Heteroplasmy Is Rare in Plant Mitochondria Compared with Plastids despite Similar Mutation Rates.

Plant cells harbor two membrane-bound organelles containing their own genetic material-plastids and mitochondria. Although the two organelles coexist and coevolve within the same plant cells, they differ in genome copy number, intracellular organization, and mode of segregation. How these attributes affect the time to fixation or, conversely, loss of neutral alleles is currently unresolved. Here, we show that mitochondria and plastids share the same mutation rate, yet plastid alleles remain in a heteroplasmic state significantly longer compared with mitochondrial alleles. By analyzing genetic variants across populations of the marine flowering plant Zostera marina and simulating organelle allele dynamics, we examine the determinants of allele segregation and allele fixation. Our results suggest that the bottlenecks on the cell population, e.g. during branching or seeding, and stratification of the meristematic tissue are important determinants of mitochondrial allele dynamics. Furthermore, we suggest that the prolonged plastid allele dynamics are due to a yet unknown active plastid partition mechanism. The dissimilarity between plastid and mitochondrial novel allele fixation at different levels of organization may manifest in differences in adaptation processes. Our study uncovers fundamental principles of organelle population genetics that are essential for further investigations of long-term evolution and molecular dating of divergence events.

Insights into response of seagrass (Zostera marina) to sulfide exposure at morphological, physiochemical and molecular levels in context of coastal eutrophication and warming.

Sulfide in sediment porewaters, is toxic to rooted macrophytes in both marine and freshwater environments. Current research on sulfide stress in seagrasses primarily focuses on morphological and physiological aspects, with little known about the molecular response and resistance mechanisms. This study first investigated the damage caused by sulfide to eelgrass (Zostera marina L.) using transcriptomic, metabolomic, and other physiological and biochemical indicators and explored the potential resistance of eelgrass at molecular level through laboratory simulated and in-situ sulfide stress experiments. Comprehensive results showed that sulfide stress severely inhibited the growth, photosynthesis, and antioxidant enzyme activities of eelgrass. Importantly, transcriptome analysis revealed significant activation of pathways related to carbohydrate and sulfur metabolism. This activation served a dual purpose: providing an energy source for eelgrass stress response and achieving detoxification through accelerated sulfur metabolism-a potential resistance mechanism. The toxicity of sulfide increased with rising temperature as evidenced by a decrease in EC50. Results from recovery experiments indicated that when Fv/Fm reduced to about 0 under sulfide stress, the growth and photosynthesis of eelgrass recovered to normal level after timely removal of sulfide. However, prolonged exposure to sulfide resulted in failure to recover, leading ultimately to plant death. This study not only enhances our understanding of the molecular-level impacts of sulfide on seagrasses but also provides guidance for the management and ecological restoration of seagrass meadows under sulfide stress.

Microbial Detoxification of Sediments Underpins Persistence of Zostera marina Meadows.

Eelgrass meadows have attracted much attention not only for their ability to maintain marine ecosystems as feeding grounds for marine organisms but also for their potential to store atmospheric and dissolved CO2 as blue carbon. This study comprehensively evaluated the bacterial and chemical data obtained from eelgrass sediments of different scales along the Japanese coast to investigate the effect on the acclimatization of eelgrass. Regardless of the eelgrass habitat, approximately 1% Anaerolineales, Babeliales, Cytophagales, and Phycisphaerales was present in the bottom sediment. Sulfate-reducing bacteria (SRB) were present at 3.69% in eelgrass sediment compared to 1.70% in bare sediment. Sulfur-oxidizing bacteria (SOB) were present at 2.81% and 1.10% in the eelgrass and bare sediment, respectively. Bacterial composition analysis and linear discriminant analysis revealed that SOB detoxified H2S in the eelgrass meadows and that the larger-scale eelgrass meadows had a higher diversity of SOB. Our result indicated that there were regional differences in the system that detoxifies H2S in eelgrass meadows, either microbial oxidation mediated by SOB or O2 permeation via the physical diffusion of benthos. However, since bacterial flora and phylogenetic analyses cannot show bias and/or causality due to PCR, future kinetic studies on microbial metabolism are expected.

