Plastisitas fenotip kerang darah Anadara granosa L. dalam merespon pencemaran lingkungan: studi kasus di perairan Pesisir Banten

Abstract

Blood cockle Anadara granosa is a commercial bivalve inhabiting intertidal ecosystem. Coastal waters of Banten such Banten Bay, Bojonegara and Lada Bay, Panimbang are potential areas for blood cockle grow out. Banten Bay is a semi-closed waters facing North Coast of Java. Such industries as coal stockpile, fibre boat manufacturer, chemical industry, steel industry, and many others have been long existed there. Lada Bay geographically is located at the west coast of Banten Province and exposed to Sunda Strait. Anthrophogenic activity is signified by coal fueled power plant, operated in 2009. Anthrophogenic sewages become a problem and lead to environmental pollution. Mercury is one of the pollution source. Inspite of being exposed to polluted habitat, therein blood cockle withstands and reproduce annually. Resistancy to such harmful environmental condition does not take for granted, there must be mechanism controlling the ballance between stress and resistancy. Without controlling factor, blood cockle in both areas is certainly extinct. The factor should be universal for individuals and able to recognize type of stress to be responded briefly. Continuous stress directs the controlling factor to acquintedly recognize and respond it; consequently, the blood cockle may adapt with the condition. The controlling factor, however, gives divergent response to stress, depending on type and level of stress. The factor comprises celluler stress response expressing stress protein and being controlled by one or more gene family. The gene family usually expressed during stress is heat shock protein (Hsp) as cytoprotector. Overexpression of a member of such Hsp gene family as Hsp70 indicates ability of the gene to protect tissue and cell, therefore they withstand to stress. Subsquently, more complex organs are protected from stress. Overexpression of Hsp70 gene is a result of individual habituation to stress. Lack of expression indicates inability of the gene to protect cell, therefore, organism’s resistancy declined. The resistancy defines threshold onto stress-stimulating environmental parameter and provides choice of phenotypic changes as an adaptation strategy. Heterogenous environmental condition in Bojonegara and Panimbang waters may result in various stress responses in blood cockle. Bojonegara blood cockle has long been acquinted with heavy metal-contaminated waters, while Panimbang blood cockle is just exposed to environmental changes. Responses resulted from heterogenous environment are biochemical, physiological, and phenotypic responses. Biochemical and physiological responses appear in the short period of time and become a bottom line for phenotypic plasticity. Phenotypic plasticity occur for longer period of time and those characters are fixed. To support the notion that blood cockle in Bojonegara and Panimbang encounter harmful environment, yet they still survive therein, this research was, thus, aimed at analyzing the ability of the blood cockle to develop phenotypic plasticity through Hsp70 gene expression, and spatial phenotypic variations. Additionally, tolerance limit of the cockle on mercury contamination through histological approach has been also studied. Prior to investigate the existence and characterization of Hsp70 gene, quantitative and qualitative standarization of mRNA materials should be conducted. Standarization comprises application of housekeeping gene as an internal control. The success of this step would facilitate target gene detection. β- actin gene has been used as the housekeeping gene. Characterization of β-actin gene produced a specific gene for blood cockle with 353 bp nucleotide in length. cDNA amplification for β-actin gene resulted in high integrity and consistency product, therefore the gene is reliable to be used for internal control. Hsp70 gene showed mercury concentration-dependent expression and the expression varied on population of origin. Hsp70 gene increased on certain mercury concentration, the increasing trend was comparable for Bojonegara and Panimbang blood cockle. However, Hsp70 gene expression on Bojonegara blood cockle was higher. The tendency of Hsp70 gene expression correlated with gill histological analysis. At the certain mercury concentration which blood cockle expressed low Hsp70 gene level, gill injury occured as a necrosis. Habituation and adaptation gave rised to Bojonegara blood cockle developed the plasticity as it was exposed to higher mercury concentration. Heavy metal contamination in Panimbang is just a beginning, therefore, habituation level of blood cockle and other organisms to the condition is still subsided. As a consequence, Panimbang blood cockle has not yet been able to overcome the challenge from high mercury concentrations. Hsp70 gene in Panimbang blood cockle has not been capable to develop plasticity as a mean of adaptation. This research prooved that heterogenous condition of Bojonegara and Panimbang supported the existence of phenotypic variation despite blood cockle population from both areas has come from one genetic source. Phenotyic plasticity has been achieved on several characters measured. Plastic phenotype such as length, height, and width of shell is a self defence to protect blood cockle soft in response to environmental challenge. It requires much time to develop phenotypic plasticity, because the plasticity involved several factors (biochemical and physiological) and phases (acclimatization, adjustment, adaptive, and adaptation). Based on time preiod of pollution exposure on ecosystem correlated with industrialization, Bojonegara blood cockle has attained phase of adaptation. During the phase, acquired character on phenotype is generated and becomes specific characters. On the other hand, Panimbang blood cockle is stil on adjustment phase.