Abstract. Imamsyah A, Arthana IW, Astarini IA. 2020. The influence of physicochemical environment on the distribution and abundance of mangrove gastropods in Ngurah Rai Forest Park Bali, Indonesia. Biodiversitas 21: 3178-3188. Ngurah Rai Forest Park is the widest mangrove ecosystem in Bali that close to the business center and tourism area. The strategic location of the Ngurah Rai Forest Park is estimated to produce anthropogenic waste that can disrupt the gastropod population and stability of the mangrove ecosystems. This study aims to analyze the mangrove density, distribution, and abundance of gastropods based on the quality of the biophysical environment. Mangrove data collection was carried out using a plot transect of 10 m x 10 m, 5 m x 5 m, and 1 m x 1 m. Meanwhile, samples gastropods were collected on a plot transect of 0.5 m x 0.5 m in plot transect of 5 m x 5 m. A total of 11 gastropods species and 6 mangrove species were recorded in this study. The dominant gastropods species found were Assiminea brevicula (28 ind/m2). Species mangrove of Sonneratia alba and Rhizophora apiculata found were in all study sites with tree density values of 1000 ind/ha. Subsequently, the ecological index calculation results show that the diversity index (H’) (2.89-3.2), evenness index (E) (0.87-0.93), and dominance index (C) (0.12-0.17). Based on the Principal Component Analysis (PCA) found was Assiminea brevicula spread on sand and silt substrates and adaptive to the temperature condition, salinity, pH, and dissolved oxygen. Furthermore, other analysis results showed that Cerithidea cingulata, Cerithidea quadrata, Littoraria articulata, and Littoraria scabra were found on clay substrate with high C-organic content. In conclusion, gastropods are evenly distributed and no species dominate the ecosystems.

Mangrove are typical coastal plants whose habitat is influenced by tidal and substrate characteristics. Mangrove ecosystems have a variety of functions that can be utilized both in terms of physical, biological, and economic. Utilization of mangrove ecosystems that do not pay attention to environmental sustainability and conservation aspects cause damage of a whole coastal ecosystems. This study aims at analyze the structure and distribution of mangrove vegetation based on biophysical environment quality. This research was conducted on February until March 2017 at Ngurah Rai Forest Park Bali. The results of study show that the conditions of temperature, pH, and salinity are still in accordance with the specified quality standards, however dissolved oxygen has been classified as polluted by anthropogenic waste. The analysis of the sturcture and distribution of mangrove vegetation found that species of S. alba dominated at the location research, followed by oleh R. apiculata, R. mucronata, B. gymnorrhiza, R. stylosa, X. granatum, A. marina, and A. corniculatum. Overall, the results showed that the mangrove condition was in the damaged cateogry with a mangrove density value < 1000 ind/ha.   Keywords: Coastal, Environmental, Mangrove, Vegetation