Effects of seagrass restoration on coastal fish abundance and diversity.

Restoration is accelerating to reverse global declines of key habitats and recover lost ecosystem functions, particularly in coastal ecosystems. However, there is high uncertainty about the long-term capacity of restored ecosystems to provide habitat and increase biodiversity and the degree to which these ecosystem services are mediated by spatial and temporal environmental variability. We addressed these gaps by sampling fishes biannually for 5-7 years (2012-2018) at 16 sites inside and outside a rapidly expanding restored seagrass meadow in coastal Virginia (USA). Despite substantial among-year variation in abundance and species composition, seine catches in restored seagrass beds were consistently larger (6.4 times more fish, p < 0.001) and more speciose (2.6 times greater species richness, p < 0.001; 3.1 times greater Hill-Shannon diversity, p = 0.03) than seine catches in adjacent unvegetated areas. Catches were particularly larger during summer than autumn (p < 0.01). Structural equation modeling revealed that depth and water residence time interacted to control seagrass presence, leading to higher fish abundance and richness in shallow, well-flushed areas that supported seagrass. Together, our results indicate that seagrass restoration yields large and consistent benefits for many coastal fishes, but that restoration and its benefits are sensitive to the dynamic seascapes in which restoration is conducted. Consideration of how seascape-scale environmental variability affects the success of habitat restoration and subsequent ecosystem function will improve restoration outcomes and the provisioning of ecosystem services.

Efectos de la restauración de pastos marinos sobre la abundancia y diversidad de peces costeros Resumen La restauración ecológica está acelerándose para revertir la declinación mundial de hábitats importantes y para recuperar las funciones ambientales perdidas, particularmente en los ecosistemas costeros. Sin embargo, hay una gran incertidumbre en cuanto a la capacidad a largo plazo que tienen los ecosistemas restaurados de proporcionar hábitats e incrementar la biodiversidad y el grado al que estos servicios ambientales están mediados por la variabilidad ambiental espacial y temporal. Abordamos estos vacíos mediante el muestreo bianual de peces durante 5-7 años (2012-2018) en 16 sitios dentro y fuera de una pradera restaurada de pastos marinos con expansión acelerada en la costa de Virginia (E.U.A.). A pesar de la variación sustancial anual en abundancia y composición de especies, la captura de cerco en los lechos de pastos marinos restaurados fue mayor (6.4 veces más peces, p< 0.001) y con más especies (2.6 veces mayor riqueza de especies, p< 0.001; 3.1 veces mayor diversidad Hill-Shannon, p= 0.03) que la captura de cerco en las áreas aledañas sin vegetación. En particular, las capturas fueron mayores durante el verano que durante el otoño (p < 0.01). Los modelos de ecuaciones estructurales revelaron que la profundidad y el tiempo de residencia acuática interactúan para controlar la presencia de los pastos marinos, lo que resulta en una mayor abundancia y riqueza de peces en áreas someras con buena circulación que fomentan los pastos marinos. En conjunto, nuestros resultados indican que la restauración de los pastos marinos produce grandes beneficios constantes para muchos peces costeros, pero también que la restauración y sus beneficios son sensibles a la dinámica marina en la que se realiza la restauración. Si se considera cómo la variabilidad ambiental a escala de paisaje afecta el éxito de la restauración del hábitat y la función ambiental subsecuente, entonces mejorarán los resultados de restauración y el suministro de servicios ambientales.

Ensemble habitat suitability modeling for predicting optimal sites for eelgrass (Zostera marina) in the tidal lagoon ecosystem: Implications for restoration and conservation.

