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ABSTRACT Aim Location Methods Results Main Conclusions Seed dispersal plays a key role in shaping the distribution and genetic complexity of seagrass populations and affects their resilience capacity under disturbance. The endemic seagrass Posidonia oceanica is a key component of Mediterranean coastal ecosystems, but knowledge about movement ecology in this species is limited, especially regarding seed movement pathways and dispersal potential.Western coast of Sicily (central Mediterranean).Beach‐cast fruits of the Mediterranean seagrass P. oceanica were collected from nine localities along the Western coast of Sicily, along with adult shoots from eight putative donor meadows. We determined pair‐wise genetic differentiation between established meadows and seed cohorts. Genetic assignment tests were used to infer the most likely meadow of origin of individual seeds and were complemented with forward and backward Lagrangian simulations of dispersal.A significant genetic differentiation was found between seed pools and the most‐likely meadow of origin. The genetic assignment confirmed that seeds from the same cohort originated from multiple meadows and emphasised the presence of long‐distance‐dispersal (LDD) events (up to hundreds of km). Genetic connectivity appeared to be greater than that predicted by oceanographic simulations, which may reflect the longer temporal scales on which gene flow is shaped, in contrast to contemporary dispersal patterns. Lagrangian simulations highlighted that fruits were physically capable of dispersing beyond the study area and that the north Tunisian coast could be a key source of propagules for the populations studied.Our study represents a significant step forward in the understanding of P. oceanica movement ecology and could guide meadows' conservation and restoration actions. Our findings are significant in a broader context outside of the research area and could be the basis of similar studies in other regions, especially considering the increasing number of fruiting events recorded across the Mediterranean likely associated with ocean warming. [ABSTRACT FROM AUTHOR]

Plant traits which vary both within and between species often drive biogeochemical cycling. Understanding the relative role of within‐ and between‐species trait variability in driving carbon cycling is essential to scaling site measurements to global carbon budgets. In seagrass meadows, carbon and nitrogen mineralization rates and associated greenhouse gas emissions are highly variable, impeding our ability to reliably predict whether meadows are net carbon sinks. Evaluating the influence of within‐ and between‐species trait variability on greenhouse gas fluxes will improve our understanding of local‐scale drivers of greenhouse gas production and consumption in seagrass meadows.To test the effects of plant traits on dissolved greenhouse gas fluxes, we performed mesocosm incubations with live, intact seagrass plants. We compared methane (CH4) and nitrous oxide (N2O) fluxes under dark and light conditions from sediments dominated by Halodule wrightii and Thalassia testudinum across dormant, early and peak growing seasons in a subtropical meadow along the west coast of peninsular Florida. We also measured oxygen (O2) fluxes to interpret greenhouse gas fluxes within the context of community metabolism. We measured several seagrass traits, such as above‐ and below‐ground biomass and leaf and root area and assessed their impact as well as the impact of species identity on dissolved gas fluxes.We found that abiotic factors linked to metabolism (i.e. light and temperature) influenced greenhouse gas fluxes across seasons. In addition to light conditions and sampling month, plant size (a composite trait variable) was a significant predictor of O2 consumption and CH4 production under dark conditions, and better predicted fluxes than individual plant traits. CH4 production was slightly higher in H. wrightii‐dominated sediments, but species identity was less important than plant size in driving CH4 production. N2O fluxes were low and not influenced by plant traits or species identity.Synthesis: Our results indicate that within‐species more so than between‐species trait variability drives the direction and magnitude of CH4 fluxes in seagrass meadows. We identified a trade‐off where seagrass biomass is often associated with enhanced sediment carbon storage, but in our study, plant size promoted CH4 production, potentially offsetting the benefits of long‐term storage. [ABSTRACT FROM AUTHOR]

Seagrass meadows, including those formed by Zostera noltei, play a crucial role in marine ecosystem health by providing habitat stability and coastal protection. In the Romanian Black Sea, Z. noltei meadows are critically endangered due to pressures from eutrophication, habitat loss, and climate change. This study presents a comprehensive baseline assessment of Z. noltei meadows near Mangalia, Romania, utilizing in situ field methods and UAV mapping conducted in the spring and summer of 2023. Seven meadow sites (Z1–Z7) were identified, with notable variability in density, shoot counts, and coverage across sites. Site Z1 exhibited the highest density (1223 shoots/m−2) and Z5 and Z7 the longest leaves (an average of 60 cm), reflecting possible environmental influences. Statistical analyses revealed significant inter-site differences in shoot density and leaf length, with density emerging as a primary differentiator. Ex situ analyses of epiphyte load indicated a median, balanced epiphyte load. This baseline dataset supported the selection of Z1 as a reference donor site for seagrass relocation activities along the Romanian coast in 2023. By providing critical insights into Z. noltei structure and health, this study supports future conservation efforts and evidence-based management of these vulnerable coastal habitats. [ABSTRACT FROM AUTHOR]

Marine Heat Waves (MHWs) occurrence has been increasing in the Mediterranean Sea. The effects of field simulated MHWs of different intensity (medium and high temperature) on the transcriptome expression of the endemic seagrass Posidonia oceanica were evaluated considering different origins of the plant. The aim of the study was reached through a common garden transplant experiment in the North-west of Sardinia (Italy), where two P. oceanica meadows characterized by different thermal regimes (cold and warm) were chosen. MHWs were simulated in front of a power plant, that creates a natural laboratory by releasing warm water in the sea. Differential gene expression and GO enrichment analyses highlighted differences in the transcriptomic profiles of plants from cold and warm environments suggesting that the MHWs induced different levels of stress due to different tolerance to the heat event. Plants from both origins activated processes to achieve protein homeostasis, but only cold plants activated an antioxidant defense and altered sugar metabolism, both indicators of heat stress. Within plants of the same origin, a different response to MHW intensity was also detected: while warm plants showed the most complex response at high temperature rather than at medium temperature, cold plants seemed to better cope with the medium temperature intensity rather than with high temperature. [ABSTRACT FROM AUTHOR]

Posidonia Oceanica (PO) is an endemic marine plant in the Mediterranean Sea. In an experimental study conducted in the Eastern Mediterranean, the effects of natural PO leaves on reducing the height of incident waves impacting a beach were measured. The transmission coefficient (Kt) was found to vary between 0.73 and 0.94, which is equivalent to a wave height decay of 6–27%. The results show that in their natural environment, free-floating dead PO leaves dissipate incoming wave energy and have the capacity to protect beaches against erosion. Further analysis in separate frequency bands showed that waves with periods between 4.5–6.2 s were more sensitive to PO leaves in terms of energy dissipation. The transmission coefficient for medium-period waves, calculated using the medium-frequency part of the wave spectrum, delivered a maximum transmission coefficient of 0.5, corresponding to a 50% decay in wave height due to PO leaves. [ABSTRACT FROM AUTHOR]

Critical seagrass ecosystems are predicted to be impacted by droughts and floods of increasing severity and frequency as the climate changes. Hyposalinity events alter seagrass composition and challenge resilience, yet understanding of the response mechanisms is incomplete but necessary for predicting outcomes. Hyposalinity stress response mechanisms in Halodule wrightii (shoal grass), a seagrass with wide salinity tolerance, were examined in mesocosm experiments by measuring monovalent and divalent ions, free amino acid (FAA) concentrations, and the Thiobarbituric Acid Reactive Substances (TBARS) indicator of lipid peroxidation. Two progressive, 3-step treatments, to moderate and extreme hyposalinity endpoints S15 and S5 were compared. Concentrations of Na+, K+, Ca2+, and Cl− decreased two to threefold with greater hyposalinity. Proline, the most abundant FAA initially, progressively decreased with increasing hyposalinity as asparagine became dominant. Glutamine and serine increased significantly, and all four FAA exhibited consistent patterns of change. Results are consistent with proline's role as osmolyte and regulator, and suggest that asparagine mobilizes or stores N, possibly due to another limiting nutrient. TBARS changed transiently at intermediate salinities, but were not significantly different at hyposalinity endpoints indicating that H. wrightii may have already reached stress equilibrium. Prolonged hyposalinity events may have consequences for seagrass resilience. [ABSTRACT FROM AUTHOR]

