An intertidal limpet species as a bioindicator: Pollution effects reflected by shell characteristics

Mollusc shells have been widely used for monitoring the bioavailability of contaminants in the aquatic environment. The present work examined malformations among the shells of the limpet Siphonaria lessoni from heavily polluted, light polluted and unpolluted sites in Argentina. Data on shell shape, thickness, dry weight, microstructure and semi-quantitative elemental composition was evaluated as well as soft tissue dry weight. Shells from the heavily polluted site were significantly (p < 0.001) thicker than those from other areas. SEM (scanning electron microscopy) analysis of thickened shells revealed the presence of globular malformations on inner shell surfaces. On heavily polluted shells, elemental composition analysis by EDS (electron dispersive spectroscopy) of such malformations indicated concentrations three times higher of carbon and four times lower of calcium and oxygen than the control. Light polluted shells presented concentrations two times lower of calcium. In addition, soft tissues were lighter at the heavily polluted site (p < 0.001). These data demonstrate the sensitivity of this abundant and widely distributed intertidal limpet to aquatic pollutants, and support the use of this limpet as a potential biomarker.