Seagrass systems are in decline, mainly due to anthropogenic pressures and ongoing climate change. Implementing seagrass protection and restoration measures requires accurate assessment of suitable habitats. Commonly, such assessments have been performed using single-algorithm habitat suitability models, nearly always based on low environmental resolution information and short-term species data series. Here we address eelgrass (Zoostera marina) meadows' large-scale decline (>80%) in Shandong province (Yellow Sea, China) by developing an ensemble habitat model (EHM) to inform eelgrass conservation and restoration strategies in the Swan Lake (SL). For this, we applied a weighted EHM derived from ten single-algorithm models including profile, regression, classification, and machine learning methods to generate a high-resolution habitat suitability map. The EHM was constructed based on the predictive performances of each model, by combining a series of present-absent eelgrass datasets from recent years coupled with oceanographic and sediment data. The model was cross-validated with independent historical datasets, and a final habitat suitability map for conservation and restoration was generated. Our EHM scheme outperformed all single models in terms of habitat suitability, scoring ∼0.95 for both true statistic skill (TSS) and area under the curve (AUC) performance criteria. Machine learning methods outperformed profile, regression and classification methods. Regarding model explanatory variables, overall, topographic characteristics such as depth (DEP) and seafloor slope (SSL) are the most significant factors determining the distribution of eelgrass. The EHM predicted that the overlapping area was almost 90% of the current eelgrass habitat. Using results from our EHM, a LOESS regression model for the relationship of the habitat suitability to both the biomass and density of Z. marina outperformed better than the classic Ordinary Least Squares regression model. The EHM is a promising tool for supporting eelgrass protection and restoration areas in temperate lagoons as data availability improves.

Assessment of pixel-oriented k-NN machine learning algorithm performance for the interannual remote sensing monitoring of eelgrass beds at the mouth of the Romaine.

Eelgrass cover extent is among the most reliable indicators for measuring changes in coastal ecosystems. Eelgrass has colonized the mouth of the Romaine River and has become a part of environmental monitoring there since 2013. The presence of eelgrass in this area is an essential factor for the early detection of changes in the Romaine coastal ecosystem. This will act as a trigger for an appropriate environmental response to preserve ecosystem health. In this paper, a cost- and time-efficient workflow for such spatial monitoring is proposed using a pixel-oriented k-NN algorithm. It can then be applied to multiple modellers to efficiently map the eelgrass cover. Training data were collected to define key variables for segmentation and k-NN classification, providing greater edge detection for the presence of eelgrass. The study highlights that remote sensing and training data must be acquired under similar conditions, replicating methodologies for collecting data on the ground. Similar approaches must be used for the zonal statistic requirements of the monitoring area. This will allow a more accurate and reliable assessment of eelgrass beds over time. An overall accuracy of over 90% was achieved for eelgrass detection for each year of monitoring.

The biogeography of community assembly: latitude and predation drive variation in community trait distribution in a guild of epifaunal crustaceans.

While considerable evidence exists of biogeographic patterns in the intensity of species interactions, the influence of these patterns on variation in community structure is less clear. Studying how the distributions of traits in communities vary along global gradients can inform how variation in interactions and other factors contribute to the process of community assembly. Using a model selection approach on measures of trait dispersion in crustaceans associated with eelgrass (Zostera marina) spanning 30° of latitude in two oceans, we found that dispersion strongly increased with increasing predation and decreasing latitude. Ocean and epiphyte load appeared as secondary predictors; Pacific communities were more overdispersed while Atlantic communities were more clustered, and increasing epiphytes were associated with increased clustering. By examining how species interactions and environmental filters influence community structure across biogeographic regions, we demonstrate how both latitudinal variation in species interactions and historical contingency shape these responses. Community trait distributions have implications for ecosystem stability and functioning, and integrating large-scale observations of environmental filters, species interactions and traits can help us predict how communities may respond to environmental change.

Rapid enhancement of multiple ecosystem services following the restoration of a coastal foundation species.

