ABNORMAL MELANIZATION AND MICROSTRUCTURAL DISTORTIONS OF THE SHELL OFGREAT SCALLOP LIVING IN SHALLOW-WATER

Modifications of great scallop (Pecten maximus) shells have been notic ed in many sites of scallop fisheries in Brittany, especially in shall ow waters. These calcification abnormalities are linked to the appeara nce of a brown colouration of the internal calcified shell layer, due to the presence of a eumelanin associated with the insoluble organic m atrix of the biocrystals. The appearance of this pigment generates man y disturbances of the calcified foliated microstructure of the scallop internal shell layer. The mantle structure is not modified in brown s hells as compared with white ones. No pathogenic signs such as hyperpl asia or haemocytic infiltration have been observed. According to this observation, we hypothesize that the brown colour phenomenon is more a result of environmental disturbance rather than a symptom of a pathog enic disease. The colour abnormalities of the internal shell layer can be detected by a spectral analysis of its reflectance before it can b e detected with the naked eye. This method, correlated to microstructu ral observations, gives a rapid and precise analysis of the appearance of the pigmentation on adult or juvenile scallops. It may be a useful method for the evaluation of the influence of environmental parameter s, for example, on calcification and its abnormalities.