Five integrative biomarker indices are compared: Bioeffects Assessment Index (BAI), Health Status Index (HSI), integrated biological response (IBR), ecosystem health condition chart (EHCC) and Integrative Biomarker Index (IBI). They were calculated on the basis of selected biomarker data collected in the framework of the Prestige oil spill (POS) Mussel Watch monitoring (2003–2006) carried out in Galicia and the Bay of Biscay. According to the BAI, the health status of mussels was severely affected by POS and signals of recovery were evidenced in Galicia after April-04 and in Biscay Bay after April-05. The HSI (computed by an expert system) revealed high levels of environmental stress in 2003 and a recovery trend from April-04 to April-05. In July-05, the health status of mussels worsened but in October-05 and April-06 healthy condition was again recorded in almost all localities. IBR/n and IBI indicated that mussel health was severely affected in 2003 and improved from 2004 onwards. EHCC reflected a deleterious environmental condition in 2003 and a recovery trend after April-04, although a healthy ecosystem condition was not achieved in April-06 yet. Whereas BAI and HSI provide a basic indication of the ecosystem health status, star plots accompanying IBR/n and IBI provide complementary information concerning the mechanisms of biological response to environmental insult. Overall, although the integrative indices based on biomarkers show different sensitivity, resolution and informative output, all of them provide coherent information, useful to simplify the interpretation of biological effects of pollution in marine pollution monitoring. Each others’ advantages, disadvantages and applicability for ecosystem health assessment are discussed.

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Lysosomal responses in mussel digestive cells are widely accepted as effective biomarkers that respond to pollutant exposure, as well as to natural factors (tide, food, temperature). The effects of tide and season on digestive cell lysosomes in mussels were determined in different transect and transplant experiments on mussels at different tide levels and in winter and summer. We measured lysosomal enlargement through the lysosomal structural changes (LSC) test after β-glucuronidase (β-Gus) histochemistry and membrane destabilisation through the lysosomal membrane stability (LMS) test after hexosaminidase (Hex) histochemistry. A marked gradient along the intertidal zone, which was more prominent in winter than in summer, was found in lysosomal size and membrane stability. A transplant experiment revealed that digestive cell lysosomes respond rapidly to immersion of mussels. The study of the time-course changes in mussels from high tidemark level indicated that lysosomes respond very promptly to air exposure conditions. We suggest that the lysosomal changes observed are the result of the digestive process in parallel with tide. Since such natural variability might mask the effects of pollution, we conclude that a standardised sampling protocol -which should include the use of mussels from low intertidal levels -is needed.

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