globally that bioengineer their local environments and preserve the coastal seascape. With the increasing realization of the planetary emergency that we face, there is growing interest in using seagrasses as a nature-based solution for greenhouse gas mitigation. However, seagrass sensitivity to stressors is acute, and in many places, the risk of loss and degradation persists. If the ecological state of seagrasses remains compromised, then their ability to contribute to nature-based solutions for the climate emergency and biodiversity crisis remains in doubt. We examine the major ecological role that seagrasses play and how rethinking their conservation is critical to understanding their part in fighting our planetary emergency.

Heavy Metal Accumulation and Phytoremediation Potentiality of Some Selected Mangrove Species from the World's Largest Mangrove Forest

Toxic metal pollution is a global issue, and the use of metal-accumulating plants to clean contaminated ecosystems is one of the most rapidly growing ecologically beneficial and cost-effective technologies. In this study, samples of sediment and three mangrove species (Excoecaria agallocha, Avicennia officinalis, Sonneratia apetala) were collected from the world’s largest mangrove forest (along the Northern Bay of Bengal Coast) with the aim of evaluating metal concentrations, contamination degrees, and phytoremediation potentiality of those plants. Overall, the heavy metals concentration in sediment ranged from Cu: 72.41−95.89 mg/kg; Zn: 51.28−71.20 mg/kg; Fe: 22,760−27,470 mg/kg; Mn: 80.37−116.37 mg/kg; Sr: 167.92−221.44 mg/kg. In mangrove plants, the mean concentrations were in the order of E. agallocha > A. officinalis > S. apetala. The mean (± SD) concentration of each metal in the plant tissue (root) was found following the descending order of Fe (737.37 ± 153.06) > Mn (151.13 ± 34.26) > Sr (20.98 ± 6.97) > Cu (16.12 ± 4.34) > Zn (11.3 ± 2.39) mg/kg, whereas, in the leaf part, the mean concentration (mg/kg) of each metal found in the order of Fe (598.75 ± 410.65) > Mn (297.27 ± 148.11) > Sr (21.40 ± 8.71) > Cu (14.25 ± 2.51) > Zn (12.56 ± 2.13). The contamination factor (CF) values for the studied metals were in the descending order of Cu > Sr > Zn > Fe > Mn. The values of Igeo (Geo-accumulation index) and CF showed that the area was unpolluted to moderately polluted by Zn, Fe, Mn, Cu and Sr. Enrichment factor (EF) values in both sampling stations portrayed moderate to minimum enrichment. Phytoremediation potentiality of the species was assessed by bio-concentration factor (BCF) and translocation factor (TF). BCF values showed less accumulation for most of the heavy metals (<1) except Mn which was highly accumulated in all mangrove plants. The translocation factor (TF) values depicted that most of the heavy metals were strongly accumulated in plant tissues (>1). However, the BCF value depicts that Mn was highly bioconcentrated in E. agallocha, but the translocation on leaves tissue were minimum, which reveals that E. agallocha is phytoextractor for Mn, and accumulated in root tissues. All the examined plants can be used as phytoextractors as they have bioconcentration factors <1 and translocation factors >1. However, A. officinalis is clearly more suitable for metal extraction than S. apetala and E. agallocha in terms of hyper-metabolizing capabilities.

Community-specific "desired" states for seagrasses through cycles of loss and recovery

Seagrass habitats provide critical ecosystem services, yet there is ongoing concern over mounting pressures and continuing degradation. Defining a desired state for these habitats is a key step in implementing appropriate management but is often difficult given the challenges of available data and an evaluation of where to set benchmarks. We use more than 20 years of historical seagrass biomass data (1995-2018) for the diverse seagrass communities of Australia's Great Barrier Reef World Heritage Area (GBRWHA) to develop desired state benchmarks. Desired state for seagrass biomass was estimated for 25 of 36 previously defined seagrass communities with the remainder having insufficient data. Desired state varied by more than one order of magnitude between community types and was influenced by the mix of species in the communities and the range of environmental conditions. We identify a historical, decadal-scale cycle of decline with recovery to desired state in coastal intertidal communities. In contrast a number of the estuary and coastal subtidal communities have not recovered to desired state biomass. Understanding a historical context is critically important for setting benchmarks and making informed management decisions on the present state of seagrass in the GBRWHA. The approach we have developed is scalable for monitoring, management and assessment of pressures for other management areas and for other jurisdictions. Our results guide conservation planning through prioritization of the at-risk seagrass communities that are continuing to fall below their desired state.

