Seagrass Area Research Articles

Monitoring seagrass meadows in Maputo Bay using integrated remote sensing techniques and machine learning

Seagrass meadows are one of the most productive and valuable ecosystems on the planet. Monitoring seagrass meadows is essential to understand how these habitats change, and to develop better management and conservation practices. This study integrated satellite imagery from Sentinel-2 and Unmanned Aerial Vehicles (UAV) using machine learning to provide a consistent classification approach for monitoring seagrass in Maputo Bay, southern Mozambique. Sentinel-2 imagery was used to map seagrass extent and changes in Maputo Bay. The UAV systems were used to map seagrass at species level and biomass. All three algorithms tested in the ArcGIS environment could detect seagrass with high producer accuracy and Kappa coefficient. The area of seagrass in Maputo Bay decreased by 33.4 % between 1991 and 2023, with a decreasing trend of 0.48 km2/yr. A zonation pattern was observed for Oceana serrulata and Zostera capensis from the UAV imagery. The small and narrow leaved species (Z. capensis) occurred in the intertidal zone replaced by the broadleaved species (O. serrulata) in the subtidal. The total average aboveground biomass was 33.2 kg dry weight for the mapped area. The results of this study will guide implementation of combined satellite and UAV imagery with machine learning techniques for seagrass monitoring and restoration in Mozambique.

The contributions of primary sources to fauna and the trophic structure in tropical seagrass areas: A case study from Thai waters

AbstractSeagrass provides habitat and resources for various organisms in coastal areas. However, the productivity of a seagrass meadow might vary by its size, which can influence the contribution of primary sources to fauna and the food web structure. This study uses stable isotopes to investigate the contribution of sources to faunas and the associated food web structure in two tropical seagrass meadows. The carbon (δ13C) and nitrogen (δ15N) stable isotopes of primary sources such as mangrove leaf, coastal and riverine particulate organic matter, seagrass material and associated fauna (fish, bivalves, gastropods, crab, shrimp) were investigated from samples collected seagrass meadows of different sizes, at Libong Island and Tharai Island in Thailand. The contribution of the primary sources to the fauna diet showed that seagrass material was the main food source for fauna in both sites. Moreover, the trophic niche did not overlap among the groups of each fauna guild, reflecting the support seagrass provides to resident fauna. The study emphasizes the important role of seagrass as a habitat and feeding ground in tropical coastal ecosystems.

Distribution, sources, impact factors and ecological risks of sediment heavy metals from typical estuarine wetlands in tropical islands

Heavy metal contamination in the estuarine wetlands of tropical islands is becoming increasingly severe. This study focused on four typical estuarine wetlands of Hainan Island, including the mangrove and seagrass areas in Lingshui County, the mangrove and seagrass areas in Xinying Port, the mangrove area in Sibi Wan, and the seagrass area in Huachang Wan. By analyzing the heavy metal content in the surface sediments of these wetlands, we investigated the distribution characteristics and levels, explored their influencing factors, and assessed ecological risk of heavy metals in these areas. It was found the accumulation of heavy metals was high from obvious sampling sites of human activities, the type of sediment could affect the adsorption of heavy metals, with silty mudflats accumulating more. TOC/TN indicated that the organic sources of mangroves were diverse, included environmental impacts and human interference. According to the soil accumulation index and potential ecological risk index in these areas, almost all heavy metals were unpolluted except for As, which showed moderate pollution levels. The overall ecological risk in these areas was relatively low. The results of principal component analysis and correlation analysis indicated that Pb, Cu, and As were primarily sourced from human activities, while Cr was mainly of natural origin. Moreover, the distribution of heavy metals in the study areas was principally affected by TOC and salinity.

Evaluating UAV‐based multispectral imagery for mapping an intertidal seagrass environment

Abstract Worldwide seagrass habitats are under severe anthropogenic threat. In the United Kingdom (UK), the health of habitats of the widely distributed Zostera species is particularly threatened by eutrophication that can lead to detrimental macroalgae overgrowth. To manage and conserve seagrass habitats, effective monitoring tools are required. We use an off‐the‐shelf consumer‐grade multispectral (RGB, red edge, and near‐infrared) camera mounted on an unoccupied aerial vehicle (UAV) to map an intertidal multispecies seagrass environment in Lindisfarne National Nature Reserve, Northumberland, UK. Field surveys were undertaken of three seagrass areas, including those dominated by Zostera noltii, Zostera marina and macroalgae. Using the Maximum Likelihood Classifier (MLC), results indicated an overall accuracy (OA) between 84% and 91% across classified habitat maps. As expected, the red edge and near‐infrared bands offered an advantage beyond RGB imagery to discriminate between the vegetation types for accurate habitat mapping. Our research provides a foundation for accurately mapping a complex intertidal seagrass environment through the utilisation of an off‐the‐shelf multispectral UAV. The study may aid the implementation and development of effective monitoring programmes for the management of Zostera spp. decline and macroalgae proliferation to prevent seagrass degradation and conserve these valuable yet fragile ecosystems.

