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 mu ssels as biomarkers of water quality in coastal and estuarine areas, t he 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 Septe mber 1991 to September 1992 and cryostat sections of the digestive gla nd were processed for cytochemical demonstration of the lysosomal mark er enzyme, beta-glucuronidase. Four stereological parameters were calc ulated: lysosomal volume density, surface density, surface to volume r atio and numerical density. Seasonal differences in the lysosomal stru cture were observed, with higher values of lysosomal volume, surface, size and numbers in the summer. Additionally, the stereological parame ters revealed differences between sampling locations except in winter- spring. In autumn, the water quality was lower in the sites on the wes t side of the estuary affected by urban and industrial activities, whe reas in summer the sites on the east also showed signs of poor water q uality. It is concluded that the structure of digestive cell lysosomes can be used as sensitive biomarkers of coastal and estuarine water qu ality.