A battery of cell and tissue-level biomarkers was applied in mussels of 6 size-classes collected from Galicia and the Basque coast in summer 2007 in an attempt to examine the health status of individuals affected as adults (mature before 2003), affected during their developmental or juvenile stages (2003-2004 offspring), or not directly affected by the Prestige oil spill (POS) exposure (presumably 2005-2006 offspring). This battery of biomarkers was akin to those formerly applied on mussels of 3.5-4.5 cm shell length for which there exist biomarker reference values in the studied geographical areas. The cause-effect relationship between biological responses and the different history of exposure to POS fuel oil was intricate for different reasons: (a) growth rate was dissimilar in mussels of the two studied localities and much lower than expected, (b) a chronological basis could not be directly associated to POS events (all mussels except the smallest from Galicia had been subjected to the direct POS impact at one or another stage of their life-cycle); and (c) some biomarkers and histopathology seemingly depended on size/age irrespectively of the locality and the POS chronology. As a whole, the present study gives a very useful set of reference values of biomarkers obtained for Mytilus galloprovincialis of different size-classes. Finally, it is recommended that Mussel Watch programmes should be designed by standardising the age of the sentinel mussels rather than their size, especially if the programme covers large or diverse geographical areas, if long-term trends are relevant or if significant pollution effects on growth are expected.
Keywords: Biomarkers; Mytilus galloprovincialis; North Iberian Peninsula; Shell length.
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