Adaptive ability of the ark cockles anadara antiquatain heavy metals contaminated seawater: biokinetics, ecobiology, histology, and molecular aspects

Abstract

The ark cockles Anadara antiquataare wide spread in Indonesia seawater, and able to live in the sediment, that are the sites of anthropogenic heavy metals deposits. A. antiquatacould not avoid the exposures ofheavy metals from surrounding environment, because of their limited mobility, and filter feeding mechanism. Muara Bama Panimbang, and Banten Bay Bojonegara in the Province of Banten, has been contaminated by heavy metals exceeding the quality standard. Panimbang areahas beenknown to have high diversity of bivalves species, thus become the center of bivalves inthe Province of Banten. A. antiquata in both location have not been exploited yet, so their economic valuesstilllow enough.Scientific information about A.antiquataarealso relatively limited, so it is interesting to study their potency,both for economical and ecological purposes. This research aimed to:1)identified the ability of mercury bioaccumulation and depuration onA. antiquata using radioactive tracer, 2) identified the effect of mercuryinduction to the histological structures of A. antiquatagills, 3) identified the ecobiological characteristics of A. antiquata in natural habitats that contaminated by heavy metals, and 4) characterizedthe metallothionein (MT)protein and gene ofA. antiquataby mercury induction. Biokinetic approachedwithradiotracer applicationhas beenconducted, to identify the capacity of mercury bioaccumulation and depurationonA. antiquata in laboratory. The results showed that smaller cockles (10-20 mm) accumulatedhigherconcentration of mercury than bigger cockles (35-45 mm). The increaseofmercury concentration in water affected the increasingof BCF values in both groups, until steady state conditions reached. Increased concentrations of mercury in water, were increased the mercuryefflux,and body contentsin both groups, but decreased the uptake rates in bigger cockles. Based on the models, lowest concentrations of dissolve mercury(0.0025 ppm) caused the highest BCF values in both groups. The steady state conditions would reachedin 15 dayson smaller cockles, andin 13 daysonbigger cockles. The mercuryelimination rates during depuration, showed no significant differences on both groups. The mercurybiological half-times in A. antiquataranged in 3.49 – 7.42 depuration days. The mercuryconcentration 0.0025; 0.005, 0.01, and 0.02 ppm have been induced for six days, to study its impact to the gills histological structures. Gills tissue samples were taken on day 2, 4, and 6 of exposures. The results showed,combination ofsix days exposuresand four mercury concentrationsdid not caused serious damages to the gills of A. antiquata.The damages appearedwerehyperplasia and necrosis, but in general,the treatmentscombinations showed no significant differences to the histological structures of gills. These facts supportsthe adaptive ability ofA. antiquata in mercury contaminated environment. The study results in natural habitat (Panimbang and Bojonegara)showed that A. antiquatawere well adaptedin heavy metals contaminated water.The shell length range in Panimbang were 8.05 - 24.65 mm (average 18.696 ± 5.946 mm), while in Bojonegara ranged 16.85 - 51.85 mm (average 25.87 ± 8.593 mm). The index of Meat Yieldsresults showed that 58.38% samples inPanimbang,and 53.85% samples inBojonegara,categorizedin moderate class, that reflectedthe ability to stored organic compounds reservesfor growth and reproduction, although they lived incontaminated environment. The Pb contents in cocklesbody ranged between 0.125-2.50 ppm; Cd contents ranged 0.125-17.60 ppm, and Hg ranged 0.02-0.3 ppm.The heavy metals contents in cocklesat Bojonegara was higher than Panimbang. The molecular studyhas beenidentifiedthe metallothionein (MT) proteinfrom hepatopancreas, and the MT gene from gills of A. antiquata. MT protein allows theability to survive, and perpetuate the metabolic activities of the body, sinceMT sequesteredheavy metals in the body, that caused elimination of metals toxicity. The SDS-PAGE analysis from hepatopancreas tissues had identified isoform MT-I, that sized 5 kDa, 10 kDa, dan 25 kDa. The research also successfully isolated total RNA fromthe gills tissues.Mercurygradient concentrationaffected the quantity of total RNA; highest mercuryconcentration produced highest RNA quantity (383.33 ng/mL) with goodpurity (score 2,01). Reverse Transcription PCR (RT-PCR) method succsessfully amplified house-keeping geneGAPDH (product size 496 bp) and MT gene(product size 356 bp) in good condition.The synthesis of MT protein by the regulation of MT gene,was the key factor that influenced the ability of A.antiquata to survived in the environment that has been contaminated by heavy metals.