Eco-geomorphic processes that maintain a small coral reef island: Ballast Island in the Ryukyu Islands, Japan

Aoki, Kenji; Suzuki, Takuya; Hongo, Chuki; Yamano, Hiroya; Ide, Yoichi; Iwatsuka, Yuudai; Takahashi, Kenya; Katayama, Hiroyuki; Sekimoto, Tsunehiro; Isobe, Masahiko

doi:10.1016/j.geomorph.2016.07.021

Cited by 27 publications

(13 citation statements)

References 42 publications

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“…Much attention has been paid to the dynamics of atoll islands. Historical aerial photographs or satellite images with different spatial resolution over a period of time were usually rectified to each other and digitalized to investigate the stability of vegetated cays or islands [79]. However, in most cases, atoll islands have a paucity of distinct and stable features for ground control points, rendering georeferencing of images problematic [80].…”

Section: Application Of Pbcd and Obcd Methods In Multiple Coral Reefmentioning

confidence: 99%

Change Detection in Coral Reef Environment Using High-Resolution Images: Comparison of Object-Based and Pixel-Based Paradigms

Zhou

et al. 2018

IJGI

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Despite increases in the spatial resolution of satellite imagery prompting interest in object-based image analysis, few studies have used object-based methods for monitoring changes in coral reefs. This study proposes a high accuracy object-based change detection (OBCD) method intended for coral reef environment, which uses QuickBird and WorldView-2 images. The proposed methodological framework includes image fusion, multi-temporal image segmentation, image differencing, random forests models, and object-area-based accuracy assessment. For validation, we applied the method to images of four coral reef study sites in the South China Sea. We compared the proposed OBCD method with a conventional pixel-based change detection (PBCD) method by implementing both methods under the same conditions. The average overall accuracy of OBCD exceeded 90%, which was approximately 20% higher than PBCD. The OBCD method was free from salt-and-pepper effects and was less prone to images misregistration in terms of change detection accuracy and mapping results. The object-area-based accuracy assessment reached a higher overall accuracy and per-class accuracy than the object-number-based and pixel-number-based accuracy assessment. methods for coral reef change detection. However, because of the limitations of medium-resolution sensors such as Landsat and SPOT, it is difficult to distinguish coral reef geomorphological dynamics from sea level rise [10], and to detect changes on the scale of a few meters in coral reef habitats [11]. With continued refinement of the spatial resolution of satellite imagery, conventional per-pixel methods have been found susceptible to a number of challenges in relation to change detection, including image misregistration [6,12] and salt-and-pepper effects [13,14]. Coral reef images, lack of distinct and stable texture features, are difficult to be accurately registered to each other [15], which makes the traditional pixel-based approach less promising in coral reef change detection using high-resolution images.Recent years have seen an increase in the number of studies using object-based image analysis (OBIA) [13]. OBIA has also been applied in coral reef environment, from geomorphological mapping to benthic community discrimination [16][17][18]. OBIA represents an effective combination of both the contextual analysis of visual interpretation and the quantitative analysis of the pixel-based method [19]. It has been proven that image registration error greatly affects the per-pixel change detection accuracy while the object-based method is less sensitive to image misregistration [20,21]. However, to the best of our knowledge, few studies have used object-based change detection (OBCD) methods in coral reef change detection. Generally, there are two possible strategies for OBCD methods: post-classification comparison and multi-temporal image object analysis [22]. The essence of the post-classification comparison approach lies in the initial classification, i.e., images acquired at different times are classifi...

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Section: Application Of Pbcd and Obcd Methods In Multiple Coral Reefmentioning

confidence: 99%

Change Detection in Coral Reef Environment Using High-Resolution Images: Comparison of Object-Based and Pixel-Based Paradigms

Zhou

et al. 2018

IJGI

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“…For the coral reefs of Nansha Islands in the SCS, the high tide features formed on the reef platforms are relatively stable due to the growth of reef-building organisms and the accumulation of calcareous materials although the migration patterns of sand cays are subject to external disturbances. Apart from global climate change, the hydrodynamic disturbance such as high waves from tropical cyclones will cause severe damage to the newly formed sand cays and change readily their landforms above water (Kayanne et al, 2016). Specifically, storm surge is constructive to the accumulations of the coral detritus and bioclast, and the exposed sand cays that can stand still above water at high tide are subsequently formed on the platform of coral reefs, under which there will be freshwater lens developing when the radius of exposed area is more than 300 m (Zhao, 2005).…”

