Biology And Distribution Of Pen Shell (Bivalvia: Pinnidae) In Selected Areas Of Peninsular Malaysia

A study on taxonomy, biology and ecology of pen shells were conducted in Merambong shoal off the south western state of Johor, Peninsular Malaysia. Several pen shells specimens were also acquired from other sites in Peninsular Malaysia to allow wider scope of sample collection. The study was conducted from August 2005 to April 2007. The site was chosen due to ample abundance of pen shells that live associatedly with the seagrass. A total of seven species have been recorded from the study areas comprising five species of Pinna and two species of Atrina. Ten internal and external morphological characteristics have been used for the taxonomic identification of pen shells. Pinna species showed that of the ten characteristics analyzed, four characteristics were highly significant (P<0.01) (WL, DPML, PAMPDNL and WS). Similar result of four morphometric characteristics showed a highly significant (P<0.01) between the characters of three closely related species, Pinna bicolor, P. deltodes and P. atropurpurea. Adductor muscle tissue used for the isolation of DNA and RAPD successfully detected polymorphisms in the pen shells populations. The result showed 19 primers have produced various banding patterns and thus provided sufficient information for reliable discrimination of the analyzed samples. The results indicated that the primers used generated a total of 160 fragments with 70% to 100% of polymorphic fragments. The genetic distance among these seven species of pen shells was in the range of 0.0197 to 0.3190. The dendrograms constructed from RAPD markers data were able to reveal the relationships between the pen shells populations. Enhalus acoroides, Halophila ovalis, Halophila minor, Cymodocea serrulata and Thalassia hemprichii were among the seagrasses associated with pen shells habitat in Merambong and Tanjung Adang shoals. However, pen shells can also be found in stony sand area of Merambong Island and live associated with zoanthid, Zoanthus pulchellus. The sediment types from four study areas were classified as sandy loam. Monthly in situ physico-chemical seawater parameters recorded showed no significant different (P>0.05) during the study period. Pen shell were recorded and classified into three classes of distribution i.e clumped, random and rare. Higher density was shown by P. bicolor in Merambong shoal (1) with the value of 0.83 ind/m2 while P. incurva showed lower density with 0.03 ind/m2 in Tanjung Adang shoal. Pinna bicolor, P. deltodes and P. atropurpurea were consistently found in these four study areas while, P. deltodes Menke and P. incurva Gmelin were both a new distribution record for Sungai Pulai seagrass beds. Merambong shoal population recorded higher diversity and richness as compared to the Tanjung Adang shoal and Merambong Island, but the value of evenness was similar between Merambong shoal, Tanjung Adang shoal and Merambong Island. Five major phyla comprising 37 species of fouling organisms were recorded. Members from phylum Crustacea and Mollusca were higher in percentage of distribution when compared to the Annelida, Echinodermata and Chordata. Phylum Mollusca showed the highest diversity while phylum Annelida was recorded the highest species richness. A symbiotic adult alpheid shrimp, Synalpheus carinatus was recorded inhabiting the mantle cavity of the pen shells. Pinna bicolor reaches sexual maturity at shell length of 170 mm. Pinna bicolor is dioecious and no hermaphrodite individual was found during the study period. Five stages of gonad development were observed and clearly been identified. Pinna bicolor showed a clear spent phase in the month of October 2006, December 2006 and March 2007 while the developing and spawning phases were observed throughout the whole study period. Monthly in situ physico-chemical parameters and rainfall recorded during the study did not significantly correlated with the reproductive activity of P. bicolor in Merambong Shoal. Pearson Correlation analysis also did not show any significant correlation between gonad index (GI) and physico-chemical parameters of seawater in Merambong shoal. Growth rate in natural habitat has been found to be indeterminate and rapid when compared to P. bicolor in culture tank. For the length-weight relationships, the growth coefficient “b” was found to be significantly higher than the isometric value (3.111) at 5% level and this is an indication of isometric growth in P. bicolor from Merambong shoal. The adductor muscle of A. vexillum was found the biggest in size when compared to other species.

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