Seagrass Research Research Articles

Influence of seasonality and edge effect on seagrass-associated macrobenthic communities: A case study from the Andaman Islands, India

Seagrass seasonality and community interactions within a meadow are local-scale ecological measures that inform management, especially in the wake of climate change. We investigated the collective influence of two ecological processes- seagrass seasonality, and edge effect, on the macrobenthic communities in the Andaman Islands, India. Thalassia hemprichii formed two mono-species intertidal meadows, while Enhalus acoroides dominated the mixed-species meadow. The study was carried out across winter (January), summer (April), and monsoon (August) in 2021 using quadrat sampling (0.5 ×0.5 m), where we surveyed the edges, center, and unvegetated micro-habitats within a meadow. Our findings suggest site-specific seasonality trends for T. hemprichii, as seasonality was governed more by the local environment than species. However, seagrass growth was the lowest in summer for both the investigated meadows. Further, we report a differential influence of seagrass seasonality on macrofaunal densities. Infaunal densities were the highest in low seagrass growth (summer), while epifaunal densities positively correlated with seagrass meadow attributes. For both investigated sites, the highest epifaunal densities were observed in winters [Site 1 = 116.8 ± 27.5 ind./m2; Site 2 = 187.8 ± 14.3 ind./m2). Lastly, we report no influence of edge effect on infauna but a little on epifauna, where for the latter, trends were site, season, and group-specific. Epifaunal holothuroids were the only group with a consistent negative edge across sites and seasons, and densities were concentrated in center > edge > unvegetated regions. In conclusion, we suggest that seagrass seasonality is a product of the local environment rather than the species type. Furthermore, seagrass seasonality substantially influenced macrofauna more than the edge effect. This study is the first attempt from the Indian waters to collectively study community responses towards seagrass seasonality and edge effect, filling a critical ecological gap in seagrass research and management in India.

A Discussion on the Renaming of \(\textit{Cymodocea serrulata}\) to \(\textit{Oceana serrulata}\): Implications for Seagrass Research and Conservation in Vietnam

The seagrass species previously classified as Cymodocea serrulata has been reclassified as Oceana serrulata. This reclassification is based on genetic analysis, which reveals a distinct separation of this species from others within the Cymodocea genus. This change will have implications for future research and taxonomy, highlighting the value of advanced genetic techniques in elucidating the relationships between seagrass species. Nevertheless, further analysis is warranted as new evidence emerges. The transition to the designation Oceana serrulata harmonizes traditional morphological descriptions with modern genetic phylogenetics, enabling a more precise classification. This adjustment will facilitate targeted research on the newly categorized Oceana genus’s biology, ecology, and conservation. We emphasize the importance of disseminating this update to inform the scientific community about these alterations in species classification. Accurate taxonomy serves as the essential foundation for biological research and conservation efforts. Presenting the rationale and process behind taxonomic changes enhances understanding of scientists’ challenges. Furthermore, evaluating name changes encourages scientific discourse and feedback, underscoring the significance of ongoing taxonomic reassessment in advancing seagrass biology and conservation.

Influence of Water Depth on the Morphology Structure of Seagrass from the Southern of Peninsular Malaysia

Globally, seagrass meadows have declined due to environmental factors and human activities, particularly by limiting light to seagrass in turbid coastal waters. Furthermore, publications of seagrass research findings from the Southeast Asia region are scarce, making understanding these habitats difficult despite their ecological and economic importance. This research aimed to provide mean and standard deviation of seagrass morphology, as well as to examine the morphology structures in response to water depth. Samples of two species of seagrass, Halodule uninervis and Halophila ovalis, were collected by using random sampling in a line transect at Pulau Besar and Pulau Tinggi in Johor, southern Malaysia, in September 2013 and April 2014. Six morphological features of each seagrass species were measured physically using CPCe software and the relationship of water depth to seagrass were evaluated using Pearson’s Correlation. The result highlights that the leaf and root morphology is larger in Pulau Tinggi because it is nearer to the Johor mainland, where the introduction of nutrients from economic activity positively influence seagrass growth. The overall morphology structures of both species in both islands are greater in 2013 than 2014. For the relationship with water depth, it had greater positive relationship to H. univervis leaf width (r = 0.7532), internode width (r = 0.6722), leaf length (r = 0.5739); whereas for H. ovalis, water depth was correlated strongly with leaf width (r = 0.6697) and leaf surface area (r = 0.6313). The morphology of seagrass species varies depending on habitat conditions, this study can fill knowledge gaps, but more fundamental research on seagrass meadows is required particularly for the seagrasses in the Southeast Asia marine region.