The global decline of marine foundation species (kelp forests, mangroves, salt marshes, and seagrasses) has contributed to the degradation of the coastal zone and threatens the loss of critical ecosystem services and functions. Restoration of marine foundation species has had variable success, especially for seagrasses, where a majority of restoration efforts have failed. While most seagrass restorations track structural attributes over time, rarely do restorations assess the suite of ecological functions that may be affected by restoration. Here we report on the results of two small-scale experimental seagrass restoration efforts in a central California estuary where we transplanted 117 0.25-m2 plots (2,340 shoots) of the seagrass species Zostera marina. We quantified restoration success relative to persistent reference beds, and in comparison to unrestored, unvegetated areas. Within three years, our restored plots expanded ~8,500%, from a total initial area of 29 to 2,513 m2 . The restored beds rapidly began to resemble the reference beds in (1) seagrass structural attributes (canopy height, shoot density, biomass), (2) ecological functions (macrofaunal species richness and abundance, epifaunal species richness, nursery function), and (3) biogeochemical functions (modulation of water quality). We also developed a multifunctionality index to assess cumulative functional performance, which revealed restored plots are intermediate between reference and unvegetated habitats, illustrating how rapidly multiple functions recovered over a short time period. Our comprehensive study is one of few published studies to quantify how seagrass restoration can enhance both biological and biogeochemical functions. Our study serves as a model for quantifying ecosystem services associated with the restoration of a foundation species and demonstrates the potential for rapid functional recovery that can be achieved through targeted restoration of fast-growing foundation species under suitable conditions.

Enhancing the resilience of Zostera noltei seagrass meadows against Arenicola spp. bio-invasion: A decision-making approach.

Seagrass meadows provide important and valuable ecosystem services. They are affected by several natural and human-induced stressors, but a combination of natural recovery and management actions have recently inverted the worldwide reduction. The main objectives of this study were to provide science-based knowledge on ecology and restoration, framed on environmental-related policies. By coupling the general guidelines with practical experience, obtained from sequential in situ experiments carried out for several months in a show-case study area, this study provides guidelines useful for restoration practitioners. A decision-making approach is proposed to answer the following questions: 1) What is the best Zostera noltei transplanting method? 2) What is the best technique to reduce the bioturbation activity of Arenicola spp.?, 3) Do bioturbation reduction techniques affect the survival rate of Z. noltei transplants?, and finally, 4) What are the key steps to maximize the success of a Z. noltei transplant and increase the species' resilience? Having a Portuguese coastal lagoon as show-case (Mira Channel, Ria de Aveiro), different transplant and restoration methodologies were tested (i.e. metal frames, nails, bamboo sticks, shoots inserted unanchored into the sediment, and intact units of sediment with seagrasses, named as SODs) to assure low environmental impact on donor meadows, high survival rate of transplanted shoots and the recovery of fragmented or lost meadows. Moreover, to potentially reverse a degraded Arenicola spp. colonized seagrass habitat, different types of natural membranes were tested. Results showed that the best transplanting method is the use of SODs as the self-facilitation process of Z. noltei is enhanced, while being the least invasive for the donor population. The use of a natural membrane can significantly decrease the bioturbation stress caused by Arenicola spp., with jute membrane being the best option, given its cost-handling-benefit trade-offs. Enhancing the success of seagrass restoration requires the implementation of effective measures by environmental restoration practitioners. We defined a three-step process to improve the resilience of Z. noltei. This stepwise approach consists on 1) Characterization of the donor population, 2) Identification of the constraints and implementation of measures to prevent them, and 3) Scale-up the restoration plan. The application of this stepwise approach in intertidal coastal and estuarine systems management will, therefore, facilitate the success of Z. noltei restoration plans.

Expansin gene loss is a common occurrence during adaptation to an aquatic environment.

Expansins comprise a superfamily of plant cell wall loosening proteins that can be divided into four individual families (EXPA, EXPB, EXLA and EXLB). Aside from inferred roles in a variety of plant growth and developmental traits, little is known regarding the function of specific expansin clades, for which there are at least 16 in flowering plants (angiosperms); however, there is evidence to suggest that some expansins have cell-specific functions, in root hair and pollen tube development, for example. Recently, two duckweed genomes have been sequenced (Spirodela polyrhiza strains 7498 and 9509), revealing significantly reduced superfamily sizes. We hypothesized that there would be a correlation between expansin loss and morphological reductions seen among highly adapted aquatic species. In order to provide an answer to this question, we characterized the expansin superfamilies of the greater duckweed Spirodela, the marine eelgrass Zostera marina and the bladderwort Utricularia gibba. We discovered rampant expansin gene and clade loss among the three, including a complete absence of the EXLB family and EXPA-VII. The most convincing correlation between morphological reduction and expansin loss was seen for Utricularia and Spirodela, which both lack root hairs and the root hair expansin clade EXPA-X. Contrary to the pattern observed in other species, four Utricularia expansins failed to branch within any clade, suggesting that they may be the result of neofunctionalization. Last, an expansin clade previously discovered only in eudicots was identified in Spirodela, allowing us to conclude that the last common ancestor of monocots and eudicots contained a minimum of 17 expansins.

