Seagrass Ecosystems Research Articles

Edge effects of a fragmented seagrass habitat on flow, bivalve recruitment, and sediment dynamics

In both continuous and fragmented seagrass ecosystems, the vegetation edge can be a location of abrupt hydrodynamic change, with impacts to both ecological and physical processes. We address how flow and wave activity change across seagrass meadow edges and the effects of vegetation on sediment dynamics and bivalve recruitment. Two Zostera marina seagrass meadow sites were monitored: a high-density site with >500 shoots m-2 and a low-density site with <250 shoots m-2. Mean flow velocities were significantly reduced in seagrass vegetation adjacent to edges, with reductions compared to unvegetated areas ranging from 30-75%. Recruitment of juvenile bivalves was significantly elevated within vegetation. No significant differences in wave activity or sediment suspension and/or deposition were found spatially across a 10 m distance from a seagrass edge, but significant temporal variability was observed, caused by periodic storms. Wave height was a major predictor for sediment movement along seagrass edges, with an observed 10-fold increase in sediment collection within benthic traps following severe storms. These results were found across various heterogeneous edge configurations and reveal abrupt hydrodynamic responses of both mean flow and turbulence to occur at short spatial scales (1-10 m), with changes to wave and sediment deposition and/or suspension conditions only occurring over larger spatial distances (~100 m). Changes to the hydrodynamic regime were therefore found to be driven by meteorological conditions (e.g. winds, storms) on daily timescales and by changes in seagrass shoot density, altering both bivalve recruitment and sediment dynamics on longer temporal and/or spatial timescales.

Remote sensing monitoring of seagrass bed dynamics using cross-temporal-spatial domain transfer learning in Yellow river Delta

ABSTRACT Seagrass beds play a vital ecological role by regulating climate, maintaining biodiversity, and sequestering carbon. Achieving accurate classification of seagrass beds across both time and space is of significant importance for efficient monitoring. This paper addresses the challenges of seagrass bed classification in remote sensing imagery and the difficulty of achieving temporal and spatial transferability of classification model. Leveraging a long-term Landsat satellite image time series spanning from 1976 to 2022 in the Yellow River Delta, we enhance the DeepLab V3+ network and propose a cross-temporal-spatial domain seagrass bed transfer learning classification approach. We utilize selectively chosen images from a few years in partial regions for training, introduce freeze-training and-unfreeze-training during the model training phase, and then transfer the model to achieve cross-temporal and cross-temporal-spatial domain classification on images from other years and regions. Additionally, we discuss the factors influencing the classification results. The research results indicate that: (1)The method we proposed has shown good results, achieving classification accuracy of 83.17% and 80.99% for seagrass beds in both cross-temporal and cross-temporal-spatial domains. (2) The classification results indicate that this method achieves an average classification accuracy higher by 16.18% compared to networks such as UNet, PSPNet, HRNet, UNet++, SegFormer, etc. under cross-temporal conditions and higher by 17.56% under cross-spatiotemporal conditions for seagrass bed classification. (3) Based on the classification results, it is observed that from 1973 to 1986, the overall area of seagrass beds in the Yellow River Delta had an initial growth trend, with the largest seagrass bed area recorded in 1986, reaching 4281.289 hectares. Subsequently, the seagrass beds showed an overall decreasing trend, and by 2019 they had almost completely disappeared. The cross-temporal-spatial domain seagrass bed transfer learning classification method proposed in this paper can provide valuable support for the monitoring, restoration, management, and utilization of seagrass ecosystems.

The potential Two Types of Green Macroalgae (Caulerpa racemose and Caulerpa lentillifera) as a Natural Food Preservative from Jepara beach, Indonesia

