Area Of Seagrass Beds Research Articles

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.

Coastal wetland degradation and ecological problems in the Yellow River Delta during 2005�2021

The Yellow River Delta wetland is one of the rare estuarine wetland ecosystems in the world, and it is also the most complete wetland ecosystem in the warm temperate zone in China. To understand its ecological problems as a sensitive and fragile new wetland ecosystem, we investigated and analyzed its coastal erosion, changes in wetland types, encroachment of invasive species, changes in the areas of seagrass beds and oyster reefs, ecosystem health status, and low salinity area. The investigation of the coastal wetlands in the Yellow River Delta revealed that from 2005 to 2020, the maximum deposition distance of the Yellow River port beach was about 10 km, and the maximum erosion distance was about 5 km. The siltation rate gradually decreased. From 2016 to 2021, the total area of the coastal wetlands in the Yellow River Delta remained stable. The area change rates of Spartina alterniflora, Phragmites australis, and Tamarix chinensis were 587, 282, and 57 ha/year, respectively, and the annual rate of change in Suaeda salsa was �60 ha/year. From 2015 to 2021, S. alterniflora increased the most sharply in the southern part of the Yellow River Estuary, and this region became the largest area of S. alterniflora in the delta. In recent years, the area of the coastal seagrass beds in the Delta has decreased sharply, and the area of the degraded oyster reefs has decreased further. The high nitrogen and phosphorus content of seawater is the main factor leading to the continuous eutrophication of the delta sea area. From 2011 to 2021, the health status of the Yellow River Estuary ecosystem remained in a sub-healthy state. The monitoring results for the low salinity area revealed that the areas of the low salinity area in 2020 and May 2021 were about 1200 and 1650 km2, respectively. Based on the survey results, the ecological problems faced by the wetlands in the Yellow River Delta such as dynamic coastline changes, coastal wetland degradation, and invasion of S. alterniflora were investigated.

Coastal wetland degradation and ecological problems in the Yellow River Delta during 2005-2021

The Yellow River Delta wetland is one of the rare estuarine wetland ecosystems in the world, and it is also the most complete wetland ecosystem in the warm temperate zone in China. To understand its ecological problems as a sensitive and fragile new wetland ecosystem, we investigated and analyzed its coastal erosion, changes in wetland types, encroachment of invasive species, changes in the areas of seagrass beds and oyster reefs, ecosystem health status, and low salinity area. The investigation of the coastal wetlands in the Yellow River Delta revealed that from 2005 to 2020, the maximum deposition distance of the Yellow River port beach was about 10 km, and the maximum erosion distance was about 5 km. The siltation rate gradually decreased. From 2016 to 2021, the total area of the coastal wetlands in the Yellow River Delta remained stable. The area change rates of Spartina alterniflora, Phragmites australis, and Tamarix chinensis were 587, 282, and 57 ha/year, respectively, and the annual rate of change in Suaeda salsa was �60 ha/year. From 2015 to 2021, S. alterniflora increased the most sharply in the southern part of the Yellow River Estuary, and this region became the largest area of S. alterniflora in the delta. In recent years, the area of the coastal seagrass beds in the Delta has decreased sharply, and the area of the degraded oyster reefs has decreased further. The high nitrogen and phosphorus content of seawater is the main factor leading to the continuous eutrophication of the delta sea area. From 2011 to 2021, the health status of the Yellow River Estuary ecosystem remained in a sub-healthy state. The monitoring results for the low salinity area revealed that the areas of the low salinity area in 2020 and May 2021 were about 1200 and 1650 km2, respectively. Based on the survey results, the ecological problems faced by the wetlands in the Yellow River Delta such as dynamic coastline changes, coastal wetland degradation, and invasion of S. alterniflora were investigated.