Seagrass meadows are increasingly threatened by anthropogenic activities and climate change, necessitating restoration efforts such as cutting transplantation. Understanding the complex interactions between plant morphology and physiology is crucial for designing robust restoration strategies and assessing the success of transplantation and recovery processes. A pilot transplantation experiment with the Mediterranean seagrass Posidonia oceanica (L.) Delile was conducted in Northwestern Corsica (Calvi, France) to evaluate the feasibility of meadows degraded due to boat anchoring. The effects of the cuttings' origin and transplanting depth were investigated. The establishment success of transplanted fragments was assessed by investigating the photo-physiological parameters, carbohydrate content, and biometric parameters of both transplanted and control plants one year after transplantation at depths of 20 and 28 m. After one year, there was a high survival rate (90%) of the transplants, but their leaf surface area and biomass were significantly reduced compared to the control plants. Photosynthetic activity remained consistent between both depths, emphasizing the ability of P. oceanica cuttings to acclimate to a new light environment in a relatively short period of time (<3 months). Furthermore, light-harvesting pigments, photoprotective pigments, and carbohydrate concentration were greater at the deeper sites. This implies that transplantation at greater depths might be more effective. Furthermore, additional research is necessary to enhance our understanding of the relationship between photosynthesis and the overall health of the plant. This study emphasizes the essential integration of morphological and physiological investigations to offer an ecologically meaningful understanding of how marine ecosystems respond to various restoration methods. [ABSTRACT FROM AUTHOR]

Posidonia oceanica is an endemic seagrass from the mediterranean that provides key ecosystem services. A protected species, its presence is regressing due to anthropogenic pressures, some associated to the tourism economy that much of the Mediterranean coast depends on. In 1992, the European Union declared it a priority habitat, and since the early 2000s, it has occupied a central space in marine conservation debates in the Balearic Islands. Popularly known as Posidonia, this seagrass went from being considered dirt that ruined virgin Balearic beaches to become an emblematic species. This article takes this U-turn in policy and public perception as a study case to think of knowledge-making practices and restoration initiatives as a form of environmental care. The relational, situated and affective character of care ethics helps to understand the human and ecological labour embedded in knowledge-making and restoration practices and its inevitable engagement with the Balearic tourism industry. Drawing on those engagements, I reflect on environmental care practices of knowledge-making and restoration, arguing that they emerge ambivalently: they challenge management logics based on economic rationales while forced to develop and coexist inside those same rationales. I conclude by arguing that developing care-centric narratives for environmental conservation and restoration is essential to continue promoting more-than-human aquatic relations in which the needs of others are the ethical basis for action. [ABSTRACT FROM AUTHOR]

Coastal marine heatwaves have destructive and lasting impacts on foundational species and are increasing in frequency, duration, and magnitude. High atmospheric temperatures are often associated with marine heatwaves (MHW) which are defined as 5 days of water temperatures above a seasonally varying 90th percentile threshold. In this study, we consider the prevalence of MHW propagation into surficial sediments to cause sediment heatwaves (SHW). Within a shallow, subtidal seagrass meadow in Virginia, USA, sediment temperature was measured at hourly intervals at a depth of 5 cm between June 2020 and October 2022 at the meadow edge and central meadow interior. The observed sediment temperature along with a 29-year record of water temperature and water level was used to develop a sediment temperature model for each location. Modeled sediment temperatures were used to identify sediment heatwaves that may thermally stress belowground seagrass. At both meadow locations, sediment heatwave frequency increased at a rate twice that of MHWs in the average global open ocean, coinciding with a 172% increase in the annual number of SHW days, from 11 to 30 days year−1 between 1994 and 2022. Sediment heatwaves at both meadow locations co-occurred with a MHW 79–81% of the time, with nearly all SHWs having a zero day lag. The top 10% most extreme MHWs and SHWs occurred between November and April when thermal stress to seagrass was unlikely. In June 2015, a SHW co-occurred with an anomalously long duration MHW that was associated with a 90% decline in seagrass from this system, suggesting that SHWs may have contributed to the observed seagrass loss. These results document heatwave propagation across the pelagic-sediment interface which likely occur broadly in shallow systems with impacts to critical coastal ecosystem processes and species dynamics. [ABSTRACT FROM AUTHOR]

The Ligurian Sea (NW Mediterranean) has been a focal point for numerous interventions aimed at restoring Posidonia oceanica meadows. The success of pioneer restoration actions in France during the 1970s stimulated similar initiatives across the Mediterranean Sea. Early attempts in the Ligurian Sea were implemented in 1993 and 1996 on limited seabed areas (i.e., tens of square meters) at the two coastal sites of Sori and Rapallo (Liguria, NW Italy). No further initiatives have been reported for the Ligurian Sea until 2022. In that year, a large-scale restoration project, which uses biodegradable mats coupled with metal mesh, began in Liguria. Different levels of anthropogenic pressure and wave exposure characterize the three investigated locations: (1) Portofino, on the eastern Liguria and on the border with the Portofino Marine Protected Area; (2) Bergeggi in the central Liguria and within the Isola di Bergeggi Marine Protected Area; and (3) Sanremo in the western Liguria, without any formal protection. Despite recent setbacks caused by severe storms in late 2023, which particularly damaged the Portofino site, ongoing monitoring revealed promising survival rates. Most notably, the site in Bergeggi displayed a 90% survival rate in September 2023. Although challenges to restore P. oceanica beds persist, such as mitigating damages caused by unpredictable events, this extensive re-implantation initiative offers the opportunity to evaluate the effectiveness of new basin-scale restoration strategies. This approach marks an important step in the conservation of Posidonia oceanica habitat. [ABSTRACT FROM AUTHOR]

An analysis of the interactions between wave-induced velocities and seagrass meadows has been conducted based on the large-scale CIEM wave flume data. Incident irregular wave trains act on an initial 1:15 sand beach profile with measurement stations from the offshore of a surrogate meadow until the outer breaking zone, after crossing the seagrass meadow. The analysis considers variability and peaks of velocities, together with their skewness and asymmetry, to determine the effects of the seagrass meadow on the near bed sediment transport. Velocity variability was characterized by the standard deviation, and the greatest changes were found in the area right behind the meadow. In this zone, the negative peak velocities decreased by up to 20.3%, and the positive peak velocities increased by up to 11.7%. For more onshore positions, the negative and positive peak velocities similarly decreased and increased in most of the studied stations. A progressive increase in skewness as the waves passed through the meadow, together with a slight decrease in asymmetry, was observed and associated with the meadow effect. Moving shoreward along the profile, the values of skewness and asymmetry increased progressively relative to the position of the main sandbar. The megaripple-like bedforms appeared earlier when the meadow was present due to the higher skewness, showing a belated development in the layout without the meadow, when skewness increased further offshore due to the proximity of the breaker sandbar. To assess the sediment transport capacity of a submerged meadow, the SANTOSS formula was applied, showing that in front of the meadow, there was a higher sediment transport capacity, whereas behind the meadow, that capacity could be reduced by up to 41.3%. In addition, this formula was able to produce a suitable estimate of sediment transport across the profile, although it could not properly estimate the sediment volumes associated with the bedforms generated in the profile. [ABSTRACT FROM AUTHOR]

Florida's Big Bend in the northeastern Gulf of Mexico contains the second-largest contiguous seagrass meadow in the continental United States, providing numerous ecosystem functions and services, including carbon cycling and storage. We present 21 years of mapping data and 13 years of annual in-water monitoring that reveal extensive declines in area, species frequency of occurrence (FO), and percent cover of seagrass. Seagrass area declined by 15% to 85,170 ha in 2022. Subregions in the southern Big Bend experienced extensive seagrass losses of 90–100%. North of the Steinhatchee River, the Northern Big Bend contained 85% of the total seagrass area and experienced losses of only 8.4%. The FO of seagrass and bare quadrats exhibited similar trends to areal coverage. The lowest FO along with complete loss of species was observed near the mouth of the Suwannee River. At a distance from the Suwannee River, FO also declined, but no species were lost. In the remainder of the Big Bend, FO remained stable except for short-term reductions in 2013–2014, which were likely related to anomalously high runoff from rainfall and tropical storm activity. Mean percent cover, however, declined throughout Big Bend, reaching minimal levels in 2014, with little to no recovery through 2019. The persistence of low percent cover may increase vulnerability of beds to continuing areal losses, but the persistence of seagrass species at a distance from the Suwannee River mouth may allow recovery if environmental conditions improve. [ABSTRACT FROM AUTHOR]

