ADEQUACY of MORFOlogical and FUNCTIONAL MECHANISMS OF MUSSEL MYTILUS GALLOPROVINCIALIS LAM. ADAPTATION TO POLLUTION

Dekhta V.A.

Research Institute of the Azov Sea Fishery Problems (AzNIIRKH), 344007, Beregovaya st.21/2, Rostov-on-Don,

Russia, ph. (8632) 62-56-45, E-mail:riasfp@aaanet.ru

Mussels populate littoral and sublittoral regions and are affected by anthropogenic pollution. They are forced «to solve problems of adaptation» to new ecological factors which have not been encountered earlier during their evolution. The main problems are the adequacy of mechanisms of adaptation and to what extent they ensure adaptation under new habitat conditions.

One of the adaptive mechanisms maintaining life of mussels in a littoral is their ability to respond to anoxia and other hazard effects by sealing a shell hermetically. We analyzed the relative height of a shell (H/L %) related to the shoulder dimensions of the back adductor (r=0.43; p=0.001). When sealing a shell the power expenditure to secure valves depends directly on the shoulder's size. In unpolluted waters the average H/L and, accordingly, the shoulder of the back adductor are greater in those areas where mussels are forced to seal their shells. For example, the H/L parameter is bigger in the surf zone than at the 6 m depth (52.9> 50.8; p <0.01). Experiments with artificial drying have shown similar dependence. 50 % of survived mussels had higher reliable estimates of H/L compared to the dead specimens.

In regions of technogenic pollution the H/L also increases in comparison with purer water areas (55.00>51.24; p=0.008). As in the previous cases, its dispersion decreases (1.10<6.81; p<0.001), which clearly points to the elimination of the mussels less adapted. Its augmentation occurs within the limits of the normal reaction and reflects the habitat conditions adequately.

The habitation in the littoral also requires resisting to significant wave activity. For this purpose «it is necessary for a mussel to build a reliable house», i.e. a stronger and streamlined shell to lessen the pressure of waves upon its surface. Therefore mussels from surf zones on a rocky substratum have more convexed and thick-walled shells, but at greater depths and soft bottoms their shells are thin-walled and flatted. These specificities of biotopes are well-known (Dragoli, 1966; Zaika, etc., 1990). In technogenically polluted areas the convexity of mussel valves (D/L %) increases even more, considerably exceeding the values typical of the natural ecological conditions (49.94> 37.54; p <0.00001). The dispersion of this ratio also increases (30.47> 1.49; p <0.001). The appearance of more convexed shells is caused by changes in its morphogenesis under conditions of technogenic pollution. We and other researchers (Dekhta, 1996, 2000, 2001; Dekhta, Katalevsky, 1998, 2000, 2001; Revkov, et al., 1999) have got reliable data confirming the dependence of shell convexity on the content of heavy metals.

The question arises why the adaptive mechanism having formed during the process of accommodation to the life in a littoral is used under conditions of pollution in the absence of wave activity. Why it is necessary for mussels to have a "safe house"? Apparently, ingredients of contamination affect the morphogenesis of a shell in a mode similar to surf regions. Technogenic pollution being a new factor, which never occurred during the long evolution, "provokes" mussels to follow adaptive strategy, useless in this case. Therefore, nonadaptive character of anomalies represented by convexity can be classified as morphosis in terms of nonhereditary modifications proposed by I.I. Schmalhausen (1966).