Multisensor and Multitemporal Data from Landsat Images to Detect Damage to Coral Reefs, Small Islands in the Spermonde Archipelago, Indonesia

Nurjannah Nurdin,Teruhisa Komatsu,Agus,M. Akbar AS,Abdul Rasyid Djalil,Khairul Amri 한국해양과학기술원 2015 Ocean science journal Vol.50 No.2

Coral reefs are important because of their high biodiversity and their key role in the tropical marine biosphere. Furthermore, coral reefs are very valuable as a socioeconomic resource as they make important contributions to the gross domestic product of many countries. Thus, it is very important to monitor dynamic spatial distributions of coral reefs and related habitats dominated by coral rubble, dead coral, and bleached corals. Despite these natural and socio-economic advantages, many factors are threatening coral reefs. The study site was selected in Spermonde archipelago, South Sulawesi, Indonesia because this area is included in the Coral Triangle, recognized as the epicenter of coral diversity and a priority for conservation. Images of Landsat MSS, Landsat TM, Landsat ETM, Landsat ETM+, and Landsat 8 data were used to examine changes in the coral reefs of Suranti Island in the Spermonde Archipelago during forty one years from 1972 to 2013. The image processing includes gap fills, atmospheric corrections, geometric corrections, image composites, water column corrections, unsupervised classifications, and reclassifications. Fill Gap processing was done on Landsat ETM+ SLC-off. Subsequently, a multi-component change detection procedure was applied to define changes. Shallow water bottom types classification was divided into live coral, rubble and sand habitats, dead coral with algae, rubble, and sand. Preliminary results showed significant changes during the period 1972-2013 as well as changes in coral reefs, likely explained partly by destructive fishing practices.

Simulation of Seagrass Bed Mapping by Satellite Images based on the Radiative Transfer Model

Tatsuyuki Sagawa,Teruhisa Komatsu 한국해양과학기술원 2015 Ocean science journal Vol.50 No.2

Seagrass and seaweed beds play important roles in coastal marine ecosystems. They are food sources and habitats for many marine organisms, and influence the physical, chemical, and biological environment. They are sensitive to human impacts such as reclamation and pollution. Therefore, their management and preservation are necessary for a healthy coastal environment. Satellite remote sensing is a useful tool for mapping and monitoring seagrass beds. The efficiency of seagrass mapping, seagrass bed classification in particular, has been evaluated by mapping accuracy using an error matrix. However, mapping accuracies are influenced by coastal environments such as seawater transparency, bathymetry, and substrate type. Coastal management requires sufficient accuracy and an understanding of mapping limitations for monitoring coastal habitats including seagrass beds. Previous studies are mainly based on case studies in specific regions and seasons. Extensive data are required to generalise assessments of classification accuracy from case studies, which has proven difficult. This study aims to build a simulator based on a radiative transfer model to produce modelled satellite images and assess the visual detectability of seagrass beds under different transparencies and seagrass coverages, as well as to examine mapping limitations and classification accuracy. Our simulations led to the development of a model of water transparency and the mapping of depth limits and indicated the possibility for seagrass density mapping under certain ideal conditions. The results show that modelling satellite images is useful in evaluating the accuracy of classification and that establishing seagrass bed monitoring by remote sensing is a reliable tool.

Ten Years' Monitoring of Intertidal Macroalgal Vegetation of Hyogo Prefecture, Northwestern Coast of Honshu, Japan to Assess the Impact of the Nakhodka Oil Spill

Kawai, Hiroshi,Kamiya, Mitsunobu,Komatsu, Teruhisa,Nakaoka, Masahiro,Yamamoto, Tomoko,Marine Life Research Group of Takeno, Marine Life Research Group of Takeno The Korean Society of Phycology 2007 ALGAE Vol.22 No.1

In order to understand the impact of the heavy-oil pollution by the 1997 Nakhodka oil spill on the intertidal macroalgal vegetation, we have been monitoring succession in the intertidal flora since 1997 at Oh-ura, Takno, and Imago-Ura Cove, Kasumi in Hyogo Prefecture, northwestern coast of Honshu, Japan. We employed two different monitoring methods: 1) The percent cover of macro-algae (seaweeds) in 1 x 1 m quadrats along 450 m intertidal transects parallel to the shoreline were assessed and recorded by photographic imaging until 2002, and for 30-40 m transects of the most heavily polluted areas in 2004 and 2006; 2) The percent cover of macro-algae in 0.5 x 0.5 m quadrats along a transect line perpendicular to the shore were recorded and all macrophytes within the quadrat were completely removed to record the wet weight of each taxon (1997-2006). Based on the monitoring data, we conclude that the high intertidal zone at Imago-ura, where a large part of the stranded oil accumulated, suffered the heaviest damage and experienced the slowest recovery. In addition, although the original status of macroalgal vegetation before the impact was not well-documented, it appeared that recovery from the damage caused by the oil pollution required four to five years.