Benthic habitat mapping for estimating seagrass carbon stock across Takabonerate Islands, Indonesia

Data on benthic habitat cover are essential for monitoring and managing coastal areas, providing valuable ecosystem services for local communities. Moreover, seagrass extent is crucial for estimating carbon stock using Tier-1 calculations. On the other side, remote sensing technology has proven effective in mapping benthic habitat cover, including seagrass, over large local areas. Therefore, this research aims to map specific benthic habitats in a local area to obtain high-accuracy estimates of seagrass extent for carbon stock estimation. The study was conducted in the Takabonerate Islands, Indonesia, using Sentinel-2A imagery. The study involved field data processing, which enabled the mapping of eight benthic habitat classes using Sentinel-2A images, along with the steps for Sentinel-2A image processing for benthic habitat mapping. The benthic habitat map was produced following image correction steps, including atmospheric, sunglint, and water column corrections, followed by image classification using a Neural Net Classifier (NNC). Seagrass carbon stock estimation was performed using the Tier-1 equation from IPCC 2013. The study revealed a total benthic habitat area of 57,538.04 ha, with a seagrass area of 3127.42 ha for carbon stock estimation. The potential seagrass carbon stock in the study area was estimated to range from 337.76 GgC/ha to 31.27 GgC/ha using the Tier-1 equation. The overall accuracy of the benthic habitat map was 80.5 %, calculated using a confusion matrix table. The spatial information from this study can be used by local coastal managers and governments for baseline and monitoring purposes. The key interpretations from this study provide valuable findings that can be adapted and improved for future local mapping purposes.

Baseline study on the seagrass distribution and species diversity of the seagrass at West Sea (Viet Nam) with integrated approaches

Seagrass beds are one of the most important marine ecosystems, but they are facing critical threats worldwide. Like other regions in the world, this fragile ecosystem is declining in Viet Nam. The seagrass distribution and species diversity of some archipelagos and islands of the West Sea of Viet Nam are still poorly studied. In this study, small scale seagrass beds from 30 sites were mapped, species diversity was also determined. Ground surveys and SENTINEL-2 image analyses were applied to determine the distribution of seagrass meadows in the region. Morphological examination was used to identify specimens. For the Halophila ovalis complex, a nuclear genetic marker (ITS1–5.8S-ITS2) was applied. In addition, the consensus ITS2 secondary structure was also used to check the genetic relationship among H. ovalis and closely related species including H. minor, H. major and H. nipponica. The results indicate that the total area of seagrass in the West Sea of Viet Nam is updated with 7632 ha.

Seagrass recovery trajectories and recovery potential in relation to nutrient reduction

Abstract Seagrass recovery has been reported across the globe where previously eutrophied waters have become less nutrient‐rich. In the European Wadden Sea, different recovery trajectories were found after riverine nutrient loads decreased, namely full, temporary and no recovery. We compiled intertidal seagrass presence (Zostera noltei and Z. marina) and eutrophication data for 1930–2020, to relate the seagrass trajectories and regional eutrophication differences to riverine nutrient loads, and inferred prospects for seagrass recovery. Seagrass fully recovered in the less eutrophic North Frisian region. The recovery trajectory was tightly coupled to riverine nutrient load reduction. Relative seagrass area (meadow area/region area) dropped from 10% prior to eutrophication to 2% during the eutrophication peak, increased to 7% during the nutrient reduction period and subsequently expanded to 13%. Colonization of marginal habitats was observed, indicating propagule spillover from neighbouring meadows. The more eutrophic southern regions showed no or only temporary seagrass recovery. Prospects for (limited) recovery are good in only two out of four southern regions, provided that riverine nutrient loads are further reduced by ~40% (reference: 2010–2017). Without this reduction, seagrasses may only temporarily recover and will remain vulnerable to erratic disturbances like macroalgae accumulation or storms. Historical evidence and application of habitat suitability models suggest that the potential relative seagrass area in the southern regions is low: less than 0.2% in the western Dutch region and maximum 2.4% in the Ems‐Jade region. Synthesis and applications. Within a large seascape (15,000 km2) the least eutrophicated region showed seagrass recovery upon nutrient reduction. We translated the critical riverine nutrient loads for this recovery, via regional eutrophication indicators, to loads that may enable a sustained recovery in the other regions. This technique is applicable in other complex systems, provided sufficient historical data are available. Propagule spillover exerts a positive feedback at metapopulation scale leading to acceleration of recovery. Occupied and potential seagrass habitat (e.g. assessed by the maximum recorded area in the past) are thus important landscape selection criteria for restoration, particularly when eutrophication is not yet sufficiently reduced.

