Assessment of Mangrove Ecosystem Degradation to the Population of Polymesoda erosa in Segara Anakan, Cilacap

Abstract

Segara Anakan is an unique ecosystem with lagoons, mangrove and lowland. Segara Anakan located in the southerncoast of Java Island at 07°34'29 .42 "S - 07º47'32.39" S and 108º46'30.12"E-109°03'21.02"E. Mangroves is inhabited by typical mangrove ecosystem biotas, ones of which is clams. Clam is one of major components in the mangrove’s soft sediment community. One of biota living in mangrove ecosystem is Polymesoda erosa called “totok” or “kepah” in local name. The species is valuable both economically and ecologically. In the other side, degradation occurred in mangrove Segara Anakan. The economic demands of growing population at Segara Anakan are continuously increasing. Resulting in various human activities which strongly alter and deteriorate environmental conditions for the flora and fauna. These activities include mangrove cutting, reclamation of agricultural land and urbanisation. They are responsible for the destruction of almost half of the mangrove area. This study has four main objectives that include the following: (1) to determine degradation of mangrove in Segara Anakan; (2) to determine population condition of P. erosa in Segara Anakan; (3) to analyze its relationship with mangrove degradation in Segara Anakan; (4) to determine utilization of P. erosa in Segara Anakan. Purposive Sampling was used to collect the clams data and plots sampling techniques were applied to obtain vegetation data. Average of P. erosa abundance ranged from 9.83 + 4.68 ind/m2. Age distribution was presented as histograms and assumed be equal to length of shell. Dominant sizes were from 4.6 – 5.8 cm. The distribution pattern determined by variance index shows aggregate distribution. Very weak correlation was found between P. erosa and mangrove that indicates not connected directly. Tree category was dominated by Nypa fructicans. Sapling category was dominated by Rhizophora apiculata and Acanthus ebracteatus, Acanthus ilicifolius for seedlings, shrubs and herbs. Based on GIS analysis, mangrove area in Segara Anakan was 8036.9 ha. P. erosa strongly correlates to environmental components based PCA namely water content of soil, temperature and light intensity. People utilized P. erosa as source of food, income and land hoard.