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Abstract Seagrass meadows are well-known for their capacity to capture and store blue carbon in sediments. However carbon stocks vary significantly between meadows, spanning more than three orders of magnitude on both local and global scales. Understanding the drivers of seagrass carbon stocks could help improve strategies for incorporating blue carbon into management plans. Here, we measured sediment carbon stocks in eelgrass (Zostera marina) meadows and unvegetated areas along the Norwegian coast, spanning wide gradients in temperature, wave exposure, water depth, salinity, and eelgrass biomass. Carbon stocks were generally higher in eelgrass meadows than in adjacent unvegetated areas, yet they displayed considerable variation (400 − 30 000 g C m−2 at 50 cm sediment depth) even among nearby sites. Overall, the highest carbon stocks were found in deeper, muddier, sheltered meadows near river mouths. These sites likely have the highest input and retention of carbon from different sources. Consequently, they should be prioritized as conservation targets for preserving coastal blue carbon stocks. Despite ever-increasing efforts to quantify seagrass blue carbon globally, high uncertainties still persist, partly due to differing methodologies, processes, and environmental context. Blue carbon stock estimates could be improved through the coordination of standardised mapping and sampling methods.

Zostera marina is an ecologically valuable species that has been declining due to anthropogenic environmental stressors. In this study, spatial and temporal indicators of eelgrass stress, such as coverage and biomass, were compared with the isotopic composition of C, N, and S to understand the mechanism(s) of plant stress. Eelgrass samples were collected in June, July, and August of 2020 at five stations along an estuary spatial gradient in the southern Gulf of St. Lawrence to measure above- and below-ground biomass and tissue isotopes in eelgrass leaves and roots/rhizomes. Eelgrass biomass was lowest at the innermost sampling station, which coincided with eutrophication-induced hypoxia relative to outer sampling stations. δ13C levels at the upstream station were depleted compared to downstream stations. Comparatively, δ15N and δ34S findings were not correlated with plant biomass. Thus, sulfide intrusion was not a major stressor for eelgrass in this estuary. Between the years 2014 and 2020, eelgrass coverage was found to have increased, which coincided with high and low recorded external nutrient loads from the Wheatley River, respectively. Ultimately, these findings indicate that isotopic composition and biomass can be useful in assessing the health of eelgrass in temperate estuaries.

Species persist through resistance and recovery traits induced by natural stressors. Whether human activities exacerbate or moderate the effects of natural stressors is an open question. Because eelgrass (Zostera marina) creates coastal habitat, its response to natural stressors and human activities is of particular management importance. In this study, traits of intertidal eelgrass were examined across cumulative stressors of emersion and oyster culture, including two culture types: oysters grown directly on sediment (ground culture) or supported by gear above the sediment (off-bottom culture). Summer eelgrass was larger above- and below-ground and branched less than in spring, while density and cover were similar seasonally but declined at higher elevation and in ground culture. Eelgrass traits were divided into those related to resistance (larger above-ground size and below-ground storage) and recovery (increased flowering, branching, and rhizome extension). Resistance traits responded additively to intertidal elevation and oyster culture, with above- and below-ground size reduced in all conditions except that rhizome mass was maintained in ground culture. Smaller above-ground size may confer resistance to emersion stress, as a departure from expectations for other stressors. For resilience traits, flowering increased and internode length declined at higher elevation, whereas these traits did not change in ground culture, and off-bottom culture was associated with shorter internodes (additive cumulative stressor) and tended to moderate the enhanced flowering at higher elevations (non-additive, P=0.058). Transitory disturbance in ground culture may reduce eelgrass density with few effects on resilience, whereas off-bottom culture involves longer-term gear placement and trait responses by eelgrass.

Abstract Seagrasses are considered to be globally important for carbon sequestration and they provide a range of ecosystem services. However, they are also known to be vulnerable to various anthropogenic activities, not least bottom contacting fishing gears such as dredging and potting. We set out to test the effects of dredge fishing, in early spring and potting in late summer, in a historically fished but considered “pristine” seagrass meadow on the west coast of Ireland. We found that despite dredging and potting pressures, growth of seagrasses was driven by seasonal changes in light and temperature and that neither fishing activity had any effect on rhizome weight or shoot or blade densities during the growing season. We hypothesize that it is possible for fishing to co‐occur with seagrass if fishing activities are restricted to winter or early spring, before the main seagrass growing season, and/or if particular types of gear, such as the traditional gears described here are used. High levels of dredging and potting had positive increases in the count of both sessile and mobile epifauna suggesting that for mobile species at least, they may take advantage of post‐fishing scavenging opportunities.

This study investigates the biomass production and growth strategies of the relict seagrass Zostera marina, a species sensitive to high temperatures, within the Venice Lagoon (Italy). Monthly data collected from January to December 2019 and November 2020 to October 2021 in a single station in proximity of one lagoon port-entrance, along with seasonal data from 2018 and 2021 for the whole lagoon, were analyzed in conjunction with environmental parameters and macroalgal presence. The objective was to understand the impact of climate changes, particularly rising water temperatures, on the cover, standing crop and net primary production of Z. marina and the effect of the MoSE gate closures designed to protect Venice from high-water events. Despite expectations of a decline due to temperature increase and reduced water exchange, our findings reveal a notable adaptability of Z. marina, with increases in both cover and biomass. This resilience suggests that Z. marina can counteract environmental challenges, making this study relevant for broader ecological and conservation contexts beyond the Venice Lagoon.

The investigation and research of the distribution, biological characteristics, water environment and sediment environmental elements of the seagrass bed in Caofeidian was conducted to define the distribution area of the seagrass bed, classify its coverage, analyze and study the ecological characteristics of the seagrass bed and the characteristics of key environmental impact factors. This provides technical references for understanding the resource and environmental background of the Caofeidian seagrass bed, delimiting the protection area, marine ecological restoration, and blue carbon research. The results show that the dominant species of the Caofeidian seagrass bed is eelgrass, The average plant height is 75.00±6.15 cm/shoot. Moreover, there are differences among different sites. The overall average stem density is 261.26±48.50 shoots/m2, and the total average aboveground and belowground biomass are 302.53±71.79 g DW/m2 and 114.71±27.40 g DW/m2, respectively. The distribution area of the seagrass bed is 42.90 km2, with dense area, relatively dense area, general area, relatively sparse area and sparse area accounting for 13.09%, 12.93%, 18.82%, 18.75% and 36.40%, respectively. The seagrass is distributed in two regions, northern and southern, with dense area and relatively dense area mostly distributed in the northern region. The difference in water environment between the grass bed area and the bare sand area is not significant, while the difference in sediment environment between the grass bed area and the bare sand area is significant. Water temperature, nutrient salts, transparency, water flow, and human engineering activities are key factors that affect the growth of seagrass in the Caofeidian sea area.

Eelgrass (Zostera marina) loss occurs worldwide due to increasing water temperatures and decreasing water quality. In the U.S., widgeongrass (Ruppia maritima), a more heat-tolerant seagrass species, is replacing eelgrass in certain areas. Seagrasses enhance sediment denitrification, which helps to mitigate excess nitrogen in coastal systems. Widgeongrass and eelgrass have different characteristics, which may affect sediment nitrogen cycling. We compared net N2 fluxes from vegetated areas (eelgrass and widgeongrass beds, using intact cores that included sediment and plants) and adjacent unvegetated areas from the York River, in the lower Chesapeake Bay during the spring and summer of one year. We found that seagrass biomass, sediment organic matter, and NH4+ fluxes were significantly higher in eelgrass beds than in widgeongrass beds. Eelgrass was also net denitrifying during both seasons, while widgeongrass was only net denitrifying in the summer. Despite differences in the spring, the seagrass beds had a similar rate of N2 production in the summer and both had higher denitrification rates than unvegetated sediments. Both species are important ecosystem components that can help to mitigate eutrophication in coastal areas. However, as the relative composition of these species continues to change, differences in sediment nitrogen cycling may affect regional denitrification capacity.

Pathogen transmission pathways are fundamental to understanding the epidemiology of infectious diseases yet are challenging to estimate in nature, particularly in the ocean. Seagrass wasting disease (SWD), caused by Labyrinthula zosterae, impacts seagrass beds worldwide and is thought to be a contributing factor to declines; however, little is known about natural transmission of SWD. In this study, we used field and laboratory experiments to test SWD transmission pathways and temperature sensitivity. To test transmission modes in nature, we conducted three field experiments out-planting sentinel Zostera marina shoots within and adjacent to natural Z. marina beds (20 ± 5 and 110 ± 5 m from bed edge). Infection rates and severity did not differ among outplant locations, implicating waterborne transmission. The infectious dose of L. zosterae through waterborne exposure was assessed in a controlled laboratory experiment. The dose to 50% disease was 6 cells ml−1 and did not differ with the temperatures tested (7.5°C and 15°C). Our results show L. zosterae is transmissible through water without direct contact with infected plants. Understanding the transmission dynamics of this disease in the context of changing ocean conditions will improve Z. marina protection and restoration in critical coastal habitats worldwide.

Abstract Background Seagrasses offer various ecosystem services and possess high levels of primary productivity. However, the development of mariculture has affected the homeostasis of seagrass meadow ecosystems. Plant-microbiome associations are essential for seagrasses health, but little is known about the role of environmental microbiomes and how they affect seagrass in a mariculture environment. In this study, we investigated the influence of mariculture on the rhizosphere and seawater microbiome surrounding Zostera marina and focused on the bacterial, eukaryotic, and fungal components in the composition, diversity, metabolism, and responses to mariculture-related environmental factors. Results Significant differences in the composition, richness, diversity, and internal relations of the bacterial community between the seawater and rhizosphere sediment surrounding Z. marina were observed, while differences in the eukaryotic and fungal communities were less significant. More complex bacterial and fungal co-occurrence networks were found in the seawater and rhizosphere sediment of the Saccharina japonica (SJ) and sea cucumber (SC) culture zones. The seawater in the SJ zone had higher levels of dissimilatory and assimilatory nitrate reduction, denitrification, and nitrogen fixation processes than the other three zones. The assimilatory sulfate reduction enzymes were higher in the rhizosphere sediments of the SJ zone than in the other three zones. Tetracycline, sulfonamide, and diaminopyrimidine resistance genes were enriched in the mariculture SJ and SC zones. Conclusions Our findings might contribute to a better understanding of the effects of mariculture on the seagrass and the meadow ecosystems and thus revealing their potential operating mechanisms. These insights may serve to raise awareness of the effects of human activities on natural ecosystems, regulation of antibiotic usage, and environmental restoration. Video Abstract

In this study, the effects of three cultivation methods (hydroponics germination promotion + germination insertion treatment, hydroponic germination promotion + germination post-insertion treatment, and substrate cultivation treatment) on seed germination, seedling establishment, and growth of Zostera marina were studied at 15 ℃, and the cultivation costs and physiological responses of Z. marina seedlings to different cultivation methods were analyzed. The experiment lasted for 42 days. The results revealed that there were no significant differences (P > 0.05) in the seed germination rate and seedling establishment rate of Z. marina between treatments of hydroponic germination promotion + germination insertion and hydroponic germination promotion + germination post-insertion. The average of the two cultivation methods reached 54.8% and 46.5%, which were 1.3 and 1.6 times higher than those under the substrate cultivation treatment, respectively (P < 0.05). There were no significant differences (P < 0.05) in the growth indices of Z. marina seedlings between the two cultivation methods of hydroponic germination promotion + germination insertion and hydroponic germination promotion + hydroponic germination post-insertion, but the average were significantly higher (P < 0.05) than those under the substrate cultivation treatment. Specifically, the average of root production rate was 1.6 times higher than that under the substrate cultivation treatment. Principal component analysis revealed that the physiological state of Z. marina seedlings was best under the hydroponics germination promotion + substrate implantation treatment. The contributions of the total nitrogen and soluble sugar contents were greater under the two treatments with an average of 16.6% and 15.0%, respectively, which were 1.2 times greater than those under the substrate cultivation treatment (P < 0.05). The analysis of cultivation costs showed that the treatment of germination promotion + germination post-insertion cultivation had the lowest cultivation costs (3.6 Yuan/plant), which was 81.9% of that under the treatment of germination promotion + germination insertion cultivation. The results showed that the hydroponic germination promotion + germination post-insertion treatment is a suitable method for cultivating Z. marina seedlings, mainly by enhancing the formation of nonstructural carbohydrates and increasing the photosynthetic pigment content of seedlings.

Extensive subtidal eelgrass (Zostera marina) meadows (~150 km2) once grew in the Dutch Wadden Sea, supporting diverse species communities, but disappeared in the 1930s and have been absent ever since. Identifying the most critical bottlenecks for eelgrass survival is a crucial first step for reintroduction through active restoration measures. Seagrasses are ecosystem engineers, inducing self-facilitating feedbacks that ameliorate stressful conditions. Consequently, once seagrass, including its self-facilitating feedbacks, is lost, reintroduction can be challenging. Therefore, we aimed to test whether 1) sediment stabilization and 2) hydrodynamic stress relief would facilitate eelgrass survival in a field experiment replicated at two sites in the Dutch Wadden Sea. We induced feedbacks using biodegradable root-mimicking structures (BESE-elements) and sandbag barriers. Root mimics had a significant positive effect, increasing the chances of short-term survival by +67% compared to controls. Contrary to our expectations, barriers decreased short-term survival probabilities by -26%, likely due to hydrodynamic turbulence created by the barrier edges, leading to high erosion rates (-14 cm). Site selection proved crucial as short-term survival was entirely negated on one of the two study sites after five weeks due to high floating and epiphytic macroalgae loads. No long-term survival occurred, as plants died at the other site two weeks later. Overall, we found that sediment stabilization by root-mimicking structures was promising, whereas manipulating hydrodynamic forces using sandbag barriers had adverse effects. A mechanistic understanding of transplant failures is required before attempting large-scale restoration. Our study indicates that for seagrass restoration in the Wadden Sea, one should carefully consider 1) the reintroduction of positive feedbacks through restoration tools, 2) donor population choice and transplantation timing, and 3) site selection based on local biotic and abiotic conditions. Optimizing these restoration facets might lower additive stress to a degree that allows long-term survival.

Ten new decalin polyketides, zosteropenilline M (1), 11-epi-8-hydroxyzosteropenilline M (2), zosteropenilline N (3), 8-hydroxyzosteropenilline G (4), zosteropenilline O (5), zosteropenilline P (6), zosteropenilline Q (7), 13-dehydroxypallidopenilline A (8), zosteropenilline R (9) and zosteropenilline S (10), together with known zosteropenillines G (11) and J (12), pallidopenilline A (13) and 1-acetylpallidopenilline A (14), were isolated from the ethyl acetate extract of the fungus Penicillium yezoense KMM 4679 associated with the seagrass Zostera marina. The structures of isolated compounds were established based on spectroscopic methods. The absolute configurations of zosteropenilline Q (7) and zosteropenilline S (10) were determined using a combination of the modified Mosher’s method and ROESY data. The absolute configurations of zosteropenilline M (1) and zosteropenilline N (3) were determined using time-dependent density functional theory (TD-DFT) calculations of the ECD spectra. A biogenetic pathway for compounds 1–14 is proposed. The antimicrobial, cytotoxic and cytoprotective activities of the isolated compounds were also studied. The significant cytoprotective effects of the new zosteropenilline M and zosteropenillines O and R were found in a cobalt chloride (II) mimic in in vitro hypoxia in HEK-293 cells. 1-Acetylpallidopenilline A (14) exhibited high inhibition of human breast cancer MCF-7 cell colony formation with IC50 of 0.66 µM and its anticancer effect was reduced when MCF-7 cells were pretreated with 4-hydroxitamoxifen. Thus, we propose 1-acetylpallidopenilline A as a new xenoestrogen with significant activity against breast cancer.

An increase in water turbidity is one of the main factors underlying seagrass meadow degradation. The effect of different water turbidity levels [2 (control), 10, 20, 30, and 40 NTU] on the survival, growth and physiology of eelgrass (Zostera marina) was studied through a 3-month indoor experiment. The results showed that the survival rate of eelgrass decreased gradually with an increase of water turbidity, and the survival rate under 10–40 NTU conditions was significantly lower than that of the control group (P < 0.05). In particular, the survival rate of eelgrass exposed to 40 NTU was only 56.1% that of the control group. With an increase of water turbidity, the growth rate and productivity of eelgrass also showed a decreasing trend. In the 40 NTU treatment group, the internode elongation rate and leaf elongation rate of eelgrass reached minimum values, which decreased to 48.9% and 61.6% of that of the control group, respectively. Compared to the productivity of the control group, aboveground and underground productivity decreased by 64.6% and 78.8%, respectively. Correlation analysis showed that the increase of water turbidity mainly affected the growth and survival of eelgrass by affecting the content of nonstructural carbohydrates. The content of nonstructural carbohydrates in eelgrass decreased gradually with an increase of water turbidity, and the content of carbohydrates in plants exposed to 10~40 NTU was significantly lower than that in the control group (P < 0.05). The aboveground soluble sugar content in eelgrass exposed to 10–40 NTU was 20.2%–74.7% lower than that in the control group. The results showed that a long-term increase of water turbidity led to a significant decrease in the nonstructural carbohydrates of eelgrass, which was not conducive to its growth and survival. The results provide a theoretical basis for clarifying the degradation mechanism of Z. marina seagrass meadows and selecting suitable restoration areas.

The effects of gibberellin and weak acid on the germination and physiological characteristics of eelgrass (Zostera marina) seeds were studied under laboratory conditions. The cumulative seed germination and seedling establishment rates were calculated. The dynamic changes in seed dry weight, water content, respiration rate, soluble sugar, starch, gibberellin, abscisic acid content, and α-amylase and β-amylase activities during seed germination were monitored. The effect of two exogenous germination-promoting treatments on seed germination was explored, and the physiological response process of the seeds to these treatments was analyzed. The results showed that the treatments effectively promoted seed germination and seedling establishment. The gibberellin treatment had the best germination-promoting effect, and the seed germination and seedling establishment rates were 1.6 times higher than those under the control. During the germination period of seeds in the two treatments, the α-amylase activity first increased and then decreased, the starch content showed a downward trend, and the soluble sugar content continued to increase. At the end of the experiment, the soluble sugar content of seeds in the gibberellin treatment attained the highest value, which was 3.3 times higher than the value before germination and was significantly higher than that in the weak acid treatment and control (P < 0.05). The starch content of seeds in the weak acid treatment attained the lowest value, which was significantly lower than that in the other two treatments (P < 0.05). There was no significant difference in α-amylase activity among the treatments (P > 0.05). Principal component analysis showed that α-amylase activity and starch and soluble sugar contents of seeds were the key factors in seed germination. Comprehensive analysis showed that exogenous gibberellin treatment was an effective method to break seed dormancy. This effect was mainly achieved by regulating amylase activity, increasing starch decomposition rate, and increasing soluble sugar content to provide energy for seed germination. The results provide a theoretical and scientific basis for the rapid germination technology of eelgrass seeds.

IntroductionEelgrass is a typical marine angiosperm that exhibits strong adaptability to high-salt environments. Previous studies have shown that various growth and physiological indicators were significantly affected after the nitrate reductase (NR) pathway for nitric oxide (NO) synthesis in eelgrass was blocked.MethodsTo analyze the molecular mechanism of NO on the adaptability to high-salt environment in eelgrass, we treated eelgrass with artificial seawater (control group) and artificial seawater with 1 mM/L Na2WO4 (experimental group). Based on transcriptomics and metabolomics, we explored the molecular mechanism of NO affecting the salt tolerance of eelgrass.ResultsWe obtained 326, 368, and 859 differentially expressed genes (DEGs) by transcriptome sequencing in eelgrass roots, stems, and leaves, respectively. Meanwhile, we obtained 63, 52, and 36 differentially accumulated metabolites (DAMs) by metabolomics in roots, stems, and leaves, respectively. Finally, through the combined analysis of transcriptome and metabolome, we found that the NO regulatory mechanism of roots and leaves of eelgrass is similar to that of terrestrial plants, while the regulatory mechanism of stems has similar and unique features.DiscussionNO in eelgrass roots regulates osmotic balance and antioxidant defense by affecting genes in transmembrane transport and jasmonic acid-related pathways to improve the adaptability of eelgrass to high-salt environments. NO in eelgrass leaves regulates the downstream antioxidant defense system by affecting the signal transduction of plant hormones. NO in the stems of eelgrass regulates ion homeostasis by affecting genes related to ion homeostasis to enhance the adaptability of eelgrass to high-salt environments. Differently, after the NO synthesis was inhibited, the glyoxylate and dicarboxylate metabolism, as well as the tricarboxylic acid (TCA) cycle, was regulated by glucose metabolism as a complementary effect to cope with the high-salt environment in the stems of eelgrass. These are studies on the regulatory mechanism of NO in eelgrass, providing a theoretical basis for the study of the salt tolerance mechanism of marine plants and the improvement of terrestrial crop traits. The key genes discovered in this study can be applied to increase salt tolerance in terrestrial crops through cloning and molecular breeding methods in the future.

Microbial communities associated with seagrass beds play a crucial role in maintaining the balance of seagrass ecosystems. However, the driving mechanisms behind the structure and functional succession of seagrass microbial communities are still unclear despite the close interaction between seagrass and surrounding microorganisms. To enhance our knowledge of the diversity and functional characteristics of microbial communities in seagrass beds, we employed 16S rRNA gene amplicon sequencing to investigate bacterial communities in seagrass leaves, roots, seawater, and sediments in Caofeidian Zostera marina seagrass beds of Hebei Province, Northern China. Our results highlighted that specific types of bacteria were enriched in different sample compartments, indicating the importance of habitat in influencing microbial diversity and community structure in seagrass bed ecosystems. Notably, the microbial community structure of seagrass leaves and roots showed more similarity to that found in seawater and sediments. Among all the samples, the phylum Pseudomonadota exhibited the highest relative abundance, particularly in sediment samples where they accounted for over 95% of the total bacterial population. In addition, the enrichment of Vibrio, an opportunistic pathogen in several plant samples, alerted us to seagrass and its surrounding marine environments. Finally, functional predictions of microbial communities using PICRUSt2 revealed variations in microbial functions, indicating specific metabolic preferences of microbial communities in different natural environments. The present research sheds light on the mechanisms underlying microbial community succession and their ecological function in seagrass beds.

The islands Iturup and Urup of Kuril Archipelago have been understudied in respect of seagrasses. The research aimed to fill this gap. In 2019 during the expedition of the Russian Geographical Society a part of the coastline has been surveyed by walking, the beached remains of seagrasses and the seagrasses growing on the littoral have been registered. The length of the routes was 95 km. The possible sources of negative anthropogenic impact have been examined. Herbarium collections of several institutions (LE, LECB, MHA, MW, MWG, SAK, Kamchatka Branch of Pacific Geographical Institute of the RAS, the Herbarium of Kronotsky Nature Reserve) have been explored. Three species of seagrasses occur at Iturup and Urup: Zostera marina L., Zostera asiatica Miki, and Phyllospadix iwatensis Makino. The last two species are of particular interest as they are threatened and distributed over a relatively small area. Unlike the habitats of the main part of their range located at the coasts of Japan and Korea, the habitats of the studied islands do not suffer from anthropogenic pressure. The discovered northern refuge is significant for the seagrasses conservation. Current global warming and increasing anthropogenic pressure on the southern habitat would increase its significance. It is especially important for Phyllospadix iwatensis as it turned out to be rather numerous at the studied islands. The other two species occur in small numbers there.