Recovery and Community Succession of the Zostera marina Rhizobiome after Transplantation.

Seagrasses can form mutualisms with their microbiomes that facilitate the exchange of energy sources, nutrients, and hormones and ultimately impact plant stress resistance. Little is known about community succession within the belowground seagrass microbiome after disturbance and its potential role in the plant's recovery after transplantation. We transplanted Zostera marina shoots with and without an intact rhizosphere and cultivated plants for 4 weeks while characterizing microbiome recovery and effects on plant traits. Rhizosphere and root microbiomes were compositionally distinct, likely representing discrete microbial niches. Furthermore, microbiomes of washed transplants were initially different from those of sod transplants and recovered to resemble an undisturbed state within 14 days. Conspicuously, changes in the microbial communities of washed transplants corresponded with changes in the rhizosphere sediment mass and root biomass, highlighting the strength and responsive nature of the relationship between plants, their microbiome, and the environment. Potential mutualistic microbes that were enriched over time include those that function in the cycling and turnover of sulfur, nitrogen, and plant-derived carbon in the rhizosphere environment. These findings highlight the importance and resilience of the seagrass microbiome after disturbance. Consideration of the microbiome will have meaningful implications for habitat restoration practices.IMPORTANCE Seagrasses are important coastal species that are declining globally, and transplantation can be used to combat these declines. However, the bacterial communities associated with seagrass rhizospheres and roots (the microbiome) are often disturbed or removed completely prior to transplantation. The seagrass microbiome benefits seagrasses through metabolite, nutrient, and phytohormone exchange and contributes to the ecosystem services of seagrass meadows by cycling sulfur, nitrogen, and carbon. This experiment aimed to characterize the importance and resilience of the seagrass belowground microbiome by transplanting Zostera marina with and without intact rhizospheres and tracking microbiome and plant morphological recovery over 4 weeks. We found the seagrass microbiome to be resilient to transplantation disturbance, recovering after 14 days. Additionally, microbiome recovery was linked with seagrass morphology, coinciding with increases in the rhizosphere sediment mass and root biomass. The results of this study can be used to include microbiome responses in informing future restoration work.

Global Diversity and Biogeography of the Zostera marina Mycobiome.

Seagrasses are marine flowering plants that provide critical ecosystem services in coastal environments worldwide. Marine fungi are often overlooked in microbiome and seagrass studies, despite terrestrial fungi having critical functional roles as decomposers, pathogens, or endophytes in global ecosystems. Here, we characterize the distribution of fungi associated with the seagrass Zostera marina, using leaves, roots, and rhizosphere sediment from 16 locations across its full biogeographic range. Using high-throughput sequencing of the ribosomal internal transcribed spacer (ITS) region and 18S rRNA gene, we first measured fungal community composition and diversity. We then tested hypotheses of neutral community assembly theory and the degree to which deviations suggested that amplicon sequence variants (ASVs) were plant selected or dispersal limited. Finally, we identified a core mycobiome and investigated the global distribution of differentially abundant ASVs. We found that the fungal community is significantly different between sites and that the leaf mycobiome follows a weak but significant pattern of distance decay in the Pacific Ocean. Generally, there was evidence for both deterministic and stochastic factors contributing to community assembly of the mycobiome, with most taxa assembling through stochastic processes. The Z. marina core leaf and root mycobiomes were dominated by unclassified Sordariomycetes spp., unclassified Chytridiomycota lineages (including Lobulomycetaceae spp.), unclassified Capnodiales spp., and Saccharomyces sp. It is clear from the many unclassified fungal ASVs and fungal functional guilds that knowledge of marine fungi is still rudimentary. Further studies characterizing seagrass-associated fungi are needed to understand the roles of these microorganisms generally and when associated with seagrasses. IMPORTANCE Fungi have important functional roles when associated with land plants, yet very little is known about the roles of fungi associated with marine plants, like seagrasses. In this study, we report the results of a global effort to characterize the fungi associated with the seagrass Zostera marina across its full biogeographic range. Although we defined a putative global core fungal community, it is apparent from the many fungal sequences and predicted functional guilds that had no matches to existing databases that general knowledge of seagrass-associated fungi and marine fungi is lacking. This work serves as an important foundational step toward future work investigating the functional ramifications of fungi in the marine ecosystem.

