Changes in digestive cell lysosomal structure in mussels as biomarkers of environmental stress in the Urdaibai Estuary (Biscay coast, Iberian Peninsula)

In order to validate the use of digestive cell lysosomal changes in mussels as biomarkers of water quality in coastal and estuarine areas, the structure of the digestive cell lysosomal system was quantified in mussels from the Urdaibai Estuary (Biscay coast, Iberian Peninsula) by automated image analysis. Mussels were collected bimonthly from September 1991 to September 1992 and cryostat sections of the digestive gland were processed for cytochemical demonstration of the lysosomal marker enzyme, β-glucuronidase. Four stereological parameters were calculated: lysosomal volume density, surface density, surface to volume ratio and numerical density. Seasonal differences in the lysosomal structure were observed, with higher values of lysosomal volume, surface, size and numbers in the summer. Additionally, the stereological parameters revealed differences between sampling locations except in winter-spring. In autumn, the water quality was lower in the sites on the west side of the estuary affected by urban and industrial activities, whereas in summer the sites on the east also showed signs of poor water quality. It is concluded that the structure of digestive cell lysosomes can be used as sensitive biomarkers of coastal and estuarine water quality.