Section: Sand Cay and Its Evolutionmentioning

confidence: 99%

“…The predominant structures of Nansha Islands are coral reefs, islands, cays, shoals, etc. Among these geographical features, islands and cays are low-lying and mostly formed on the coral reef flats or infilled lagoons, which have an elevation of ranging from 1.0 m to 3.0 m (Kayanne, 2016). The accumulations are mainly composed of coral sand and gravel and stand above water at low or high tide, which are produced by reef-building organisms such as hermatypic corals and zooxanthellae (Perry et al, 2011).…”

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confidence: 99%

The geographical characteristics of Nansha Islands in the South China Sea

Jiang

Zhou

et al. 2018

J. Geogr. Sci.

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As is well-known, Nansha Islands in the South China Sea (SCS) are of important strategic position and invaluable ecological value. Therefore, many attentions are paid to either the political and legal aspects of exposed features that matter in the maritime delimitation, or the physical and geographical characteristics of coral reefs that are the predominant structures of these islands. However, it seems that they consistently lose the connection of sciences and humanities in the research of Nansha Islands in the SCS. In this study, we carry out a combinative research, based on remote sensing data using satellite imagery analysis together with historical materials using literature investigation, so as to reconsider to the geographical characteristics of Nansha Islands from a standpoint of the United Nations Convention on the Law of the Sea (UNCLOS). After thoroughly appraising the statuses of these newly formed sand cays, several high tide features of Nansha Islands are identified. By means of the comparison of satellite images coupled with reference to nautical charting and sailing directions during different time periods, we can conclude that the statuses of these high tide features formed on reef platforms are relatively stable due to the growth of reef-building organisms although their migration patterns are subject to external disturbances, and hence the cursory judgment pursuant to the relevant provisions of the UNCLOS about whether a coral reef belongs to a low tide elevation only based on outdated references or ex parte evidences is not reliable. Moreover, it is accordingly justified to improve further development and perfection of the maritime legislation by eliminating such ambiguities with the growth of coral reefs and the evolution of sand cays being both taken into account.

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“…Tropical cyclones have both positive (supply of bioclastics for cay accretion) and negative (erosion) influence on sand cay formation (Kayanne et al, ), which results in mixing and reworking of cay deposits. Consequently, radiometric dating of cay deposits can be problematic, as time lags may exist between the death of calcareous organisms and their final deposition within cays (Liu et al, ; Montaggioni et al, ; Woodroffe et al, ).…”

Section: Introductionmentioning

confidence: 99%

Tropical Sand Cays as Natural Paleocyclone Archives

Chen

Roff

Feng

et al. 2019

Geophysical Research Letters

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Sand cays are valuable paleo‐archives that can significantly increase our understanding of Holocene tropical cyclone variability. Here we conducted detailed sedimentological and chronological analyses from a 195‐cm‐depth pit excavated on Guangjin Island (northern South China Sea), a cay influenced by frequent tropical cyclones. Radiometric dating of multiple deposits revealed that foraminifera, soft coral spicules, and gastropod shells yielded variable age distributions, while U/Th ages of pristine Acropora branches provided a clear record of deposition and cay formation. Based on this robust chronostratigraphy, the proportions of >2‐mm grain size fraction within the deposits corresponded with the frequency of paleotyphoons recorded by historical records in recent centuries. U/Th ages (CE 1687 ± 12, CE 1735 ± 6, and CE 1813 ± 5) of Acropora branches from the deposits matched with three known historical typhoon events. Our results highlight the potential of cyclone‐deposited sand cays as new archives for recording paleocyclones.

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Eco-geomorphic processes that maintain a small coral reef island: Ballast Island in the Ryukyu Islands, Japan

Cited by 27 publications

References 42 publications

Change Detection in Coral Reef Environment Using High-Resolution Images: Comparison of Object-Based and Pixel-Based Paradigms

Change Detection in Coral Reef Environment Using High-Resolution Images: Comparison of Object-Based and Pixel-Based Paradigms

The geographical characteristics of Nansha Islands in the South China Sea

Tropical Sand Cays as Natural Paleocyclone Archives

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