Microeukaryotic Communities Associated With the Seagrass Zostera marina Are Spatially Structured.

Epibiotic microorganisms link seagrass productivity to higher trophic levels, but little is known about the processes structuring these communities, and which taxa consistently associate with seagrass. We investigated epibiotic microeukaryotes on seagrass (Zostera marina) leaves, substrates, and planktonic microeukaryotes in ten meadows in the Northeast Pacific. Seagrass epibiotic communities are distinct from planktonic and substrate communities. We found sixteen core microeukaryotes, including dinoflagellates, diatoms, and saprotrophic stramenopiles. Some likely use seagrass leaves as a substrate, others for grazing, or they may be saprotrophic organisms involved in seagrass decomposition or parasites; their relatives have been previously reported from marine sediments and in association with other hosts such as seaweeds. Core microeukaryotes were spatially structured, and none were ubiquitous across meadows. Seagrass epibiota were more spatially structured than planktonic communities, mostly due to spatial distance and changes in abiotic conditions across space. Seawater communities were relatively more similar in composition across sites and more influenced by the environmental component, but more variable over time. Core and transient taxa were both mostly structured by spatial distance and the abiotic environment, with little effect of host attributes, further indicating that those core taxa would not show a strong specific association with Z. marina.

Integrating genetics, biophysical, and demographic insights identifies critical sites for seagrass conservation.

The eelgrass Zostera marina is an important foundation species of coastal areas in the Northern Hemisphere, but is continuing to decline, despite management actions. The development of new management tools is therefore urgent in order to prioritize limited resources for protecting meadows most vulnerable to local extinctions and identifying most valuable present and historic meadows to protect and restore, respectively. We assessed 377 eelgrass meadows along the complex coastlines of two fjord regions on the Swedish west coast-one is currently healthy and the other is substantially degraded. Shoot dispersal for all meadows was assessed with Lagrangian biophysical modeling (scale: 100-1,000 m) and used for barrier analysis and clustering; a subset (n = 22) was also assessed with population genetic methods (20 microsatellites) including diversity, structure, and network connectivity. Both approaches were in very good agreement, resulting in seven subpopulation groupings or management units (MUs). The MUs correspond to a spatial scale appropriate for coastal management of "waterbodies" used in the European Water Framework Directive. Adding demographic modeling based on the genetic and biophysical data as a third approach, we are able to assess past, present, and future metapopulation dynamics to identify especially vulnerable and valuable meadows. In a further application, we show how the biophysical approach, using eigenvalue perturbation theory (EPT) and distribution records from the 1980s, can be used to identify lost meadows where restoration would best benefit the present metapopulation. The combination of methods, presented here as a toolbox, allows the assessment of different temporal and spatial scales at the same time, as well as ranking of specific meadows according to key genetic, demographic and ecological metrics. It could be applied to any species or region, and we exemplify its versatility as a management guide for eelgrass along the Swedish west coast.

Nearshore seascape connectivity enhances seagrass meadow nursery function.