KOMPARASI JUMLAH HASIL TANGKAPAN JARING INSANG DASAR PADA DAERAH KARANG DAN LAMUN DI DESA LEBETAWI, KOTA TUAL

Bottom gillnet is a fishing gear which is operated in the morning, afternoon, and evening in the waters around Lebetawi Village. However, there is limited information about the specific composition of catch, especially the differences of catch between coral and seagrass areas. The aim of this study is to compare the number of catches from coral and seagrass areas and how the fish were first caught. The research was conducted for two months, from December 2023 to January 2024, in the waters of Lebetawi Village, Tual City, Southeast Maluku Regency. Data was collected from precisely observation on bottom gillnet aperated at seagrass and coral habitatss. The catches consisted of 18 species, with total 220 individuals fish and weight 34,161.18 grams. Throughout the fishing operations at both habitats, all demersal and pelagic fish were captured by way of gilled and wedged.

Insights on Evaluating Commercially Important Macroinvertebrate Species in Danjugan Island Marine Reserve, Philippines

The commercial importance of benthic macroinvertebrates like echinoderms and molluscs has led to the overexploitation of wild stocks in many areas around the Philippines. Despite their ecological and economic importance, studies on the status of wild populations of commercial macroinvertebrates in unexploited habitats such as marine protected areas (MPAs) are very scarce. The diversity and abundance of commercially valuable echinoderms and molluscs in the seagrass and reefs of Danjugan Island Marine Reserve were assessed. Shallow areas (1-3 m depth) around the island were surveyed both during the day and after dusk using belt transects. A total of 226 individuals belonging to 21 different taxa were recorded during the surveys, of which 71% were molluscs and 29% were echinoderms. In the seagrass habitat, Cypraeidae, Toxopneustidae, and Conidae were the dominant families, while molluscs from the Cardiidae family comprised more than half of the total assemblage in the reef flat. The most diverse commercial macroinvertebrate group was Holothuriidae with five different species. The densities of the families were higher during dusk than during the day in both habitats, except for Cardiidae in the seagrass. The highest values of species richness and H´ index were observed during dusk surveys in the reef habitat (H´= 1.57), while the lowest was observed in seagrass areas during morning surveys (H´= 1.37). This is the first study that assessed commercially valuable macroinvertebrates during day and night in two connected habitats within a protected area. The differences in diversity and abundance in each habitat depending on the time of day highlight the importance of considering these factors when evaluating macroinvertebrate populations in unexploited areas.

Rapid seagrass meadow expansion in an Indian Ocean bright spot

The areal extent of seagrass meadows is in rapid global decline, yet they provide highly valuable societal benefits. However, their conservation is hindered by data gaps on current and historic spatial extents. Here, we outline an approach for national-scale seagrass mapping and monitoring using an open-source platform (Google Earth Engine) and freely available satellite data (Landsat, Sentinel-2) that can be readily applied in other countries globally. Specifically, we map contemporary (2021) and historical (2000–2021; n = 10 maps) shallow water seagrass extent across the Maldives. We found contemporary Maldivian seagrass extent was ~ 105 km2 (overall accuracy = 82.04%) and, notably, that seagrass area increased threefold between 2000 and 2021 (linear model, + 4.6 km2 year−1, r2 = 0.93, p < 0.001). There was a strongly significant association between seagrass and anthropogenic activity (p < 0.001) that we hypothesize to be driven by nutrient loading and/or altered sediment dynamics (from large scale land reclamation), which would represent a beneficial anthropogenic influence on Maldivian seagrass meadows. National-scale tropical seagrass expansion is unique against the backdrop of global seagrass decline and we therefore highlight the Maldives as a rare global seagrass ‘bright spot’ highly worthy of increased attention across scientific, commercial, and conservation policy contexts.