Estimation of Seagrass Biomass by In Situ Measurement and Remote Sensing Technology on Small Islands, Indonesia

Nurjannah Nurdin,Khairul Amri,Supriadi Mashoreng,Teruhisa Komatsu 한국해양과학기술원 2022 Ocean science journal Vol.57 No.1

As one of the major blue carbon ecosystems, studying, conserving, and monitoring seagrass meadows, especially on small populated islands, has become very important due to their vulnerability to anthropogenic and global environmental factors. In this study, we used satellite image analysis and biological data to map seagrass percent cover (SPC), above-ground biomass (AGB), and below-ground biomass (BGB) on the three most populated islands of the Spermonde Archipelago, Indonesia, i.e., Kodingareng Lompo, Barrang Lompo, and Barrang Caddi. Reflectance and Normalized Difference Vegetation Index (NDVI) values of Sentinel-2 (S2) imagery were used to classify and calculate SPC and AGB. In situ biological data measurements were carried out from 3 to 14 of June, 2020, on the three islands to measure AGB and BGB. The result from image classification shows a total area of 126.37 Ha of seagrass, which was divided into three SPC categories: medium (30–59.9%) with a total area of 78.38 Ha; low (0–29.9%) with a total area of 13.1 Ha; and high (60–100%) with a total area of 34.89 Ha. The highest SPC area was observed on Kodingareng Lompo Island with 61.07Ha, followed by Barrang Lompo Island with 53.18Ha, and Barrangcaddi Island with 12.12Ha. The total AGB on Barrang Lompo, Kodingareng Lompo, and Barrangcaddi in tons of dry weight/ha were 1.83, 1.05, and 2.38, respectively. The highest BGB was reported on Barrangcaddi Island with 8.61 tons of dry weight/ha, followed by Barrang Lompo Island with 6.78 tons of dry weight/ha, and Kodingareng Lompo Island with 2.78 tons of dry weight/ha. Regression analysis showed a linear correlation between NDVI value and in situ SPC with R2 = 0.8255. The framework of this study can be applied to monitor temporal changes of seagrass meadows distribution on small islands to promote a more sustainable ecosystem.

Systematics of Marine Brown Alga Sargassum from Thailand: A Preliminary Study Based on Morphological Data and Nuclear Ribosomal Internal Transcribed Spacer 2 (ITS2) Sequences

Attachai Kantachumpoo,Shinya Uwai,Thidarat Noiraksar,Teruhisa Komatsu 한국해양과학기술원 2015 Ocean science journal Vol.50 No.2

The marine brown algal genus Sargassum has been investigated extensively based on genetic information. In this report, we performed the first comparative study of morphological and molecular data among common species of Sargassum found in Thailand and explored the phylogenetic diversity within the genus. Our results revealed an incongruent pattern for species classification in Thai Sargassum. Morphologically, our Sargassum specimens were distinguishable and represented 8 species, namely, S. aquifolium (Turner) C.Agardh, Sargassum baccularia (Mertens) C. Agardh, S. cinereum J. Agardh, S. ilicifolium (Turner) C.Agardh, S. oligocystum Montagne, S. plagiophyllum C. Agardh, S. polycystum C. Agardh and S. swartzii (Turuner) C. Agardh. In contrast, using three different methods, phylogenetic analysis of nuclear ribosomal internal transcribed spacer 2 (ITS2) revealed six distinct clades, including S. baccularia/S. oligosyntum clade, S. aquifolium/S. swartzii clade, S. cinereum clade, S. aquifolium/S. ilicifolium clade, S. polycystum clade, and S. plagiophyllum clade, which was suggestive of a phenotypic plasticity species complex. Our molecular data also confirmed the paraphyletic relationship in the section Binderianae and suggested that this section requires reassessment. Overall, further studies are required to increase our understanding of the taxonomy, phylogenetic relationships and species boundaries among Sargassum species in Thailand.