The Dynamics of Seagrass Ecosystems: History, Past Accomplishments, and Future Prospects

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.

Taxonomic revisions in Zosteraceae (Zostera, Nanozostera, Heterozostera and Phyllospadix)

Advances in research reveal multiple lines of evidence for monophyletic evolution of three genera in the Zosteraceae. Our review synthesizes results from several fields of seagrass research, including taxonomy, biogeography, anatomy, pathology, phylogeny, and physiology to demonstrate distinct and redundant divergences among Zosteraceae genera and across multiple measures. These data provide substantial biological and ecological support for conserving four distinct genera in the family Zosteraceae: Phyllospadix, Zostera, Nanozostera, and Heterozostera. We expect recognizing the four-genera concept to improve the resolution of coastal ecological research, including global seagrass conservation and restoration efforts.

Hydrodynamics across seagrass meadows and its impacts on Indonesian coastal ecosystems: A review

Seagrass canopies are important components of the world’s coastal environments providing critical ecological services. Nearshore hydrodynamics, i.e., waves and currents, are essential in controlling the ecological processes across coastal environments. Seagrass meadows can impose more complex hydrodynamics processes by attenuating sea-swell waves and decreasing the impact of nearshore mean water level rise due to wave setup and Infragravity (IG) waves. Consequently, the seagrasses dissipate waves and reduce flows allowing sediments to settle and accrete the shorelines. However, despite their significant roles, knowledge of hydrodynamics in the Indonesian seagrass ecosystems is relatively limited compared to other coastal ecosystems such as sandy beaches, mangroves, and coral reefs. This review highlights the dynamics of waves and currents, and their interaction with sediment transport and ecological processes, including biogeochemical and dispersal processes on the seagrass ecosystem contributing to the existing seagrass research in Indonesia. The associated literature is collected from scientific databases such as Scopus and Google Scholar that range between 1965 and 2021. The result showed that most of the research on hydrodynamic in seagrass ecosystems was carried out in temperate zones. Until recently, there have been limited publications discussing the interaction between the Indonesian (tropical) seagrass ecosystem and hydrodynamics parameters, even though the region has abundant seagrass species. Moreover, Indonesia is strongly influenced by various atmospheric-oceanic forcing, including the Asian monsoon affecting the dynamic of the coastal area with seagrass ecosystems. At a canopy scale, the correlation between the nearshore (tropical) hydrodynamics and ecological processes in the system is yet to be explored. Considering the potential benefit of seagrasses to coastal ecosystems, developing future research in hydrodynamics across the ecosystem is critical to overcoming the knowledge gaps in Indonesia. The knowledge gained could support the Indonesian seagrass ecosystem services and their resilience to potential hazards and climate change.

Trends in Seagrass Research and Conservation in Malaysian Waters

The seagrass ecosystems found in the marine and coastal areas, with substantial eco-nomic and ecological services and span all over the globe excluding the Antarctic region. The Coral Triangle and Southeast Asia are recognized as a worldwide hotspot of seagrass species and habitats, encompassing 10-21 species of seagrass in every na-tion, although the study, understanding, and quantity of publications on seagrass eco-systems are rather limited in the region, including Malaysia. Malaysia contains 18 seagrass species from three families, which occupy 16.8 km2of coastal area, where the study and discovery of seagrass species and meadows began in 1904 with the re-port of Beccari. All of the published papers reviewed reported on Malaysian seagrass-related research, which was divided into nine topic groups: biology and distribution, carbon sequestration, fauna, remote sensing, impact and pollution genetic study, res-toration, microbiological investigation, and others. The extensive study of the seagrass ecosystem began in 1993, and we have identified 183 published papers from Scopus, 141 publications from Web of Science, and 42 from Google Scholar. However, the average trend of the number of publications from 1993 to 1999 was 0.71 ± 0.36, while from 2000 to 2022 was 7.70 ± 1.16 followed by the average trend of the yearly number of publications was 6.78 ± 1.08. The highest number of publications was found on faunal categories (43.17%), followed by biology and distribution (21.85%). The num-ber of articles that were published on Malaysian seagrass meadows each year has been discovered to be rising, which indicates that the trends in seagrass study and publish-ing were progressively garnering the attention of researchers, academics, and the gov-ernment. However, to better understand the sustainable ecology and ecosystem ser-vices provided by seagrass habitats, an emphasis on certain research niches, such as the genetic study of flora and fauna in seagrass meadows, microbial ecology, and res-toration as well as conservation of seagrass species might be helpful.