On 10 October 2018, Hurricane Michael made landfall along the Florida panhandle as a category 5 storm, with maximum sustained winds of 259 km h−1 and storm surge of 4.3 m. To assess impacts on seagrass meadows and nekton communities, we sampled seagrass beds in three estuaries along a gradient of storm intensity: one proximate to the hurricane track (St. George Sound, FL), one that experienced storm surge without hurricane-force winds (Cedar Key, FL), and one outside the storm path (Chandeleur Islands, LA). The nekton community and seagrass characteristics were assessed prior to and shortly after the storm and again 1 year later. In St. George Sound, we observed post-storm changes in seagrass species composition and declines in seagrass cover, shoot count, and canopy height as well as a shift in associated fauna. Seagrass cover declined from 83 ± 9 to 50 ± 8% following the storm. Shoot height and shoot count were also reduced by over 50%. Nekton species most commonly found prior to the storm were Lagodon rhomboides (pinfish), Orthopristis chrysoptera (pigfish), and Bairdiella chrysoura (silver perch). Two weeks following the storm, the most commonly collected species shifted to pinfish, penaeid shrimp, Chilomycterus schoepfi (striped burrfish), and Eucinostomus argenteus (spotfin mojarra). Widespread declines in species-specific nekton abundances were also observed, with continued reductions in some species the following year. Overall, both the seagrass and nekton communities showed signs of recovery. Cedar Key and Chandeleur Islands both exhibited minimal changes in vegetation and nekton. Despite storm intensity and substantial physical damage to upland habitats, the estuarine seagrass communities were resilient to the effects of a powerful category 5 hurricane. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Populations of the green turtle (Chelonia mydas), a megaherbivore that maintains distinct areas of seagrass via cultivation grazing, are recovering worldwide. Evaluating seagrass regrowth dynamics in grazed areas following prolonged, known-durations of herbivory is challenging in situ, but is critical to understand ecosystem function as meadows return to a natural grazed state. Based on a 27-month study in a subtropical Caribbean seagrass meadow (The Bahamas; 23.46° N, 76.06° W), we evaluate Thalassia testudinum regrowth dynamics over 11 months following two durations of simulated green turtle grazing (11 and 16 months; 11clip and 16clip, respectively). By the end of the clipping treatments, simulated grazing had induced significant changes in most T. testudinum leaf morphology and nutrient variables in clipped plots compared to reference plots, while belowground biomass and nutrient content were unaffected. However, most leaf variables in clipped plots returned to levels comparable to reference plots by 6.5 months after the cessation of clipping, with the exception of leaf area index (LAI) and leaf width. The effects of grazing duration on regrowth in clipped treatments were evident in 11clip and 16clip plots. In 11clip plots, LAI increased to reference plot levels within 6.5 months after cessation of clipping, while leaves did not rewiden until 11 months post-clipping. However, LAI in 16clip plots did not reach reference plot levels until 11 months post-clipping, and leaves remained significantly narrow throughout the experiment. These regrowth patterns indicate the capacity of T. testudinum to rebound following prolonged, repetitive cropping of leaf biomass by green turtles, and that decreased leaf width and LAI after cessation of grazing may be a lingering effect of shifts in plant growth allocation in grazed systems. This study provides a valuable contribution to understand the effects of cultivation grazing and grazing duration on T. testudinum regrowth dynamics and tolerance to herbivory. [ABSTRACT FROM AUTHOR]

The goal of this perspective is to review how seagrass research has evolved over the past half century to our current state of knowledge. We review how our knowledge of seagrass ecosystems changed from the pre-1970s when so little was known about seagrasses and how it progressed during the next 5 decades when seagrass knowledge rapidly expanded. Here, we concentrate on accomplishments in the areas of reproductive biology and ecology, population biology, seagrass-animal relationships, conservation and restoration, and mapping and monitoring. We also look ahead and discuss some areas that are ripe for future research, especially those employing new mapping and monitoring technologies, improved restoration methods that include multiple genetic variants, rhizosphere studies that result in a deeper understanding of microbial effects on nitrogen availability, sulfide levels and carbon sequestration, and how changing climatic regimes and tropicalization will likely affect temperate and tropical seagrass-dominated ecosystems. [ABSTRACT FROM AUTHOR]

Due to climate change and human activities, seagrass is in crisis as the coverage of seagrass declines at an accelerated rate globally. In this paper, the severe challenges of seagrass ecosystem were briefly reviewed, including adverse effects of natural factors and human activities on seagrass beds. The research status of pollutants and pollution in seagrass bed ecosystem was reviewed, the future research directions in related fields were proposed as well. The eutrophication in coastal waters and discharge of pollutants such as sulfide, heavy metals, organic matter and microplastics caused by human activities are important reasons for seagrass loss. In addition, environmental stressors lead to reduced immunity and decreased resistance of seagrass to various pathogens, leading to seagrass wasting diseases. Future studies concerning the influence of novel pollutants, i.e., plastic waste on non-native algae, microorganisms and seagrasses, as well as their interrelationships, will be of vital importance. In addition, researches on seagrass wasting diseases and their pathogens should be much accounted in China, to fill in gaps in related fields and improve the response ability to emergent seagrass diseases. In conclusion, this review was proposed to arouse the concern about the seagrass bed pollution, and provide possible enlightening information for the protection and restoration of this significant ecosystem. [ABSTRACT FROM AUTHOR]

Seagrasses provide ecosystem services worth USD 2.28 trillion annually. However, their direct threats and our incomplete knowledge hamper our capabilities to protect and manage them. This study aims to evaluate if the NICFI Satellite Data Program basemaps could map Seychelles' extensive seagrass meadows, directly supporting the country's ambitions to protect this ecosystem. The Seychelles archipelago was divided into three geographical regions. Half-yearly basemaps from 2015 to 2020 were combined using an interval mean of the 10th percentile and median before land and deep water masking. Additional features were produced using the Depth Invariant Index, Normalised Differences, and segmentation. With 80% of the reference data, an initial Random Forest followed by a variable importance analysis was performed. Only the top ten contributing features were retained for a second classification, which was validated with the remaining 20%. The best overall accuracies across the three regions ranged between 69.7% and 75.7%. The biggest challenges for the NICFI basemaps are its four-band spectral resolution and uncertainties owing to sampling bias. As part of a nationwide seagrass extent and blue carbon mapping project, the estimates herein will be combined with ancillary satellite data and contribute to a full national estimate in a near-future report. However, the numbers reported showcase the broader potential for using NICFI basemaps for seagrass mapping at scale. [ABSTRACT FROM AUTHOR]

Seagrasses provide crucial ecosystem services in the coastal environment, but are under increasing threat associated with anthropogenic activities. Seagrass meadows effectively trap suspended sediment, a key vector for trace metal transport, by altering local hydrodynamic conditions around their leaves and stems. As a result, seagrass meadows often have different geochemical sediment characteristics compared to adjacent bare sediments and may accumulate higher concentrations of trace metals. The aim of this systematic review was to identify research trends and knowledge gaps in the relationships between metals and seagrasses. The systematic search of the literature identified a total of 191 relevant articles. Although seagrasses have a broad geographic distribution, the highest diversity and endemism exists in the Indo-Pacific region, yet most studies (40%) were conducted in the Mediterranean Sea. There were also taxonomic gaps with some common species groups, including Amphibolis and Thalassodendron spp., being poorly studied. The reviewed studies examined the relationship between seagrass and 39 metal elements. There were no studies examining rare-earth elements (REEs) or platinum-group elements (PGEs), both of which are critical classes of metals in emerging technologies. Furthermore, the review determined that all 191 studies focused on the impact of metals on seagrasses, while only six also considered the effect of seagrasses on metal geochemistry in sediments. We conclude that further research is necessary to address these key gaps in knowledge to better understand the role(s) of seagrasses in the distribution, immobilization, and release of trace metals in coastal ecosystems. [ABSTRACT FROM AUTHOR]

Seagrass Zostera muelleri has been reported to reproduce mainly asexually in New Zealand. However, a recent study in Tauranga Harbour suggested that flowering might occur more often than previously thought. Here we provide evidence of intertidal seagrass flowering events in six New Zealand estuaries in which it has not before been documented. Further research on seagrass sexual reproduction is desirable as we hypothesise that either flowering events have formerly been missed due to the cryptic nature of the flowers, or that sexual reproduction is emerging as a response to increasing pressures on seagrass ecosystems. In addition, with evidence of seagrass decline occurring globally, and likely also in New Zealand, we recommend collection of seagrass seeds to preserve genetic variability and to attempt restoration efforts through assisted sexual reproduction techniques that have not yet been used in New Zealand. [ABSTRACT FROM AUTHOR]

Macrophytes and seagrasses play a crucial role in a variety of functions in marine ecosystems and respond in a synchronized manner to a changing climate and the subsequent ecological status. The monitoring of seagrasses is one of the most important issues in the marine environment. One rapidly emerging monitoring technique is the use of acoustics, which has advantages compared to other remote sensing techniques. The acoustic method alone is ambiguous regarding the identities of backscatterers. Therefore, a computer program package was developed to identify and estimate the leaf biometrics (leaf length and biomass) of one of the most common seagrasses, Posidonia oceanica. Some problems in the acoustic data were resolved in order to obtain estimates related to problems with vegetation as well as fisheries and plankton acoustics. One of the problems was the "lost" bottom that occurred during the data collection and postprocessing due to the presence of acoustic noise, reverberation, interferences and intense scatterers, such as fish shoals. Another problem to be eliminated was the occurrence of near-bottom echoes belonging to submerged vegetation, such as seagrasses, followed by spurious echoes during the survey. The last one was the recognition of the seagrass to estimate the leaf length and biomass, the calibration of the sheaths/vertical rhizomes of the seagrass and the establishment of relationships between the acoustic units and biometrics. As a result, an autonomous package of code written in MATLAB was developed to perform all the processes, named "POSIBIOM", an acronym for POSIdonia BIOMass. This study presents the algorithms, methodology, acoustic–biometric relationship and mapping of biometrics for the first time, and discusses the advantages and disadvantages of the package compared to the software dedicated to the bottom types, habitat and vegetation acoustics. Future studies are recommended to improve the package. [ABSTRACT FROM AUTHOR]

