This study was conducted to analyze the changes in mangrove area and the density level of mangrove based on satellite imagery and field surveys in Untung Jawa Island. The image data used was Landsat image data acquired in 2000, 2005, 2010, 2015 and 2019. Apart from those, sentinel-2 data received in April 2019 were also retrieved to be compared with field data to see the density level and its accuracy. Image analysis to determine the area and density of mangroves was the Normalized Difference Vegetation Index (NDVI) model. Measurement of mangrove vegetation in the field was obtained by the line plot transect method. The results of temporal image data analysis showed the changes in mangrove area from 2000 (8.46 ha), 2005 (7.56 ha), 2010 (8.45 ha), 2015 (10.65 ha) and 2019 (6.89 ha). In 2019 the mangrove density was dense, while the result of the field survey was categorized as very dense. The level of accuracy for density using remote sensing data is 92.5%. Through the results of the field survey, the mangrove diversity was relatively low, mangrove species on the island was very uneven, and the dominant species was Rhizophora mucronata.

Sabira Island is an island close to Jakarta Province but still has good water conditions and a coral reef ecosystem with a high level of diversity. The condition of the coral reef ecosystem affects the community structure of the reef fish there. This study aims to determine the community structure of the reef fish on Sabira Island. The research was conducted in August 2019 on Sabira Island, Kepulauan Seribu Regency, DKI Jakarta Province. Observations of reef fish were carried out using the Underwater Visual Census method at four observation stations. There were 47 species of reef fish found on Sabira Island from 12 families. The total reef fish found were 1315 individuals, consisting of 79 indicator fish, 417 individual target fish, and 819 major fish. The highest diversity index value on Sabira Island was found at the South Station, with a diversity index value of 2.39. Based on the community structure index at the four observation stations, the reef fish community’s condition on Sabira Island is still good ranging from unstable to stable condition with moderate diversity and low dominance index values.