Current advances in seagrass research: A review from Viet Nam.

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

Seagrass Factor in Climate Change Mitigation in the Philippines

Despite their importance, seagrasses are facing a global decline due primarily to increased nutrient loading and sedimentation resulting from deforestation and agriculture, and, more recently, from seawater warming in shallow coastal waters. With the advent of new technology and a concerted understanding of seagrass ecosystems as vulnerable social-ecological systems, there has been a dramatic increase in the number of studies focusing on the effects of climate change on seagrasses. Here, I provide an account of the status, role, and future of Philippine seagrasses in an era of climate-driven environmental change. I have gathered information from published studies and actual accounts to identify potential commonalities in the effects of climate change and the responses of seagrasses across the molecular, community, and ecosystem levels. Occupying 13.3% or 4,826 km of the total length of the Philippine coastline, seagrass species composition and diversity remain relatively stable. The seagrass beds of the Philippines and Southeast Asia are declining at an estimated rate of 2.62% or 391 km2 yr–1. Coupled with the apparent neglect in accounts of global carbon, this decline indicates a potential to lose an effective source of blue carbon useful in mitigating the impacts of climate change. In this study, I evaluate the combined effects of climate change with other environmental stressors on the ecosystem services of seagrasses and emphasize the need to apply the lessons learned from three decades of local studies to provide a more inclusive science-based knowledge of seagrass- climate interaction and a deeper understanding of the ecosystem’s resilience. I conclude by presenting the most significant knowledge and management gaps and future directions for seagrass research in the Philippines.

Genetic diversity of seagrass Cymodocea species as an ecological indicator on the Palk Bay Coast, India

Seagrass meadows are rapidly vanishing due to coastal development and climate change. In seagrass research, omics and molecular profiling tools are timely, allowing for new prospects to worldwide concerns. Hence, the present study tested the eight SCoT primers on Cymodocea serrulata and Cymodocea rotundata, which showed 591 polymorphic bands (90.92%), indicating that the individuals are from different populations from the Palk Bay Coast. The Nei-based genetic distance matrix of eight populations of C. serrulata and C. rotundata showed high genetic distance at the intraspecies level in 0.325–0.506. The Nei genetic diversity (h), Shannon information index (I), and allelic number (Ne) of C. serrulata and C. rotundata were low to moderate. C. serrulata had a higher Shannon index (0.54) and genetic diversity (0.36) than the other seven populations, whereas C. rotundata had a higher Shannon index (0.5) and genetic diversity (0.33) in Kattumavadi. The study concludes that the genetic diversity of C. serrulata and C. rotundata shows moderate levels across the study. The Cymodoacea species showed low genetic diversity and heterozygosity due to habitat degradation. These restricted gene flow and fragmented populations are typically exposed to increase their risk of extinction. The population genetics of Cymodoacea species from the Palk Bay region is the first to use SCoT markers to provide insight on seagrass genetics as an ecological indicator for conservation and coastal management.

Mapping and Spatial Variation of Seagrasses in Xincun, Hainan Province, China, Based on Satellite Images

Seagrass is an important structural and functional component of the global marine ecosystem and is of high value for its ecological services. This paper took Xincun Bay (including Xincun Harbor and Li’an Harbor) of Hainan Province as the study area, combined ground truth data, and adopted two methods to map seagrass in 2020 using Chinese GF2 satellite images: maximum-likelihood and object-oriented classification. Sentinel-2 images from 2016 to 2020 were used to extract information on seagrass distribution changes. The following conclusions were obtained. (1) Based on GF2 imagery, both the classical maximum likelihood classification (MLC) method and the object-based image analysis (OBIA) method can effectively extract seagrass information, and OBIA can also portray the overall condition of seagrass patches. (2) The total seagrass area in the study area in 2020 was about 395 hectares, most of which was distributed in Xincun Harbor. The southern coast of Xincun Harbor is an important area where seagrass is concentrated over about 228 hectares in a strip-like continuous distribution along the coastline. (3) The distribution of seagrasses in the study area showed a significant decaying trend from 2016 to 2020. The total area of seagrass decreased by 79.224 ha during the five years from 2016 to 2020, with a decay rate of 16.458%. This study is the first on the comprehensive monitoring of seagrass in Xincun Bay using satellite remote sensing images, and comprises the first use of GF2 data in seagrass research, aiming to provide a reference for remote sensing monitoring of seagrass in the South China Sea.

