Occurrence of pearls in mussels (Mytilus spp.) from the Norwegian coast

Mussels (Mytilus spp.) from the Norwegian coast produce pearls, up to as many >360 pearls per individual, and it seems to be a southern-northern gradient with more pearls in mussels from the south than from the north. Out of the 280 mussels studied, nearly 2000 pearls were found, and the mussels producing pearls were all >4 cm. Size and condition index did correlate with the pearl frequency, while microplastics did not. Mussel health is important to study as they are important actors in the coastal ecosystem, as bioindicators for environmental monitoring, as a food source as well as the recent reports on changes in their distribution across the Norwegian coast.