| dc.description.abstract | During summer 2001, blue mussels Mytilus edulis with abnormal shell growth were collected
near Kragerø, southern Norway. The mussels had green spots in their mantle tissues, mainly
posteriorly and ventrally, and in the adductor muscle. Mussels from 4 sites had a prevalence of green
spots varying from 2 to 71% that correlated well with shell deformities. Histological examination
revealed the presence of round or ovoid algae, 0.9 to 1.5 × 1.2 to 2.4 μm, free within haemocytes and
in the lesions, characterised by an inflammatory response and the presence of cellular debris. The
alga contain a relatively large nucleus, 1 chloroplast and 1 mitochondrion. Size and morphology suggest
that the alga might be a picoeucaryot green alga. Infection of mussel tissues appears to start in
the posterior mantle edge, near the siphons, and spread anterior-ventrally in the mantle connective
and storage tissues—occasionally spots were also found in the gonad follicles. Large infected areas
were also observed in sinuses within the adductor muscle. Only mussels that were 3 yr old or more
were infected. Deformations apparently resulted from years of continuous shell formation by a contracted,
partly deformed mantle. Most deformed mussels had eroded shells, allowing some light penetration
through the exposed, thin nacre. Young, thin-shelled mussels were not infected. The present
work suggests that the alga has, at least partially, a parasitic relationship with the mussels, and is
associated with pathological alterations in mussel tissues. | no_NO |