Distribusi Spasial Lamun di Perairan Sekotong Barat-TWP Gita Nada Lombok Barat Menggunakan Citra Landsat 8 OLI

West Sekotong Village is one of the coastal water areas included in the Gita Nada Aquatic Tourism Park (TWP) area which has a seagrass habitat. Seagrass beds in West Sekotong are threatened due to increased tourism and community activities. This research aims to determine the distribution and extent of seagrass beds on the coast of West Sekotong-TWP Gita Nada. This research uses a remote sensing approach through interpretation of Landsat 8 OLI imagery. This research consists of 2 steps, namely image data processing and supporting data. Image data processing includes several stages, namely image data collection, geometric correction, radiometric correction, image cutting, image composite, image data sharpening, image data interpretation, accuracy testing, area measurement, and final layout. Supporting data was obtained by searching related literature, interviews and surveys of activities that have the potential to have an impact on seagrass ecosystems. The research results show that the distribution of seagrass in West Sekotong-TWP Gita Nada covers the coast of the large island (mainland) and the coast of small islands. The distribution of seagrass on the mainland is found on the coasts of Medang, Tanjung Kelor, Batu Kijuk, Tawun, Labu, Kelapa, Pandanan, Gili Genting, Labuan Petung, Temeran, and Gawah Pudak. In the coastal areas of small islands, seagrass is found on Gili Sudak, Gili Tangkong, Gili Nanggu, Gili Poh, and Gili Lontar. The total area of seagrass beds in West Sekotong is around 144.68 ha. On the mainland coast the area is 118.96 ha (82.2%) and on small islands the area is around 25.72 ha (17.8%). The distribution of seagrass in West Sekotong is influenced by many factors, among which those observed in this research are the type of substrate, the presence of river estuaries, and the use of land and coastal waters.

Long-time monitoring of seagrass beds on the east coast of Hainan Island based on remote sensing images

Seagrass beds have extremely high ecological service value, so their protection and management are very important. The coastal area that stretches from Wenchang to Qionghai in the eastern part of Hainan Island is the largest seagrass bed distribution area in China’s South China Sea Bioregion. Understanding the local distribution and changes in seagrass beds is a prerequisite for implementing the protection and management of seagrass bed resources in this area. In this study, Landsat satellite remote sensing images of the study area from 1986 to 2021 were selected; seagrass bed survey data and field investigation data were combined; the Sum Green Index was used to extract and plot seagrass bed distribution information; the spatial distribution changes in seagrass beds in the region over the past thirty years were analyzed; and the driving factors of these changes are discussed. The following conclusions were drawn: (i) The water quality in the study area is clear, the marine sediment is mainly composed of coral debris and sand, and the seagrass plants are relatively tall. The Sum Green Index can effectively extract seagrass bed information and achieve good mapping accuracy. (ii) Between 1986 and 2021, there were significant changes in seagrass bed distribution in the study area, showing a trend of slow growth followed by rapid decline. Overall, over the past thirty years, the total area of seagrass beds in the study area has declined, coverage has decreased, and patches have become fragmented. (iii) The construction of marine and coastal engineering projects, as well as large-scale aquaculture, are important reasons for the decline of seagrass beds in the study area. Other types of mechanical physical damage, such as shipping and shells raking can also have serious impacts on seagrass beds. This study is the first to conduct distribution range mapping and long time series change monitoring based on satellite remote sensing images for the largest seagrass beds in China’s South China Sea Bioregion, with the aim of providing a reference for the monitoring and protection of seagrass beds in the South China Sea.

Preliminary study on restoration of tropical seagrass ecosystem through utilization of Enhalus acoroides seedling in Bintan Island, Indonesia

There has been a global decline in the area of seagrass ecosystems caused by the increasing number of human activities in coastal areas. It is suspected that the decline in the area of seagrass beds in Indonesia is 2%-5% per year. It takes an effort that can be used to restore the condition of seagrass beds. So far, efforts have been made to do seagrass transplants. There is a weakness in the transplant method, namely the reduction of seagrass stands in the origin (donor) area. Another effort that can be used is planting seagrass using seagrass seeds derived from seedlings. Seagrass seeds come from the seagrass, Enhalus acoroides, which is found throughout the year in the waters of Bintan Island. Furthermore, the seeds obtained will be sown for three months in the laboratory. Generally, the survival rate of seagrass seeds during the seedling process has a value of more than 90%, which is very good. Furthermore, the seeds produced from the nursery process are planted in the field. In this experimental study, 25 seedlings were planted. Seedlings were planted directly into the substrate at a depth of 10 cm (sprig method). During the four-month observation period, the survival rate declined to 20%. Several factors that affect the survival rate include the condition of the aquatic environment and human activities around it.