Seagrasses and local environment control the bacterial community structure and carbon substrate utilization in brackish sediments

Seagrasses are complex benthic coastal ecosystems that play a crucial role in organic matter cycling and carbon sequestration. However, little is known about how seagrasses influence the structure and carbon utilization potential of benthic bacterial communities. This study examined the bacterial communities in monospecific and mixed meadows of seagrasses and compared with bulk (unvegetated) sediments from Chilika, a brackish water coastal lagoon of India. High-throughput sequencing of 16S rRNA genes revealed a vegetation effect in terms of differences in benthic bacterial community diversity, composition, and abundances in comparison with bulk sediments. Desulfobacterales, Chromatiales, Enterobacteriales, Clostridiales, Vibrionales, and Acidimicrobiales were major taxa that contributed to differences between seagrass and bulk sediments. Seagrasses supported ∼5.94 fold higher bacterial abundances than the bulk due to rich organic carbon stock in their sediments. Co-occurrence network demonstrated much stronger potential interactions and connectedness in seagrass bacterial communities compared to bulk. Chromatiales and Acidimicrobiales were identified as the top two keystone taxa in seagrass bacterial communities, whereas, Dehalococcoidales and Rhizobiales were in bulk communities. Seagrasses and local environmental factors, namely, water depth, water pH, sediment salinity, redox potential, total organic carbon, available nitrogen, sediment texture, sediment pH, and sediment core depth were the major drivers of benthic bacterial community composition. Carbon metabolic profiling revealed that heterotrophic bacteria in seagrass sediments were much more metabolically diverse and active than bulk. The utilization of carbon substrate guilds, namely, amino acids, amines, carboxylic acids, carbohydrates, polymers, and phenolic compounds was enhanced in seagrass sediments. Metabolic mapping predicted higher prevalence of sulfate-reducer and N₂ fixation metabolic functions in seagrass sediments. Overall, this study showed that seagrasses control benthic bacterial community composition and diversity, enhance heterotrophic carbon substrate utilization, and play crucial roles in organic matter cycling including degradation of hydrocarbon and xenobiotics in coastal sediments.

Warming northward shifting southern limits of the iconic temperate seagrass (Zostera marina)

Global warming can shift the range edges of numerous species poleward. Here, eelgrass distribution was reinvestigated at its southern limits on the eastern coast of China, which indicated that there has been a northward shift in the southern limit of Z. marina. To determine if regional warming resulted in a northward shift in suitable eelgrass habitats, sixteen transplantations of adult eelgrass shoots and seeds at the historical southern distribution limit of eelgrass were conducted between 2016 and 2021. The results showed that high water temperatures in summer had negative effects on eelgrass growth, and directly triggered shoot mortality during 2016–2018. Under heat stress, antioxidant enzyme activity was initially increased, but then decreased under more stressful heat conditions; and the HSP70 protein and its molecular chaperone protein were highly expressed under heat stress. These results demonstrated that suitable eelgrass habitat was now located further north along the eastern coast of China.

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High temperatures trigger seagrass (Zostera marina L.) restoration failure

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None seedlings and adult shoots survived the first or second summer

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Over-summering shoots with lower density, height, and rhizome diameter

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Warming northward shifting eelgrass habitat range along the eastern coast of China

An examination of seed germination and seedling growth of Zostera marina for planting-time selection in Rongcheng Bay, Shandong Peninsula, China

This study firstly quantified the responses of seeds of Zostera marina to different planting times (22 September, 5 October, 23 October, 7 November and 20 November in 2015) through a field seed-planting experiment over a two year period. The suitable seed planting time required by the seeds of Z. marina was evaluated. The seedling establishment rate of Z. marina subjected to different planting times ranged from 7% to 55%, with the higher values attained on the treatments of 22 September and 5 October. New plant patches from seed were fully developed and well maintained on the planting time of 22 September, 5 October and 23 October after 2 years following planting. The shoot density under the three treatments ranged from 62 shoots per replicate to 72 shoots per replicate with an average of 67 shoots per replicate in September 2017. According to the propagation assessment and growth analysis, we found that the planting time from mid-September to mid-October may be the optimal time to plant seeds of Z. marina in our experimental site. Our results demonstrate that seed planting time has an important effect on the effectiveness of eelgrass restoration and provide data that could prove helpful in the development of successful eelgrass restoration.