Simple Summary: The French Polynesian islands represent a unique insular system in the Pacific Ocean. Previous surveys of the marine flora of French Polynesia were mostly established on traditional morphology-based taxonomy. DNA barcoding allowed us to provide a major revision of French Polynesian marine flora, with an updated total of 702 species from French Polynesia, including 119 species of Chlorophyta, 169 Cyanobacteria, 92 Ochrophyta, 320 Rhodophyta, and 2 species of seagrasses (Alismatales)—nearly a two-fold increase from previous estimates. In addition to improving and refining our knowledge of French Polynesian marine flora, this study also provides a valuable DNA barcode reference library for identification purposes and future taxonomic and conservation studies. A significant part of the diversity uncovered corresponds to unidentified lineages, which will need careful taxonomic examination. Located in the heart of the South Pacific Ocean, the French Polynesian islands represent a remarkable setting for biological colonization and diversification, because of their isolation. Our knowledge of this region's biodiversity is nevertheless still incomplete for many groups of organisms. In the late 1990s and 2000s, a series of publications provided the first checklists of French Polynesian marine algae, including the Chlorophyta, Rhodophyta, Ochrophyta, and Cyanobacteria, established mostly on traditional morphology-based taxonomy. We initiated a project to systematically DNA barcode the marine flora of French Polynesia. Based on a large collection of ~2452 specimens, made between 2014 and 2023, across the five French Polynesian archipelagos, we re-assessed the marine floral species diversity (Alismatales, Cyanobacteria, Rhodophyta, Ochrophyta, Chlorophyta) using DNA barcoding in concert with morphology-based classification. We provide here a major revision of French Polynesian marine flora, with an updated listing of 702 species including 119 Chlorophyta, 169 Cyanobacteria, 92 Ochrophyta, 320 Rhodophyta, and 2 seagrass species—nearly a two-fold increase from previous estimates. This study significantly improves our knowledge of French Polynesian marine diversity and provides a valuable DNA barcode reference library for identification purposes and future taxonomic and conservation studies. A significant part of the diversity uncovered from French Polynesia corresponds to unidentified lineages, which will require careful future taxonomic investigation. [ABSTRACT FROM AUTHOR]

Comprehensive information on seagrass biodiversity indicators, such as species composition, percentage cover, and biomass carbon stock, remains limited across various regions globally. Mapping these indicators using remote sensing images requires extracting maximum information from the input images to achieve effective results. This study aims to map seagrass distribution, percent cover (PC), and aboveground carbon stock (AGC) as biodiversity indicators in the optically shallow waters surrounding Pari Island. We integrate WorldView-2 (WV2) derivatives, field seagrass data, and RF classification and regression algorithms to accomplish this objective. The WV2 image derivatives encompass surface reflectance bands, band ratios, mean and variance co-occurrence texture bands, and principle component bands. These inputs are used individually and collectively for mapping, employing a random forest algorithm trained with field seagrass data. Our results demonstrate that the most accurate benthic habitat map achieves an overall accuracy (OA) of 65.2%, with a user's accuracy of 65.2% and a producer's accuracy of 72.8% for the seagrass-dominated class. Seagrass PC mapping yields a root mean square error (RMSE) of 17.1%, with an average PC of 47.4 ± 9.9%. Seagrass AGC mapping achieves an RMSE of 5.0 g C m-2, with an average AGC range of 6.2 -- 29.1 g C m-2, estimating the study area's aboveground biomass carbon stock at 27.9 tons C. Combined inputs produce the most accurate results for all biodiversity indicators, emphasizing the importance of utilizing combined bands from SR band derivatives to maximize information input for training mapping algorithms, instead of using derivative bands individually or as replacements for the initial SR bands. [ABSTRACT FROM AUTHOR]

The present work was performed to evaluate the levels of phytochemical constituents and the antioxidant and antibacterial properties of marine red seaweed (Kappaphycus alvarezii) and seagrass (Cymodocea serrulata). Quantitative phytochemical analysis, antioxidant activity and antimicrobial activity against five potential pathogenic bacteria was investigated. In each case, we found the presence of flavonoids, tannins, phenolic compounds, glycosides, steroids, carbohydrates and ashes. Alkaloids were only found in K. alvarezii, though they were not found in C. serrulata. The antimicrobial properties of both K. alvarezii and C. serrulata chloroform extracts were found to be antagonistically effective against the Gram-positive bacteria Bacillus subtilis and the Gram-negative bacteria Vibrio parahaemolyticus, Vibrio alginolyticus, Vibrio harveyi and Klebsiella pneumoniae. GC-MS analysis revealed the presence of 94 bioactive compounds in K. alvarezii and 104 bioactive compounds in C. serrulata, including phenol, decane, dodecane, hexadecane, vanillin, heptadecane, diphenylamine, benzophenone, octadecanoic acid, dotriaconate, benzene, phytol, butanoic acid and 2-hydroxyl-ethyl ether, which all played important roles in antioxidant and antibacterial activities. Thus, in view of the results, both K. alvarezii and C. serrulata could be considered to be sources of ingredients with appreciable nutritional and medicinal value. [ABSTRACT FROM AUTHOR]

Seagrasses are marine flowering plants, which form extensive meadows in intertidal and shallow water marine environments. They provide a wide range of ecosystem services, which directly or indirectly benefit humans and can be grouped into four broad categories: provisioning (e.g. food production); regulating (e.g. carbon sequestration); supporting (e.g. primary production); and cultural (e.g. recreational, and eco-tourism). This study provides a review of publications focusing on seagrass ecosystem services provision to identify knowledge gaps and improve our understanding of the use of these habitats as nature-based solutions to societal challenges, such as climate change. Results showed that some ecosystem services, namely food provision, carbon sequestration, and maintenance of biodiversity/nursery habitats receive a higher level of focus and attention than others, such as regulation of diseases and social relations, which are rarely, if ever, included in studies. It is clear that in order to fully comprehend the nature-based solution potential held by seagrass ecosystems, studies need to consider ecosystem services as a whole, and also combine and share results across global regions, to better understand the potential impacts of degradation and loss of these ecosystems worldwide. Suggestions include applying novel technologies such as remote sensing and ecological niche modelling to address some of the main gaps in seagrass research, like meadow extent and connectivity within landscapes, to better incorporate preservation of seagrass ecosystems in marine management plans. [ABSTRACT FROM AUTHOR]

Coastal wetlands are key in regulating coastal carbon and nitrogen dynamics and contribute significantly to climate change mitigation and anthropogenic nutrient reduction. We investigated organic carbon (OC) and total nitrogen (TN) stocks and burial rates at four adjacent vegetated coastal habitats across the seascape elevation gradient of Cádiz Bay (South Spain), including one species of salt marsh, two of seagrasses, and a macroalgae. OC and TN stocks in the upper 1 m sediment layer were higher at the subtidal seagrass Cymodocea nodosa (72.3 Mg OC ha−1, 8.6 Mg TN ha−1) followed by the upper intertidal salt marsh Sporobolus maritimus (66.5 Mg OC ha−1, 5.9 Mg TN ha−1), the subtidal rhizophytic macroalgae Caulerpa prolifera (62.2 Mg OC ha−1, 7.2 Mg TN ha−1), and the lower intertidal seagrass Zostera noltei (52.8 Mg OC ha−1, 5.2 Mg TN ha−1). The sedimentation rates increased from lower to higher elevation, from the intertidal salt marsh (0.24 g cm−2 y−1) to the subtidal macroalgae (0.12 g cm−2 y−1). The organic carbon burial rate was highest at the intertidal salt marsh (91 ± 31 g OC m−2 y−1), followed by the intertidal seagrass, (44 ± 15 g OC m−2 y−1), the subtidal seagrass (39 ± 6 g OC m−2 y−1), and the subtidal macroalgae (28 ± 4 g OC m−2 y−1). Total nitrogen burial rates were similar among the three lower vegetation types, ranging from 5 ± 2 to 3 ± 1 g TN m−2 y−1, and peaked at S. maritimus salt marsh with 7 ± 1 g TN m−2 y−1. The contribution of allochthonous sources to the sedimentary organic matter decreased with elevation, from 72% in C. prolifera to 33% at S. maritimus. Our results highlight the need of using habitat-specific OC and TN stocks and burial rates to improve our ability to predict OC and TN sequestration capacity of vegetated coastal habitats at the seascape level. We also demonstrated that the stocks and burial rates in C. prolifera habitats were within the range of well-accepted blue carbon ecosystems such as seagrass meadows and salt marshes. [ABSTRACT FROM AUTHOR]