Mapping of seagrass ecosystem on Bontosua Island, Pangkep District, South Sulawesi, Indonesia

Abstract. Rosalina D, Jamil K, Arafat Y, Amalia R, Leilani A. 2023. Mapping of seagrass ecosystem on Bontosua Island, Pangkep District, South Sulawesi, Indonesia. Biodiversitas 24: 2023-2030. Bontosua Island is one of the islands in South Sulawesi, Indonesia, that has a seagrass ecosystem. The purpose of this study was to assess the density, cover, area, and condition of seagrass on Bontosua Island. The data collection involved the use of a quadratic transect method in the field and the Lyzenga method for remote sensing. The identification of seagrass areas was made using Landsat 8 OLI/TIRS satellite. Six seagrass species were identified, namely Cymodocea rotundata, Thalassia hemprichii, Halodule uninervis, Halodule pinifolia, Syringodium isoetifolium and Halophila sp. The results showed that C. rotundata had the highest density value of 89 Ind/m² and was categorized as rather dense, while C. rotundata also had the highest percentage cover of 58%, and Halophila sp. had the lowest percentage cover of 2%. The distribution area of seagrass beds on Bontosua Island was approximately 28.26 ha, out of a total area of 92 ha, of which approximately 6 ha was land. Observations on the condition of seagrass beds showed that 16.65 ha was healthy, 6.3 ha was unhealthy, while 5.31 ha was poor.

Mapping Sea Grass Coverage of Tanjung Benoa Bali Using Medium Resolution Satellite Imagery Sentinel 2B

Seagrass beds are important components of a coastal ecosystem. This ecosystem serves as the primer producers of the water food chain, habitat for marine biota, produces organic carbon, and indirectly contributes to the economic well-being of coastal communities. However, the ecosystem is vulnerable to damage caused by natural factors and human activities. The objectives of this study were, firstly to identify the distribution of seagrass beds in Tanjung Benoa using Sentinel 2B satellite imagery and secondly to compare classification results from two different approaches namely pixel-based image classification and object-based image classification. Accuracy-test was carried out using field data reference of 195 sample points in the form of a 10 m X 10 m transect. The image pre-processing process was conducted with Bottom of Atmosphere (BoA) correction using the Dark Object Subtraction (DOS) method. Furthermore, the water column correction was performed using the Depth Invariant Index (DII) and the Lyzenga algorithm. The mapping results showed that the area of seagrass beds in the shallow waters of Tanjung Benoa reaches 242.99 ha. There were seven seagrass species in the study area, with an average cover of 75%. The accuracy of object-based image classification was higher than that of pixel-based classification with a difference up to 25% for six classes classification and 15% for two classes classification. Excellent results for classifying seagrasses based on cover density can be obtained when high-resolution satellite imagery and OBIA are combined with the SVM or Fuzzy Logic algorithm.

Estimation of Seagrass Beds Changes in the Barugaiya Village Waters over a Period of 5 Years 2019-2023.

<b>Background and Objective:</b> Barugaiya Village is one of the villages located in Selayar Islands Regency, South Sulawesi, which has seagrass beds that are spread almost evenly in its waters. Environmental changes are in the form of declining water quality and damage to coastal ecosystems, one of which is seagrass. Therefore, it is necessary to observe changes in the area of seagrass beds in the waters of Barugaiya Village so that it is known how much seagrass has actually been in the area in the last 5 years. <b>Materials and Methods:</b> Observations were made from March to May, 2023 in the waters of Barugaiya Village, Selayar Islands Regency, South Sulawesi. The method used is seagrass classification using Sentinel-2A images corrected by the water column with the Lyzenga algorithm to reduce the effect of depth. <b>Results:</b> The distribution area of seagrass in Barugaiya Village for the 2019-2023 period was 111.03, 107.16, 103.81, 102.54 and 99.70 ha, respectively. Every year there is a decrease in seagrass area, the rate of decline is around 0.02% each year (1.27-3.87 ha). The change in area over the past 5 years has decreased by 0.11% (11.33 ha). <b>Conclusion:</b> Therefore, long-term monitoring of seagrass beds in the waters of Barugaiya Village which are experiencing a decline is needed so that effective management strategies can be identified.