Green macroalgae, known locally as Latoh, is one of the green seaweeds consumed by the local community in Jepara and is beneficial for health. This study explores the potential of secondary metabolites from seaweed and its symbiotic bacteria as natural food preservatives and antibacterials. Seaweed samples were collected from the seagrass ecosystem of Panjang Island, Jepara, Indonesia. Subsequently, the samples were subjected to scanning electron microscopy analysis, proximate analysis, phytochemical analysis, thin layer chromatography, and high-performance liquid chromatography for amino acid analysis. A sample was subjected to a multistage extraction process using n-hexane, ethyl acetate, and methanol (1:5 w/v), each for 24 h. Symbiotic bacteria from seaweed were isolated, and enzymatic (proteolytic, amylolytic, and cellulolytic) and antibacterial testing against pathogenic bacteria Staphylococcus aureus and Escherichia coli was conducted using the disc diffusion method. The selected bacteria were subjected to molecular identification. The research showed that Caulerpa lentillifera had an ash content of 3.24 %, protein content of 0.57 %, and fat content of 0.337 %. Phytochemical analysis shows that the sample contains flavonoids, steroids, and alkaloids. HPLC analysis reveals that Caulerpa lentillifera has the highest content of aspartic acid (relative area: 11.90 %), glutamic acid (relative area: 13.43 %), and alanine (relative area: 9.03 %). Caulerpa racemosa sample shows the highest detector response for glutamic acid (relative area: 12.19%), aspartic acid (relative area: 11.10 %), and alanine (relative area: 9.63 %). The results indicate that 14 bacterial isolates were successfully isolated, with 6 isolates from Caulerpa lentillifera and 8 isolates from Caulerpa racemosa, all exhibiting enzymatic and antibacterial abilities. The research results concluded that the Latoh seaweed species Caulerpa lentillifera and Caulerpa racemosa and their symbiotic bacteria have the potential to be used as food preservatives. HIGHLIGHTS HPLC analysis showed that Caulerpa lentillifera had the highest content of aspartic acid, glutamic acid, and alanine. Caulerpa racemosa also had high levels of glutamic acid, aspartic acid, and alanine The research successfully isolated 14 bacterial isolates, with 6 isolates from Caulerpa lentillifera and eight isolates from Caulerpa racemosa, all exhibiting enzymatic and antibacterial abilities Molecular identification revealed the presence of identified bacteria such as Pseudoalteromonas arabiensis, Pseudoalteromonas piscicida, Pseudoalteromonas shioyasakiensis, and Vibrio alginolyticus seaweed species Caulerpa lentillifera and Caulerpa racemosa, along with their symbiotic bacteria, have the potential to be used as natural food preservatives due to their antibacterial and enzymatic pro perties GRAPHICAL ABSTRACT

Assessment of Seagrass Ecosystems’ Goods and Services of India

Nearly every shallow coastal region on Earth is home to seagrass, a type of marine flowering plant. They grow down to depths where just 11% of surface light reaches the bottom after colonizing soft substrates like mud, sand, and cobbles. Seagrasses often choose wave-sheltered environments where sediments are shielded from waves and currents. The seagrass environment serves as a home to large animals like dugongs and marine mammals like ducks and geese. The seagrass serves as a feeding and refuge area for the related creatures for the entirety or a portion of their life cycles. Raw materials and food, medicine, fertilizer, coastal protection, erosion control, water purification, fisheries maintenance, nursery grounds, invertebrate habitats, carbon sequestration, tourism, recreation, support for education, and research are just a few of the goods and services provided by seagrass to the coastal community. The value of a seagrass ecosystem's products and services to human well-being can be measured, and this can be used to support the need for seagrass ecosystem preservation, transfer, and regeneration. Many valuation studies are conducted to estimate the various goods and services produced by the seagrass ecosystem. The total area of seagrass distribution in the coastal States and UTs of India is 51822 ha, distributed in 4162 seagrass patches. Using meta-analysis and an average of Benefit Transfer (BT) method, the Total Economic Value (TEV) of seagrass has been estimated as Rs. 2594342/ha/yr. ($ 55,637/ha/yr.) with a maximum of Rs. 5948650 ha/yr. ($1,27,571/ha/yr.) and a minimum of 791448/ha/yr. ($ 16,973/ha/yr.). Subsequently, the total equivalent economic benefit from seagrass beds in India has been quantified at Rs.13444 crore/yr. ($ 2,88,31,22,453/yr.).

Climate Change Impact Vulnerability Assessment: The Case of Coastal Communities in Central Zambales, Philippines

The Philippines is one of the countries most affected by climate change. As an archipelago country, coastal areas are at high risk of sea level rise due to climate change. This study investigated the vulnerability of coastal areas to sea level rise in selected municipalities in Zambales province, Philippines. The results showed that the coastal barangay of Iba City has a “moderate” to “high” level of vulnerability, while Botolan City has a “high” to “very high” level of vulnerability. Limited areas of nature reserves, such as mangrove, seagrass, and coral reef ecosystems, are one of the key factors contributing to high vulnerability. Concerted efforts of the local government units and the residents play a vital role to mitigate impacts of climate change including regular mangrove tree planting, coastal clean-up drive, and strict implementation of environmental policies. While there are many tools used in vulnerability assessment, a simpler yet reliable is recommended as an appropriate for barangay levels. With the identified vulnerability of the communities in sea level rise, possible mitigation measures to cope with the fast-changing climate could now be established.

