**7. Choice of biomonitors for environmental study**

 Aquatic organisms can transport pollutants and contaminants into, within, and out of the marine aquatic ecosystem. These organisms can ingest the pollutants via water and food and inhale them as they breathe and during feeding process [103]. When the pollutants enter the organism body, some contaminants can quickly pass through several organs; however, some may be absorbed and accumulated in organism tissues, particularly fatty tissues [104]. Certain contaminants such as mercury and PCBs are easily dissolve in organism fats and oils but do not dissolve in water. Due to the organism metabolism process, bioaccumulation process can be clearly seen in carnivorous animals in higher tropic of food chain, ranging from big organism such as fishes and to human [105].

 The choice of a suitable biomonitor needs to consider the potential sources of metals to the organism. For example, sea grass not in contact with sediments, therefore, will take up metals from dissolved sources only [99]. Suspension feeders take up metals both directly from seawater and from the suspended particles collected during feeding. Thus, mussels, oysters, and barnacles are all candidates as suspension feeding biomonitors, and a careful choice will differentiate between suspended particles of different size ranges. As a generalization, sessile barnacles, but not stalked barnacles, have evolved micro-feeding, using the first thoracic legs to filter small suspended particles which would pass through the setae of the expanded cirral net formed by the more posterior thoracic legs [106].

Deposit feeding bivalves will reflect the bioavailability of metals in the surrounding water via respiratory currents but also metal bioavailability in newly deposited particles, for they suck up such particles via the inhalant siphon during feeding [107]. Some bivalves are protected by the shell from contact with the interstitial water of the sediment, a protection not offered, for example, to a sediment burrowing polychaete,

#### *Monitoring of Marine Pollution*

the soft epidermis of which may be bathed directly by interstitial water with a redox potential possibly very different from that of the overlying water [108].

As concluded by monitoring scientists [109, 110], species to be chosen as biomonitors should fulfill several criteria such as:

