Ekobiologi kerang sepetang (Pharella acutidens Broderip & Sowerby, 1828) di Ekosistem Mangrove Pesisir Kota Dumai Riau

Abstract

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.