Resolving Chemical Gradients Around Seagrass Roots—A Review of Available Methods

Steep geochemical gradients surround roots and rhizomes of seagrass and protect the plants against the harsh conditions in anoxic sediment, while enabling nutrient uptake. Imbalance of these gradients, due to e.g., low plant performance and/or changing sediment biogeochemical conditions, can lead to plant stress and large-scale seagrass meadow die-off. Therefore, measuring and mapping the dynamic gradients around seagrass roots and rhizomes is needed to better understand plant responses to human impact and environmental changes. Historically, electrochemical microsensors enabled the first measurements of important chemical species like O2, pH or H2S with high sensitivity and spatial resolution giving important insights to the seagrass rhizosphere microenvironment; however, such measurements only provide information in one dimension at a time. In recent years, the use of reversible optical sensors (in the form of planar optodes or nanoparticles) and accumulative gel sampling methods like Diffusive Gradients in Thin films (DGT) have extended the array of analytes and allowed 2-D mapping of chemical gradients in the seagrass rhizosphere. Here, we review and discuss such microscale methods from a practical angle, discuss their application in seagrass research, and point toward novel experimental approaches to study the (bio)geochemistry around seagrass roots and rhizomes using a combination of available techniques, both in the lab andin situ.

Current Trends In Seagrass Research In Indonesia (2010-2020)

Seagrass is a higher plant (Anthophyta) that lives and grows immersed in the marine environment. Seagrass provides important ecosystem services include coastal protection, carbon absorption for climate change mitigation, nutrient storage for eutrophication mitigation and shelter for small fish, and high biodiversity conservation efforts for iconic endangered species. The current lack of global attention, therefore seagrass research is important to increase knowledge on a local and national scale. Given the extent of seagrass beds and the length of Indonesia's coastline which ranges 95,181 km, so it still needs to understand seagrass more deeply, because this is very important for conservation and restoration. The purpose of this review article is to comprehensively review research on seagrass in Indonesia in five years that expected to provide a future perspective for seagrass research in Indonesia. In the publication regarding seagrass studies in Indonesia, there are 7 categories of topics discussed, distribution and biology, plant physiology, microbial ecology, fauna, impacts and potential, carbon absorption, and restoration. In general, the focus on seagrass research in Indonesia includes seagrass species, seagrass communities, nutrient cycles in seagrass ecosystems, physiology, and the impact of pollution on seagrass habitats. The results presented in seagrass research in Indonesia are still quite descriptive and lagging when compared to studies that have been carried out in developed countries. The developed countries have developed new methods for seagrass restoration activities to new knowledge about seagrass genetics that has never been disclosed previously.

Seagrasses in an era of ocean warming: a review.

Seagrasses are valuable sources of food and habitat for marine life and are one of Earth's most efficient carbon sinks. However, they are facing a global decline due to ocean warming and eutrophication. In the last decade, with the advent of new technology and molecular advances, there has been a dramatic increase in the number of studies focusing on the effects of ocean warming on seagrasses. Here, we provide a comprehensive review of the future of seagrasses in an era of ocean warming. We have gathered information from published studies to identify potential commonalities in the effects of warming and the responses of seagrasses across four distinct levels: molecular, biochemical/physiological, morphological/population, and ecosystem/planetary. To date, we know that although warming strongly affects seagrasses at all four levels, seagrass responses diverge amongst species, populations, and over depths. Furthermore, warming alters seagrass distribution causing massive die-offs in some seagrass populations, whilst also causing tropicalization and migration of temperate species. In this review, we evaluate the combined effects of ocean warming with other environmental stressors and emphasize the need for multiple-stressor studies to provide a deeper understanding of seagrass resilience. We conclude by discussing the most significant knowledge gaps and future directions for seagrass research.

The microbiome of the seagrass Halophila ovalis: community structuring from plant parts to regional scales