Zostera marina is a seagrass species that acts as an ecosystem engineer, creating biodiversity-rich habitats that offer important ecosystem services. The species is, however, in decline across its range owing to environmental change and anthropogenic impacts. Conservation work includes the use of seeds and shoots to restore seagrass meadows, although ex situ storage of Z. marina seeds is a small area of research and there is no one set protocol. This study investigated the effects of salinity and temperature on the maintenance of dormancy and viability of Z. marina seeds during cold storage. Seeds were stored at 1 °C and 4 °C, in a range of salinity solutions (20, 30, 40, 50, 60 and 70 psu) over a period of 112 days. Results were collected by a velocity-based viability test at 28-day intervals, with seeds categorised as either viable, non-viable or germinated. Over the course of the storage period, results indicated that low salinities (20, 30, 40 and 50 psu) would exhibit premature germination during storage as well as loss of viable seeds at either temperature, while 60 and 70 psu groups have zero germinations and the highest viable seed number is found in 70 psu groups. Analysis revealed that overall temperature was only statistically significant in relation to viable seeds at 1 °C, suggesting that this is the better temperature to maintain viability. The study indicates that low salinity should be avoided for Z. marina seed storage; instead, a salinity solution of 70 psu at 1 °C storage for up to 4 months could ensure seed dormancy is unbroken and few seeds become non-viable. Overall, results from this study were used to create a simple storage protocol that could contribute to community-based restoration projects.

Seagrass meadows act as an effective carbon sink and store carbon in the sediments for substantial periods of time. The drivers of carbon sequestration are complex, and global and regional estimates of carbon stocks have large uncertainties. Here, we report new carbon stock estimates from 14 sites along the Swedish coast and compile existing literature to estimate the magnitude of carbon stocks of Zostera marina (eelgrass) meadows in the Baltic Sea. Eelgrass meadows in the Baltic Sea have considerably lower carbon content and lower stocks (0.25 ± 0.21% DW, 635 ± 321 g C m-2) than in the Kattegat-Skagerrak region (3.25 ± 2.78% DW, 3457 ± 3382 g C m-2) and the average for temperate regions in general (1.4 ± 0.4% DW, 2721 ± 989 g C m-2). Unfavorable growing conditions for eelgrass in the Baltic Sea often lead to meadows occurring in areas of high hydrodynamics, preventing significant carbon accumulation. Stable isotopes revealed that the dominating source of organic carbon in the meadows was planktonic, further highlighting that Baltic Sea eelgrass meadows are not major carbon reservoirs in comparison to unvegetated sediments and other seagrass areas. The results also highlight that environmental conditions drive intraspecific variation of carbon sequestration on large spatial scales. Overall, the carbon stocks and sequestration potential in eelgrass meadows of the Baltic Sea are small compared to other temperate regions.

IntroductionSeagrass meadows serve as an integral component of coastal ecosystems but are declining rapidly due to numerous anthropogenic stressors including climate change. Eelgrass wasting disease, caused by opportunistic Labyrinthula spp., is an increasing concern with rising seawater temperature. To better understand the host-pathogen interaction, we paired whole organism physiological assays with dual transcriptomic analysis of the infected host and parasite. MethodsEelgrass (Zostera marina) shoots were placed in one of two temperature treatments, 11° C or 18° C, acclimated for 10 days, and exposed to a waterborne inoculation containing infectious Labyrinthula zosterae (Lz) or sterile seawater. At two- and five-days post-exposure, pathogen load, visible disease signs, whole leaf phenolic content, and both host- and pathogen- transcriptomes were characterized. ResultsTwo days after exposure, more than 90% of plants had visible lesions and Lz DNA was detectable in 100% percent of sampled plants in the Lz exposed treatment. Concentrations of total phenolic compounds were lower after 5 days of combined exposure to warmer temperatures and Lz, but were unaffected in other treatments. Concentrations of condensed tannins were not affected by Lz or temperature, and did not change over time. Analysis of the eelgrass transcriptome revealed 540 differentially expressed genes in response to Lz exposure, but not temperature. Lz-exposed plants had gene expression patterns consistent with increased defense responses through altered regulation of phytohormone biosynthesis, stress response, and immune function pathways. Analysis of the pathogen transcriptome revealed up-regulation of genes potentially involved in breakdown of host defense, chemotaxis, phagocytosis, and metabolism. DiscussionThe lack of a significant temperature signal was unexpected but suggests a more pronounced physiological response to Lz infection as compared to temperature. Pre-acclimation of eelgrass plants to the temperature treatments may have contributed to the limited physiological responses to temperature. Collectively, these data characterize a widespread physiological response to pathogen attack and demonstrate the value of paired transcriptomics to understand infections in a host-pathogen system.

Climate change associated sea surface temperature rise could significantly affect the physiology, and consequently geographic distribution of seagrasses. Photosynthetic and respiratory responses of warm affinity Halophila nipponica and cold affinity Zostera marina to a change in water temperature (7–26°C) were investigated to estimate whole-plant carbon balance for prediction of the future geographic distributions of these seagrasses in the northwestern Pacific region. It was hypothesized that H. nipponica and Z. marina showed distinctly different patterns of carbon balance with changes in water temperature. Photosynthetic and respiratory rates of H. nipponica and Z. marina generally increased with increasing water temperature, except for Ic and Ik of H. nipponica and α of Z. marina. H. nipponica showed high Pmax and α values, which could support a greater respiratory demand related to the higher proportion of non-photosynthetic tissues (~67%), compared with Z. marina (~34%). The whole-plant carbon balance of Z. marina remained positive throughout the experiment, although it decreased to nearly zero during the high water-temperature period. H. nipponica exhibited a negative carbon balance during winter and early spring, which corresponded with severely limited growth at water temperatures< 15°C. These results suggest that increases in water temperature, particularly during winter, in relation to continuous climate change, could induce substantial changes in the seagrass ecosystem structure and corresponding changes in coastal ecosystem services in the temperate coastal waters of the northwestern Pacific region. The results of this study will provide valuable information on the effective management and conservation of coastal and estuarine ecosystems under ongoing climate change.

Information on seagrass in the Russian section of the Baltic Sea – Sambia Peninsula, Curonian Spit, and Gulf of Finland (water area of Kaliningrad and Leningrad regions) is generalized based on a recent survey, literature search, and study of herbarium samples. Seagrasses are found in the emissions of most of the coast of the Kaliningrad region, but they are extremely few. All discovered seagrasses belong to one species – Zostera marina L. In the absence of an opportunity to distinguish the emissions of Zostera marina brought in by currents from other regions of the Baltic Sea from local emissions, the possibility of the presence of a small number of single individuals of this species in the seawater area of the Sambia Peninsula and the Curonian Spit remains. Specimens of Zostera marina brought in by storms from the western part of the Baltic Sea, as well as an individual found during diving studies in 2009, can take root and form small meadows in the future, provided they are protected from surf waves and a stable substrate, settling with the help of vegetative shoots. Poorly rooted seagrasses can also be washed ashore. The mobile sandy ground found in most of the study area may be the reason why seagrass plants do not form stable communities. In the Russian section of the Gulf of Finland, seagrass had not been recorded. Probably, they occur in small numbers in its northern part.

The current distribution of Zostera spp. seagrass meadows along the Bulgarian Black Sea coast was studied. We used a combination of historical and recent observations of the habitat along the studied coastline. Remote sensing data (satellite images, sonar side-scans) was groundtruthed with georeferenced drop camera observations, scuba diving sampling and georeferenced scuba diving photo and video transects.Тhe total area of the habitat type ‘MB548 - Black Sea seagrass meadows on lower infralittoral sands’ (EUNIS habitat type list 2019) in the study area is 916.9 ha, of which only 17.9 ha are in man-made sheltered environments (harbours). All seagrass meadows identified in 1978-79 were also located during the current survey, despite the increased eutrophication pressure and overall degradation of benthic habitats in the western Black Sea during the 1980s and early 1990s.

