||Research Contract MAS 2 CT94-0100 - Marine Science & Technology - Programme MAST-III of the European Union
||Goulletquer Philippe, Geairon Philippe, Faury Nicole, Razet Daniel, Soletchnik Patrick, Adessi L., Gras Paul
||Bivalvia, Mussel, Mytilus edulis, Copper-Chrome-Arsenic (CCA), Treatment, Feeding, Absorption
||Experiments were canied out to assess the copper-chrome-arsenic (CCA) trealment effeets on the Blue mussel Mytilus edulis physiology. Experimental design included two complementary approaches: 1) scope for growth esrimates based upon the energy balance between respiration energy loss and energy gained from feeding processes. 2) a biological early waming system for valve behavior monitoring under CCA exposures. Various temperature range (seasonal effeet). physiological status (mature & immature mussels) as weil as CCA concentrations (from 0 to 48kg/m3) and rime exposure were tested. Significant monality rates for the experimental mussel populations were recorded in alI experimental modalities but the 2kg/m3 CCA treatment concentration. Overall results showed that exposure to CCA treated woods induced significant effeets on mussel valve behavior as weil as on their physiology. Besides that. the wood treatment completion (e.g .• dryness). affecring leaching rates. was critical when assessing precisely CCA induced effects. In severe environmental conditions (limited seawater renewal rate). CCA exposure led to mussel dry meat weight deerease. and eventually to high monality rates. However. in less stressful conditions with a daily complete seawater renewal rate. significant monality rates were observed. although without significant dry meat weight decrease.
Therefore. the dry meat weight variable is not sufficient to assess CCA physiological impacts on a midterm basis. The use of valvometers. as biological ealy waming system recording continuously valve aperture, demonstrated that mussels are able to detect and change their valve behavior at a very low CCA concentration exposure below the I0kg/m3 (treatment) CCA concentration. These results confirmed literature data on several metal effects on mussels. Meanwhile. valve behavior is increasingly disrupted with concomitant increased CCA concentration up to definitive valve closure for the highest concentration. Individual response showed a large variability likely due to initial physiological status. The initial valve opening behavior change. when exposed to limited CCA concentration. was likely to result in chemical bioaccumulation since mussels kept a significant filtering activity. changing only frequency and valve opening range. Abnormal and irregular behavior trends were reeorded for midrangeCCA concentrations while permanent valve closure likely led to mussel anoxia for highest CCA concentrations. and eventually death. With regard to the main physiological functions. experiments demonstrated that CCA leachates affected primilarly the feeeding processes rather than respiration rates. Filtration activity was affected at a 2kg/m3 CCA concentration while respiration at 8kg/m3. For all experiments. slightly increased physiological rates were observed for limited CCA concentration exposure compared to the controls. Otherwise, decrease physiological activity were systematically reported concomitantly to increased CCA leachate concentrations. With a significant seawater renewal rate, a recovery of physiological functions was observed after three days and one day of CCA exposure for feeding functions and respiration rate, respectively. Both results demonstrated the various sensitivity of physiological functions exposed to CCA leachates. Based on these results, several recommandations can be provided for funher assessments of CCA effects. First of all, a comprehensive model estimaring CCA leaching rates is critical in developing further experiments since several variables have both effects on leaching and physiology (e.g . temperature). Our approaches. namely biological early waming system and ecophysiology were complementary to provide preeise insights on how mussels reacted to CCE leachates. Therefore. both approaches are necessary for funher tests. Funhermore. for the first approach. it appears critical to get appropriate background knowledge on species behavior so as to distinguish between natural fluctuations in valve movements and those caused by toxicants. Time-series analysis were appropriate to distinguish CCA impacts on mussel behavior. For the second approach. we have seen that filtration rate was the first physiological function affected by chemicals. well before respiration rate. Since physiological responses vary for a single CCA leaching concentrations, the effect thresholds are likely different when considering filtration, respiration and scope for growth. and therefore should be established separately.