Seagrass meadows are critical marine ecosystems. They are significant carbon sinks and play numerous important roles in coastal areas. They help to prevent shoreline erosion and serve as nursery grounds for many marine species. Like their terrestrial counterparts, seagrasses form symbiotic relationships with diverse communities of bacteria that help to promote and maintain host fitness. In this study, we sampled the seagrass Halophila ovalis throughout Singapore and Peninsular Malaysia to characterise the associated bacterial communities and distributions in this acknowledged seagrass biodiversity hotspot. Three different parts of the seagrass (leaves, roots and rhizomes) were collected, and a sediment sample was collected in close proximity to each host. We used high-throughput 16S rRNA amplicon sequencing to examine the bacterial communities associated with each plant part and location. Our analyses indicated that bacterial assemblages associated with H. ovalis were distinct among locations, and different plant parts harboured divergent bacterial communities. We uncovered a significant distance-decay relationship, suggesting that dispersal limitations could explain the observed bacterial community structuring. We further identified bacterial indicator amplicon sequence variants (ASVs) that were associated with degraded or healthy seagrass meadows. The identification of indicator ASVs that are indicative of anthropogenically stressed seagrass, or a declining environment, could be used to implement proactive seagrass conservation and management schemes. This study addresses a current scientific gap within the characterisation of seagrass microbiomes, specifically of those from Southeast Asia, a region of acute seagrass losses, and provides a solid foundation for future seagrass research in the region.

Over a decade monitoring Fiji's seagrass condition demonstrates resilience to anthropogenic pressures and extreme climate events

Seagrass are an important marine ecosystem of the Fiji Islands. We confirm six seagrass species from the archipelago and defined five broad categories of seagrass habitat. We report, with high confidence, seagrass meadows covering 59.19 km2 of Fiji's shallow water habitats from literature and this study. Long-term monitoring of seagrass abundance, species composition, and seed banks at eight sentinel sites, found no long-term trends. Examination of key attributes that affect seagrass resilience identified meadows as predominately enduring and dominated by opportunistic species which had moderate physiological resistance, and high recovery capacity. We examined threats to Fiji's seagrass meadows from extreme climatic events and anthropogenic activities using a suite of indicators, identifying water quality as a major pressure. Based on these findings, we assessed existing protections in Fiji afforded to seagrass and their services. This understanding will help to better manage for seagrass resilience and focus future seagrass research in Fiji.

Advances in seagrass’ omics research

Seagrasses are submerged marine macrophytes, they form highly productive ecosystems that play a critical role in climate change mitigation. Seagrass meadows are known to stabilise coastal sediments, recycle nutrients, and provide nursery grounds and food sources for fishes and megafauna. However, nearly 30% of seagrass habitats have been lost worldwide because of global climate change and sustained negative pressure from coastal developments, as well as eutrophication and dredging. This global decline and ongoing threat from climate change have weakened their capacity to support coastal productivity. This alarming decline highlights a global urgency for the implementation of effective seagrass management strategies to prevent their decline. Until now, the physiological indicators used to monitor seagrass health, including seagrass species composition, above ground biomass, and spatial coverage, have failed to provide any insights into the intensity of environmental stress at the physiological and/or molecular level, which has led to their decline. Therefore, seagrass restoration efforts require highly accurate and novel tools for monitoring seagrass health and effective management strategies. In the era of systems biology, omics (transcriptomics, proteomics, and metabolomics) and their integration have shown promise in the identification of biomarkers of phenotypic plasticity of an organism under specific environmental conditions. Recently, with the influx of genomic information regarding seagrasses, omics have emerged as a new frontier in seagrass research and have deepened our understanding of their adaptation and underlying tolerance mechanisms to environmental stresses. This review article provides a state-of-art on seagrass’ omics and discusses their potential to discover stress biomarkers, and thereby aid in developing robust diagnostic tools for monitoring seagrass’ health and their management for protection and conservation. We discuss how omics platforms are advancing in technology, such as whole-genome shotgun, RNA-seq, 2-DE, and multidimensional GC- and MS-based platforms, which helps in developing high-throughput protocols for possible implementation in seagrass research. This article further discusses how such innovations can provide knowledge on: (1) Molecular adaptation and acclimatisation mechanisms in seagrass responses to light, salinity, thermal, carbon dioxide, eutrophication, and heavy metal concentration, (2) their genetic diversity and evolution, and (3) seagrass reproduction and development. Moreover, we discuss the organelle, such as the chloroplast, based omics frontier to explore its potential in seagrass research to better understand the biological processes at the organelle level and how it may help determine the role of different organelles in providing tolerance against various environmental stresses. Lastly, we discuss the do’s and don’ts of the experimental designs, methodological procedures, and analytical tools learned from higher plant studies to facilitate multi-omics studies and data integration in seagrass research. Creating an online user friendly database sourced from multi-omics studies and a suite of tools for analysis will attract seagrass molecular biologists and ecologists working on seagrass ecology, restoration, development, and evolution, and will improve the molecular horizons of seagrass research.