Diverse habitats composing coastal seascapes occur in close proximity, connected by the flux of materials and fauna across habitat boundaries. Understanding how seascape connectivity alters important ecosystem functions for fish, however, is not well established. For a seagrass-dominant seascape, we predicted that configuration and composition of adjacent habitats would alter habitat access for fauna and trophic subsidies, enhancing nursery function for juvenile fish. In an extensive Zostera marina seagrass meadow, we established sites adjacent to (1) highly complex and productive kelp forests (Nereocystis luetkeana), (2) unvegetated sand habitats, and (3) in the seagrass meadow interior. Using SCUBA, we conducted underwater observations of young-of the-year (YOY) rockfish (Sebastes spp.) recruitment across sites. Using generalized linear mixed effects models, we assessed the role of seascape adjacency relative to seagrass provisions (habitat complexity and prey) on YOY recruitment. YOY rockfish collections were used to trace sources of allochthonous vs. autochthonous primary production in the seagrass food web, via a δ13 C and δ15 N isotopic mixing model, and prey consumption using stomach contents. Overall, seagrass nursery function was strongly influenced by adjacent habitats and associated subsidies. Allochthonous N. luetkeana was the greatest source of energy assimilated by YOY rockfish within seagrass sites. In seagrass sites adjacent to N. luetkeana kelp forests, YOYs consumed higher quality prey, which corresponded with better body condition relative to sites adjacent to sand. Moreover, kelp forest adjacency enhanced YOY rockfish recruitment within the seagrass meadow, suggesting that habitat complexity is a key seascape feature influencing the nursery function of nearshore habitats. In general, to promote seascape connectivity, the conservation and restoration of nursery habitats should prioritize the inclusion of habitat mosaics of high structural complexity and productivity. We illustrate and emphasize the importance of using a seascape-level approach that considers linkages among habitats for the management of important nearshore ecosystem functions.

Variation of carbon contents in eelgrass ( Zostera marina) sediments implied from depth profiles.

Seagrass meadows are able to store significant amounts of organic carbon in their underlying sediment, but global estimates are uncertain partly owing to spatio-temporal heterogeneity between and within areas and species. In order to provide robust estimates, there is a need to better understand the fate of, and mechanisms behind, organic carbon storage. In this observational study, we analyse a suite of biotic and abiotic parameters in sediment cores from 47 different eelgrass ( Zostera marina) beds spanning the distributional range of the Northern Hemisphere. Depth profiles of particulate organic carbon (POC) revealed three patterns of vertical distribution where POC either increased, decreased or showed no pattern with sediment depth. These categories exhibited distinct profiles of δ13C and C:N ratios, where high POC profiles had a proportionally larger storage of eelgrass-derived material whereas low POC profiles were dominated by phytoplanktonic and macroalgal material. However, high POC did not always translate into high carbon density. Nevertheless, this large-scale dataset provides evidence that the variability in organic matter source in response to natural and anthropogenic environmental changes affects the potential role of eelgrass beds as POC sinks, particularly where eelgrass decline is observed.

Eelgrass pathogen Labyrinthula zosterae synthesizes essential fatty acids.

Negative consequences of parasites and disease on hosts are usually better understood than their multifaceted ecosystem effects. The pathogen Labyrinthula zosterae (Lz) causes eelgrass wasting disease but has relatives that produce large quantities of nutritionally valuable long-chain polyunsaturated fatty acids (LCPUFA) such as docosahexaenoic acid (DHA). Here we quantify the fatty acids (FA) of Lz cultured on artificial media, eelgrass-based media, and eelgrass segments to investigate whether Lz may similarly produce LCPUFA. We also assess whether field-collected lesions show similar FA patterns to laboratory-inoculated eelgrass. We find that Lz produces DHA as its dominant FA along with other essential FA on both artificial and eelgrass-based media. DHA content was greater in both laboratory-inoculated and field-collected diseased eelgrass relative to their respective controls. If Lz's production scales in situ, it may present an unrecognized source of LCPUFA in eelgrass ecosystems.

Rapid Metabolome and Bioactivity Profiling of Fungi Associated with the Leaf and Rhizosphere of the Baltic Seagrass Zostera marina.