Improving Approaches to Mapping Seagrass within the Great Barrier Reef: From Field to Spaceborne Earth Observation

Seagrass meadows are a key ecosystem of the Great Barrier Reef World Heritage Area, providing one of the natural heritage attributes underpinning the reef’s outstanding universal value. We reviewed approaches employed to date to create maps of seagrass meadows in the optically complex waters of the Great Barrier Reef and explored enhanced mapping approaches with a focus on emerging technologies, and key considerations for future mapping. Our review showed that field-based mapping of seagrass has traditionally been the most common approach in the GBRWHA, with few attempts to adopt remote sensing approaches and emerging technologies. Using a series of case studies to harness the power of machine- and deep-learning, we mapped seagrass cover with PlanetScope and UAV-captured imagery in a variety of settings. Using a machine-learning pixel-based classification coupled with a bootstrapping process, we were able to significantly improve maps of seagrass, particularly in low cover, fragmented and complex habitats. We also used deep-learning models to derive enhanced maps from UAV imagery. Combined, these lessons and emerging technologies show that more accurate and efficient seagrass mapping approaches are possible, producing maps of higher confidence for users and enabling the upscaling of seagrass mapping into the future.

Invasion of Spartina alterniflora on Zostera japonica enhances the abundances of bacteria by absolute quantification sequencing analysis

Plant invasion can alter soil organic matter composition and indirectly impact estuary ecology; therefore, it is paramount to understand how plant invasion influences the bacterial community. Here, we present an absolute quantification 16S rRNA gene sequencing to investigate the bacterial communities that were collected from Zostera japonica and Spartina alterniflora covered areas and Z. japonica degradation areas in the Yellow River Estuary. Our data revealed that the absolute quantity of bacteria in the surface layer was significantly (p < .05) higher than that in the bottom and degradation areas. Following the invasion of S. alterniflora, the abundances of Bacteroidia, Acidimicrobiaceae, and Dehalococcoidaceaewere enriched in the S. alterniflora sediment. In addition, variations in the composition of sediment bacterial communities at the phylum level were the most intimately related to total organic carbon (TOC), and the content of heavy metals could reduce the abundance of bacteria. This study provided some information to understand the effects of S. alterniflora invasion on Z. japonica from the perspective of microbiome level.

The success of seagrass restoration using Enhalus acoroides seeds is correlated with substrate and hydrodynamic conditions

The extent of seagrass areas and their associated ecosystem functions and services have been declining due to many factors. Seagrass restoration is important to mitigate such declines. Seagrass restoration using seeds can be a viable method due to the high seed availability of some seagrass species and could enhance seagrass resilience to climate change stress. However, this method sometimes has low success rates due to high seed predation and seeds being washed away by wave action or substrate movement. The research was conducted to compare the settlement of Enhalus acoroides seeds and the establishment of seedlings on different sediment types (fine sand, coarse sand, and hard substrate with rubble) combined with different wave exposure levels (high and moderate). This is the first study to observe seed survival and seedling establishment of the tropical seagrass E. acoroides in the wild. On average, 64% of seeds dispersed on fine sand substrate at a moderate exposure site survived and developed into established seedlings by the end of the 40 days observation period, but the survival of seeds dispersed on coarse sand at high exposure and hard substrate at moderate exposure only remained above 50% for up to 3 days, and had declined to 2% and 1.4%, respectively, by day 40. Six years later, surviving E. acoroides sample from the coarse sand and hard substrate both had well-developed rhizomes but fewer roots than the plant from the fine sand site, these rhizome and roots characteristics were likely adaptations to increase anchoring capacity in the specific site. The results indicate that Enhalus seed settlement and seedling establishment can readily occur at sites with fine sand substrate and lower wave exposure; however, additional measures may be required at more exposed sites with mobile or hard substrates until seedlings become established.

Bioinformatics of Corals: Investigating Heterogeneous Omics Data from Coral Holobionts for Insight into Reef Health and Resilience

Coral reefs are home to over two million species and provide habitat for roughly 25% of all marine animals, but they are being severely threatened by pollution and climate change. A large amount of genomic, transcriptomic, and other omics data is becoming increasingly available from different species of reef-building corals, the unicellular dinoflagellates, and the coral microbiome (bacteria, archaea, viruses, fungi, etc.). Such new data present an opportunity for bioinformatics researchers and computational biologists to contribute to a timely, compelling, and urgent investigation of critical factors that influence reef health and resilience. Expected final online publication date for the Annual Review of Biomedical Data Science, Volume 5 is August 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.