One hundred priority questions for advancing seagrass conservation in Europe

Societal Impact StatementSeagrass ecosystems are of fundamental importance to our planet and wellbeing. Seagrasses are marine flowering plants, which engineer ecosystems that provide a multitude of ecosystem services, for example, blue foods and carbon sequestration. Seagrass ecosystems have largely been degraded across much of their global range. There is now increasing interest in the conservation and restoration of these systems, particularly in the context of the climate emergency and the biodiversity crisis. The collation of 100 questions from experts across Europe could, if answered, improve our ability to conserve and restore these systems by facilitating a fundamental shift in the success of such work.SummarySeagrass meadows provide numerous ecosystem services including biodiversity, coastal protection, and carbon sequestration. In Europe, seagrasses can be found in shallow sheltered waters along coastlines, in estuaries & lagoons, and around islands, but their distribution has declined. Factors such as poor water quality, coastal modification, mechanical damage, overfishing, land‐sea interactions, climate change and disease have reduced the coverage of Europe’s seagrasses necessitating their recovery. Research, monitoring and conservation efforts on seagrass ecosystems in Europe are mostly uncoordinated and biased towards certain species and regions, resulting in inadequate delivery of critical information for their management. Here, we aim to identify the 100 priority questions, that if addressed would strongly advance seagrass monitoring, research and conservation in Europe. Using a Delphi method, researchers, practitioners, and policymakers with seagrass experience from across Europe and with diverse seagrass expertise participated in the process that involved the formulation of research questions, a voting process and an online workshop to identify the final list of the 100 questions. The final list of questions covers areas across nine themes: Biodiversity & Ecology; Ecosystem services; Blue carbon; Fishery support; Drivers, Threats, Resilience & Response; Monitoring & Assessment; Conservation & Restoration; Governance, Policy & Management; and Communication. Answering these questions will fill current knowledge gaps and place European seagrass onto a positive trajectory of recovery.

Individual variation in home‐range across an ocean basin and links to habitat quality and management

Abstract Overgrazing may lead to management intervention (e.g. culling, animal relocation) to try and prevent habitat destruction. Overgrazing leading to seagrass meadow collapse has been recorded for green turtles (Chelonia mydas) at several sites around the world, although the generality of this phenomenon and the need for intervention to prevent widespread seagrass destruction is unknown. Where turtles have degraded seagrass meadows, home‐ranges are expected to be large and turtles will relocate as meadows are destroyed. We used high resolution Fastloc GPS tracking (n = 32 individuals, mean = 171 days per individual, SD = 99) to record the home‐range of adult green turtles at foraging sites spanning 4523 km of longitude across the Western Indian Ocean. Contrary to predictions if overgrazing was occurring, we recorded small home‐ranges and turtles rarely relocated their daytime foraging areas. Based on all locations received, the mean 50% and 95% utilisation distributions (UD50 and UD95) were 2.4 km2 (SD = 2.7) and 15.4 km2 (SD = 17.7). Space use was often particularly small at night, when turtles rest, averaging 11% of the overall space use with the mean night‐time UD50 and UD95 being 0.15 km2 (SD = 0.1) and 1.1 km2 (SD = 0.8), respectively. Variation in home‐range across individuals was not influenced by the data volume (number of locations per day, duration of tracking) or animal size (carapace length) but increased significantly as the distance between the centre of day and night areas increased, that is individuals that had a larger daily commute had the larger home‐ranges. Synthesis and applications. Comparisons with home‐range estimates from 16 previous studies, showed that those we recorded are among the smallest for adult green turtles globally. These results suggest that despite population size increases at several major nesting sites in the Western Indian Ocean, green turtles are generally not destroying the seagrass meadows on which they forage and so management intervention to prevent overgrazing is not needed. In this way, our work illustrates how movement data may inform management decisions for green turtles. Further targeted work on the seagrass ecosystem health could help confirm this suggestion.