UKURAN KEPADATAN DAN POTENSI IKAN BARONANG TOMPEL (Siganus guttatus Bloch 1787) DI TELUK KOTANIA SERAM BAGIAN BARAT

Spotted rabbitfish (Siganus guttatus Bloch 1787) are valuable commercial fish species. Research on the fish species has been carried out in the waters of Kotania Bay, aiming to obtain information about size, density and potential of the fish species. Data are collected about total length (TL), weight and number of individual fish at four observation stations using 120m length of bottom gillnet with mesh size of 2.0, 2.5, 3.0 dan 3.5 inches. The bottom gillnet is operated in a circle that starting two hours before the low tide then the spotted rabbitfish caught are collected at the low tide. The results showed that the total length of the spotted rabbitfish is in the range of 11,3 – 33,9 cm which has dominated by fish with sizes of 18, 24 and 26 cm. Mean density of the fish is 209 individual/ha, so the abundance the fish in the area of seagrass beds 823.62 ha was estimated as 172.486 of fish individual, it’s 72,51% or 125.070 individuals are those fishes that has spawned for the first time. The mean weight of the spotted rabbitfish at this size is 533,51 grams, so calculated biomass is 66,73 tons and MSY value is 33,365 tons in wet season.

Dynamics of seagrass beds and land use–land cover characteristics in Vietnamese Marine protected areas

Seagrass beds are considered ecosystem engineers with important roles in the marine environment. Although the area of seagrass beds is declining in Marine Protected Areas (MPAs) of Vietnam, no study has compared the changes in the area of seagrass beds among MPAs using remote sensing technology and GIS for mapping temporal and spatial changes. This is the first study assessing the ecological characteristics of seagrass beds in Ly Son, Nha Trang and Phu Quoc MPAs. In this study, we characterized the current status and historical changes of seagrass beds in three MPAs between 2001 and 2018, but Ly Son MPA between 2001 and 2019. Field surveys, historical satellite remote sensing data and GIS technology were applied to interpret Landsat images and evaluate the relationship between the cover of terrestrial vegetation and seagrass bed ecosystems. The results indicated that the average coverage and shoot density were highest in Phu Quoc MPA (92.5 ± 6.6%, 6635 ± 5,111 shoot m−2, respectively), while the total dry biomass was dominant in Ly Son MPA with 2000.3 ± 949.8 g DW m−2. The Kappa coefficients and overall accuracies of the years 2001 and 2018 (2019) were generally higher than 87% and 0.83, respectively. Between 2001–2018 (2019), the loss of seagrass area was 307.3 ha in Ly Son MPA, 268.4 ha in Nha Trang MPA and 13,225.6 ha in Phu Quoc MPA. Besides the decline in seagrass area, the artificial land covers witnessed a significant increase during the study period. Thus, this study could contribute to basic information for the conservation and management of seagrass resources in MPA.

Distribution, Temporal Change, and Conservation Status of Tropical Seagrass Beds in Southeast Asia: 2000–2020

Although Southeast Asia is a hotspot of global seagrass diversity, there are considerable information gaps in the distribution of seagrass beds. Broad-scale seagrass distribution has not been updated in the global seagrass database by UNEP-WCMC since 2000, although studies on seagrasses have been undertaken intensively in each region. Here we analyze the recent distribution of tropical seagrass beds, their temporal changes, causes of decline and conservation status in Southeast Asia (plus southern mainland China, Taiwan and Ryukyu Island of Japan) using data collected after 2000. Based on the 195 literature published since 2000, we identified 1,259 point data and 1,461 polygon data showing the distribution of seagrass beds. A large discrepancy was found in the seagrass bed distribution between our updated data and the UNEP-WCMC database, mostly due to inaccurate and low resolution location information in the latter. Temporal changes in seagrass bed area analyzed for 68 sites in nine countries/regions demonstrated that more than 60% of seagrass beds declined at an average rate of 10.9% year–1, whereas 20% of beds increased at an average rate of 8.1% year–1, leading to an overall average decline of 4.7% year–1. Various types of human-induced threats were reported as causes for the decline, including coastal development, fisheries/aquaculture, and natural factors such as typhoons and tsunamis. The percentage of seagrass beds covered with existing marine protected areas (MPAs) varied greatly among countries/regions, from less than 1% in Brunei Darussalam and Singapore to 100% in southern Japan. However, the degree of conservation regulation was not sufficient even in regions with higher MPA coverage. The percentage of seagrass beds within EBSAs (Ecologically and Biologically Significant Area determined by the Convention of Biological Diversity) was higher than that within MPAs because EBSAs cover a greater area than MPAs. Therefore, designating EBSAs as legally effective MPAs can greatly improve the conservation status of seagrass beds in Southeast Asia.