Zostera marina (eelgrass) is classified as one of the marine angiosperms and is widely distributed throughout much of the Northern Hemisphere. The present study investigated the microbial community structure and diversity of Z. marina growing in Futtsu bathing water, Chiba prefecture, Japan. The purpose of this study was to provide new insight into the colonization of eelgrass leaves by microbial communities based on leaf age and to compare these communities to the root-rhizome of Z. marina, and the surrounding microenvironments (suspended particles, seawater, and sediment). The microbial composition of each sample was analyzed using 16S ribosomal gene amplicon sequencing. Each sample type was found to have a unique microbial community structure. Leaf-attached microbes changed in their composition depending on the relative age of the eelgrass leaf. Special attention was given to a potential microbial source of leaf-attached microbes. Microbial communities of marine particles looked more like those of eelgrass leaves than those of water samples. This finding suggests that leaf-attached microbes were derived from suspended particles, which could allow them to go back and forth between eelgrass leaves and the water column.

Habitat suitability modelling (HSM) is a tool that is increasingly being used to help guide decision making for conservation management. It can also be used to focus efforts of restoration in our oceans. To improve on model performance, the best available environmental data along with species distribution data are needed. Marine habitats tend to have ecological niches defined by physical environmental conditions and of particular importance for shallow water species is wave energy. In this study we examined the relative improvements to HSM outputs that could be achieved by producing high-resolution Delft-3D modelled wave height data to see if model predictions at a fine-scale can be improved. Seagrasses were used as an exemplar and comparisons at fine-scale showed considerable differences in the area predicted suitable for seagrass growth and greatly increased the importance of waves as a predictor variable when compared with open-source low resolution wave energy data.

Background Seagrass beds are essential habitats in coastal ecosystems, providing valuable ecosystem services, but are threatened by various climate change and human activities. Seagrass monitoring by remote sensing have been conducted over past decades using satellite and aerial images, which have low resolution to analyze changes in the composition of different seagrass species in the meadows. Recently, unmanned aerial vehicles (UAVs) have allowed us to obtain much higher resolution images, which is promising in observing fine-scale changes in seagrass species composition. Furthermore, image processing techniques based on deep learning can be applied to the discrimination of seagrass species that were difficult based only on color variation. In this study, we conducted mapping of a multispecific seagrass bed in Saroma-ko Lagoon, Hokkaido, Japan, and compared the accuracy of the three discrimination methods of seagrass bed areas and species composition, i.e., pixel-based classification, object-based classification, and the application of deep neural network. Methods We set five benthic classes, two seagrass species (Zostera marina and Z. japonica), brown and green macroalgae, and no vegetation for creating a benthic cover map. High-resolution images by UAV photography enabled us to produce a map at fine scales (

Some components of alcohol extracts from seagrass of genus Zostera were fractioned in the column filled with sorbent Sephadex LH-20 using the methods of size exclusion chromatography. Content of polyphenols in the fractions and their antioxidant activity were determined. The total content of polyphenols in the extracts from Zostera asiatica collected in the Rudnaya Bay (Japan Sea) and Zostera marina from the Aniva Bay (Okhotsk Sea) was 2.10 and 2.15 mg/mL, or 0.4 and 1.8 mg/g DW, respectively. The antioxidant activity varied by fractions in the range 19.1–118.0 μg of ascorbic acid per mL for Z. asiatica and 96.2–213.9 μg of ascorbic acid per mL for Z. marina, in dependence on qualitative and quantitative composition of the fractions. The alcohol extracts of Zostera were heterogeneous systems with different polyphenol components and included protein substances covalently bound with polysaccharides and/or polyphenols, that was confirmed by UV spectrometry and thin-layer chromatography. Phenolic acids, flavones and flavonols were presented in the extracts.

Coastal vegetative ecosystems are among the most threatened in the world, facing multiple anthropogenic stressors. A good example of this is seagrass, which supports carbon capture, coastal stabilization, and biodiversity, but is declining globally at an alarming rate. To understand the causes and consequences of changes to these ecosystems, we need to determine the linkages between different biotic and abiotic components. We used data on the seagrass, Zostera marina, collected by citizen scientists across 300 km of the south coast of the United Kingdom as a case study. We assembled data on seagrass genotype, phenotype, infauna, and associated bathymetry, light, sea surface temperature, and wave and current energy to test hypotheses on the distribution and diversity of this temperate sub-tidal ecosystem. We found spatial structure in population genetics, evident through local assortment of genotypes and isolation by distance across a broader geographic scale. By integrating our molecular data with information on seagrass phenotype and infauna, we demonstrate that these ecosystem components are primarily linked indirectly through the effects of shared environmental factors. It is unusual to examine genotypic, phenotypic, and environmental data in a single study, but this approach can inform both conservation and restoration of seagrass, as well as giving new insights into a widespread and important ecosystem.

ABSTRACT Predicting outcomes of marine disease outbreaks presents a challenge in the face of both global and local stressors. Host-associated microbiomes may play important roles in disease dynamics but remain understudied in marine ecosystems. Host–pathogen–microbiome interactions can vary across host ranges, gradients of disease, and temperature; studying these relationships may aid our ability to forecast disease dynamics. Eelgrass, Zostera marina, is impacted by outbreaks of wasting disease caused by the opportunistic pathogen Labyrinthula zosterae. We investigated how Z. marina phyllosphere microbial communities vary with rising wasting disease lesion prevalence and severity relative to plant and meadow characteristics like shoot density, longest leaf length, and temperature across 23° latitude in the Northeastern Pacific. We detected effects of geography (11%) and smaller, but distinct, effects of temperature (30-day max sea surface temperature, 4%) and disease (lesion prevalence, 3%) on microbiome composition. Declines in alpha diversity on asymptomatic tissue occurred with rising wasting disease prevalence within meadows. However, no change in microbiome variability (dispersion) was detected between asymptomatic and symptomatic tissues. Further, we identified members of Cellvibrionaceae, Colwelliaceae, and Granulosicoccaceae on asymptomatic tissue that are predictive of wasting disease prevalence across the geographic range (3,100 kilometers). Functional roles of Colwelliaceae and Granulosicoccaceae are not known. Cellvibrionaceae, degraders of plant cellulose, were also enriched in lesions and adjacent green tissue relative to nonlesioned leaves. Cellvibrionaceae may play important roles in disease progression by degrading host tissues or overwhelming plant immune responses. Thus, inclusion of microbiomes in wasting disease studies may improve our ability to understand variable rates of infection, disease progression, and plant survival. IMPORTANCE The roles of marine microbiomes in disease remain poorly understood due, in part, to the challenging nature of sampling at appropriate spatiotemporal scales and across natural gradients of disease throughout host ranges. This is especially true for marine vascular plants like eelgrass (Zostera marina) that are vital for ecosystem function and biodiversity but are susceptible to rapid decline and die-off from pathogens like eukaryotic slime-mold Labyrinthula zosterae (wasting disease). We link bacterial members of phyllosphere tissues to the prevalence of wasting disease across the broadest geographic range to date for a marine plant microbiome-disease study (3,100 km). We identify Cellvibrionaceae, plant cell wall degraders, enriched (up to 61% relative abundance) within lesion tissue, which suggests this group may be playing important roles in disease progression. These findings suggest inclusion of microbiomes in marine disease studies will improve our ability to predict ecological outcomes of infection across variable landscapes spanning thousands of kilometers.