Quantifying the direct and indirect relationships linking the environment, seagrass, and their associated fauna

AbstractFoundation species such as seagrasses modulate critical ecosystem processes, promote biodiversity, and structure community spatial and temporal dynamics. Hence, they play a key role in mediating the response of biodiversity to environmental changes. The breadth of their contribution to biodiversity maintenance and the potential cascading effects of their alteration remain unclear as we lack a comprehensive understanding of the intricate mechanisms governing their response to environmental changes and that of their associated fauna. Indeed, the mechanisms involved are often studied in isolation or at scales that only provide incomplete representations of the complex functioning of these ecosystems. This study aimed to clarify the direct and indirect relationships linking the environment, seagrass, and their associated faunal assemblages, using structural equation modeling (SEM). To this end, we review the literature to derive theoretical models of the functioning of seagrass ecosystems and test them using long‐term monitoring data covering 14 years of nine different Zostera marina seagrass beds across 500 km of coastline. We show that contradictory relationships and ambiguities regarding seagrass–biodiversity relationships emerge from the currently available literature (covering experimental, observational, and modeling studies). The SEM approach allowed us to clarify these direct and indirect relationships and resolve most ambiguities. In particular, we show that seagrass mediates the effect of the environment on its associated communities. However, this mediating effect is different, both qualitatively and quantitatively, for epifauna and infauna. Unexpectedly, the diversity of benthic macrofauna appeared to be controlled and promoted by the biomass rather than by the shoot density of the seagrass beds. We also provide quantitative estimates for the direct and cascading pathways linking seagrass biodiversity to environmental changes. Overall, by synthesizing, clarifying, and quantifying the multiple relationships linking a foundation species such as seagrass to its environment and associated biodiversity, we contribute to a better understanding of seagrass meadows functioning and help predict the potential consequences of foundation species alteration on their associated fauna.

Anthropogenic Activities Alter The Seagrass Ecosystem In Southern Philippines

Seagrasses are economically and ecologically important marine habitats. However, anthropogenic activities resulted in their decline globally. In the Philippines, MPAs were established, but most seagrasses need to be acknowledged and directly protected, thus affecting the ecosystem productivity. To prevent this scenario, baseline information that describes the status of seagrass beds is highly needed to help implement sound management practices. The present investigation was carried out to assess the effect of anthropogenic activities on the seagrass ecosystem in 15 municipalities as sampling areas across Southern Philippines. The study used focus group discussions, key informant interviews, and household interviews guided by structured questionnaires. Some 30 to 45 fishers and gleaners were interviewed in every municipality with 476 individuals. A matrix was developed for measuring anthropogenic activities complementary to random sampling of seagrass cover assessment. The anthropogenic activities considered to degrade the seagrass ecosystem and were analyzed in the matrix included tourism, gleaning/fishing, aquaculture, industrial and domestic activities. The result of the study showed that domestic, tourism and gleaning are the prevalent anthropogenic activities affecting seagrasses. The result further showed that higher anthropogenic activities affected lower seagrass percentage cover (R2=0.56). The result indicates that as anthropogenic activity increases, the cover condition of the seagrass ecosystem is averted. This implies that seagrasses should be acknowledged and included in the coastal management plans.

Health Status of Seagrass Meadows Around the Special Economic Zone (SEZ), West Likupang, North Sulawesi

Seagrass ecosystems offer valuable ecosystem services but are highly vulnerable to physical damage caused by human activities and rapid environmental change. Currently, there is very limited information available on monitoring and reporting the health of seagrass beds in Indonesian waters. This study aims to assess the species composition, density, diversity index, percentage of seagrass cover, health condition, and identification of threats to seagrass ecosystems around the West Likupang Special Economic Zone (SEZ), North Sulawesi. The method used was a seagrass watch with line transects and quadrant-shaped frames measuring 50x50 cm2. Transect lines were established through the seagrass ecosystem area at 50 m. There were three line transects at each station 25 m apart. Quadrant frame measuring 50x50 cm2. West Likupang has eight seagrass species including C. rotundata, E. acoroides, H. pinifolia, H. uninervis, H. ovalis, O. serrulata, S. isoetifolium, dan T. hemprichii. The health status of the seagrass is currently healthy, with a dense percentage of coverage. The identification of potential risks from anthropogenic activities such as the household disposal of waste at sea, gleaning, the use of boat anchors and propellers, and the construction of infrastructure in coastal areas, such as hotels and harbonurs, pose significant threats.