Impacts of urbanization and land transitions on seagrass beds in tropical lagoon in central Vietnam

Socio-economic development activities have significantly affected biodiversity of seagrass beds in the coastal lagoon areas in central Vietnam. This study was carried out to investigate the major past and potential impacts on seagrass changes in Lang Co lagoon. In this study, historical satellite remote sensing data and GIS technology were used to evaluate the variation of seagrass beds during the period of 1998 to 2020. Bottom Reflectance Index (BRI) was employed with the correlation coefficient between the band pairs and the depth, which fluctuated between 0.76 and 0.90 with the bottom reflectance of the bands including bands 1, 2 and 3 ranging between 0.59 to 3.10, 0.66 to 2.35 and 0.45 to 1.95, respectively. Two coefficients were used to evaluate the accuracy of underwater objects including Kappa coefficient (K) and overall accuracy (OA) which ranged from 0.78 to 0.88 and 83.78 to 91.22, respectively. The classification results of terrestrial layers recorded Kappa coefficients and overall accuracies ranging from 0.76 to 0.90 and 85.35 to 99.27, respectively. The change in the area of seagrass beds and other land use types around Lang Co lagoon was studied during the period of 22 years. In the period of 1998–2004, seagrass was not clearly affected by socio-economic development activities, while the period of 2006–2012 witnessed significant impacts of socio-economic activities on seagrass beds. The period of 2014–2020 revealed the most apparent impacts of economic development on seagrass beds. The results of analyzing land use transitions indicated that while water, sand and artificial layers were stable over time; bare soil, forest and agricultural soil layers combined with plantation areas tended to change continuously over the years. The study results provide a scientific database for sustainable management of the Lang Co lagoon ecosystem in particular and coastal area in central Vietnam in general.

Changes in seagrass carbon stock: implications of decreasing area and percentage cover of seagrass beds in Barranglompo Island, Spermonde archipelago, South Sulawesi, Indonesia

Seagrass ecosystems in shallow waters, including in highly dense small islands, are vulnerable to anthropogenic activities and may lead to a decreasing in seagrass area and percentage cover. As a result, it will negatively affect climate change mitigation, i.e. a decrease in seagrass carbon stock. This research was conducted to evaluate seagrass carbon stock changes in Barranglompo Island, Spermonde archipelago, in 2001 and 2017. Carbon stock estimation was carried out by collecting seagrass biomass based on the category of a sparse, medium, and dense seagrass coverage (each with 20 replications) and analysing their carbon concentrations. Changes in carbon sequestration were analysed using an estimated approach to the changes in the seagrass bed areas. Landsat and Worldview-2 image analysis were utilized to estimate the area of seagrass beds in 2001 and 2017, respectively. Results showed a decrease in seagrass beds by 9.9 ha, from 66.8 ha in 2001 to 56.9 ha in 2017, or an average of 0.62 ha per year. Based on that, it was estimated that seagrass carbon stocks had declined from 74.19 tons in 2001 to 65.21 tons in 2017 or decreased by an average of 0.75% per year. Anthropogenic activities, such as boat anchors as well as household waste disposal in the seagrass area, are considered having the potential in causing a decrease in seagrass area and the percentage coverage.

Update of seagrass cover and species diversity in Southern Viet Nam using remote sensing data and molecular analyses

Along with coral reefs and mangroves, seagrass meadows are being threatened globally Southeast Asia is considered within the area of seagrasses’ cradle of diversity. However, information on the current status of seagrass beds from Southern Viet Nam is limited due to lack of reliable data about seagrass species occurring in the Southeast Asian region. One factor is the difficulty of unambiguous species identification. For example, the leaf morphological characteristics of Halophila ovalis and closely related species are overlapping which leads to misidentifications. In this study, the latest satellite Landsat 8 OLI and SENTINEL-2B image analyses were applied to determine the distribution of seagrass beds in Southern Viet Nam. Detailed morphological and genetic marker analyses were used to determine and update the species composition. The present study together with literature reviews indicate that the total area of seagrass beds from Southern Viet Nam are 10,832.1 ha. 2562 ha (or 19.1%) of seagrass coverage has been lost. The seagrass beds at Phu Quoc Island are the largest with 7579 ha. The occurrence of Halophila major is updated for almost all off-shore islands and open-water areas.