Utilization of Satellite Imagery for Mapping the Distribution of Seagrass on Buhung Pitue Island

Buhung Pitue Island has seagrass beds those which are spread almost evenly along its coast. Research using remote sensing technology in an effort to support seagrass conservation in Indonesia needs to be carried out. Spatial data is relatively easy to obtain because there are many types of images with various spatial resolutions. The image can be obtained on google earth. Analysis of the distribution of seagrass areas was obtained by digitizing on screen in ArcGIS software, namely in seagrass areas where the boundaries are known. Digitizing is conducted by enlarging the seagrass area in the downloaded image, performing radiometric and geometric corrections, and digitizing to create a shapefile (shp) storing the location, shape, and attributes of geographic features. The seagrass distribution area of Buhung Pitue Island was of 36.5 Ha in 2014 and was of 39.6 in 2021. The rate of change in area from 2014 to 2021 was of 0.085% (an increase of 3.1 ha). The distribution area of seagrass has increased due to natural factors and restrictions on human activities during the COVID-19 pandemic. In addition, another factor supporting the increase in seagrass distribution is the abundance of Enhalus acoroides seagrass species growing and spreading over long distances. The sea surface temperature was high, which was 30.37 °C, while the current speed was categorized as slow because it was around 0.01 m/s. Although the results are obtained from high-resolution imagery, an accuracy test still needs to be conducted.

Use and management of seagrass ecosystems in southwestern Madagascar

Madagascar’s seagrass meadows are among the least-studied ecosystems in the western Indian Ocean region. To facilitate sustainable management, understanding the traditional uses of seagrass areas in relation to current management policies is necessary. This study assessed the uses of, and policies relevant to, seagrass ecosystems off southwestern Madagascar. We interviewed 131 community members in five coastal villages around the Bay of Ranobe in Toliara Province. Answers to the survey revealed a good level of awareness of seagrass, though 55% of respondents perceived the status of the seagrass areas as deteriorating. Opinions varied on the source or degree of threats to seagrass, but 74.8% of respondents suggested destructive fishing methods or other factors, including natural phenomena and animal grazing. The responses highlight that seagrass meadows serve as areas important for fishing, seaweed cultivation or sea cucumber farming, and the passage of boat/pirogue transportation. There are currently no tangible policies that directly protect or manage the seagrass areas regarding these activities, although some national regulations and local management initiatives are indirectly relevant, notably no-take zones and the local-level codes known as Dina. Development and implementation of a national management plan for seagrass ecosystems is a key gap. This demands the collection of scientific data to support decision-making to ensure long-term provision of the services provided by seagrass meadows. The involvement of coastal communities in the management of seagrass ecosystems will be necessary for the success of any new policies.

Carbon Sequestration Potential of Seagrasses species in the selected sites of Don Marcelino, Davao Occidental, Philippines

The study determined the carbon sequestered by seagrasses from the three (3) coastal sites of Don Marcelino, namely Talagutong, Kinanga, and Lawa. The study employed one-shot sampling as part of a preliminary survey visit at the study sites. The survey was conducted during the lowest tide of the day, and the observation of seagrass species was limited to a depth of 0–3 meters. A total of four species of seagrasses were identified using taxonomic field guides. The species Halodule pinifolia, Thalassia hemprichii, and Cymodocea rotundata were present in Talagutong, while Thalassia hemprichii, Cymodocea rotundata, Halophila ovalis, and Halodule pinifolia were recorded in Kinanga and Lawa. Thalassia hemprichii is the most dominant seagrass species and has the highest percent cover, followed by Cymodocea rotundata. Moreover, Thalassia hemprichii is more dominant in the study area, which also obtained the highest shoot density, followed by Cymodocea rotundata. Cymodocea rotundata obtained the highest sequestered total carbon from Lawa compared to the other two (2) sites. The carbon sequestered by Thalassia hemprichii in Talagutong and Lawa is significantly higher compared to Kinanga. Furthermore, the carbon sequestered by Halophila sp. in Lawa and Kinanga is significantly higher (21.56 and 18.56 (g/m²) than in Talagutong. It is highly recommended to the local government units to include seagrass areas of Don Marcelino into marine protected areas as a part of the implementation of proactive climate change mitigation.

Extensive and Continuing Loss of Seagrasses in Florida's Big Bend (USA).