Seagrass diversity in Pulau Banyak, Aceh Singkil District, Indonesia

Abstract. Erniati, Andika Y, Imanullah, Imamshadiqin, Erlangga, Rahmad, Tauladan TA, Siregar FR, Fitri A, Ritonga GH. 2023. Seagrass diversity in Pulau Banyak, Aceh Singkil District, Indonesia. Biodiversitas 24: 6621-6628. Seagrass is a high-level plant where life activities are submerged in seawater. Currently, the seagrass ecosystem is threatened with destruction and disappearance. The extent of seagrass ecosystems globally was estimated to have declined by about 58%. The solution to this problem is to balance local communities' utilization of biological resources and biodiversity maintenance. The biodiversity aspect of seagrass is key to the sustainability of seagrass ecosystems. Banyak Island is one of the sub-districts in Aceh Singkil Regency, which consists of a cluster of small islands and has rich fisheries and marine potential, one of them is seagrass, where station 1 is Balong Island, Stasion 2 is Balong Island, Stasion 3 is Lamun Island and Stasion 4 is Rago-Rago Island. This study aimed to assess the diversity of seagrass beds, including seagrass species composition, density, percentage cover, and water quality that affect the existence of seagrass ecosystems. This study used a purposive sampling method with 3 transect lines spaced 50 m perpendicular from the shoreline to the sea. Each transect line has 5 plots with a distance of 10 meters measuring 50 x 50 cm2, and the water quality parameters were measured in situ. This research found 5 seagrass species, namely T. hemprichii, C. rotundata, E. acroides, S. isoetifolium, and H. ovalis. C. rotundata is the species with the highest density on Matahari Island, but seagrass diversity is low, and no species were dominant in the groups. The results of PCA analysis showed that the environmental factors that most influenced the pattern of seagrass distribution and density were nitrate, phosphate, and substrate. The conclusion revealed that seagrass diversity on Banyak Islands is relatively low.

High-frequency dynamics of pH, dissolved oxygen, and temperature in the coastal ecosystems of the Tanga-Pemba Seascape: implications for upwelling-enhanced ocean acidification and deoxygenation

Ocean acidification, deoxygenation, and warming are three interconnected global change challenges caused by increased anthropogenic carbon emissions. These issues present substantial threats to marine organisms, ecosystems, and the survival of coastal communities depending on these ecosystems. Coastal upwelling areas may experience significant declines in pH, dissolved oxygen (DO), and temperature levels during upwelling events, making marine organisms and ecosystems in these areas more susceptible to ocean acidification and deoxygenation. Understanding the dynamics of pH, DO, and temperature in coastal upwelling areas is essential for evaluating the susceptibility of resident organisms and ecosystems to lower pH and DO conditions occurring during upwelling events. To accomplish this, we used the pH and the DO loggers to measure high-frequency data for pH and DO, respectively, over six months in the open ocean and for a 24-hour cycle within the mangrove, seagrass, and coral reef ecosystems of the Tanga-Pemba Seascape (T-PS) during the northeast monsoon season. Our findings revealed the occurrence of multiple upwelling events, with varying durations, that result in significant declines in pH, DO, and temperature within the seascape. This is the first study to confirm the occurrence of multiple upwelling events in the T-PS. Moreover, the study has revealed a pH threshold value of 7.43 for ocean acidification in the T-PS. This is the first study to report a threshold value for ocean acidification in coastal upwelling areas of the Western Indian Ocean (WIO). Furthermore, it revealed that the extremely low levels of pH that occurred during upwelling events were above the pH threshold value of 7.43 for ocean acidification, while the extremely low levels of DO fell below the oxygen threshold value of 4.6 mg/L for deoxygenation. During upwelling events, seagrass and coral reef ecosystems, but not mangrove ecosystems, demonstrated elevated mean hourly values of pH and DO compared to those of the open ocean. These findings show that marine organisms and ecosystems in the T-PS are frequently exposed to lower pH and DO conditions due multiple upwelling events. However, their susceptibility to these conditions is reduced to some extent by the presence of seagrass meadows within these interconnected systems.

