As a way of turning sea into land for living space for humans, the actions of sea reclamation bring about significant benefits. Nevertheless, it is also an under-recognized threat to the environment and the marine ecosystem. Based on images in two periods, sea reclamation information of countries around the South China Sea was extracted from 1975 to 2010. The spatial state and driven forces of sea reclamation are then discussed. Results show that the overall strength of sea reclamation in the South China Sea was great. New reclaimed land added up to 3264 km². Sea reclamation for fish farming was the main reclamation type and widely distributed in the whole area, especially on the coast from the Pearl River Delta to the Red River Delta, and the coast of Ca Mau Peninsula. Sea reclamation in China and Vietnam was rather significant, which occupies 80.6% of the total reclamation area. Singapore had the highest level of sea reclamation. New reclaimed land for fish farming holds a key role in China, Vietnam, and Indonesia, while new reclaimed land for construction and docks dominated in Malaysia, Singapore, and Brunei. Areas and use-type compositions of new reclaimed land in countries varied greatly due to the differences of economic factors, policy inclination, and landscapes in the respective countries.

Specific knowledge about the characteristics of coastal land use along the sea–land direction helps to better understand the spatial heterogeneity of coastal land use, which could offer scientific support for rational land management and the sustainable development of the coastal zone. However, the traditional methods including buffering or the regional method are hard to extract detailed spatial structure and location correlations of coastal land use along the sea–land direction. Therefore, we developed a model, called sequence–based clustering of coastal land use pattern (SCCLUP), to mine the coastal land use sequence patterns (CLUSPs) along the sea–land direction. As a case study in the major coastal zone of Bohai Bay and the Yellow River Delta from 1990 to 2010, we found that: (1) The land use showed a sequential distribution along the sea–land direction. And the land use closed to shoreline and inland boundary had relative stable sequential location along the sea–land direction. However, the middle land uses had dynamic sequential locations that led to multiple CLUSPs; (2) due to the increasing percent of construction land, the artificial level of CLUSPs was continuously increasing and new CLUSPs tended to distribute around port areas. Different CLUSPs with similar land use sequential relationships tended to have similar land use structure along the sea–land direction; (3) the land uses sequential location along the sea–land direction revealed the actual distance of land use to the shoreline and had a tight correlation with environmental factors (salinity, water, and landform). The land use with large increasing and wide adaptivity (like construction land) had a large impact on the changes of CLUSPs in the study area. Therefore, strong control should be provided for the excessive expansion of land use like construction land to limit the over changes in land use pattern along the sea–land direction. Additionally, the spatial heterogeneity of land use along the sea–land direction should be considered to a better understanding of anthropic impacts on the coastal zone.

Bays are some of the core areas for marine economic development. The South China Sea coast is one of the most developed and dynamic places in the Asia-Pacific. In this study, we focused on the large bays surrounding the South China Sea. The techniques of image segmentation and supervised classification as well as image interpretation were used to acquire land-use data of 41 bays from 1988 to 2018. Then, we quantified the intensity and pattern of land-use and land-cover change during the two periods. Plantation land was the dominant agriculture land type as well as the second land use type after natural forest. Agriculture land cover increased from 29.8% to 40.9% and the growth was driven by plantation expansion. Deforestation was serious, including both natural forests and mangroves. Natural forest cover decreased by 31.6% and mangrove cover decreased by 16.2%. The vast majority of forest loss occurred in Sumatra and western Kalimantan. Commodity-driven deforestation for plantations was the major reason for forest loss.

The amount of live and dead coral is related to recruitment, but differentiating them by remote sensing techniques is difficult. We measured change in the amount of live, bleached, and recently (<6 months) dead coral cover (CCA6) for an island archipelago in the South China Sea. Six Landsat 4/7 ETM/8 OLI images from 1989–1990, 2005, and 2014 were analyzed to assess changes in CCA6 at 14 coral reefs in the western Xisha Islands. Satellite images were georectified and calibrated to remote sensing reflectance. Models for three shallow water (<6 m) geomorphic zones throughout the western Xisha Islands are proposed based on ground-truthed data collected in 2014 and satellite-determined spectral values for 2014 images. Nonlinear models based on Landsat image blue spectral bands for reef slope and lagoon habitats, and green bands for reef flat habitats, are determined as optimal models. Significant changes in CCA6 from 2005 to 2014, and changes in coral reefs and geomorphic zones, correlate with increased numbers of both crown-of-thorns starfish, and sea surface temperature in 2007. Detecting change in CCA6 by remote sensing can provide large-scale information of value for coral reef management, restoration, and protection.

Current studies of urban spatial morphology have rarely focused on the particularity of coastal cities, such as sea–land gradient features and bay types. In this paper, we provide a method to analyze the spatial and vertical distribution of construction land in the bay area and discuss the influence of bay type on the distribution characteristics. Landscape indexes and a clustering algorithm were used to identify the spatial pattern of construction land distribution. Strip division was used to analyze the landscape features of construction land in the sea–land direction. We established eight large bays in Vietnam as the study area. According to the formation and geomorphology of the bay, the eight bays were divided into five types: delta bay, lagoon bay, structural bay, bedrock erosion-stacking bay and estuary bay. The construction land data were generated from Landsat images captured in 1988 and 2015 or so. The study effectively identified five spatial patterns of construction land distribution in bays without prior knowledge. Danang Bay (a bedrock erosion-stacking bay) had a typical high intensity-high concentration pattern, and Hai Loc Bay (a delta bay) had a typical high intensity-low concentration pattern. In the sea–land gradient, the proportions of construction land in the 0–2 km zone were greatest. In Danang Bay, the proportion generally decreased in the sea–land direction; while in Hai Loc Bay, the proportion increased.