Opportunities for seagrass research derived from remote sensing: A review of current methods

Abstract Seagrass communities provide critical ecosystem and provisioning services for both human populations and a wide range of associated species globally. However, it has been reported that seagrass area is decreasing at a rapid rate in many parts of the world, mostly due to anthropogenic activities including global change (pollution and climate change). The aim of this review article is to highlight the range of current tools for studying seagrasses as well as identify the benefits and limitations of a range of remote sensing and traditional methodologies. This paper provides a discussion of the ecological importance of seagrass meadows, and recent trends and developments in seagrass research methods are discussed including the use of satellite images and aerial photographs for seagrass monitoring and various image processing steps that are frequently utilised for seagrass mapping. The extensive use of various optical, Radar and LiDAR data for seagrass research in recent years has also been described in detail. The review concludes that the recent explosion of new methods and tools available from a wide range of platforms combined with the recent recognition of the importance of seagrasses provides the research community with an excellent opportunity to undertake a range of timely research. This research should include mapping the extent and distribution of seagrasses, identifying the drivers of change and factors that confer resilience, as well as quantification of the ecosystem services provided. Whilst remotely sensed data provides an important new tool it should be used in conjunction with traditional methods for validation and with a knowledge of the limitations of results and careful interpretation.

Differential Leaf Age-Dependent Thermal Plasticity in the Keystone Seagrass Posidonia oceanica.

Introduction: Gene-expression patterns and their upstream regulatory mechanisms (e.g. epigenetic) are known to modulate plant acclimatability and thus tolerance to heat stress. Within species, thermal plasticity (i.e. temperature-sensitive phenotypic plasticity) and differential thermo-tolerance are recognized among different genotypes, development stages, organs or tissues. Leaf age and lifespan have been demonstrated to strongly affect photosynthetic thermo-tolerance in terrestrial species, whereas there is no information available for marine plants. Materials and Methods: Here, we investigated how an intense warming event affects molecular and photo-physiological functions in the large-sized seagrass Posidonia oceanica, at fine spatial resolution. Plants were exposed for one week at 34°C in a controlled-mesocosm system. Subsequent variations in the expression of 12 target genes and global DNA methylation level were evaluated in three leaf-age sections (i.e. basal, medium and high) established along the longitudinal axis of youngest, young and fully mature leaves of the shoot. Targeted genes were involved in photosynthesis, chlorophyll biosynthesis, energy dissipation mechanisms, stress response and programmed cell death. Molecular analyses paralleled the assessment of pigment content and photosynthetic performance of the same leaf segments, as well as of plant growth inhibition under acute warming. Results: Our data revealed, for the first time, the presence of variable leaf age-dependent stress-induced epigenetic and gene-expression changes in seagrasses, underlying photo-physiological and growth responses to heat stress. An investment in protective responses and growth arrest was observed in immature tissues; while mature leaf sections displayed a higher ability to offset gene down-regulation, possibly through the involvement of DNA methylation changes, although heat-induced damages were visible at photo-physiological level. Discussion: Overall, mature and young leaf tissues exhibited different strategies to withstand heat stress and thus a variable thermal plasticity. This should be taken in consideration when addressing seagrass response to warming and other stressors, especially in large-sized species, where sharp age differences are present within and among leaves, and other gradients of environmental factors (e.g. light) could be at play. Molecular and physiological evaluations conducted only on adult leaf tissues, as common practice in seagrass research, could give inadequate estimates of the overall plant state, and should not be considered as a proxy for the whole shoot.

Observations on the female flowers and fruiting of Tape Grass Enhalus acoroides from South Andaman Islands, India

Documenting phenologic events is crucial in obtaining deeper insights into the life cycle of seagrasses. We documented and compared the flowering and fruiting of the seagrass Enhalus acoroides from multispecies seagrass meadows at two sites, Henry Lawrence and Tarmugli islands located inside the marine national parks in South Andaman Islands. At these two locations, the average density of shoots ranged between 30.9/m2 and 18.16/m2, fruits between 5/m2 and 2.33/m2, and flowers between 6.7/m2 and 3.83/m2, whereas the mean length of the peduncles ranged from 40.59cm at Henry Lawrence to 32.44cm at Tarmugli Island. We observed significant differences between the densities of shoots and fruits and peduncle lengths in the two sites. The density of flowers, however, did not vary significantly. These observations of fruiting and flowering in E. acoroides establish an important reproductive stage in the life cycle of the species and open avenues for further seagrass research in the Andaman Islands. We describe the findings and emphasize on the need to establish a long-term phenology monitoring program for E. acoroides in the Andaman Archipelago.