Judul: Ecobiology of “Sepetang” (Pharella acutidensBroderip & Sowerby, 1828) clamin mangrove ecosystem Dumai Coastal Riau
Abstrak: The“Sepetang” (P. acutidens) clam population in Dumai mangrove ecosystem seemed to decrease due to the increase of mangrove degradation and clam exploitation. The aims of the study were todetermine the population and reproductive biology character of the“sepetang” (P. acutidens)clam and their relationship with biophysical and chemical characteristic of mangrove ecosystem.The study was carried out from November 2010 to October 2011 inDumai mangrove ecosystem. Population biology aspects such as patterns of the population growth, mortality and recruitment of the clam P. acutidens were determined.Reproductive biology aspects such as sex ratio, gonadal development,gonadosomatic index, fecundity and oocytes diameter were also studied.The “sepetang” clam habitat characteristic was evaluated based on biophysical and chemical parameters of mangrove environment at each station using principal component analysis. Descriptive analysis was used to evaluate relationship between “sepetang” biological character and mangrove ecosystem environment characteristics. Correspondence analysis was used to analyze spatial distribution of “sepetang” clam in relation with biological character. The results showed that the study area was classified into four groups of stations. First, consists of station SM1 and SM2 was characterized by high concentration of nitrate and phosphate, organic sediment, silt fraction, X. granatum andR. apiculata mangrove species density. Seconds, consists of station P1, P2 and P3 characterized by high salinity, sand and clay fraction, and H. littoralis mangrove species density. Third, consist of station SM3 characterized by high pH of water and sediment and plankton density. Fourth, consists of stasion SD1, SD2 and SD3 characterized by high density of B. gymnorrhiza and A. alba. The growth pattern of P. acutidens was negative allometric with asymptotic length (L ) was 92.71 mm. The annual growth coefficient (K) and total mortality were 0.59 and 1.87 per year, respectively. The recruitment occurred every month.Sex of the sepetang clam can be determined at the size more than 35 mm. The male to female ratio was 1 : 1.12 and no specimen hermaphroditism was observed. Histological analysis indicated that P. acutidenswas partially spawned. The fecundity increase with an increase of shell length and correlated significantly with shell length. The sepetang clam probably spawn continuously throughout the year with a peak spawning season between May-June. The results showed that high gonadosomatic index and fecundity of “sepetang” clam in station SM1, SM2 and SM3. The stations were characteristized by high organic sediment, silt fraction, andR. apiculata density.
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Judul: Kajian Degradasi Ekosistem Mangrove Terhadap Populasi Polymesoda erosa di Segara Anakan, Cilacap
Abstrak: 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.
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Judul: Construction of Strongly Optimal Binary Linear Code with Minimum Distance 9 and 11
Abstrak: A binary linear code of length n over q F is a subspace of n q F . A code has three parameters that attached to it, namely length, dimension, and minimum distance. A code with length n, dimension k and minimum distance d is often called [n, k, d ]-code. Usually, when two parameters are given, then we want to find a code that has the best value for the last parameter. Based on Gilbert- Varshamov bound, if a [n, k, d ]-code exists and can not be expanded, we call it a strongly optimal code. In this paper, we construct strongly optimal code with minimum distance 9 and 11. In constructing the code, we created a theorem and algorithm based on Gilbert-Varshamov bound before we implement the algorithm to MAPLE programming language. Because of computational limitations, the program can only construct up to k = 10 for d = 9 and k = 12 for d = 11.
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