The Impact of Tsunami on Mangrove Spatial Change in Eastern Coastal of Biak Island, Indonesia

This study was conducted to find out how large was the impact of the tsunami incident of 1996 on the mangrove spatial change and also to understand the distribution and level of mangrove density before and after tsunami in Biak Island (Oridek District and East Biak District), Biak Numfor Regency, Indonesia. In order to determine the condition of mangrove before tsunami, landsat 5 TM satellite image acquisition of July 6, 1994 and landsat 7 ETM+ satellite image acquisition of August 31, 2000 were used. The information about the distribution and extent of mangroves was obtained by analyzing the spectral values based on color composite image (RGB 453) and NDVI analysis. Overlay map of the result satellite image interpretation was used to learn the change of mangrove spatial extent area due to tsunami. The result showed that the mangrove area before the tsunami was 286.83 Ha (high density 36.63 Ha, medium density 140.60 Ha and small density 109.60 Ha), meanwhile the mangrove extent area after the tsunami was 102.51 Ha (high density 24.39 Ha, medium density 22,86 Ha and small density 55.26 Ha). The mangrove conditions before tsunami were crucial to the impact of mangrove area degradation directly. The change of mangrove spatial extent into two districts after tsunami occurred in 1996 amounts to 184.32 Ha, which it approximately 202.50 Ha mangrove being lost and the addition of mangrove in the new area are 18.18 Ha. The tsunami that occurred in 1996 affected the coastal ecosystems, especially the mangrove ecosystems in Oridek District.