Prioritising plastic pollution research in blue carbon ecosystems: A scientometric overview

The Blue Carbon Ecosystems (BCEs), comprising mangroves, saltmarshes, and seagrasses, located at the land-ocean interface provide crucial ecosystem services. These ecosystems serve as a natural barrier against the transportation of plastic waste from land to the ocean, effectively intercepting and mitigating plastic pollution in the ocean. To gain insights into the current state of research, and uncover key research gaps related to plastic pollution in BCEs, this study conveyed a comprehensive overview using bibliometric, altmetric, and literature synthesis approaches. The bibliometric analysis revealed a significant increase in publications addressing plastic pollution in BCEs, particularly since 2018. Geographically, Chinese institutions have made substantial contributions to this research field compared to countries and regions with extensive BCEs and established blue carbon science programs. Furthermore, many studies have focused on mangrove ecosystems, while limited attention was given to exploring plastic pollution in saltmarsh, seagrass, and multiple ecosystems simultaneously. Through a systematic analysis, this study identified four major research themes in BCE-plastics research: a) plastic trapping by vegetated coastal ecosystems, b) microbial plastic degradation, c) ingestion of plastic by benthic organisms, and d) effects of plastic on blue carbon biogeochemistry. Upon synthesising the current knowledge in each theme, we employed a perspective lens to outline future research frameworks, specifically emphasising habitat characteristics and blue carbon biogeochemistry. Emphasising the importance of synergistic research between plastic pollution and blue carbon science, we underscore the opportunities to progress our understanding of plastic reservoirs across BCEs and their subsequent effects on blue carbon sequestration and mineralisation. Together, the outcomes of this review have overarching implications for managing plastic pollution and optimising climate mitigation outcomes through the blue carbon strategies.

FIRST REPORT ON THE DISTRIBUTION AND EXTENSION OF SEAGRASS MEADOWS IN QUITASUEÑO CORAL BANK, SOUTHWESTERN CARIBBEAN

Seagrass beds constitute one of the world’s most productive marine ecosystems and are a source of food and shelter for a wide variety of species. The largest extension of seagrass meadows in the Seaflower Biosphere Reserve (Seaflower BR) is found around the Caribbean islands of San Andres, Old Providence, and Santa Catalina, with small patches around the cays Bolivar, Albuquerque, and Serranilla. Previous studies have reported the presence of seagrass beds in the Quitasueño Bank; however, they remain undescribed, without previous information about their extent and distribution within the coral complex. In November 2021, during the Seaflower Plus 2021 scientific expedition, extensive seagrass meadows were detected, and their distribution was determined through the interpretation of satellite images and analyses of information obtained in the field through rapid ecological assessments. It was determined that these meadows cover 619.7 ha, positioning Quitasueño as the second largest area in terms of seagrass coverage in the Seaflower BR after Old Providence and Santa Catalina islands. This new information increases the representativeness of the seagrass ecosystem within the National System of Protected Areas of Colombia and should be considered in future research and management efforts.

Relative Abundance of Megabenthic Organisms in the Seagrass Ecosystem of Mantang Island, Riau Islands Province, Indonesia

Seagrass ecosystems play a crucial role in coastal environments, providing essential habitats for the survival of various marine species. One significant group associated with these ecosystems is benthic organisms, which inhabit the ocean floor. This study aims to evaluate the relative abundance of megabenthic organisms in the seagrass ecosystem surrounding Mantang Island. Sampling was conducted at three stations. The results showed that seagrass cover in the waters of Mantang Island ranged from 25.5% to 40.31%, indicating a moderate level of seagrass coverage. Four main groups of megabenthic organisms were identified: Astropecten sp., Atrina pectinata, Strombus sp., and Trachycardium sp., with Strombus sp. exhibiting the highest relative abundance. These findings provide insight into the ecological health of the seagrass ecosystem in the region.

Temporal variability on Seagrass Cover and Species Composition in a Tourism Hotspot: A case study in Derawan Island

Seagrass ecosystems in Derawan Island provide crucial services to coastal communities, including serving as a food source for sea turtles. However, like many coastal areas, seagrass ecosystem in Derawan Island faces significant challenges. One major issue is related to tourism, which affects seagrass both through land use changes for tourism development and through various tourism activities. This study aims to assess the resilience of the seagrass ecosystem on Derawan Island by examining temporal variability in seagrass cover and community structure. Permanent plots were established to monitor changes in seagrass cover and community composition. The observations were conducted following the SeagrassWatch method. Data were collected three times, in September 2018, March 2019, and August 2019. Seagrass cover during 3 times monitoring showed fluctuate trend (averaging 42.3%, 33.2%, and 32.3%, respectively). Pioneer species such as H. pinifolia dominated the seagrass meadow, maintaining a consistently higher cover compared to other species. Conversely, the species T. hemprichii was observed at lower levels, likely due to overgrazing by sea turtles, which may have prevented its recovery. This study provides valuable insights into the status and resilience of seagrass ecosystems in a tourism hotspot and offers information that could be useful for managing seagrass ecosystem on Derawan Island.