Plant–herbivore interactions are often regulated by a series of direct and indirect buffer mechanisms (compensatory or defensive plant responses, population control, alternative resources) that can determine the relative stability of the system. In plant‐dominated marine environments, these mechanisms are particularly important given how vulnerable these systems are to strong consumer pressure. Here, we evaluate the presence and, where possible, the strength, of five mechanisms that get activated under high herbivory pressure and are capable of dampening their effects in a seagrass meadow ecosystem: 1) seagrass compensatory growth, 2) increase in plant resistance, 3) availability of alternative resources, 4) predatory control and 5) density‐dependent control. We assessed these mechanisms for the interaction between the Mediterranean seagrass Posidonia oceanica and the sea urchin Paracentrotus lividus through a short‐term series of controlled field and laboratory experiments after simulated or natural herbivory events. Of the five mechanisms tested, we found that three mechanisms – availability of alternative resources, increased predation rate and reduction in sea urchin numbers – effectively dampened herbivory and worked as potential buffering mechanisms. In contrast, plant compensatory growth and resistance did not show clear responses. While compensatory growth and plant resistance are direct plant mechanism to tolerate the effects of herbivory, the rest are indirect mechanisms that begin with a modification of a plant trait (i.e. canopy height) that influences other species preference and/or behaviour, which in turn influences plant consumption. These adaptive behaviours may be a crucial and often overlooked factor in the remarkable resilience that Mediterranean seagrass ecosystems show to herbivory. [ABSTRACT FROM AUTHOR]

A study was conducted to evaluate in vitro efficacy of seaweed (Sargassum myriocystum and Sargassum wightii) and seagrass (Cymodocea serrulata and Syringodium isoetifolium) extract against the mycelial growth of Macrophomina phaseolina at different concentrations of 5, 10, 15 and 20% along with control by poison food technique. The result revealed that, the extract of S. wightii (20%) exhibited the highest suppression of mycelial growth (10, 25 and 38 mm) at 24, 48 and 72 h after incubation. Among the antagonists tested against Macrophomina phaseolina, the fungal Trichoderma viride was found to be the most effective in reducing mycelial growth than the bacterial antagonist Pseudomonas fluorescens. Both the antagonistic fungi and bacteria have compatibility with seaweed and seagrass extracts in the concentrations. [ABSTRACT FROM AUTHOR]

The aim of this study was to test seagrass-associated fungi that have antibacterial activity against Vibrio alginolyticus and Vibrio parahaemolyticus. Seagrass sampling, fungi isolation, antibacterial screening, and molecular identification were used in this study. The antibacterial screening found that 2 out of 10 isolates were positive for antibacterial activity. This includes a seagrass-associated fungi of Thalassia hemprichii, which has green colonies. This isolate has no exudates and has a green reverse. The other isolate TA.EA.1.3 was a seagrass-associated fungi of Enhalus acoroides, white in color, with exudates and a brown reverse. The isolate extracts weighed 256 mg and 2017.9 mg, respectively. The antibacterial activity of the TA.TH.1.1 fungal isolate extract against V. alginolyticus and Vibrio parahaemolyticus was classified as strong because of the inhibition zone produced, which was 10-20 mm. The antibacterial activity of the TA.EA.1.3 isolate, classified as moderate, produced 5-10 mm of inhibition zone. Molecular identification showed that isolate TA. TH.1.1 was Aspergillus unguis (100% homology) and TA.EA.1.3 was Aspergillus versicolor (100% homology). In conclusion, A. unguis and A. versicolor have antibacterial ability against Vibrio alginolyticus and V. parahaemolyticus as antifouling bacteria. [ABSTRACT FROM AUTHOR]

Seagrass meadows are effective carbon sinks due to high primary production and sequestration in sediments. However, methane (CH4) emissions can partially counteract their carbon sink capacity. Here, we measured diffusive sediment‐water and sea‐air CO2 and CH4 fluxes in a coastal embayment dominated by Posidonia oceanica in the Mediterranean Sea. High‐resolution timeseries observations revealed large spatial and temporal variability in CH4 concentrations (2–36 nM). Lower sea‐air CH4 emissions were observed in an area with dense seagrass meadows compared to patchy seagrass. A 6%−40% decrease of CH4 concentration in the surface water around noon indicates that photosynthesis likely limits CH4 fluxes. Sediments were the major CH4 source as implied from radon (a natural porewater tracer) observations and evidence for methanogenesis in deeper sediments. CH4 sediment‐water fluxes (0.1 ± 0.1–0.4 ± 0.1 μmol m−2 d−1) were higher than average sea‐air CH4 emissions (0.12 ± 0.10 μmol m−2 d−1), suggesting that dilution and CH4 oxidation in the water column could reduce net CH4 fluxes into the atmosphere. Overall, relatively low sea‐air CH4 fluxes likely represent the net emissions from subtidal seagrass habitat not influenced by allochthonous CH4 sources. The local CH4 emissions in P. oceanica can offset less than 1% of the carbon burial in sediments (142 ± 69 g CO2eq m−2 yr−1). Combining our results with earlier observations in other seagrass meadows worldwide reveals that global CH4 emissions only offset a small fraction (<2%) of carbon sequestration in sediments from seagrass meadows. Plain Language Summary: Seagrass meadows are hotspots for marine carbon storage in sediments. Part of the sediment carbon can be released as carbon dioxide and methane (CH4). Methane has 45–96 times more powerful global warming effect than carbon dioxide. If seagrass meadows release CH4, the emissions counteract their climate mitigation potential. We measured greenhouse gas concentrations and fluxes in a seagrass‐dominated Mediterranean embayment. Low CH4 coincided with oxygen produced from seagrass photosynthesis. Areas with dense seagrass meadows had lower CH4 emissions. Overall, seagrass‐dominated coasts were a small source of CH4 that offset only <2% of carbon buried in sediments on local and global scales. Hence, seagrass meadows remain an effective carbon sink. Key Points: High‐resolution CH4 observations reveal diel cycles linked to seagrass photosynthesisDense seagrass meadow had lower sea‐air CH4 flux than the area with patchy and dead seagrassCH4 emissions were a small offset to seagrass C sequestration on local and global scales [ABSTRACT FROM AUTHOR]

Simple Summary: The present review provides (1) an updated checklist of the Vietnamese marine flora, (2) a review of molecular-assisted alpha taxonomic efforts, (3) an analysis of marine floral biodiversity spatial distribution nationally and regionally (South China Sea), (4) a discussion on the impact of anthropogenic and environmental stressors on the Vietnamese marine flora, and (5) the efforts developed in the last decade for its conservation. The updated checklist consists of 878 species, including 439 Rhodophyta, 156 Ochrophyta, 196 Chlorophyta, 87 Cyanobacteria, and 15 seagrasses. The South Central Coast supports the highest species diversity of marine algae, which coincides with the largest density of coral reefs along the Vietnam coast. Vietnam holds one of the richest marine floras in the South China Sea owing to the country's coastline length and associated marine habitat diversity. However, the Vietnamese marine floral biodiversity is facing critical threats, and present management efforts are yet insufficient for their conservation. A methodical molecular-assisted re-examination of Vietnam marine floral biodiversity is urgently needed, complemented with in-depth investigations of the main threats targeted against it; and finally, conservation measures should be urgently implemented. Part of the Indo-Chinese peninsula and located on the northwest edge of the Coral Triangle in the South China Sea, the Vietnamese coastal zone is home to a wealthy marine biodiversity associated with the regional geological setting and history, which supports a large number of marine ecosystems along a subtropical to tropical gradient. The diversity of coastal benthic marine primary producers is also a key biological factor supporting marine biological diversity. The present review provides: (1) an updated checklist of the Vietnamese marine flora, (2) a review of molecular-assisted alpha taxonomic efforts, (3) an analysis of marine floral biodiversity spatial distribution nationally and regionally (South China Sea), (4) a review of the impact of anthropogenic and environmental stressors on the Vietnamese marine flora, and (5) the efforts developed in the last decade for its conservation. Based on the studies conducted since 2013 and the nomenclatural changes that occurred during this period, an updated checklist of benthic marine algae and seagrasses consisted in a new total of 878 species, including 439 Rhodophyta, 156 Ochrophyta, 196 Chlorophyta, 87 Cyanobacteria, and 15 phanerogam seagrasses. This update contains 54 new records and 5 new species of macroalgae. The fairly poor number of new records and new species identified in the last 10 years in a "mega-diverse" country can be largely attributed to the limited efforts in exploring algal biodiversity and the limited use of genetic tools, with only 25.4% (15 species) of these new records and species made based on molecular-assisted alpha taxonomy. The South Central Coast supports the highest species diversity of marine algae, which coincides with the largest density of coral reefs along the Vietnamese coast. Vietnam holds in the South China Sea one of the richest marine floras, imputable to the country's geographical, geological, and climatic settings. However, Vietnam marine floral biodiversity is under critical threats examined here, and current efforts are insufficient for its conservation. A methodical molecular-assisted re-examination of Vietnam marine floral biodiversity is urgently needed, complemented with in-depth investigations of the main threats targeting marine flora and vulnerable taxa, and finally, conservation measures should be urgently implemented. [ABSTRACT FROM AUTHOR]

Halophila stipulacea is an invasive seagrass in the Caribbean Sea that also harbors a phytomyxid endoparasite. Phytomyxean parasites are known to cause disease in agricultural crops and are documented to form galls in some seagrass species. Here we make the first report of phytomyxid infection of Halophila stipulacea in the Bahía de Jobos in Salinas, Puerto Rico. We found phytomyxid infected H. stipulacea at 3 of 5 sites examined, expanding the documented range of the Marinomyxa marina phytomyxid infection by almost 400 km from where it was first documented in 2018. Presence of the endoparasite has not impeded H. stipulacea dispersal and continued expansion of H. stipulacea will likely spread both the host seagrass and the endoparasite. [ABSTRACT FROM AUTHOR]

Clonal reproduction, the formation of nearly identical individuals via mitosis in the absence of genetic recombination, is a very common reproductive mode across plants, fungi and animals. To detect clonal genetic structure, genetic similarity indices based on shared alleles are widely used, such as the Jaccard index, or identity by state. Here we propose a new pairwise genetic similarity index, the SH index, based on segregating genetic marker loci (typically single nucleotide polymorphisms) that are identically heterozygous for pairs of samples (NSH). To test our method, we analyse two old seagrass clones (Posidonia australis, estimated to be around 8500 years old; Zostera marina, >750 years old) along with two young Z. marina clones of known age (17 years old). We show that focusing on shared heterozygosity amplifies the power to distinguish sample pairs belonging to different clones compared to methods focusing on all shared alleles. Our proposed workflow can successfully detect clonemates at a location dominated by a single clone. When the collected samples involve two or more clones, the SH index shows a clear gap between clonemate pairs and interclone sample pairs. Ideally NSH should be on the order of approximately ≥3000, a number easily achievable via restriction‐site associated DNA (RAD) sequencing or whole‐genome resequencing. Another potential application of the SH index is to detect possible parent–descendant pairs under selfing. Our proposed workflow takes advantage of the availability of the larger number of genetic markers in the genomic era, and improves the ability to distinguish clonemates from nonclonemates in multicellular diploid clonal species. [ABSTRACT FROM AUTHOR]

Seagrass ecosystem provides valuable ecosystem services and is significant blue carbon sink. This resource, however, has been degraded across the globe with a loss rate of 7% year−1 to the end of twentieth century. The loss of seagrass meadows might lead to an unexpected emission of CO2 into the atmosphere, aggravating global warming and resulting in potential damages to regional ecology and economies. Accurate mapping of meadows extent in different coverages from remotely sensed data, therefore is in high demand as the first step in the strategy of monitoring, report, verification (MRV) that underpins large scale conservation of global seagrass. Despite the higher accuracy of seagrass mapping in recent years, several challenges still persist, particularly when dealing with degraded, sparse seagrass meadows. In this research, we propose a novel and high accuracy approach for mapping dense and sparse meadows of the small size Zostera muelleri seagrass, using high spatial resolution imagery (PlanetScope) at 3 m spatial resolution, and advanced machine learning (ML) models for a ten-fold cross-validation superpixel-based classification in Tauranga Harbour, New Zealand. We archive high mapping accuracy (overall accuracy = 0.913, Kappa coefficient (κ) = 0.786, Matthews correlation coefficient (MCC) = 0.796 and F1 = 0.908) using the LightGBM model from a set of superpixel image coupled with the Bayesian optimization for hyper-parameter tuning. Our proposed approach is solid and reliable with evidences of improving κ (10%) and MCC (11%) when compared with pixel-based image classification, and is expected to provide novel, effective techniques for quantifying the spatial distribution and area of seagrass ecosystem worldwide. [ABSTRACT FROM AUTHOR]

Meadows of the seagrass Posidonia oceanica inhabit most infralittoral bottoms of the Mediterranean Sea and are considered one of the main climax stages of the infralittoral environment. This seagrass has its western distributional limit along the coast of the Alboran Sea. Taking into account the decline of P. oceanica meadows and the global scenario of ocean warming, it becomes essential to know the structure, temporal dynamics, sexual reproduction and conservation status of this seagrass, across its geographical distribution, including the distribution boundaries where the meadows withstand limiting environmental conditions. In the present work, we studied the structure, phenology and flowering events of four P. oceanica meadows located in the northwestern Alboran Sea (close to the Strait of Gibraltar). Results indicate a decreasing trend of patch size, bathymetric range and number of leaves per shoot towards the Strait (and the Atlantic Ocean), as well as an increasing trend of shoot density and leaf height. Phenological parameters of the northwestern Alboran Sea P. oceanica meadows presented temporal dynamics similar to meadows from other locations within the biogeographical distribution of this seagrass, with similar or even less annual variability in the former. Although most of the studied P. oceanica meadows seem to present a good health status (BiPo index ~0.6) with high shoot densities and some flowering events, some of them showed evidence of regression. [ABSTRACT FROM AUTHOR]

Seagrass restoration requires information on a range of factors including site environmental conditions, appropriate planting techniques, and the identification of sites most likely to support seagrass. To address the question of where to focus restoration efforts, a key first step is to identify trends in the spatio‐temporal distribution of seagrasses to identify areas of persistence, loss, and recent gains. Areas of recent recovery (and adjacent areas), can then be targeted by practitioners for assisted recovery and restoration, whilst areas of persistent loss can be avoided. Here we identified the contemporary distribution, density, and species composition of seagrass ecosystems (using Sentinel 2 imagery and supervised object‐based imagery analysis) and integrated these data with historic extents to identify spatio‐temporal trends in seagrass distribution in Western Port, Victoria, Australia. Contemporary classifications demonstrated acceptable accuracies (Overall Accuracy 0.77–0.85, User Accuracy 0.76–0.97) and predicted a contemporary seagrass extent of 222 km2; with 48 km2 of low‐density recovery predicted to have occurred since 1999. Comparisons with historical seagrass extents indicated some seagrass recovery since large‐scale losses in 1983, although some areas of loss were also present. Recovery included a net gain of approximately 95 km2 in the past 20 years and an eastward range expansion; suggesting environmental conditions have improved and are now conducive for restoration efforts in some areas. Results demonstrate that accurate, low‐cost, remote sensing of seagrass ecosystems is possible and show how understanding spatio‐temporal trends can guide the spatial allocation of resources by prioritizing areas for restoration where recovery is beginning to occur. [ABSTRACT FROM AUTHOR]

Although seagrass ecosystems are valued for the services they provide, anthropogenic impacts have led to global declines in seagrass area. South Florida harbors one of the most extensive and iconic seagrass landscapes in the world, but historic seagrass losses appeared to threaten their integrity. The establishment of the Florida Keys National Marine Sanctuary (FKNMS) in 1995 created a benthic community and water quality monitoring network to aid management efforts. With this study, we report on the status and trajectories of benthic communities in South Florida using 25 years of monitoring data. Overall, most of our permanent monitoring sites maintained stable benthic communities over the period of observation. However, for areas that did experience decline, we identified mechanisms for loss of the climax seagrass Thalassia testudinum in the FKNMS with no or only partial recovery over decadal timescales. We observed a shift towards fast-growing Halodule wrightii meadows at anthropogenically nutrient-enriched nearshore sites along the Florida Keys. In addition, we describe almost complete loss of seagrass meadows at some exposed, back-reef sites offshore from the Florida Keys resulting from physical disturbance by major hurricanes. This study demonstrates the utility of long-term monitoring programs for the identification of benthic community trajectories and their putative drivers on the seascape scale, offering valuable lessons for the design of future seagrass monitoring programs. [ABSTRACT FROM AUTHOR]

This study is the first large-scale genetic population study of the three dominant tropical species of seagrass in the southern Philippines. The aim was to understand the genetic diversity, population structure, and clonality of Enhalus acoroides, Thalassia hemprichii, and Cymodocea rotundata for appropriate ecosystem management and conservation. Population genetics analysis for the 15 sites was performed by using polymorphic microsatellite markers within the regional geographical scale. The results showed that the population genetic parameters across the Mindanao region are low to high. Overall, Clonal richness was highest in E. acoroides, followed by T. hemprichii and C. rotundata, indicating sexual reproduction is prevalent. The largest genet found in the study was at Rizal, Northern Mindanao, wherein throughout the sampling area only one genet was identified. The mean FIS (coefficient of local inbreeding) values were positive (heterozygous deficit) with some sites deviating from Hardy-Weinberg equilibrium. Significant pairwise population genetic differentiation was found among many sites. Isolation by distance (IBD) was detected in T. hemprichii and C. rotundata (P < 0.05) but not in E. acoroides (P = 0.253). IBD is present among populations, maybe influenced by the ocean current system in the southern Philippines, but it has to be confirmed yet in the future study. If the goal is to maintain the genetic connectivity of these ecologically important seagrass species, conservation planning and implementation of marine protection should be considered at the regional scale - following the Mindanao Ocean currents. [ABSTRACT FROM AUTHOR]

Leaf decay in seagrasses is enhanced in some seasons since large green senescent beach-cast seagrass leaves are frequently recorded during autumn and winter seasons. Here, we explore if senescence is operating in seagrass leaf decay or if hydrodynamic stress is responsible for the seasonal leaf abscission. A seasonal study on the temperate seagrass Cymodocea nodosa was carried out in four locations with contrasting hydrodynamic regimes. The morphological, biomechanical and material properties of C. nodosa were measured. The force required to break the ligule was always lower than that required to break the blade. This could be considered an adaptive strategy to reduce acute drag forces and thus lessen the chance of plant uprooting. The absolute force needed to dislodge the blade at the ligule level varied with season and location, with the lowest forces recorded in autumn. This may indicate that senescence is operating in this species. On the other hand, the minimum estimated failure velocities for leaf abscission were also recorded in autumn. Consequently, this may cause the premature shedding of leaves in this season before the senescence process has finished and can probably explain the occurrence of green beach-cast seagrass leaves usually found during autumn and winter. [ABSTRACT FROM AUTHOR]

In coastal lagoons, marine benthic macrophyte meadows can be an important element in the resistance to eutrophication of the ecosystem, as they can function as temporary nitrogen sinks, limiting the availability of this nutrient for opportunistic organisms. The role of nitrogen sinks for two dominant macrophyte species of Mediterranean coastal lagoons, the seagrass Cymodocea nodosa and the seaweed Caulerpa prolifera, was analysed by two different approaches: (i) studying nitrate (NO3-) and ammonium (NH4+) uptake kinetics of aboveground tissues in a laboratory and (ii) estimating nitrogen stocks and demands of meadows under natural conditions. The studies were carried out in the coastal lagoon of the Mar Menor, which has been subjected to high anthropogenic nitrogen inputs for decades. While both macrophytes were efficient in exploiting NH4+ from the water column, only C. prolifera showed a high NO3- uptake capacity. Large N pools in the C. nodosa and C. prolifera meadows of the Mar Menor were detected, suggesting that these habitats may have the potential to be essential reservoirs for this nutrient. However, the major role of belowground tissues of the seagrasses in nitrogen accumulation may determine important differences between the two species in temporary N storage and sequestration. The data on N demands for the meadows of both macrophytes in the Mar Menor suggest an important contribution of these habitats in controlling the inputs of this nutrient into the lagoon. We conclude that C. nodosa and C. prolifera meadows can play a key role as a sink for dissolved inorganic nitrogen in temperate coastal lagoons, being an important mechanism of resistance to eutrophication. [ABSTRACT FROM AUTHOR]

The Posidonia oceanica decline due to climate change and other anthropogenic pressures, such as chemical pollution, is well known in the scientific community. However, a comprehensive study of the full content of the organic micropollutants found in this significant seagrass has not yet been carried out. Second, an eco-friendly extraction procedure that does not require a large sample, preserves the seagrass's ecological integrity and functions, and follows green-chemistry principles, is lacking. These information gaps represent the aims of this study. For this purpose, trials with diverse simple and affordable extraction methods to detect one of the most ubiquitous contaminants (polycyclic aromatic hydrocarbons or PAHs) were conducted. As a result, the use and validation of a polytron homogenizer and an ultrasonic bath were proposed for the extraction of priority PAHs from tissues of P. oceanica and marine sediments, respectively. Tissues (leaves and rhizomes) of P. oceanica and sediment samples were collected, extracted, and subjected to a thorough analysis, i.e., target, suspect, and unknown screenings, using gas chromatography coupled to high resolution mass spectrometry (GC-Q-Orbitrap MS). Target analysis revealed seven priority parent-PAHs, whilst during the suspect screening, four PAH-derivatives and three other parent-PAHs were tentatively identified. In the additional third unknown analysis, 11 structures, several with concerning toxicity, were also tentatively identified. Numerous of the identified compounds showed elevated detection frequency in the environmental samples, even reaching 100%, such as the cases of the parent-PAHs (naphthalene, phenanthrene and retene), some PAH-derivatives, one UV stabilizer, and plastic additives along with pesticides. The methods proposed here should be considered for future monitoring of P. oceanica, as well as the three-way analytic approach (target, suspect and unknown), to obtain a more real and accurate idea of the organic micropollutants content in the environment. [ABSTRACT FROM AUTHOR]

The highly efficient carbon storage capacity of beds formed by Posidonia oceanica , an endemic Mediterranean seagrass species, has been widely recognized. Recently, the supra-littoral deposits of leaf litter (i.e., banquettes) have been investigated in terms of their nutrients, biomass and associated community. Nevertheless, an overlooked fraction of the P. oceanica detritus never reaches the shore and sinks far away to deeper seafloor. Additionally, part of the supra-littoral deposit goes back to the sea during winter swells. This deep detrital compartment, mainly composed of sediment mixed with dead leaves and rhizomes coming from P. oceanica beds, has only been described once by Pères in 1953, who focused on the macrofaunal component. Here, we investigated for the first time the meiofaunal community inhabiting sediments characterized by P. oceanica detritus in a deposit located at 65−80 m depth off the Ischia Island (Gulf of Naples, Italy, Tyrrhenian Sea). Our results show that the meiofaunal community appears highly diversified and strongly dominated by nematodes (from 85% to 93%). Differences in meiobenthic assemblage structures were significant only when rare taxa were considered (i.e. taxa found in low abundances and characterized by a sporadic distribution in the study area). The nematode community revealed a very high biodiversity (number of families and genera: 31 and 104, respectively), with a clear prevalence of selective and non-selective deposit feeders that suggest the key role of this habitat in the benthic detrital food web. The richness of meiofauna and the taxonomic and functional diversity of the nematode assemblages account for a "good" to "moderate" ecological quality status. These findings support the high ecological value of the macerating seagrass bottoms, an overlooked component of the blue carbon cycle that deserves to be further investigated. • Re-discovering the overlooked deep macerating Posidonia oceanica bottoms. • First description of the meiofaunal community inhabiting this detrital habitat. • Meiofaunal community is highly diversified and strongly dominated by nematodes. • Dominance of deposit feeders suggests the habitat role in the detrital food web. • Taxonomic/functional diversity supports the high ecological value of this habitat. [ABSTRACT FROM AUTHOR]

Coastal ecosystems are exposed to anthropogenic pressures worldwide. Seagrasses are sensitive to human activities, especially through physical stress. Among them, boats induce many pressures including physical degradation through anchoring. Mapping the anchoring pressure of large boats (≥24 m) can be done with traditional methods but is still challenging for smaller boats. Thus, the impact of large boats on coastal ecosystems is better documented and more efficiently regulated in comparison with small ones. Here, we characterize the pressure and the impact of boats anchoring on Posidonia oceanica seagrass beds through the proxy of three landscape indices and compare anchoring surveillance methods. We show that small boats also have an impact on P. oceanica when anchoring. AIS (Automatic identification System) and low resolution satellite imagery are poorly adapted to detect small boat anchoring. High resolution satellite imagery is a very efficient tool suitable even for small boats detection, but is for now limited to targeted surveys due to its high costs. We propose an automatic detection/localization tool adapted to multisource imagery and test it successfully on a case study in Corsica (France). Overall our study provides key quantified elements for the design of future efficient surveillance and management of anchoring pressure. • Small boats have an impact on Posidonia oceanica when they anchor. • AIS and low resolution satellite imagery are not sufficient to map small boats anchoring. • High resolution optical satellite imagery allows to detect small boats at anchor. • We developed an automatic detection/localization tool adapted to multisource imagery. [ABSTRACT FROM AUTHOR]

The dead seagrass leaves accumulated on the seashores, also known as beach (seagrass) wracks, can be considered a sustainable and ecologically beneficial source for application in the construction sector. An innovative thermal insulation material composed of Zostera marina seagrass leaves was developed using bicomponent fibers as a binding agent. The bicomponent fibers consisted of polypropylene in the core and polyethylene in the sheath. This work aimed to investigate the effect of mat density on mechanical properties (compression and internal bond strength), thermal conductivity and fire properties. The seagrass-based (SG) mats were compared to reference mats consisting of wood fibers (WF). The digital and scanning electron microscopy investigation revealed the differences in the bonding mechanism between the two types of mats. Although slightly higher than WF mats, the thermal conductivity of SG mats still varied from 0.039 to 0.051 W m−1 K−1 and is comparable to those of other natural fiber-based boards with the same density range. The low peak heat release of SG mats (up to 63% lower than wood fiber-based mats) indicates their high resistance to fire. SG mats provide novel possibilities for using new environmentally friendly materials intended for ceiling and partition applications. [ABSTRACT FROM AUTHOR]