During the past century, bivalve populations across the globe have collapsed, resulting in negative ecosystem consequences due to their outsized impact on shallow estuaries. In response, there has been strong interest in the restoration of marine bivalve populations. Here, we present a decade-long restoration effort that sought to rebuild a collapsed (99.5% reduction in harvest) and recruitment-limited population of hard clams (Mercenaria mercenaria) in Shinnecock Bay, NY, USA, using spawner sanctuaries: no-harvest zones where adults were planted at high densities (~27 m-2). Between 2012 to 2019, more than 3.2 million clams were planted in 64 discrete sanctuary plots (~1,850 m2 each) located in zones with maximal larval retention and sediment and seawater characteristics that would maximize the conditioning and spawning of adults. Hydrodynamic models, quantification of hard clam larvae, and spatial recruitment patterns demonstrated larvae spawned within sanctuaries were transported to regions where clam densities significantly increased 18-fold over seven years (2015-2021; p

Sea surface temperature (SST) has increased worldwide since the beginning of the 20th century, a trend which is expected to continue. Changes in SST can have significant impacts on marine biota, including population-level shifts and alterations in community structure and diversity, and changes in the timing of ecosystem events. Seagrasses are a group of foundation species that grow in shallow coastal and estuarine systems, where they provide many ecosystem services. Eelgrass, Zostera marina L., is the dominant seagrass species in the Northeast United States of America (USA). Multiple factors have been cited for losses in this region, including light reduction, eutrophication, and physical disturbance. Warming has the potential to exacerbate seagrass loss. Here, we investigate regional changes in eelgrass presence and abundance in relation to local water temperature using monitoring data from eight sites in the Northeastern USA (New Hampshire to Maryland) where a consistent monitoring protocol, SeagrassNet, has been applied. We use a hurdle model consisting of a generalized additive mixed model (GAMM) with binomial and beta response distributions for modeling eelgrass presence and abundance, respectively, in relation to the local summer average water temperature. We show that summer water temperature one year prior to monitoring is a significant predictor of eelgrass presence, but not abundance, on a regional scale. Above average summer temperatures correspond to a decrease in probability of eelgrass presence (and increased probability of eelgrass absence) the following year. Cooler than average temperatures in the preceding year, down to approximately 0.5°C below the site average, are associated with the highest predicted probability of eelgrass presence. Our findings suggest vulnerability in eelgrass meadows of the Northeast USA and emphasize the value of unified approaches to seagrass monitoring, conservation and management at the seascape scale.

Because sexual reproduction is essential for the establishment and persistence of seagrass meadows, flowering intensity is an important trait that influences the resilience and stability of seagrass populations. Although the effects of excessive coastal nutrient loading on seagrass vegetative growth have been extensively documented, the effects on seagrass reproductive phenology and intensity remain unclear. To examine the reproductive responses of seagrass populations to increased coastal nutrient loading, the flowering phenology and intensity of Zostera marina were compared between sites with high-nutrient, low-light conditions (Deukryang Bay and Dongdae Bay) and low-nutrient, high-light conditions (Koje Bay) on the southern coast of Korea. Nutrient contents of the above- and below-ground tissues of Z. marina reflected in situ nutrient and light availability at the study sites. Reproductive shoot density and biomass, as well as flowering frequency and reproductive effort, were much higher (1.5–4.6-fold) at the high-nutrient, low-light study sites of Deukryang Bay and Dongdae Bay than at the low-nutrient, high-light site of Koje Bay. Consequently, potential seed production was higher in Deukryang Bay and Dongdae Bay than in Koje Bay. Chronic high-nutrient and low-light conditions significantly increased the reproductive intensity of Z. marina, supporting the persistence and resilience of Z. marina populations. The results of this study could provide insights into the conservation and management of seagrass meadows under increased coastal nutrient loading.

Prolongation of light duration is one of the effective methods to improve the current seagrass propagation technique. We subjected plants of eelgrass Zostera marina to different prolonged light durations [0 (control), 2, 4, 6, 8 h d−1] for 6 weeks under controlled laboratory conditions. We measured plant response in terms of survivorship, growth, productivity, leaf pigment and carbohydrate concentrations. Survival analysis combined with growth assessment suggested that the optimum range of prolonged light durations for the establishment of Z. marina plants is 3.9–4.6 h d−1. The propagation coefficient of Z. marina plants exposed to 4 h d−1 was 1.4 times higher than that of plants under the control. Pearson and Mantel correlation analysis indicated that the promotion of prolonged light duration to the survival and growth of Z. marina plants mainly depended on the increase of chlorophyll content and the accumulation and synthesis of non-structural carbohydrate. The total chlorophyll content of leaves and soluble sugar content of aboveground tissues of Z. marina plants exposed to 4 h d−1 were 1.6 times and 2.9 times higher than those of plants under the control, respectively. The results will provide data that could prove helpful in the development of efficient artificial propagation technology of Z. marina plants.

Species, including seagrasses, at their range limits are uniquely vulnerable to climate change. In the western Atlantic Ocean, the biogeographic transition zone between temperate and tropical ecosystems is recognized as one of several global hotspots where poleward-flowing western boundary currents are forecast to warm faster than the global average. In this region seagrass ecosystem services are primarily supplied by two species, Zostera marina, a temperate seagrass at its southern range limit and Halodule wrightii, a tropical seagrass at its northern limit. Water temperatures in the study location in Back Sound, North Carolina, USA have gradually increased the length of the stressful summer season for Z. marina (beginning after 3 consecutive days of daily mean water temperatures >23°C, ending after 3 consecutive days

Seagrass meadows are among the most productive and diverse marine ecosystems, providing essential structure, functions, and services. They are also among the most impacted by human activities and in urgent need of better management and protection. In Canada, eelgrass (Zostera marina) meadows are found along the Atlantic, Pacific, and Arctic coasts, and thus occur across a wide range of biogeographic conditions. Here, we synthesize knowledge of eelgrass ecosystems across Canada’s coasts, highlighting commonalities and differences in environmental conditions, plant, habitat, and community structure, as well as current trends and human impacts. Across regions, eelgrass life history, phenology, and general species assemblages are similar. However, distinct regional differences occur in environmental conditions, particularly with water temperature and nutrient availability. There is considerable variation in the types and strengths of human activities among regions. The impacts of coastal development are prevalent in all regions, while other impacts are of concern for specific regions, e.g., nutrient loading in the Atlantic and impacts from the logging industry in the Pacific. In addition, climate change represents a growing threat to eelgrass meadows. We review current management and conservation efforts and discuss the implications of observed differences from coast to coast to coast.

This study is to provide information on levels of the elements in leaves and roots-rhizomes of Zostera marina and Zostera noltei, their surrounding sea water and sediments collected from Akliman and Türkeli coastal areas of Sinop city in the Black Sea four times between September 2015 and July 2016. The concentrations of Al, Mn, Fe, Co, Ni, Cu, Zn, As, Cd, Hg and Pb in digested samples were measured by Agilent Technologies, 7700X ICP-MS (inductively coupled plasma mass spectrometer). The results showed that the concentrations of metals were found in the order Hg < Cd < Co < As < Pb < Ni < Cu < Zn < Mn < Al = Fe. Zostera species were bio-accumulative for Al and Mn (BCF ≥ 5000); and macro-consantrator for Zn and Cd (BSAF > 2). The general capacities of element translocation were found as acropetal for Al, Mn, Ni, Cd and Hg in eelgrass. The present findings interpreted for the first time in the Turkish Black Sea waters. Both species of Zostera in high concentrations of these elements may be due to untreated wastes that are discharging from different sources such as harbor activities, agricultural and domestic wastes in coastal areas. In order to assess the impact of contaminants and take necessary actions, the region needs to be monitored regularly.