Seagrass Aboveground Carbon Stock Mapping using PlanetScope SuperDove Imagery in Nemberala, Rote Island, East Nusa Tenggara

Seagrass ecosystem is natural objects that can be used to adapt and mitigate climate change through blue carbon sequestration. There are 16 seagrass species in Indonesia and the high diversity of these species supports the high potential of carbon that can be absorbed and stored. This study aimed to develop a general equation to estimate seagrass aboveground carbon stock (AGC) from the percent cover (PC), and to map seagrass AGC using PlanetScope imagery in Nemberala, Rote Island. Nemberala has very diverse seagrass species such as Enhalus acoroides (Ea), Cymodocea rotundata (Cr), Halophila ovalis (Ho), Syringodium isoetifolium (Si), Thalassodendron ciliatum (Tc) and Thalassia hemprichii (Th). The results of laboratory analysis to obtain the value of carbon stocks using the Loss on Ignition method from each species were 0.016, 0.004, 0.001, 0.002, 0.001, and 0.0001 (gC/leaf) for Ea, Th, Cr, Si, Tc, and Ho, respectively. The general equation for predicting AGC from PC is SeagrassAGC = (0.051*SeagrassPC) – 0.635 with r of 0.61 and R2 of 0.36. This formula will be applied to convert field seagrass PC data to AGC, which will then be used to train and test the accuracy of seagrass AGC mapping based on PlanetScope SuperDove 8 bands image.

Temperature threshold for seagrass (Zostera marina) ecosystem production derived from in situ aquatic eddy covariance measurements

As seagrass meadows are increasingly threatened by warming oceans and extreme heating events, it is critical that we enhance our understanding of their ecosystem response to heat stress. This study relied on our extensive database of hourly eelgrass Zostera marina ecosystem metabolism to determine, for the first time, the temperature stress threshold (Tth) of Z. marina meadows under naturally varying in situ conditions. Eelgrass ecosystem metabolism was measured using the aquatic eddy covariance technique in a 20 km2 meadow at the Virginia Coast Reserve (USA). We constructed and fitted a non-linear multivariate model to identify 28.6°C as the threshold above which substantial negative effects on net photosynthesis occur. On average, daytime oxygen fluxes decreased by 50% on afternoons when Tth was exceeded, which shifted daily net ecosystem metabolism from metabolic balance to net heterotrophy and therefore a loss in carbon. This study highlights the vulnerability of eelgrass meadows to future warming projections.

Impact of invasive seagrass Halophila stipulacea on life history characteristics of juvenile yellowtail snapper (Ocyurus chrysurus)

Seagrass ecosystems provide essential nursery habitat to numerous coral reef fishes. Native Caribbean seagrasses Syringodium filiforme and Thalassia testudinum provide several juvenile fish species with foraging habitat and protection during this vulnerable stage of life. In 2002, an invasive seagrass Halophila stipulacea was discovered off the coast of Grenada and has since rapidly spread throughout the Caribbean. Halophila stipulacea has been shown to displace native seagrass species and may pose additional threats to juvenile reef fish populations that depend on native seagrass habitats as nurseries. The purpose of this study was to determine the effects of H. stipulacea on the early life history of yellowtail snapper (Ocyurus chrysurus). Settlement, mortality, and condition of juvenile yellowtail snapper were compared among native and invasive seagrass habitats around southern St. Thomas, United States Virgin Islands. From May 2020 to June 2021, monthly surveys within fixed plots during new moon periods provided information on settlement rates and survivorship among seagrass types. Length and weight of 260 juvenile yellowtail snapper were measured to derive condition factor among seagrass species. Significantly higher settlement and similar trends in mortality were seen in H. stipulacea when compared to native seagrasses. No significant difference was observed in condition factor of juvenile yellowtail snapper among seagrass species, although trends demonstrated a higher condition in individuals from native seagrass species. This study is the first of its kind to identify the direct effects of H. stipulacea during the early life history stages of a commercially important fish species in the Caribbean.

Hydrogen peroxide fluxes and fate in a temperate seagrass ecosystem

Hydrogen peroxide fluxes and fate in a temperate seagrass ecosystem