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

Substantial blue carbon sequestration in the world’s largest seagrass meadow

Seagrass meadows are important sinks for organic carbon and provide co-benefits. However, data on the organic carbon stock in seagrass sediments are scarce for many regions, particularly The Bahamas, which accounts for up to 40.7% of the documented global seagrass area, limiting formulation of blue carbon strategies. Here, we sampled 10 seagrass meadows across an extensive island chain in The Bahamas. We estimate that Bahamas seagrass meadows store 0.42–0.59 Pg organic carbon in the top-meter sediments with an accumulation rate of 2.1–2.9 Tg annually, representing a substantial global blue carbon hotspot. Autochthonous organic carbon in sediments decreased from ~1980 onwards, with concomitant increases in cyanobacterial and mangrove contributions, suggesting disturbance of seagrass ecosystems, likely caused by tourism and maritime traffic activities. This study provides seagrass blue carbon data from a vast, understudied region and contributes to improving climate action for The Bahamas and the Greater Caribbean region.

The influence of freshwater inflow and seascape context on occurrence of juvenile spotted seatrout Cynoscion nebulosus across a temperate estuary.

Spotted seatrout, a popular recreational sport fish in the southeastern United States, are affected by freshwater flow conditions and the availability of estuarine habitat. However, the relative influence of these factors, particularly on early life stages of seatrout, remains uncertain. We used generalized linear models to quantify relationships between the probability of encountering juvenile spotted seatrout during seine surveys and various factors, including freshwater inflow conditions, the availability and richness of estuarine habitats (seagrass, salt marsh, oyster beds) around (400-m radius) fish collection sites (seascape-scale context), as well as distance to the nearest inlet to the Gulf of Mexico (estuary-scale context) across shallow waters (< 1.5 m depth) of Apalachicola Bay, Florida. Modelling results showed a consistent positive correlation between seagrass area and the probability of encountering juvenile seatrout (all four size classes from 15mm-200mm Standard Length (SL)). The probability of encountering the two smallest juvenile seatrout size classes (15-50mm and 51-100mm SL) was also related to freshwater inflow conditions, particularly within a 3-month period prior to and including peak recruitment. Freshwater inflow may affect early life stages by influencing passive transport of eggs and larvae, planktonic food availability, and predation pressure through increases in turbidity. In contrast, encounter probabilities of the two larger size classes (101-150mm and 151-200mm) were unrelated to freshwater inflow. Inflow-related processes may be less important to the larger juveniles as they have typically settled out of the plankton into benthic habitats which provide refuge from predation and abundant benthic food sources which are not as closely tied to freshwater inflow effects. In addition, models revealed that occurrence of the larger juveniles was related to the availability of nearby habitat types such as oyster beds and salt marshes, suggesting that increased mobility as seatrout grow may allow them to use nearby habitat types as additional sources of food and refuge. These results add to a growing body of literature aimed at understanding the influence of freshwater inflow as well as seascape context on vulnerable juvenile life stages of fishery species to provide more informed strategies for freshwater inflow management and habitat conservation.

Species Identification of Sea Bamboo (Isis hippuris) using COI-based DNA Barcoding

Conservation and effective management of marine ecosystems and biodiversity requires accurate species identification. This study classifies sea bamboo (Isis hippuris) specimens using DNA barcoding, a technique widely recognized for its speed, accuracy, and objectivity. This study examines the cytochrome c oxidase subunit I (COI) gene analysis for species identification. Isis hippuris was collected from two stations (coral and seagrass areas) of Tanjung Tiram Waters, South Konawe, Southeast Sulawesi. Genomic DNA was extracted from the base, main, and lateral stem of I. hippuris. Polymerase chain reaction (PCR) was used to amplify the mtDNA of I. hippuris with HCO2198 and LCO1490 primers. The highest quality PCR product based on the COI gene was chosen for sequencing analysis. The study revealed that COI gene analysis could only be performed on the base and main stem of the I. hippuris. Samples from coral and seagrass-coral areas on lateral stems were not further analyzed due to low concentration and purity values, which could potentially fail DNA sequencing. Each part of I. hippuris may have unique genetic differences. This study highlights the advantages of DNA sequencing in providing a unique genetic fingerprint for each species, enabling accurate species identification. This research provides insight into using DNA barcoding for sea bamboo species identification.