Water quality deterioration is expected to worsen the light conditions in shallow coastal waters with increasing human activities. Temperate seagrasses are known to tolerate a highly fluctuating light environment. However, depending on their ability to adjust to some decline in light conditions, decreases in daily light quantity and quality could affect seagrass physiology, productivity, and, eventually, survival if the Minimum Quantum Requirements (MQR) are not reached. To better understand if, how, and to what extent photosynthetic adjustments contribute to light acclimation, eelgrass (Zostera marina L.) shoots from the cold temperate St. Lawrence marine estuary (Rimouski, QC, Canada) were exposed to seven light intensity treatments (6, 36, 74, 133, 355, 503, and 860 μmol photons m–2 s–1, 14:10 light:dark photoperiod). Photosynthetic capacity and efficiency were quantified after five and 25 days of light exposure by Pulse Amplitude Modulated (PAM) fluorometry to assess the rapid response of the photosynthetic apparatus and its acclimation potential. Photoacclimation was also studied through physiological responses of leaves and shoots (gross and net primary production, pigment content, and light absorption). Shoots showed proof of photosynthetic adjustments at irradiances below 200 μmol photons m–2 s–1, which was identified as the threshold between limiting and saturating irradiances. Rapid Light Curves (RLC) and net primary production (NPP) rates revealed sustained maximal photosynthetic rates from the highest light treatments down to 74 μmol photons m–2 s–1, while a compensation point (NPP = 0) of 13.7 μmol photons m–2 s–1 was identified. In addition, an important package effect was observed, since an almost three-fold increase in chlorophyll content in the lowest compared to the highest light treatment did not change the leaves’ light absorption. These results shed new light on photosynthetic and physiological processes, triggering light acclimation in cold temperate eelgrass. Our study documents an MQR value for eelgrass in the St. Lawrence estuary, which is highly pertinent in the context of conservation and restoration of eelgrass meadows.

Shallow coastal soft bottoms are important carbon sinks. Submerged vegetation has been shown to sequester carbon, increase sedimentary organic carbon (Corg) and thus suppress greenhouse gas (GHG) emissions. The ongoing regression of seagrass cover in many areas of the world can therefore lead to accelerated emission of GHGs. In Nordic waters, seagrass meadows have a high capacity for carbon storage, with some areas being recognized as blue carbon hotspots. To what extent these carbon stocks lead to emission of methane (CH4) is not yet known. We investigated benthic CH4 emission (i.e., net release from the sediment) in relation to seagrass (i.e. Zostera marina) cover and sedimentary Corg content (%) during the warm summer period (when emissions are likely to be highest). Methane exchange was measured in situ with benthic chambers at nine sites distributed in three regions along a salinity gradient from ∼6 in the Baltic Sea (Finland) to ∼20 in Kattegat (Denmark) and ∼26 in Skagerrak (Sweden). The net release of CH4 from seagrass sediments and adjacent unvegetated areas was generally low compared to other coastal habitats in the region (such as mussel banks and wetlands) and to other seagrass areas worldwide. The lowest net release was found in Finland. We found a positive relationship between CH4 net release and sedimentary Corg content in both seagrass meadows and unvegetated areas, whereas no clear relationship between seagrass cover and CH4 net release was observed. Overall, the data suggest that Nordic Zostera marina meadows release average levels of CH4 ranging from 0.3 to 3.0 μg CH4 m–2 h–1, which is at least 12–78 times lower (CO2 equivalents) than their carbon accumulation rates previously estimated from seagrass meadows in the region, thereby not hampering their role as carbon sinks. Thus, the relatively weak CH4 emissions from Nordic Z. marina meadows will not outweigh their importance as carbon sinks under present environmental conditions.

Marine flowering plants can reproduce sexually and clonally, and the relative contribution of these two modes can be dependent on the environmental conditions. Zostera marina, a seagrass widely distributed in the northern hemisphere, can form annual and perennial meadows with different proportions of sexual versus clonal propagation depending on the environmental disturbance regime. We study the hypothesis that the contribution of sexual propagation varies during the recovery of a seagrass meadow. In this case study, we compare the proportion of sexual versus clonal propagation of a perennial Z. marina meadow before its disappearance due to winter storms and after recovery. Before disturbance, genotypic diversity was high, indicating frequent sexual reproduction events likely to create an abundant seed bank. Seedling germination allowed the population to recover after the extreme disturbance. As months passed, seedlings became rare and finally absent, giving place to adult shoots. In an advanced stage of colonization, the shoots colonized the area by vegetative growth, which lowered the genotypic diversity. Despite this reduction over time, the genotypic diversity of the new meadow is still high, demonstrating the importance of sexual reproduction in meadow recovery and persistence.

Chalcone synthase (CHS) family are plant type III polyketide synthases that participate in the flavonoid synthesis pathway to induce plant resistance to various biotic and abiotic stresses. Zostera marina, a common seagrass, migrated to terrestrial conditions and returned to the sea, achieving the most severe habitat shift of flowering plants. Given the special evolutionary process, we conducted genome-wide, expression and enzyme activity analyses of the ZosmaCHS family to understand its phylogenetic implications. Various duplication modes led to the expansion of 11 CHS homologs in Z. marina. Based on the phylogenetic relationships, ZosmaCHSs were classified into three clades. Further quantitative real time-PCR analyses of the ZosmaCHS homologs showed different light responses and tissue-specific expression, indicating functional diversification of the ZosmaCHSs. Moreover, the ZosmaCHS proteins clustering with the validated chalcone synthases were recombined into prokaryotic expression systems. All the recombinant proteins showed CHS activity to generate naringenin chalcone with varying catalytic efficiencies. ZosmaCHS07 was regarded as the dominant CHS because of its significant light response and the higher catalytic efficiency. Taken together, the disparity of the expression and enzyme activity indicated that sub-functionalization is the primary mechanism of the expansion of the ZosmaCHSs family.

Seagrass meadows provide valuable ecosystem benefits but are at risk from disease. Eelgrass (Zostera marina) is a temperate species threatened by seagrass wasting disease (SWD), caused by the protist Labyrinthula zosterae. The pathogen is sensitive to warming ocean temperatures, prompting a need for greater understanding of the impacts on host health under climate change. Previous work demonstrates pathogen cultures grow faster under warmer laboratory conditions and documents positive correlations between warmer ocean temperatures and disease levels in nature. However, the consequences of disease outbreaks on eelgrass growth remain poorly understood. Here, we examined the effect of disease on eelgrass productivity in the field. We coupled in situ shoot marking with high-resolution imagery of eelgrass blades and used an artificial intelligence application to determine disease prevalence and severity from digital images. Comparisons of eelgrass growth and disease metrics showed that SWD impaired eelgrass growth and accumulation of non-structural carbon in the field. Blades with more severe disease had reduced growth rates, indicating that disease severity can limit plant growth. Disease severity and rhizome sugar content were also inversely related, suggesting that disease reduced belowground carbon accumulation. Finally, repeated measurements of diseased blades indicated that lesions can grow faster than healthy tissue in situ. This is the first study to demonstrate the negative impact of wasting disease on eelgrass health in a natural meadow. These results emphasize the importance of considering disease alongside other stressors to better predict the health and functioning of seagrass meadows in the Anthropocene.

Seagrass wracks, the remains of dead leaves accumulated on seashores, are important ecosystems and beneficial for the marine environment. Their presence on the touristic beaches, however, is a problem for the tourism industry due to the lack of aesthetics and safety reasons. At the present time, seagrass leaves are landfilled, although this is not considered an ecological waste management practice. Among other proposed practices for more sustainable and environmentally friendly management, such as composting and biogas or energy generation, in this study we aim to use seagrass leaves for the production of insulation materials. Insulation boards from two types of seagrass leaves (Posidonia oceanica and Zostera marina) at densities varying from 80 to 200 kg m−3 were prepared and their physical and mechanical properties were examined and compared to those of wood fiber insulation boards. The thermal conductivity of seagrass-based insulation boards varied from 0.042 to 0.050 W m−1 K−1, which was up to 12% lower compared to the latter. The cone calorimetry analysis revealed that seagrass-based insulation boards are more fire resistant than those from wood fibers, as they release very low amounts of heat during combustion and do not ignite when exposed to a single flame (Bunsen burner). A simplified cost analysis showed that insulation boards made from seagrass leaves can be up to 30% cheaper compared to those made from wood fibers. After their end of life, seagrass leaves can again be considered a valuable resource and be further utilized by adopting other management strategies.