Zostera marina (eelgrass) is a marine foundation species with key ecological roles in coastal habitats. Its bacterial microbiota has been well studied, but very little is known about its mycobiome. In this study, we have isolated and identified 13 fungal strains, dominated by Penicillium species (10 strains), from the leaf and the root rhizosphere of Baltic Z. marina. The organic extracts of the fungi that were cultured by an OSMAC (One-Strain-Many-Compounds) regime using five liquid culture media under both static and shaking conditions were investigated for their chemical and bioactivity profiles. All extracts showed strong anti-quorum sensing activity, and the majority of the Penicillium extracts displayed antimicrobial or anti-biofilm activity against Gram-negative environmental marine and human pathogens. HPLC-DAD-MS-based rapid metabolome analyses of the extracts indicated the high influence of culture conditions on the secondary metabolite (SM) profiles. Among 69 compounds detected in all Penicillium sp. extracts, 46 were successfully dereplicated. Analysis of SM relatedness in culture conditions by Hierarchical Cluster Analysis (HCA) revealed generally low similarity and showed a strong effect of medium selection on chemical profiles of Penicillium sp. This is the first study assessing both the metabolite and bioactivity profile of the fungi associated with Baltic eelgrass Z. marina.

On the suitability of an allometric proxy for nondestructive estimation of average leaf dry weight in eelgrass shoots I: sensitivity analysis and examination of the influences of data quality, analysis method, and sample size on precision.

BACKGROUND: The effects of current anthropogenic influences on eelgrass (Zostera marina) meadows are noticeable. Eelgrass ecological services grant important benefits for mankind. Preservation of eelgrass meadows include several transplantation methods. Evaluation of establishing success relies on the estimation of standing stock and productivity. Average leaf biomass in shoots is a fundamental component of standing stock. Existing methods of leaf biomass measurement are destructive and time consuming. These assessments could alter shoot density in developing transplants. Allometric methods offer convenient indirect assessments of individual leaf biomass. Aggregation of single leaf projections produce surrogates for average leaf biomass in shoots. Involved parameters are time invariant, then derived proxies yield simplified nondestructive approximations. On spite of time invariance local factors induce relative variability of parameter estimates. This influences accuracy of surrogates. And factors like analysis method, sample size and data quality also impact precision. Besides, scaling projections are sensitive to parameter fluctuation. Thus the suitability of the addressed allometric approximations requires clarification. RESULTS: The considered proxies produced accurate indirect assessments of observed values. Only parameter estimates fitted from raw data using nonlinear regression, produced robust approximations. Data quality influenced sensitivity and sample size for an optimal precision. CONCLUSIONS: Allometric surrogates of average leaf biomass in eelgrass shoots offer convenient nondestructive assessments. But analysis method and sample size can influence accuracy in a direct manner. Standardized routines for data quality are crucial on granting cost-effectiveness of the method.

Environment, dosage, and pathogen isolate moderate virulence in eelgrass wasting disease.

Eelgrass wasting disease, caused by the marine pathogen Labyrinthula zosterae, has the potential to devastate important eelgrass habitats worldwide. Although this host-pathogen interaction may increase under certain environmental conditions, little is known about how disease severity is impacted by multiple components of a changing environment. In this study, we investigated the effects of variation in 3 different L. zosterae isolates, pathogen dosage, temperature, and light on severity of infections. Severity of lesions on eelgrass varied among the 3 different isolates inoculated in laboratory trials. Our methods to control dosage of inoculum showed that disease severity increased with pathogen dosage from 104 to 106 cells ml-1. In a dosage-controlled light and temperature 2-way factorial experiment consisting of 2 light regimes (diel light cycle and complete darkness) and 2 temperatures (11 and 18°C), L. zosterae cell growth rate in vitro was higher at the warmer temperature. In a companion experiment that tested the effects of light and temperature in in vivo inoculations, disease severity was higher in dark treatments and temperature was marginally significant. We suggest that the much greater impact of light in the in vivo inoculation experiment indicates an important role for plant physiology and the need for photosynthesis in slowing severity of infections. Our work with controlled inoculation of distinct L. zosterae isolates shows that pathogen isolate, increasing dosage of inoculum, increasing temperature, and diminishing light increase disease severity, suggesting L. zosterae will cause increased damage to eelgrass beds with changing environmental conditions.