In the last two decades, major taxonomic modifications have taken place on marine macroalgae with important changes at the genera level and discovery of cryptic species worldwide. These updates have an important role by serving as a baseline for future ecological interpretations related to on-going climate changes in the marine environment. Hence, this study aimed to elaborate a comprehensive and revised checklist of seaweeds and seagrasses reported in the literature over the years for Syrian Mediterranean Sea shorelines. It was found that the marine flora is quite diverse with a recounted total of 290 species of which 52 are Chlorophyta, 178 Rhodophyta and 60 Ochrophyta (Phaeophyceae). The Syrian shores also host five marine angiosperms (seagrasses), even though Zostera marina Linnaeus has been unaccounted for in recent years. This study will further contribute to a better understanding of seaweed distribution within the Levant basin. [ABSTRACT FROM AUTHOR]

The classic paradigm, not always unequivocal though, that seagrass macrobenthic abundance and diversity are greater than those in adjacent unvegetated areas, was tested in a Mediterranean lagoon for which evidence is lacking. We compared the community structure and species composition of macrobenthic assemblages in three distinct areas of the Mistras Lagoon (Sardinia, Italy) dominated by i) the seagrass Cymodocea nodosa (Cym), ii) mixed-macrophyte/detritus (Mix), and iii) unvegetated sediments (Unv). Samplings were conducted in each area twice in spring (April and May) and twice in autumn (October and November) 2010. Multivariate analyses showed significant differences among the three areas and a marked separation between the two vegetated (Cym and Mix) and the unvegetated (Unv) areas. The top discriminating species, indicated by SIMPER analysis, were characterized by direct development lacking free living larvae. They included marine species, e.g. Cerithium lividulum, Microdeutopus gryllotalpa, Loripes orbiculatus and Gammarus aequicauda, at Cym vs Mix, whereas the pair discrimination of the areas Cym vs Unv and Mix vs Unv mostly depended on the marine Abra tenuis, the opportunistic Chironomidae and Capitella capitata, and the brackish Hydrobia acuta. Both vegetated areas showed a higher species number than the unvegetated area. Differently, abundance was higher in Unv than in Cym and Mix in all sampling dates, most notably in spring likely because of reproductive events, due to both opportunistic (C. capitata, chironomids) and halolimnobic (H. acuta, Cerastoderma glaucum) species. Overall, the present study demonstrated the importance of biological factors in structuring the macrobenthic assemblages of the Mistras Lagoon. Habitatforming phanerogams hosted species-rich assemblages, species-specific reproductive cycles and adaptive strategies contributed to drive species colonization and abundance distribution. Both vegetated and unvegetated patches were found to contribute greatly to the local-scale heterogeneity of the habitat, highlighting the importance of coastal lagoons as hotspots for benthic biodiversity. For these reasons, lagoons must be considered major targets for conservation measures. [ABSTRACT FROM AUTHOR]

Posidonia oceanica is an endemic seagrass species from the Mediterranean Sea that provides critical ecological services to coastal environments. This species is distributed from the Turkish to the Spanish coast, where its westernmost record was documented in Punta Chullera, Malaga (36°18′36.45′′ N, 5°14′54.31′′ W). Nevertheless, previous studies suggested that its distribution was even further west, although these populations were never described. In this study, we documented and characterised the only known P. oceanica population on the coast of Cadiz, in Cala Sardina (36°18′38.80′′ N, 5°15′15.13′′ W). The newly documented population of P. oceanica presented a fragmented structure, consisting of nine patches found in a rocky shallow area surrounded by the invasive algae Rugulopteryx okamurae, with a total size of 61.14 m2. Shoots had a relatively small size (21.0 ± 2.9 cm) in comparison with centrally-distributed populations. The relatively small size of the plants, alongside the observed low shoot density (437 ± 42 shoots m−2) and leaf area index (4.8 ± 0.7 m2 m−2), may indicate that this meadow could be exposed to sub-optimal environmental conditions for plant development. By contrast, the meadow showed relatively high production rates (0.03 ± 0.01 leaf day−1 shoot−1) in comparison with other Mediterranean populations. The percentage of carbon in plant leaves was 38.73 ± 1.38%, while the nitrogen and C/N were 1.38 ± 0.37% and 29.93 ± 6.57, respectively. The documentation of this meadow extends the distribution of this species to the Mediterranean coast of Cadiz, making this region the place with the highest seagrass biodiversity (four species) in the Iberian Peninsula, and potentially in Europe. This exploratory study provides a baseline to examine the potential effects of climate change, anthropogenic disturbances or the presence of invasive species. [ABSTRACT FROM AUTHOR]

The implementation of ecosystem-based adaptation (eba) and blue carbon (bc) favors climate change management; the Greater Caribbean has great potential to develop both measures, however, there is limited contextualization on the support provided by the countries for their implementation. Under this approach, the article analyzes the inclusion of eba and bc measures in regulations and institutions as a mechanism for climate change management in the Greater Caribbean. For this purpose, it conducts a qualitative documentary review (n = 77) in which 25 % of the records address the regulations and institutions that support climate change adaptation and mitigation, 35 % present regulatory impacts in the execution of eba and bc, and 40 % of the texts relate the marine protected areas as propitious policy instruments for the management of both measures. The records show that eba and bc need specific support regulations, the application of eba in mangroves and seagrasses is limited, and the bc is incipient. There are difficulties to access funding and a need to strengthen governance and improve stakeholder participation and institutional capacity. [ABSTRACT FROM AUTHOR]

Temperate lagoonal estuaries contain a mosaic of subtidal habitats including salt marsh creeks, sand, and seagrass. Studies comparing fish use of estuarine habitats have focused disproportionately on sand and seagrass habitats, and along the U.S. east coast, previous studies that have made the direct comparison between subtidal salt marsh creeks, sand, and seagrass habitats were spatially narrow in scope. Here, we performed a comprehensive comparison of fish species composition, abundance, diversity, richness, and fish lengths across subtidal salt marsh creek (upper creek and creek mouth sites), sand, and seagrass habitats within a temperate lagoonal estuary. Daytime otter trawl sampling occurred at 45 sites within Barnegat Bay (New Jersey) in April, June, August, and October during 2012–2014. Seventy species representing estuarine transients, residents, southern strays, and shelf strays were observed, and juvenile and small adult fishes dominated the collections. There were some differences in species composition between habitats, with the assemblages in upper creek and seagrass habitats being the most dissimilar. Fish abundance, diversity, and richness were often higher in creek mouth and seagrass habitats than in sand habitat. Similar to seagrass habitats, creek mouths were shallow, more saline, and contained complex physical structure (macroalgae, marsh banks). Many fishes used all habitats (e.g., bay anchovy Anchoa mitchilli), but others were partial to certain habitats (e.g., fourspine stickleback Apeltes quadracus in seagrass). This study reaffirmed that many interacting factors shape fish assemblages and demonstrated the significance of marsh creeks to the subtidal habitat mosaic of this temperate lagoonal estuary. [ABSTRACT FROM AUTHOR]

Although it is well established that human activities are linked to the loss of seagrasses worldwide, the influence of anthropogenic disturbances on the habitat fragmentation of seagrass meadows is less understood. This information is essential to identify how humans are modifying seascapes and what disturbances pose the greatest risk to seagrasses, which is pertinent given the rapid urbanization occurring in coastal areas.This study examined how the habitat fragmentation of an endangered seagrass Posidonia australis varied in relation to several anthropogenic disturbances (i.e. human population, marine infrastructure, terrestrial run‐off and catchment land‐usage) within 10 estuaries across 620 km of coastline in New South Wales, Australia.When comparing between estuaries, the fragmentation of P. australis meadows was significantly greater in estuaries adjacent to highly populated metropolitan centres – generally in the Greater Sydney region. At sites within estuaries, the density of boat moorings was the most important predictor of habitat fragmentation, but there was also evidence of higher fragmentation with increased numbers of jetties and oyster aquaculture leases.These results suggest that the fragmentation of seagrass meadows will become more pervasive as the human population continues to grow and estuarine development increases. Strategies to mitigate anthropogenic disturbances on seagrass meadow fragmentation could include prohibiting the construction of boat moorings and other artificial structures in areas where seagrasses are present or promoting environmentally friendly designs for marine infrastructure. This knowledge will support ongoing management actions attempting to balance coastal development and the conservation of seagrasses. [ABSTRACT FROM AUTHOR]