Macroinvertebrate assessment in seagrass ecosystem in Sinacaban Municipality, Misamis Occidental, Philippines

Abstract. Mahilac HMO, Tandingan JP, Torres AG, Amparado JRR, Roa-Quiaoit HA. 2023. Macroinvertebrate assessment in seagrass ecosystem in Sinacaban Municipality, Misamis Occidental, Philippines. Biodiversitas 24: 5586-5597. Marine ecosystems such as seagrasses are economically and ecologically important in tropical coastal areas like Sinacaban municipality, southern Philippines. This study assessed the macrobenthic species and water quality (e.g., pH, salinity, temperature, Dissolved Oxygen (DO), and total suspended solids (TSS) in three seagrass areas in the municipality. The study showed the seagrass habitats with 40 macrofaunal species from the classes Gastropoda (27), Bivalvia (11), and Crustacea (2), with Clibanarius longitarsus as the most abundant species (77 individuals or 24% relative abundance). The Strombidae family holds the highest dominance within the Gastropoda class, whereas the Arcidae family is the most dominant within the Bivalvia class. However, there is no dominant family within the Crustacea class. Water quality showed pH at 7, 30 ppt salinity, and 28? within their standard limits, while DO (8 mg/L) and TSS (127 mg/L) exceeded their range. This study recorded eight economic important species and five least concern International Union for Conservation of Nature (IUCN) species. Among the three (3) sites, the seagrass area in Libertad has the highest species richness (28), Shannon’s Index (2.92), and species evenness (0.66). The Chao estimation result revealed that Libertad (37.17) and Poblacion (18.5) have lower uncertainty in their species estimates than Colupan (39.60), which has a wider range of potential species richness. The Canonical Correspondence Analysis (CCA) proved that there are species that can adapt to a certain level of environmental parameters, like Angaria delphinus, while Decatopecten radula is one of the species that does not correlate with the water parameters in the study. The findings are critical for biodiversity conservation, ecosystem management, sustainable resource use, and adaptation to changing environments in order to maintain ecological balance and the long-term health of the seagrass ecosystem.

Effects of heatwave events on the seagrass-dwelling crustacean Pandalus latirostris in a subarctic lagoon

Heatwaves often cause mass mortality of organisms in seagrass areas, and they eventually alter some ecological functions of seagrass ecosystems. In subarctic regions, however, the effects of heatwaves on seagrass areas are still unclear. In a subarctic lagoon of northern Japan, we examined the effects of heatwaves on the Hokkai shrimp, Pandalus latirostris, a commercially exploited species distributed in seagrass areas of northern Japan and eastern Russia. A long-term survey of the surface water temperature in the lagoon clarified a gradual increase in the frequency and intensity of heatwave events since 1999. Surveys of the water temperature at a seagrass area in the lagoon during summer have also demonstrated that the maximum water temperature had been exceeding 25 °C, unusually high for this location, regardless of water depth. These results indicate that the effects of heatwaves in seagrass areas in a subarctic region had become as severe as those in tropical and temperate regions. We also experimentally evaluated the effects of this unusually high water temperature (25 °C) on the survival of P. latirostris by changing the length of exposure time. Some individuals suffered damage to their intestinal mucosal structure after exposure for 12 h or longer, and all individuals died after exposure for 120 h. Our results suggest that heatwaves possibly cause mass mortality in P. latirostris in the following sequence: heat stress, damage to the intestinal epithelial mucosal structure, degradation of nutrient absorption and immunological function of the intestine, energy deficiency and disease infection, and finally mortality. This study, conducted in subarctic closed waters, concludes that it is essential to become familiar with not only trends in heatwaves but also the intermittent occurrence of unusually high water temperature in seagrass areas in order to better understand the process of mortality of organisms that inhabit these ecosystems.

Microplastic contamination in sediment and Strombus sp. on Bintan Island, Indonesia

The high level of public plastic consumption can trigger the increase of plastic and waste in marine areas. Plastic floats in the ocean will then be degraded into smaller sizes (<5 mm), namely microplastics. Microplastic can be dangerous to marine environments, especially to natural resources, including sediment and marine biotas., where microplastics are easily eaten by diverse marine biota. Bintan Island is a conservation area with abundant seagrass and associated biota resources, especially Strombus sp. This study examines microplastic contamination in sediment and Strombus sp. on Bintan Island, Indonesia. Samples (Strombus sp.) were collected from a 100 x 20 meter seagrass area, while sediment samples were taken in a 1 m x 1 m quadrant. The sediment was dried, and the biota was dissected to see the presence of microplastics. All microplastics collected from both samples were identified in shape and colour. The results showed that microplastics had been found in sediment and Strombus sp. Based on the characteristics of microplastics, the highest abundance of colour found was white, while the highest abundance of types found was a fragment