Diversity, distribution and conservation of seagrass in coastal waters of the Liaodong Peninsula, North Yellow Sea, northern China: Implications for seagrass conservation

Seagrass beds are highly productive coastal ecosystems that are widely distributed along temperate and tropical coastlines globally. Although seagrass distribution and diversity have been widely reported on a global scale, there have been few reports on seagrass distribution and diversity in northern China, especially for coastal waters of the Liaodong Peninsula in the North Yellow Sea. In the present study, we investigated the distribution and diversity of seagrass in coastal waters of the Liaodong Peninsula in the North Yellow Sea, northern China. Field surveys of seagrass wrack were conducted along shorelines, to identify whether seagrass beds occurred in nearby waters, and sonar methods were then used to collect data relating to seagrass bed extent. Also, we analyzed the major threats facing seagrass beds. The results of the study revealed that four species (Zostera marina L., Z. japonica Aschers. & Graebn., Z. caespitosa M., and Phyllospadix iwatensis M.) were found in study area, covering a total area of 1253.47 ha. Seagrass bed area significantly decreased with increasing water depth, and most seagrass was recorded at depths of 2–5 m. Due to the steep slope of the seabed, seagrass beds exhibited a zonal distribution in most of the study areas. In addition, the amount of seagrass wrack along shorelines could be used to infer the size and distance of seagrass beds. Human activities, such as clam harvesting, land reclamation, coastal aquaculture pose a threat to the seagrass beds. This study provides new information to fill knowledge gaps regarding seagrass distribution in northern China and it provides a baseline for further monitoring of these seagrass beds.

Seagrass vegetation affect the vertical organization of microbial communities in sediment

Seagrasses represent high primary productivity and provide important ecosystem services to the marine environment. Seagrass-associated microbial communities are playing essential ecological functional roles in biogeochemical cycles. However, little is known about the effect of seagrass vegetation on microbial communities in sediment. In the present study, the sediment cores of seagrass bed (dominated by Zostera japonica and Zostera marine) and degradation area in Swan Lake (China) were sampled; then, biogeochemical parameters were analyzed, and microbial community composition was investigated by using high-throughput sequencing of the 16S rRNA gene.The results showed that the presence of seagrass could lead to a decrease in the richness and diversity of the microbial community. In the vertical direction, a pronounced shift from Proteobacteria-dominated upper layers to Chloroflexi and Crenarchaeota-dominated deep layers in all sediment cores were observed. Besides, Bathyarchaeia is more abundant at degradation area, while Vibrionaceae, Sulfurovum and Lokiarchaeial overrepresent at the seagrass bed area. Vibrionaceae was abundant in the rhizosphere of Z. marina and Z. japonica, and the proportions reached 84.45% and 63.89%, respectively. This enrichment of Vibrio spp. may be caused by the macrobenthic species near the seagrass rhizosphere, and these Vibrio spp. reduced the diversity and stability of microbial community, which may lead to the degradation of seagrass.This study would provide clues for the distribution patterns and niche preferences of seagrass microbiome. The conservation strategy of seagrass would be further elucidated from the perspective of the microbiome.

Decline in seagrass carbon uptake on Bonebatang Island, Spermonde Archipelago, Indonesia during the period of 2001-2017

The activities of coastal and small islands communities can have an impact on the condition of the adjacent aquatic ecosystems. The magnitude of the impact depends on the type and intensity of the activities carried out. One ecosystem that is prone to be affected is the seagrass ecosystem due to its presence in shallow waters and proximity to the coast. The study was conducted to examine changes in seagrass carbon uptake on Bonebatang Island over a period of 16 years from 2001 to 2017. Estimation of carbon uptake of seven species of seagrasses, i.e., Enhalus acoroides, Thalassia hemprichii, Cymodocea rotundata, Halodule uninervis. Halophila ovalis, Halophila minor, and Syringodium isoetifolium were carried out using the oxygen change method that utilized clear bottles. The percentage of seagrass coverage was calculated using a 50cm x 50cm plot. The average composition of seagrass species from all plots and the capability of each seagrass species to uptake carbon was used as a basis to estimate the capability of seagrass to uptake the carbon per unit area. Changes in carbon uptake were determined using an approach that estimates changes in the seagrass bed areas. Landsat image analysis was used to estimate the area of seagrass in 2001, 2009, and 2017. The results showed that the area of seagrass beds in the period of 2001-2017 decreased by 8.62 ha, from 37.08 ha in 2001 to 28.46 ha in 2017 or decreased by approximately 1.54% per year. As a result of this diminishing in the area, carbon uptake by seagrasses was estimated to decrease by 19.67 MgCO2 per year from 79.62 MgCO2 per year in 2001 to 59.95 MgCO2 per year in 2017. The average decrease in a year reached 1.23 MgCO2.