Three-Dimensional Mapping of Red Stingray (Dasyatis akajei) Movement with Reference to Bottom Topography

Takayoshi Otaki,Masahiro Hamana,Hideaki Tanoe,Nobuyuki Miyazaki,Takuro Shibuno,Teruhisa Komatsu 한국해양과학기술원 2015 Ocean science journal Vol.50 No.2

Most demersal fishes maintain strong relations with bottom substrates and bottom depths and/or topography during their lives. It is important to know these relations to for understand their lives. In Tokyo Bay, red stingray, Dasyatis akajei, classified as near-threatened species by IUCN, has increased since the 1980s. It is a top predator and engages in ecosystem engineer by mixing the sand bed surface through burring behavior, and greatly influences a coastal ecosystem. It is reported that this species invades in plage and tidal flats and has sometimes injured beachgoers and people gathering clams in Tokyo bay. Thus, it is necessary to know its behavior and habitat use to avoid accidents and to better conserve the biodiversity of ecosystems. However, previous studies have not examined its relationship with the bottom environment. This study aims to describe its behavior in relation to the bottom environment. We sounded three dimensional bottom topography of their habitat off Kaneda Cove in Tokyo Bay with interferometric sidescan sonar system and traced the movement of red stingrays by attaching a data logger system to survey their migration. The results revealed that red stingray repeated vertical movement between the surface and bottom, and used not only sand beds but also rocky beds.

Introduction of Geospatial Perspective to the Ecology of Fish-Habitat Relationships in Indonesian Coral Reefs: A Remote Sensing Approach

Shuhei Sawayama,Nurjannah Nurdin,Muhammad Akbar AS,Shingo X Sakamoto,Teruhisa Komatsu 한국해양과학기술원 2015 Ocean science journal Vol.50 No.2

Coral reef ecosystems worldwide are now being harmed by various stresses accompanying the degradation of fish habitats and thus knowledge of fish-habitat relationships is urgently required. Because conventional research methods were not practical for this purpose due to the lack of a geospatial perspective, we attempted to develop a research method integrating visual fish observation with a seabed habitat map and to expand knowledge to a two-dimensional scale. WorldView-2 satellite imagery of Spermonde Archipelago, Indonesia obtained in September 2012 was analyzed and classified into four typical substrates: live coral, dead coral, seagrass and sand. Overall classification accuracy of this map was 81.3% and considered precise enough for subsequent analyses. Three sub-areas (CC: continuous coral reef, BC: boundary of coral reef and FC: few live coral zone) around reef slopes were extracted from the map. Visual transect surveys for several fish species were conducted within each sub-area in June 2013. As a result, Mean density (Ind. / 300 m2) of Chaetodon octofasciatus, known as an obligate feeder of corals, was significantly higher at BC than at the others (p < 0.05), implying that this species’ density is strongly influenced by spatial configuration of its habitat, like the “edge effect.” This indicates that future conservation procedures for coral reef fishes should consider not only coral cover but also its spatial configuration. The present study also indicates that the introduction of a geospatial perspective derived from remote sensing has great potential to progress conventional ecological studies on coral reef fishes.

Ten Years’ Monitoring of Intertidal Macroalgal Vegetation of Hyogo Prefecture, Northwestern Coast of Honshu, Japan to Assess the Impact of the Nakhodka Oil Spill

Hiroshi Kawai,the Marine Life Research Group of Takeno,Tomoko Yamamoto,Masahiro Nakaoka,Teruhisa Komatsu,Mitsunobu Kamiya 한국조류학회I 2007 ALGAE Vol.22 No.1

In order to understand the impact of the heavy-oil pollution by the 1997 Nakhodka oil spill on the intertidal macroalgal vegetation, we have been monitoring succession in the intertidal flora since 1997 at Oh-ura, Takno, and Imago-Ura Cove, Kasumi in Hyogo Prefecture, northwestern coast of Honshu, Japan. We employed two different monitoring methods: 1) The percent cover of macro-algae (seaweeds) in 1 x 1 m quadrats along 450 m intertidal transects parallel to the shoreline were assessed and recorded by photographic imaging until 2002, and for 30-40 m transects of the most heavily polluted areas in 2004 and 2006; 2) The percent cover of macro-algae in 0.5 x 0.5 m quadrats along a transect line perpendicular to the shore were recorded and all macrophytes within the quadrat were completely removed to record the wet weight of each taxon (1997-2006). Based on the monitoring data, we conclude that the high intertidal zone at Imago-ura, where a large part of the stranded oil accumulated, suffered the heaviest damage and experienced the slowest recovery. In addition, although the original status of macroalgal vegetation before the impact was not well-documented, it appeared that recovery from the damage caused by the oil pollution required four to five years.