Coastal biogenic habitats are vulnerable to human impacts from both terrestrial and marine realms. Yet the broad spatial scale used in current approaches of quantifying anthropogenic stressors is not relevant to the finer scales affecting most coastal habitats. We developed a standardized human impact metric that includes five bay-scale and four local-scale (0–1 km) terrestrial and marine-based impacts to quantify the magnitude of anthropogenic impacts to coastal bays and nearshore biogenic habitats. We applied this metric to 180 seagrass beds (Zostera marina), an important biogenic habitat prioritized for marine protection, in 52 bays across Atlantic Canada. The results show that seagrass beds and coastal bays exist across a wide human impact gradient and provide insight into which are the most and least affected by human threats. Generally, land alteration, nutrient loading, and shellfish aquaculture were higher in the Gulf of St. Lawrence, whereas invasive species and fishing activities were higher along the Atlantic coast. Sixty-four percent of bays were at risk of seagrass decline from nitrogen loading. We also found high within-bay variation in impact intensity, emphasizing the necessity of quantifying impacts at multiple spatial scales. We discuss implications for management and conservation planning, and application to other coastal habitats in Canada and beyond.

Three types of Zostera marina L. collection were extracted using the supercritical CO2-extraction method. For the purposes of supercritical CO2-extraction, old seagrass ejection on the surf edge, fresh seagrass ejection on the surf edge and seagrass collected in water were used. Several experimental conditions were investigated in the pressure range 50–350 bar, with the used volume of co-solvent ethanol in the amount of 1% in the liquid phase at a temperature in the range of 31–70 °C. The most effective extraction conditions are: pressure 250 Bar and temperature 60 °C for Z. marina collected in sea water. Z. marina contain various phenolic compounds and sulfated polyphenols with valuable biological activity. Tandem mass-spectrometry (HPLC-ESI–ion trap) was applied to detect target analytes. 77 different biologically active components have been identified in Z. marina supercritical CO2-extracts. 38 polyphenols were identified for the first time in Z. marina.

Vegetated coastal ecosystems have an important role as contaminant filters. Temporal variations in concentrations, enrichment factors (EF), and fluxes of trace elements (As, Cd, Co, Cr, Cu, Ni, Pb, V, and Zn) were evaluated in 210Pb-dated sediment cores from salt marsh and seagrass ecosystems at San Quintín Bay (Mexican northern Pacific). Trace element contamination was negligible in seagrass sediments, but minor to severe, depending on the element, in salt marsh cores, owing to higher organic carbon and fine sediment contents. EF temporal variation in salt marsh cores was attributed to agriculture technology changes (e.g. installation of greenhouses, and improved irrigation and fertilization systems). Trace element flux ratios increased during the past 100 years, likely caused by steadily increasing sediment accumulation rates promoted by land-use changes in the catchment. The conservation of salt marsh areas is important to preserve their function as contaminants biofilters and the health of adjacent ecosystems.

The phenotypic plasticity of seagrasses enables them to adapt to changes in environmental conditions and withstand or recover from disturbance. This plasticity was demonstrated in the large variation recorded throughout a suite of bioindicators measured within Zostera marina meadows around Wales and SW England, United Kingdom. Short-term spatial data were analysed alongside long-term monitoring data to determine which bioindicators best described the status of eelgrass meadows subjected to a range of environmental and anthropogenic drivers. Shoot density, leaf length, leaf nutrients (C:N ratio, %N, %P) including stable isotope of δ13C and δ15N provided insight into the longer-term status of the meadows studied and a good indication of the causes of long-term decline. Meadows ranged from those in the Isles of Scilly with little evidence of impact to those in Littlewick in Milford Haven, Wales that showed the highest levels of impacts of all sites. Bioindicators at Littlewick showed clear warning signs of nutrient loading reflected in the long-term decline in shoot density, and prevalence of wasting disease. This study highlights the need for continuous consistent monitoring and the benefits of using extra tools in the form of shoot nutrient analysis to determine causes of decline.

Worldwide, seagrass meadows accumulate significant stocks of organic carbon (C), known as “blue” carbon, which can remain buried for decades to centuries. However, when seagrass meadows are disturbed, these C stocks may be remineralized, leading to significant CO2 emissions. Increasing ocean temperatures, and increasing frequency and severity of heat waves, threaten seagrass meadows and their sediment blue C. To date, no study has directly measured the impact of seagrass declines from high temperatures on sediment C stocks. Here, we use a long-term record of sediment C stocks from a 7-km2, restored eelgrass (Zostera marina) meadow to show that seagrass dieback following a single marine heat wave (MHW) led to significant losses of sediment C. Patterns of sediment C loss and re-accumulation lagged patterns of seagrass recovery. Sediment C losses were concentrated within the central area of the meadow, where sites experienced extreme shoot density declines of 90% during the MHW and net losses of 20% of sediment C over the following 3 years. However, this effect was not uniform; outer meadow sites showed little evidence of shoot declines during the MHW and had net increases of 60% of sediment C over the following 3 years. Overall, sites with higher seagrass recovery maintained 1.7x as much C compared to sites with lower recovery. Our study demonstrates that while seagrass blue C is vulnerable to MHWs, localization of seagrass loss can prevent meadow-wide C losses. Long-term (decadal and beyond) stability of seagrass blue C depends on seagrass resilience to short-term disturbance events.

Seagrass meadows are recognized as critical and among the most vulnerable habitats on the planet. There is an urgent need to develop techniques to restore and preserve these vital coastal ecosystems. So far little work has been done to develop effective long-term storage methods for desiccation sensitive seagrass seeds. In the present study, we developed a long-term seed storage method for desiccation sensitive seagrass seeds using Zostera marina L. as model species. During the storage, Z. marina seeds from the 0 °C treatments had lower seed loss percentages and high seed vigor, compared to the 4 °C treatments. Salinity significantly influenced seed vigor after storage. Seeds stored at a salinity of 40–50 psμ had the highest vigor. Wet storage at a salinity of 40–50 psμ and 0 °C was the optimal long-term storage condition, considering factors such as seed loss percentage, seed germination percentage, and seed germination value during or after the long-term storage. By controlling temperature and salinity, we could store Z. marina seeds for ca. 17 months because the collection of the seeds from reproductive shoots and maintain low seed losses and high seed vigor. The findings revealed the optimal conditions for long-term storage of desiccation sensitive Z. marina seeds and provided a useful reference for the establishment of Z. marina seed banks. Our results could also provide information to support Z. marina seagrass meadow restoration efforts using seeds.

Climate change is characterized not only by an increase in mean temperature, but also an increase in the variability around the means causing extreme events like marine heatwaves. These events are expected to have strong influence on the ecology of marine foundation species such as the eelgrass Zostera marina. Bacterial and macroscopic foulers are ubiquitous in the marine environment; they can have detrimental impacts on macrophytes and warming is known to enhance bacterial fouling. Thus, to investigate the consequence of heatwaves on the chemical defense of eelgrass against microbial colonizers, we incubated Z. marina plants in the Kiel Outdoor Benthocosm system under ambient control conditions and two different heatwave treatments: a treatment experiencing two spring heatwaves followed by a summer heatwave, and a treatment only experiencing just the summer heatwave. The capacity to deter microbial colonizers was found to be significantly up-regulated in Z. marina from both heatwave treatments in comparison to Z. marina under control conditions, suggesting defense regulation of Z. marina in response to marine heatwaves. We conclude climate extremes such as heatwaves can trigger a regulation in the defense capacity, which could be necessary for resilience against climate change scenarios. Such dynamics in rapid regulation of defense capacity as found in this study could also apply to other host plant – microbe interactions under scenarios of ongoing climate change or extreme climate events like heatwaves.