The population andlength-frequency distribution diversity of kopah clams gafrarium tumidun rodiing 1798 (bivalvia: veneridae)in coastal water of South Kabung bay, West Sumatra, Indonesia

Abstract

The population and length-frequency distribution diversity of Kopah clams Gafrarium tumidum (Reding. 1798) in coastal waters of South Kabung Bay, West Sumatra, was studied from November 2006 to February 2008. The sampling were conducted at northern part (sandJlats, gravel-sandjlats and mudflats) and southern part (mudflats, in the front of mangrove forest) of Kabung Bay. Clams were collected monthly by using belt transects based on the sediment depth and zonation areas (upper, middle and lower). The highest clams density was found in the middle zone with the population tended to concentrate in the smaller size classes in the northern part of Kabung Bay. At mudflats, in front of mangrove forest, the highest density was found at the middle zone and dominated by the larger sizes. The biomass of clams found at Kabung Bay somewhat different from its density patterns. Based on the sampling periods, the high density of Kopah clams were found only on February 2007 and October 2007 by average lowest sheff length. The density fluctuation of these clams reflects the similar pattern with its mean biomass. The environmental conditions such as temperature and salinity plays an important role in the density fluctuations of clams. The length sizes of Kopah clams showed that the average shell length sizes found in the zonation area ranged from 1.3 to 58.6 mm (n=5083). The smaller size classes (juvenile) of Kopah clams were found only at the gravel-sandflats while the larger size classes (young and adult) were found only at the sandflats and mudflots. The mean density of clams decreased from sediment surface to >0-6 em in substratum depth but increase in the larger size classes. it indicated that the length- frequency distributions diversity of Kopah clams were different in each substratum depth. It was also influenced by habitat types and substratum particles size.