STRUKTUR KOMUNITAS LAMUN DI PULAU WANCI, KABUPATEN WAKATOBI, SULAWESI TENGGARA

Lamun merupakan tumbuhan laut yang memiliki peran yang tidak kalah penting dengan ekosistem pesisir lainnya seperti terumbu karang dan mangrove baik dari segi fisik, ekologi, dan ekonomi. Indonesia memiliki 12 jenis lamun dari 58 jenis lamun di dunia. Tidak semua wilayah di Indonesia memiliki jumlah jenis yang sama karena perbedaan kondisi lingkungan atau tekanan antropogenik, sehingga perlu ada kajian keragaman jenis lamun di wilayah perairan Indonesia. Penelitian ini bertujuan untuk mengidentifikasi struktur komunitas lamun dan keterkaitan antara kerapatan lamun dan parameter lingkungan di perairan Pulau Wanci, Sulawesi Tenggara. Stasiun pengamatan berada pada daerah padang lamun yang dibagi menjadi 4 stasiun. Metode sampling yang digunakan mengacu pada McKenzie et al. (2001) menggunakan transek kuadrat 50 cm x 50 cm. Selanjutnya menghitung jumlah tegakan lamun dan mencatat jenis lamun yang ditemukan pada tiap transek kuadrat. Hasil penelitian menunjukkan bahwa ditemukan 7 jenis lamun di perairan Pulau Wanci yaitu Halophila ovalis, Halodule uninervis, Cymodocea rotundata, Thalassia hemprichii, Enhalus acroides, Thalasodendron ciliatum, dan Syringodium isoetifolium dengan kerapatan tertinggi didominasi oleh T. hemprichii, H. uninervis, dan C. rotundata dengan pola sebaran keseluruhan adalah mengelompok. Terdapat keterkaitan antara kerapatan lamun dengan parameter lingkungan, substrat berpasir memiliki korelasi positif yang tinggi terhadap kerapatan lamun sedangkan substrat liat, kecepatan arus, salinitas, dan suhu memiliki korelasi negatif yang rendah sampai tinggi terhadap kerapatan lamun di perairan Pulau Wanci.

Decadal dynamics and challenges for seagrass beds management in Cu Lao Cham Marine Protected Area, Central Vietnam

Seagrass beds in central Vietnam plays an important role in the aquatic ecosystem. The area of seagrass beds in Cu Lao Cham Marine Protected Area (MPA), central Vietnam, has been reported to be declining in recent years. However, there has not been any study on assessing the changes in the area of seagrass beds in Cu Lao Cham MPA, especially by the application of remote sensing technology for evaluating temporal and spatial changes. The aim of this study is to establish the current status and document historical changes using maps of seagrass area in Cu Lao Cham MPA, central Vietnam, during the period of 2003–2017. This is the first study on assessing the temporal and spatial changes in the area of seagrass beds in central Vietnam using remote sensing technology. The study integrated field surveys, satellite remote sensing and GIS methods to analyse ALOS AVNIR-2 and Landsat satellite image data during the period of 2003–2017. The Kappa coefficients and overall accuracies of the years 2003, 2010 and 2017 were generally higher than 89% and 0.83, respectively, in all cases. Seagrass beds have mainly distributed near small islands such as Hon La, Hon Tai and Hon Dai. In particular, seagrass beds have almost disappeared at Bai Ong and Bai Huong in April 2017. In the period of 2003–2017, the area of the seagrass bed experienced significant changes. The seagrass area loss was 40.17 ha, and it gained 58.6 ha in the period of 2003–2010. In the period of 2010–2017, the loss of seagrass area was 68.76 ha, and the new addition was 7.27 ha. The study has identified a number of impacts of declining seagrass areas including marine pollution, changes in natural conditions and some other direct impacts from human activities and tourism. The results of this study could contribute to conservation of seagrass resources and sustainable livelihood development for the local community.